Report on Practical Training

From 07.06.2010 to 06.07.2010

Rajasthan Atomic Power Station, Rawatbhata

Session 2009-2010

SUBMITTED BY :

DILRAJ MEENA

II-YR (MECHANICAL)

REVIEWED BY:

SH. R.L. MALI, SO/D, NTC

SUBMITTED TO:

SH. R.K. SHARMA,

TRAINING CO-ORDINATOR

NUCLEAR POWER CORPORATION

(A GOVT. OF INDIA ENTERPRISES)

FROM: 07TH JUNE TO 06TH JULY 2010 AT

RAJASTHAN ATOMIC POWER STATION

RAWATBHATA

Prepared by:- DILRAJ MEENA

II-YR (MECHANICAL)

Submitted to:-

Mr. R.K.SHARMA

(Training Co-ordinator)

PREFACE

I DILRAJ MEENA student of second year Mechanical have completed practical training at Rajasthan Atomic Power Station(RAPS) for 30 days.

The training at Rajasthan Atomic Power Station (RAPS) has been particularly beneficial for me. I saw various processes and equipments used in production of electricity by nuclear power that were studied in books and this had help me in understanding of power generation and various aspects related to it.

DILRAJ MEENA

II-YEAR

GOVT. POLY. COLLEGE

BANSWARA Acknowledgement

It was highly educative and interactive to take training at Rajasthan Atomic Power Station, as technical knowledge is incomplete without the practical knowledge, I couldnt find any place better than this to update myself.

I am highly grateful to the our Training Co-coordinator Mr. R.K.SHARMA (Training Co-coordinator) to grant me permission to take training at such a coveted institute. Apart from him, there was always a friendly guidance from Mr. R.P.SAINI (SO/F) and Mr. K.M.JAIN (SO/C) for the betterment of this Training Report.

I am also thankful to all those engineers and technicians without whom it was not possible for me to clear my doubts and difficulties. After coming to this institute and knowing State of Art Technology available with learned Training staff, I would like to come again to this coveted institute if got a chance.

DILRAJ MEENA

II-YEAR

GOVT. POLY. COLLEGE

BANSWARA

S.NO.CONTENTS

1.INTRODUCTION

2.NEED FOR NUCLEAR POWER

3.INDIAN NUCLEAR POWER PROGRAMME

4.PRINCIPLE OF NUCLEAR POWER REACTION

5.CLASSIFICATION OF A POWER REACTOR

6.PRINCIPLE OF OPERATION RAPS

7.METHODS OF MEASURING DOSE

8.RADIOACTIVE WASTE MANAGEMENT

9.RADIATION SAFETY

10.MACHANICAL COMPONENT

11.CONCLUSION

1. INTRODUCTION

Nuclear energy has turned out to be the achievement of the past century. The most clean environmental friendly and of less running cost mode of power generation is now in our hand.

At present it is estimated that our natural reserves of U3O8 is about 70,000 tones, but the long run potentials depends upon the large reserves of Thorium which is about 3,60,000 tones. The optimum usage of the available resources takes place via three stages namely:-

The first stage and perhaps used widely is using natural uranium as fuel.

The plutonium thus yield by first stage along with thorium is fed in Fast Breeder Reactors.

The third stage would employ the U-233 obtained from second stage together with thorium is employed. Perhaps the third stage could either be a fast reactor or a thermal reactor.

In fact reactors high energy neutrons are required to bring about fission. It is most common with element having even number of mass number.

In thermal reactors, thermal neutrons i.e. slow moving neutrons are required to being about the fission. Those having mass number as an odd number possess this type of property. 2. NEED FOR NUCLEAR POWER:

The exploration of natural resources for generation of electricity has been an evolutionary process. Over the years, it has progressed from tapping the potential energy of falling water to burning of fossil fuels. But the quest for more sources of electricity, which is the cleanest and most efficient form of energy, is unending and the limits of the conventional sources have served to heighten mans anxious efforts in this regard. The discovery of fission and the promise of abundance which nuclear energy came to hold subsequently turned mans attention to utilize the potential of this source.

Considering the current population growth which has already crossed 100 crores in the 21st century and improvements in standard of living of the forth coming generations, there will be a large increase in the need of MACHANICAL energy particularly from clean, green and safe energy sources. The MACHANICAL energy will play a vital role in sustainable development of the country. Among all the available conventional and non conventional energy sources, the nuclear energy is most efficient, abundantly available, sustainable and cost effective energy sources. It does not emit obnoxious gases that cause global warming, ozone hole and acid rain.

SO THE NUCLEAR POWER:- It is thus evident that some new from of energy, such as nuclear, which is a large addition to our energy resources, has to be developed in a big way. The currently known uranium reserves in the country can support a PHWR programme of 10,000MW for a design life of 30 years. Even though there is every reasons can support an ultimate capacity of 350,000 MW(e) by fast breeder .the long range potential of so, on thorium resources which exceed 360,000tonnes.when used in the breeder reactors, the thorium reserves would be equivalent to 600 billion tones of coal. This is explained below.

NUCLEAR POWER IS SAFE:-

Improving the quality of life has been the driving force for making to push ahead with the use of modern technology. That these benefits carry along with them some risks, has been known for sometimes and one has also to recognize that there is nothing like an absolutely safe technological products be it the automobile, aircraft, chemical industry, or for that matter, a nuclear reactor. If mankind had decided to take a zero-risk approach, we would not have undertaken space exploration or developed nuclear technology. They would have burnt more coal and oil, resulting in more acid rain, pollution and scarce oil.

3. INDIAN NUCLEAR POWER PROGRAMME

The Headquarters of Indian Nuclear Power Projects are located at Mumbai It is the Department of Atomic Energy (DAE) which covers all the aspects of R&D and power production. It is at Bhabha Atomic Research Centre where all the research works regarding the new technologies and nuclear science. Other than the power production plants there are various other institutions that come under DAE like, Nuclear Fuel Compels (NFC) at Hyderabad, Mines at Jadugura, and Centre for Advance Technology, Indo session re etc.

The first nuclear power plant was constructed at Tarapur in 1969. It was a Boiling Water Reactor. The purpose of this reactor was to give the ground for development of Pressurized Heavy Water Reactors (PHWRs). The two units setup on turnkey basis by G.E., America is still working successfully.

The list of various Nuclear Power Plants in India is as follows:-

StationRated Capacity (Mwe)Year of Criticality

TAPS-1&22 x 1601969

RAPS-11001972

RAPS-22001980

RAPS-32351999

RAPS-42352000

RAPS-52352010

RAPS-62352010

MAPS-12201983

MAPS-22201985

NAPS-12201989

NAPS-22201991

KAPP-12201992

KAPP-22201993

KAIGA-12351996

KAIGA-22351996

KAIGA-32352010

KAIGA-4235Project under construction

TAPS-35402006

TAPP-45402005

MADRAS500Fast breeder reactor Project under construction

Kk project 11000Light water reactor under construction

Kk project 21000Light water reactor under construction

The list of proposed sites in India-

KAPP3&4740X2Pressurized HeavyWater Reactor

RAPP7&8740X2Pressurized HeavyWater Reactor

Jetapur(Maharastra)740X4Pressurized HeavyWater Reactor

RAJASTHAN ATOMIC POWER STATION

INTRODUCTION

PHYSICAL LOCATION

Rawatbhata is located at the bank of river Chambal near the Rana Pratap Sagar Dam. The nearest city is Kota situated at a distance of 60 KMs from the plant.

There are four units of 220 MWe each and two units of 235 MWe newly constructed. There is lush greenery around the site. For employees various colonies are constructed with all the domestic facilities.

4. PRINCIPLE OF NUCLEAR REACTION:

When a heavy nucleus split into smaller nuclei, a small amount of mass is converted into energy. The amount of energy produced is given by Einsteins mass energy relation (E=m*c2) .this breaking up of nuclei is called nuclear fission. Natural uranium has two type s of isotopes, U238 and U235 isotope in the ratio of 139:1. The less abundant U235 isotopes that fissions when a U235 atom is struck by allows (or thermal) neutron, it splits into two or refragments. This splitting is a compiled by release of energy in the form of heat, radio-ability and two or there atom at high speed, are made to slow down in the split atom at high speed, are made to slow down in a moderation, i.e. heavy water, so that they have a high probability of hitting other U235 atoms which in turn release more energy and further sets of neutrons. Attenuation of self sustained stage of spilling of uranium atom is called chain reaction. There is a particular size of fissionable material for which the neutron production by fission is exactly balanced by leakage and absorption. This is called the critical size at which the chain reaction is self sub staining the size of a reaction.

ENERGY RELEASE DURING FISSION

In the above equation, (1) the total mass before fission, is the sum of the masses of U235 and the neutrons. Mass after fission is the sum of fission fragments and neutrons.

Since loss of mass of 1 a.m.u is equivalent to an energy release of 931 MeV. Therefore energy release in the above reaction could be calculated as follows. Since

5. Classification of power reactors:Each fission process produces 2.5 new neutrons and, at least one of these must produce a further fission for a chain reaction to be maintained. So for every 100 neutrons, produced in one neutron generation, at least 40 must cause further fissions so as to produce 40 x 2.5 or 100 neutrons in the next generation. Now the neutrons produced at fission are fast neutrons with an average energy of 2 MeV. If the fissions occur in natural uranium fuel, 99.3% of the nuclei are U- 238 which will only fission with neutrons having energies greater than 1.2 MeV. Therefore only half the fission neutrons can cause U-238 fissions. So out of the 100 neutrons produced at fission, only 50 can cause U-238 fissions. The inelastic scattering cross-section of U-238 is 10 times greater than the fission cross-section at these neutron energies. So, out of these 50 neutrons 5 will be able to cause fission and remaining 45 will be scattered and lose so much energy that they can no longer cause U-238 fission. The fast fission cross section in U-235 is only 1.44 barns and U-235 fast fissions can be ignored with so little U-235 in natural uranium, Therefore, out of the 100 fast neutrons produced at fission only 5 will cause further fissions and produce 5 x 2.5 or 12.5 new neutrons. Thus, even if leakage and radiative capture are ignored the chain reaction can not be maintained by fast neutrons in natural uranium. One of two alternatives is available which lead to a power reactor classification as follows:

Fast Reactors:

The U-235 content of the fuel can be increased, i.e., the fuel is highly enriched in U-235 with a substantial decrease in U-238. The U-235 fast fissions are thus, considerably increased in a fast reactor. Some reduction in neutron energy does occur due to inelastic collisions of neutrons with nuclei of the fuel and structural material but most of the fissions are caused by neutrons of energies greater than 0.1Mev.The mass of U-235 required for the reactor to be critical varies with a mount of U-235 enrichment. In all cases the critical mass of fissile material required increases rapidly below 15% to 20% U-235 enrichment. To avoid large fuel inventories a practical fast reactor, such as case C above, would require fuel containing at least 20% U-235 by volume. Incidentally the critical mass of U-235 in a fast reactor is considerably greater than in a thermal reactor with the same fuel composition. The highly enriched fuel and absence of moderator results in a small core. Therefore, fast reactors have high power density cores. The average power density in a Fast Breeder Reactor (FBR) is 500 MW/m3 compared with 100 MW/ m3 for a Pressurized Water Reactor (PWR). It is therefore essential that a heat transport fluid with good thermal properties be used. The choice is also limited to a non-moderating fluid and liquid metals seem to satisfy both requirements. The capture cross-sections of most elements for fast neutrons are small and since there is a relatively large mass of U-235 in the reactor, the macroscopic capture cross-sections of structural material and fission products are small compared with the macroscopic fission cross-section of the U-235. Consequently there is more flexibility in the choice of materials and stainless steel can be used instead of aluminum or zirconium. Fission product poisoning is not significant and for this reason, (and the fact that temperature coefficient of reactivity is low), the excess reactivity required in a fast reactor is small.

Thermal Reactors:

Since a chain reaction can not be maintained with fast neutrons without considerable enrichment, the alternative is to reduce the neutron energy until the fission cross-section of U-235 is sufficiently increased. If the neutrons are reduced to thermal energies, the U-235 fission cross-section is 580 barns whereas the radioactive capture cross-section is 106 barns. Thus, even allowing for the low percentage of U-235 in natural uranium, the thermal neutron fission cross-section in natural uranium is 4.2 barns whereas the radioactive capture cross-section is 3.5 barns. Thus, for every 77 neutrons captured in natural uranium about 40 will cause fission and produce 40 x 2.5 or 100 new neutrons. For 77 neutrons out of every 100 to be captured, fewer than 23 neutrons can be lost by escape or radioactive reaction could be sustained. In thermal reactors the fission neutrons are thermalised by slowing them down in a moderator. Most of the power reactors in existence are thermal reactors.

Types of Heterogeneous Reactors:

The classification of heterogeneous reactors may be based on the type of moderator used or on the heat transport system employed. The basic requirements and properties of moderators and heat transport systems will be discussed at length later. It is sufficient, for the moment to list the moderators and heat transport fluids in general use.

The moderator may be:

1. Light water

2. Heavy water

3. Graphite

The heat transport system may be:

1. Pressurized light water

2. Pressurized heavy water

3. Boiling light water

4. Boiling heavy water

5. Gases such as CO2 or helium

6. Liquid metals

7. Steam or fog

8. Organic liquids

Heavy Water Moderated Reactors:

Heavy water has a much lower neutron capture cross section than both light water and graphite. The principal advantage of using heavy water as a moderator is, therefore, the neutron economy that can be achieved with it. The thermal utilization factor, f, in the four factor formula, is increased because of lower neutron capture in the moderator. Neutron economy is so much improved that not only can natural uranium fuel be used, but that this fuel can be used in oxide or carbide form. Thus, there is no longer any need for an enrichment plant. In addition oxide or carbide fuel improve the fuel integrity and the fuel in less susceptible to distortion.

Pressurized Heavy Water Reactor (PHWR)

PHWRs have established over the years a record for dependability, with load factors in excess of 90% over extended periods. In the PHWR, the heavy water moderator is contained in a large stainless steel tank (calandria) through which runs several hundred horizontal zircaloy calandria tubes. The D2O moderator is maintained at atmospheric pressure and a temperature of about 70C. Concentric with the calandria tube, but separated by a carbon dioxide filled annulus which minimizes heat transfer from fuel to the moderator, is the zircaloy pressure tube containing the natural UO2 fuel assemblies and the heavy water coolant at a pressure of about 80 kg/cm and a temperature of about 300C. The term pressurized refers to the pressurized D2O coolant which flows in opposite directions in adjacent tubes and passes its heat to the secondary coolant via the steam generators. System pressure is maintained by a pressuriser on one of the legs of a steam generator.

Graphite Moderated Reactors:

With a graphite moderator, a liquid or a gas must be used as the coolant. Although there are water cooled graphite-moderated reactors, e.g., the Soviet Unions RBMK series of power stations, of which Chernobyl is one, only gas cooled reactors will be referred to here. Whilst the United States and Canada pioneered, respectively, the light and heavy water moderated designs, France and United Kingdom undertook the early development of the graphite moderated reactor, selecting carbon dioxide as the coolant because of its relative chemical inertness and low neutron activation. France abandoned this approach in favor of an extensive PWR programme. The UK continued to be heavily committed to gas cooled reactors in the form, initially, of magnox and subsequently the advanced gas cooled reactor.

6. PRINCIPLE OF OPERATION OF RAPS

The Nuclear Power plant works on two cycles:-

1. Secondary Cycle (Rankine Cycle)

2. Primary Cycle (Primary Heat Transport)

Rankine Cycle.

Rankine cycle is a vapour power cycle having two basic characteristics:

The cycle consists of a succession of steady flow processes, with each process carried out in a separate component specially designed for the purpose. The working fluid used in the plant, i.e. water substance, when passes through the cycle of operation undergoes changes in pressure and temperature (enthalpy). It receives heat in various feed heaters and undergoes pressure change by pumps in the circuit. The preheated water is converted into saturated steam inside steam generators and finally supplied to the turbine, in which it undergoes a fall in pressure and increase in volume and gives up a certain amount of energy to the turbine shaft. On reaching the lowest pressure in the system, in the condenser, heat is extracted from it by the cooling water and it is thus restored to its original conditions as condensate. In the simplest possible form of heat cycle for a steam turbine power plant, the process thus comprises four steps.

1) Increase of pressure of the condensate in the feed pump, with a resultant very small absorption of work.

2) The supply of heat by the combustion of fuel to produce steam in the steam generator.

3) The expansion of the steam in the turbine, with the production of work.

4) The rejection of heat by the steam to the cooling water at constant pressure in the condenser, and the return of the water to its original condition. The cycle is rarely as simple as this and is often complicated by such devices as regenerative feed heating and reheating. Under ideal conditions of expansion in the turbine the above cycle is known as the Rankine cycle .The cycle shown in figure represents a power station cycle without feed heating. 1-2-3-4-5-6 Feed water receives the sensible heat 6-7.Feed water receives the latent heat 7-8 Adiabatic expansion of steam through high pressure turbine 8-9 Moisture removal and reheating 9-10 Adiabatic expansion of steam through the low pressure turbine.10-1 Condensation of steam in condenser at constant pressure.

RANKINE CYCLE

SECONDARY CYCLE

THE PRIMARY HEAT TRANSPORT SYSTEM

a)Principle operationThe PHT system provides continuous circulation of coolant through the reactor at all times by various modes as listed below:

i) Normal operation - By primary coolant pump.

ii) Sudden loss of power to pumps - By inertia of pump flywheels to avoid a sudden drop in coolant flow.

iii) Thermo siphoning - By placing main equipment above the elevation of reactor core.

iv) Loss of primary coolant - By receiving emergency injection of heavy water from moderator system after depressurization of primary heat transport system. In case of paucity of heavy water from moderator system light water injection is initiated.

b)DescriptionThe heavy water runs through the feeders into 306 coolant tubes, through the end fittings and feeders to the reactor outlet headers. The reactor utilizes restriction orifices in selected inlet feeders to achieve the flow required by the reactor channel ratings, commensurate with equal temp. from all channels. The reactors outlet headers distribute the flow through 8 boiler inlet valves, 4 on the north and 4 on the south, to the respective 8 boilers (in new PHWR it is only 4 boilers 2 on each side). From the boilers through the boiler outlet valve the heavy water arrives at the pumps. Each pump is associated with a respective boiler through an individual suction line. The pumps discharge the flow through pump discharge valves into the reactor inlet header. No common suction header has been provided and pumps are attached directly to the boilers, the only common connection being reactor inlet and outlet headers. This arrangement allows the isolation of any of the circulating pumps and leads to the loss of a boilers, the circuit has no spare pump. This situation is acceptable in view of the expected high reliability of the heat transport pumps and also that the loss of a pump and a boiler does not result in a substantial loss of plant capacity. From the reactor inlet headers the heavy water flows through the feeders and end fittings to the reactor coolant tubes. Corrosion products and fission products are removed from the system by purification circuit. Purification circuit also helps to achieve a pH value between 9.5 to 10.5 and to maintain the conductivity of heavy water between 20 to 30 micromoh/cm. In addition it reduces radiolysis decomposition of heavy water by controlling ionic impurities. The operating design pressure in the reactor outlet headers is controlled at 87 Kg/cm2 (1237.5 psig). The pressure is controlled by a feed and bleeds system. In the event of a leak in the primary system, no matter how large it is, cooling of the fuel can be maintained or restored by the emergency injection system which is designed to pump heavy water from the moderator system into the primary system. For cooling the system below 300(F and for holding the system at low temp. during plant maintenance, an auxiliary cooling system is provided which is known as standby cooling system or shutdown cooling system. The system is connected between reactor outlet and inlet header at each end of the reactor. If normal heat removal fails and normal pressure control fails or their capacities are exceeded, the increase in coolant volume caused by the reactor heat would be passed out of the primary system by relief valves. One relief line connects the pressurized end of the north standby cooling loop, to the bleed condenser through these instrumented safety relief valves in parallel. Isolated boilers are protected against accidental high pressure by system relief valves. The PHT pumps are provided with flywheels to provide better flow coast down after pump trip. The system layout as discussed above assures adequate flow for decay heat removal from reactor during shutdown by thermosyphoning action. A separate shutdown cooling system is provided to remove reactor decay heat during cold shutdown conditions. This mode of cooling permits the draining of the steam generators and pumps in the PHT system for maintenance. An emergency core cooling system provides adequate coolant flow to prevent overheating of the fuel in the unlikely event of loss of coolant accident.

PRIMARY HEAT TRANSPORT

REACTOR BUILDING

FOLLOWING ARE THE PARTS OF REACTOR BUILDING:-

1. Calandria

8. Dump Tank

2. Control Rods

9. Dousing Tank

3. Fuelling Machine

10. Reactor Dome

4. Heat Exchanger

11.Coolant Channel

5. PHT Pump

12. Fuel Bundles

6. Moderator Pump

13. Coolant Tower

7. Boiler (Steam Generator) 14. Turbine

REACTOR

Reactor is the place where actual nuclear fission takes place. The building that houses reactor and other accessories is called Reactor Building. Following are the ingredients of Reactor Building:-

Calandria

Calandria is a huge cylindrical structure which houses bundles. The specifications regarding 200 MWe reactors calandria are:-

Weight

-22 tons

Length

-4645 mm

Main Shield I.D. -5996 mm

Small Shell I.D. - 4928 mm

Thickness of Shell- 25 mm

There are 306 channels each accommodating 12 bundles. The calendria is housed in steel lined concrete. calandria vault filled with light water which provides shielding and cooling of vault structure. Calendria tubes made up of zircaloy.

CUT SECTION OF CALANDRIA CONTROL RODS-

The control rods contain material that regulates the rate of the chain reaction. If they are pulled out of the core, the reaction speeds up. If they are inserted, the reaction slows down.

In RAPS, cobalt is used as control rods. The used cobalt is then processed and enriched .The enriched cobalt is then used for different purposes such as cobalt therapy etc.

FUELLING MACHINE-

Reactor fuel is moved into and out of reactor by a pair of fuelling machines that is clamped to channels on north and south ends of the reactor. It consists of Head, which contains positioning the mechanisms for manipulating the fuel, a carriage for Head in line with any desired fuel channel, and numerous houses and cables, which supplies fluid and MACHANICAL services. A ram and associated mechanism is provided for pushing reactor fuel and handling plugs in the reactor channels. The ram is operated by the hydraulic pressure of Heavy water. The fuelling machine is left in the vault when not in the use, unless maintenance operations are required on it.

The various plugs and fuel handled by the fueling machines are stored in the various chambers of the rotary magazine. The magazine has twelve chambers. Refueling can be done in a number of channels during one refueling session

HEAT EXCHANGER-

Tube-and-shell type heat exchangers are suitable in this type of system. The U type heat exchanger, shown in Fig simplifies expansion problems and reduces the number of tube sheet joints. Heavy water holdup is reduced by passing the heavy water through the tubes and the cooling water on the shell side. Double tube sheets with interspaces draining to leakage collection system are used to reduce leakage. The moderator pumps maintain the heavy water at a higher pressure than the cooling water. This ensures that any leakage that does occur will be from the heavy water to the cooling water. This is done to prevent any downgrading of moderator D2O as a result of cooling water leakage. A system for detecting radioactive nuclei, in the cooling water leaving the heat exchanger, would indicate D2O leakage into the cooling water. The tube material would probably be copper-nickel alloy, whereas the shell would be made of carbon steel. In RAPS cupronickel was used as tube material but to reduce probability of tube failure stainless steel is now being used as tube material. In order to maintain moderator cooling at all times the cooling water supply has to be very reliable. Should the normal process water supply fail an alternative source of cooling water must be available.Heat Exchanger

PRIMARY HEAT TRANSPORT PUMPS

The primary heat transport pumps in PHT system circulate the coolant past the fuel in the reactor core, to the steam generators to generate steam in the secondary system. The system is a high pressure and temperature as compared to the moderator system. The complete system contains 8-circulating pumps, 8 set of boilers, isolating valves of special design, 2-pressurising pumps, a stand by cooling system, a feed and bleed system and over pressure relief control valves.MODERATOR PUMPS AND AUXILLARIES

The main moderator circulating system consists of 5 pumps, 2 heat exchangers and necessary valve and piping. The pump circulate moderator from the calandria through the two shell and the tube type heat exchanger to keep the moderator temperature between 70f and 145 f. the cooled heavy water (moderator)is again fed into the calandria. The cooling necessities to reduce of capture of thermal neutrons in the moderator and also keep the thermal stress in the structure within permissible limits. The moderator receives about 37 MW fission heat. The auxiliary structure like calandria tubes, expansion bellows, support rods, absorber rods all are supplied with cooled heavy water from this system.STEAM GENERATORS

Steam generators are the units where the PHT gives away the thermal energy to DM water and hence it gets converted to steam. It is a continuous process. There are 4 boilers or steam generators.

The inlet water through the condenser cycle and the steam tapped are maintained such that there is a constant water level in the steam generators. Even at the time of shutdown there is continuous flow of PHT to take away the reaction heat and as a result there is always some steam generator even at non-working condition.

The water chemistry of Steam Generator is maintained in such a way that feed water is not causing scale formation in the boilers for this regular feed and bleed is done from each Steam Generator at regulator interval. Steam Generator level and pressure are maintained through triplicate control systems. In case of very high water level quality of steam to get into the turbine. In case of low level reactor trips to prevent less of heat sinks in boiler.

DUMP TANK

Just below the calandria and connected to it by a transition section and the expansion joint is dump tank. The purpose is to provide containment to the moderator when dumped through the S-shaped dump ports. In the normal operation the tank will be empty and contain helium at 24psi to support the moderator in the calandria.

Dump tank is connected to the bottom portion of calandria through a transition section and an expansion joint. Its purpose is to store the D2O of reactor under dump (shut down) condition. Dump ports are provided in the bottom portion of calandria near the transition section and in between the two stiffener rings. Under normal operation the dump tank remains empty of water (d2o) and is filled with helium at a pressure of 24 psig. to hold the heavy water in calandria. Dump ports are in transverse direction to the calandria axis

NUCLEAR FUEL

The fuel used in a PHWR type reactor is sintered natural uranium di-oxide in the form of small pellets. These pellets are kept in the zircalloy tubes and are 24 per tube. The tubes are known as pencils and 19 pencils make a complete fuel bundle. The pencils are held between end plates and zircalloy provide spacing between the tubes and zircalloy pads provide bearing action. This help mixing of the coolant flow with the sub channels between the elements.

COOLING TOWERS Mainly there are two types of cooling towers:-

-IDCT : Induct Draft Cooling Towers

-NDCT : Natural Draft Cooling Towers

The main purpose of these cooling towers is to bring down the temperature of circulating water. This is light water that circulates through the heat exchanger and carried away the heat generated by the DM water.

This DM water condenses the steam. Hence the application of cooling towers enhances the efficiency of the plant.

Following is the description of the types of cooling towers:-

IDCT

As the name indicates it requires induced draft for cooling the active process water. Big fans are used to produce the draft. The active water is used in Reactor Building to cool various process equipment etc.

NDCT

The inductive water that is used to condense water is further cooled by natural draft. They are 150M high with hyperbolic shape atomizing action.

STEAM TURBINE

Steam turbine is a rotating machine in which heat energy of steam is converted into mechanical energy.

WORKING PRINCIPLE OF STEAM TURBINE

The steam is caused to fall in pressure in a passage or nozzle; due to this fall in pressure a certain amount of heat energy is converted into mechanical kinetic energy, and the steam is set moving with a greater velocity. The rapidly moving particles of steam enter the moving part of the turbine and here suffer a change in direction of motion which gives rise to a change of momentum and therefore to a force. This constitutes the driving force of the machine.

IMPORTANT ELEMENTS OF TURBINE

i. The Nozzle:

This is the element in which the steam expands from a high pressure and a state of comparative rest to a lower pressure and a state of comparatively rapid motion.

ii. The Blades or deflector:

This is the element in which the stream of steam particles strike and experience a change in momentum due to change in direction resulting in a tangential force for rotation of turbine. The blades are attached to the rotating element of the machine, or rotor; whereas, in general the nozzles are attached to the stationary part of the turbine, which is usually termed the stator, casing or cylinder. They are of two types:

1.Impulse turbine :-In this, steam is expanded in turbine nozzle and attains a high velocity, also complete expansion of steam takes place in the nozzle & steam pressure during the flow of steam over turbine blades remains constant. The blades have symmetrical profile.

2.Reaction turbine :-In this, only partial expansion takes place in nozzle and further expansion takes place as the steam flows over the rotor blades.

7. METHODS OF MEASURING DOSE:

For measuring dose absorbed by a person, devices known as dosimeters are used. Generally there are two types of dosimeters these are:

1. Direct Reading Dosimeters (DRD).

2. Thermo Luminescence dosimeter (TLD).

Direct Reading Dosimeters (DRD):

This device measures the dose directly and is used for day to day dose control. It is a pen shaped device and lenses are fitted on both the ends. On bigger lens, a scale is marked which directly tells about the dose absorbed. For reading the DRD it is so held that the bigger lens should face the light source and it is seen from the smaller lens. This dosimeter is used in Third and Fourth Zone only.

Thermo Luminescence dosimeter (TLD):

This is a badge type device and is used to dose absorbed during one months time. TLD badge consists of a TLD CARD loaded in a CASSETTE. The dose measured by TLD is based on the phenomenon of THERMOLUMINISCENSE. TLD cassette has a dual metallic filter and an open window to distinguish between doses received due to different type of radiation (alpha, beta & gamma) and provides energy dependence correction. Personal data such as Name, TLD No., Service months etc. are written on it.

The person has to wear his TLD badge at his chest level when entering the operating island. After one month, the TLD card is sent to the TLD laboratory where the absorbed dose is measured.

DOSE CLASSIFICATION:

ABSORBED DOSE: Absorbed dose is simply the dose absorbed by a person and is measured by using the dosimeters. It is denoted by D.

EQUIVALENT DOSE: for calculating equivalent dose the type of radiation is also taken into account and the absorbed dose is multiplied by a factor wr.

EFFECTIVE DOSE: For effective dose despite of type of radiation the effective area of the body is also taken into account, and the absorbed dose is multiplied by factors wr & wt.

EMERGENCY DECLARATION:

To declare an Emergency in a plant a blinking siren is blown. After the declaration of emergency, each person in the plant is supposed to assemble in the assembly area.

To terminate the Emergency a continuous siren of 2 min. is blown. This siren indicates the termination of the Emergency8. RADIOACTIVE WASTE MANAGEMENT

GENERAL

Operation of a nuclear facility like nuclear power station inevitably leads to the production of low level radioactive wastes which are collected segregated to select best processing method, and conditioned for either interim site storage or for disposal. The design of facilities is such that the average public exposure from radioactive materials at the exclusion boundary is a small fraction of the recommended AERB limits. The radioactive wastes produced at the site may belong to one of the following categories:

Spent Fuel, Solid Wastes, Liquid Wastes & Gaseous Wastes.

Spent fuel is stored in a pool of water until it is ready for shipping for reprocessing at special facilities.

SOLID RADIOACTIVE WASTE MANAGEMENT SYSTEM

Solid radioactive waste in segregated into three general categories based on contact dose.

Category -1 wastes. : Largely originates

Protective clothing, contaminated metal parts and miscellaneous items. As it may contain no radioactivity. This waste will be collected in unshielded standard drums.

Category-II & III Wastes. : Filter cartridges and ion exchanges resins typically this waste has an unshielded radiation fielded greater than 1 R/hr. on contact. These require additional shielding and greater precautions than for category-I during transportation, handling and storage operation.

LIQUID RADIOACTIVE WASTE MANAGEMENT SYSTEM

The Liquid Radioactive Waste Management System provides for collection, storage, sampling and necessary treatment and dispersal of any liquid waste produced by the station. The system is designed to control the release of radioactivity in the liquid effluent streams so that radiations dose to members of the public is with in those stipulated by the regulatory board. This system handles radioactive wastes that are carried in liquid streams from the laundry active floor drains, decontamination center and chemical laboratories.

GASEOUS RADIOACTIVE WASTE MANAGEMENT SYSTEM

An extensive ventilation system collects potentially active exhaust air from such areas as the Reactor Building. The spent fuel handling and storage area, the decontamination center and the heavy water management area. The active and potentially active exhaust air and gases are all routed to a gaseous effluent exhaust duct. This exhaust flow is monitored for noble gases, tritium, iodine and active particulate before being released. Facilities for filtration are provided. Signals from the iodine, wide range beta-gamma and particulate monitors are recorded in the control center. Tritium monitoring is carried out by laboratory analysis.

SAFETY

INDUSTRIAL SAFETY

By Industrial safety we mean that the measures adopted as a whole in a industry so that occurrence of the accidents can be reduced to bare minimum.

Factors responsible for Safety:

Plant layout

Design of machinery

Safety Gadgets and equipments

Protective aids

Safety culture & Respect for Safety

Attitude of the management/ employer - Caution Boards

Display of Good practices about Safety

Safety meetings, Open discussion and other motivation about Safety

Safety Manual

Enforcement

Unsafe Act & Unsafe conditions

Causes of Accidents:

Hazards are the risks and perils or dangers that contribute to accidents and injuries.

"HAZARDS DO NOT CAUSE ACCIDENTS, PEOPLE DO".Kinds of Hazards:

Fire

Heat

Material Handling

Floors

Ladders

Tools

Machinery

Walking and Working surfaces

Process

Chemicals

Electricity

Unsafe Act

Unsafe Condition

9. RADIATION SAFETY

In a Nuclear reactor the Radiation is produced in following ways:

i) Directly in fission reaction

ii) By decay of fission products

Following types of radiations are encountered:

i) Alpha radiation

ii) Beta radiation

iii) Gamma radiation

iv) Neutron radiation

Out of the above types of radiations Alpha radiation is practically zero, whereas Beta and Gamma radiation fields may be present almost everywhere inside the reactor building and in negligible amount even outside the reactor building. Neutron radiations are mainly present inside the reactor vault. It is worth noting that the secondary side of the plant i.e. feed water and steam cycle etc. are completely separate from the nuclear systems and are therefore not supposed to be and neither they are to carry any sort of radioactive particle and therefore free of contamination and radiation. It is also wroth noting that all radiations are emited from the nucleous of every radioactive nuclide which will always have a tendency to become stable by emitting radiations through disintegration.

The following reactions show the emmision of Alpha, Beta, Gamma and Neutron.

92U238 ( 2He4 ( 92U234 + (alpha)

It has very low penetrating power and can be stopped by simple paper.

1H3 ( 2He3 (18 Kev) +beta

It also does not have good penetrating power and in human skin it can penetrate up to about half mm. It can be very easily shielded

92U235 + 0n1 ( 92U236 ( Xe + Kr + 0n1 + gamma + Heat

Following methodologies are used to control the exposure to the radiation and therefore resive of the radiation dose.

(1) Administrative Control

(2) Zoning Technique

(3) Design Control

(4) Operation Control

(5) Maintenance and house keeping

Exposure to any kind of radiation can be controlled by an individual by following methods:

(1) Distance

(2) Shielding

(3) Decay (Time to Decay)

MACHANICALCOMPONENTS

BEARINGS

THE BASIC PURPOSE OF BEARING IS TO:

1. Support the load

2. locate the part in motion

3. reduce friction

CLASSIFICATION OF BEARING

1. Plain bearing

2. rolling element bearing

BEARING ARE ALSO CLASSIFIED AS:

Friction: dry, semi dry

Motion: sliding or rolling

Load: radial, axial and combination

Duty: heavy or light

Lubrication: type of lubrication involved

Manufacture: manufacturing process involved e.g. forming heat treatment, finishing and impregnation of lubricants

Application: instrument, special, self-aligning

PLAIN BEARING

Plain bearing includes types in which primary motion is sliding. They handle radial and thrust loads, as well as linear motion. These bearings are broadly classified as

1. journal or sleeve bearing

2. self aligning bearing

3. thrust bearing

4. compliant bearing

1. JOURNAL BEARING:

Widely used bearing are cast bronze and porous bronze cylindrical bearing. Cast bronze bearings are oil and grease lubricated. Porous bearings are oil lubricated.

Application of cast bronze bearing: power tools linkage and valve guides.

Porous bearings: electric motor and fans

They are further classified as:

Solid bearings

Split bearing

Plumber block

2. SELF ALIGNING BEARING:

These bearings are used where bending of the shafts or other misaligning factors cant be avoided during the operation period. It compensates angular misalignment resulting from errors in mounting, shaft deflections during operation and distortion of foundation. It is used in applications requiring extreme accuracy at high speeds.

3. THRUST BEARINGS:

They are intended to take axial loads. They are used in horizontal as well as vertical applications. It can be designed for unidirectional or bi-directional thrust loads. They are classified on the basis of bearing design.

Taper land thrust bearing: in this the load carrying section is made as a radially grooved. The grooves are slightly tapered to facilitate the penetration of oil. The taper end is very small, so that the pressure film is formed between the bearing ring and the collar of the shaft and is known as HYDRODYNAMIC FILM.

Tilting pad thrust bearing: this type of bearing is used to minimize local overheads on the bearing, which may arise due to possible shaft misalignment. They are used for high speeds where low wear rates are essential.

The bearing member in this type are tilt able independent shoes arranged segmental around the shaft in the bearing housing and they are free to tilt on their pivot points. They can be used for unidirectional and bi-directional thrust loads.

4. COMPLIANT BEARING:

They are fluid lubricated bearing with surfaces that elastically deform equal to or more than the lubricating film due to fluid pressure induced in the film.

All the above bearing can be of following three types depending on the method of lubrication.

Boundary lubrication: in this a full fluid film doesnt support the shaft in the bearing.

Hydrodynamic lubrication: the load bearing surfaces are completely separated by the fluid film. The fluid pressure to separate the surfaces developed by shearing of viscous fluid film between surfaces due to rotation of shafts. The developed pressure supports the applied load.

Hydrostatic lubrication: this type also uses a fluid film to separate the bearing surfaces. However the pumps to support the applied load supply pressurized fluid externally.

ADVANTAGES OF PLAIN BEARING:

Less radial space required.

Less noise

Better load carrying capacity.

Close tolerances not required.

Easy installation and maintenance.

No damage on the increase of speed.

MATERIAL FOR PLAIN BEARING:

Babbitt, bronze, copper and its alloys, aluminum and its alloys, carbon, Teflon, rubber, plastics

DESIRABLE PROPERTIES OF PLAIN BEARING MATERIALS: SCORE RESISTANCE: ability of the material to the shaft because of friction.

LOAD CAPACITY: ability of the material to handle maximum amount of pressure without failure.

FATIGUE STRENGTH: ability of material to resist failures caused by cyclic loads.

CORROSION RESISTANCE: ability of material to resist oxidation. Corrosion may take place due to surrounding atm. Or lubricants.

CONFORMABILITY: ability of the material to wear to adjust for the misalignment of the shaft.

EMBED ABILITY: ability of the material to absorb foreign particles.

ROLLING ELEMENT BEARING:

Basically they consist of inner race, outer race, rolling element, and cage. Rolling element can be balls, cylindrical rollers, spherical rollers or tapered rollers.

Types:

Ball bearing

Roller bearing

BALL BEARING:

They are divided into three-category radial, angular contact and thrust bearing. Radial bearings are designed for application in which loading is primarily radial. Angular contact bearings are used where loads are combined radial and high thrusts. Thrust bearings handle only axial loads.

1. DEEP GROOVE: This bearing is designed primarily for radial loads but it is capable of carrying equal amounts of thrust loads in either direction. They are also available with two or more no. of rows, accordingly they are called as single rowed or double rowed.

2. ANGULAR CONTACT BALL BEARING: In this type of bearings there is central line of contact angle and is between 15 and 45 degrees. These bearings are capable of carrying higher axial loads but in one direction only. They are also available with two or more no. of rows, accordingly they are called as single row or double row angular contact ball bearings.

3. SELF ALIGNING BALL BEARING: In this type of bearing the tract on the outer race is grounded spherically and its this feature which gives these bearings the property of self alignment. The shaft deflection up to 4( is automatically adjusted without damaging the bearing. These carry radial loads.

4. THRUST BALL BEARINGS: They are of two types single and double thrust. Single thrust bearings consist of two rings and a set of ball in a retainer. Double thrust bearings consists of one rotating ring in the middle with two ball tracks, two sets of balls in a retainer and two stationary rings. Single thrust bearings are designed for carrying load in one direction only. Whereas double thrust can take load in both directions. But these bearings can never take any radial loads.

ROLLER BEARINGS:

1. CYLINDRICAL ROLLER BEARINGS: In this type of bearings, the roller and the racetracks are essentially cylindrical. The rollers are guided between two lips on either the inner race or outer race. In this type of bearing the rolling element has only line contact on the races. They have high radial load carrying capacity and are more convenient for mounting than ball bearings.

2. SELF-ALIGNING SPHERICAL ROLLER BEARING: This type of bearings consists of spherical outer race and inner race with two tracks, a cage and complement of spherical shaped rollers. These bearings are thrust loaded in either direction.

3. TAPER ROLLING BEARINGS: Taper roller bearings consists of two main units a cup and a cone. The cup is on the outer surface and the cone is on inner race, the separator and the complement of taper rollers. These bearings are capable of capable carrying axial loads but in one direction. They can also carry radial loads.

4. NEEDLE ROLLER BEARINGS: These comprises the special form of cylindrical roller bearing in which the rollers are of very small diameter and comparatively long length therefore they have the advantage of very small difference between bore and outside diameter. They carry only radial loads. In this bearing L/D >2.

CAUSES OF BEARING FALIURE:

Improper mounting

Loose or excessive tight fit on the shaft

Misalignment

MACHANICAL damage

Vibration brandling

Inadequate lubrication

ADVANTAGES OF BALL BEARINGS

1. Low friction

2. Ability to support both radial and thrust load.

3. Accurate performance under changing load and speed.

4. High load carrying capacity.

5. Practically no wear in running

6. Simple lubrication

7. Inherently precise mechanism

PUMPS

PUMP: Pump is a mechanical device which is used to suck liquid from particular level and then discharge to the required level by providing it the K.E. as well as P.E. that is pressure and velocity (flow).

CLASSIFICATION OF PUMPS: basically pumps are classified as following tree diagram:

PUMPS

POSITIVE DISPACEMENT ROTODYANAMIC

PUMP PUMP

RECIPROCATING ROTARY PUMP CENTRIFUGAL

PUMP

PUMP

AXIAL ORRADIAL MIXED

PROPELLER PUMP FLOW

PISTONPLUNGERBUCKETPUMPPUMP

PUMPPUMPPUMP

GEAR PUMPSCREW PUMP VANE PUMP RADIAL PISTON PUMP

CENTRIFUGAL PUMP:

A centrifugal pump consists of a rotating element including impeller and a shaft and a stationary element made of a casing, stuffing box and a bearing. Vanes of the impeller impart energy to the fluid through the centrifugal force. The fluid is forced into impeller due to the differential pressure between pressures at the water surface in the section tank and pressure at the section eye of the impeller. Fluid is discharged through impeller output at higher pressure and velocity. The velocity is converted into pressure by means of the involutes or set of stationary diffusers vane surrounding impeller.

ROTARY PUMPS

It is a positive displacement pump, i.e. they will provide discharge to there rated value even if the discharge valve is closed to some extend. These types of pumps are involving the rotating motion. This pump has a number of advantages such as

( Can operate under low NPSH requirements and produce high suction lift.

( Relatively high efficiency, when pumping viscous liquids.

( Hydraulic characteristics are good with high head at a wide range of capacities.

( Have extensive speed range, generally limited only by fluid viscosity.

( Inherently self-priming since they are virtually operated as compressor.

SLIDING VANE TYPE PUMPS

It is a type of rotatory pump, used in many applications in industrial plants. In these types of pumps the vanes are made up of softer material then the pump casing and hence they wear less and are easily replaceable at low cost.

In these pumps as the impeller rotates, its offset position above the pump centerline allows the vanes or blades to extend and draw in fluid on one side. The open space between the impeller and housing at the bottom of the pump allows the movement of the fluid through the pump. As the continues its rotation, the vanes are pushed back in there slots as they near the top of the pump this contraction of available space forces the fluid out of discharge port. In some vane type pumps the impeller vanes are spring loaded which assures that there will be complete contact with the casing of the vane.

Usually operate up to differential pressure of 50 psi and capacities up to 375gpm. Practical limit on liquid viscosity is about 100000 SSU. This type is subjected to wear and should not be specified when liquid has poor lubricating qualities

GEAR TYPE PUMP

Two types of gear pumps are there:

(a) External gear pump

(b)Internal gear pump

It is also a rotatory pump

Gear pumps along with their industrial use some times are also used for bearing lubrication and supplying cutting fluid.

In these type of pumps the fluid being pumped is drawn through the space between the rotors and the pimp casing by the gear teeth and forced out by discharge port. The meshing gears just only prevent the back flow of the fluid to the suction side.

These gears are classified on the basis of the type of gear used in the pump and are SPUR GEAR PUMP, HELLICAL GEAR PUNP and HERRINGBONE GEAR PUMP. Spur gear pump is used mostly because it is economical, but its power transmission is unsmooth because very less area of its teeth of either gear comes in contact.

To overcome this problem of un-smooth power transmission helical gear pump is used, in helical gear pump the contact area of the teeth increases and the power transmission becomes smoother but since the teeth of helical gear are on an angle therefore the problem of axial thrust arises.

To overcome this problem of axial thrust the herringbone gear pump is used since in this the teeth are in opposite direction therefore they can bear the axial thrust along with the smooth power transmission.

Gear pump are used to about 650 gpm and 350 psi. They can handle viscosity approaching 5 million SSU. These pumps are self-priming; give constant delivery at the set rotor speed, negligible pressure pulsation. They can pump in either direction if necessary.

SCREW PUMP

It is another type of rotary pump. It has a double impeller design and hence it is able to pump large amount of fluid easily. It is expensive to manufacture and is quite susceptible to damage from abrasive material.

In operation the screw type pump is driven by the center rotor called the power rotor. It drives two idler rotors, which meshes with it. Both idler rotors are identical being threaded to mesh with power rotor.

As the power turns fluid is drawn in from one end of the pump and is discharged out from the other end. As the thread of power rotor met with the idler rotor the fluid is forced along the opening in the threaded area towards the discharge section of the pump.

Screw pumps are applied to large flows, since they have capacities up to 4000GPM and 3000psi. Viscosity capability is about 100 million SSU (say bolt seconds unit). Screw pumps have bearing and time gear requirements. Screw pumps can operate at high speeds because of lower fluid velocities. The reason is that in this type the flow is axial, as opposite to flow around the periphery of gear or the vane pump.

RECIPROCATING PUMPS

These are also positive displacement pumps. In these types there is cylinder in which a reciprocating part reciprocates, this may be piston, plunger or diaphragm.

The fluid is pumped out due to the pressure exerted on it by this reciprocating part, the inlet and outlet valves are mounted on the cylinder through the fluid is taken in and pumped out. The reciprocating part is connected to a crankshaft, through which it gets its reciprocating motion

TYPES OF RECIPROCATING PUMPS:

(a) Diaphragm pumps

(b)Plunger pumps- simplex, triplex

(c)Piston types- single acting and double actingPiston pumps:

In this type of pump the reciprocating part is the piston, this piston is connected to the crankshaft through the connecting rod, there are inlet and outlet valves mounted on the head of the cylinder, in the reverse stroke of the piston the fluid is sucked in the cylinder and in its forward stroke the fluid is pumped out of the cylinder

The piston pump may be single acting or double acting, in single acting the fluid is sucked in and discharged out from one side of the piston. But in double acting the fluid is sucked in and discharged out from both side of the cylinder.

Plunger pump:

From construction point of view plunger pump is similar to that of the piston pump; the only difference is that the length to dia ratio of plunger is more than that of the piston. It imparts more pressure to the fluid. The plunger pump may be simplex, duplex or triplex.

Simplex plunger pump is the plunger pump in its simplest form.

In duplex pump there are two cylinders and two plungers one installed in each cylinders, and both the cylinders are connected to the same crankshaft in this type of arrangement when first cylinder is taking suction the second one is giving out its discharge, and vice versa in the second stroke.

In triplex plunger three plungers and three cylinders are connected to the same crankshaft And each of them will give discharge in different times. The duplex and triplex arrangements are made to give a smooth discharge

Diaphragm pump:

In this type of pump a diaphragm is there just below the cylinder head. This diaphragm is connected to the crankshaft and provide the reciprocating motion, when the suction valve is open the comes in the orifice of the diaphragm of the, and then it is pumped out in the forward stroke of the diaphragm. The pump is used for low pressure and low discharge.

Diaphragm pumps are used in control volume application, capacities 600 gal/hr at discharge pressure to 3500 psi. Plunger pumps have larger capacities than diaphragm pumps- up to 1000 gal/hr and 7500 psi. Large plunger types often called power pump, turn out 600 gpm, at pressure up to 10000 psi. Piston pumps are generally less expensive than plunger types but have shorter service life. Maximum performance of piston type is in the range of 600 gpm and 750 psi.

Pulsation is inherent in reciprocating pump. Multi cylinder pump arranged at different crank angles will reduce pressure pulsation. Accumulator can be used for high-pressure application and as a metering pump. Plunger pumps are necessarily single acting devices. Plunger moves through stationary packet seal whereas in the piston the seal is carried on the piston.

VALVES

Valves:

Valves are mechanical device used to isolate, regulate or release the process the fluid flow through pipeline.

Principle functions of valve:

Starting and stopping flow

Regulating or throttling flow

Preventing back flow

Regulating pressure

Relieving pressure

Different types of valves are used for different types of functions such as:

Gate valve is used for starting and stopping process.

Globe and angle valves are used for regulating and throttling flow.

Check valve are used foe preventing back flow.

Pressure regulator is used for regulating pressure.

Safety or relief valve are used for relieving pressure.

Classification of valve on the basis of function performed by them:

1. Isolating valves: This type of valve are either fully opened or fully closed. Gate valve, plug Valve and ball valve are examples of this type.

2. Regulating valve: These types of valves regulates or control the rate of flow of fluid according to the requirements. They can be opened in any position from fully opened to fully close. Globe valve, angle valve are examples of this type.

3. Non return/check valve: These types of valves permits the flow of fluid in one direction only and automatically shuts off if a reversal flow occurs. The direction of fluid flow is indicated by an arrow on valve body. Swing check non-return valve and lift check non-return valve are examples of this type.

4. Safety valve: These type of valve are designed to open as soon as the predetermined and set pressure has been reached on the system. Spring load safety valve and torsion bar type safety valve are examples of this type.

Gate valve:

( It is used to close or full open the valve.

( The flow is perpendicular to the seat of the valve.

( Slightly pen valve cause vibration and chattering of disc. Flow cause erosion of seat.

( Repeated movement of disc near closing under high pressure flow may gal or score seating.

( Refacing seats is difficult and time-consuming operation.

Globe valve:

( Seat parallel to line of flow and are used for regulating.

( No contact of seat and disc when flow begins.

(Operator can gauge the rate of flow by the no of turns of hand wheel.

( Fever turns are required to operate the valve.

( Seat and disc can be repaired without removing the valve easily online.

Check valve:

( They protect fro-reverse flow.

( Open in flow direction only and closed in other.

( They work by pressure and gravity.

( Greater the pressure difference greater will be the seating force.

( Fluctuations cause severe operating conditions.

( These valves can be regrinding or replaced.

Butterfly valve:

( Saves space and less hold up.

( Doesnt require support.

( Resilient liner provides tight shut off.

( At high temperature piston ring minimizes the leakage.

( Any accumulator can be used.

( Double ported valve increases the control range.

Diaphragm valve:

( These types of valves are used for chemicals and slurries.

( They have tight shut off.

( They are generally used for on/off service.

( The operating temperature is limited on the basis of material used for diaphragm.

Plug valve:

( These are quickly operated valves; they can be fully opened or fully closed by the quarter turn of spindle.

( They are used in the line where quick shut off is required.

( There is a conical plug, which fits into a matching seat in the body. The hole or the port in the plug is usually rectangular.

( They are not suitable for throttling, but with special port design they can be used for low flow regulation.

( They are externally lubricated through the spindle.

( Non-lubricated valves use a special seat of Teflon or plastic.

Ball valves:

( Ball valves are improved version of tapered plug valves.

( Their operation is similar to that of plug operation.

( They exhibit a negligible pressure drop because of their smooth full opening port.

( Seat material includes plastic, synthetic rubber, and plate of which also limits the operating temperature.

Bellow seat valve:

In these valves a stainless steel bellow is attached to the movable stem at one end and to the stationary bonnet at the other end. The purpose of using metal bellows is to limit the stem leakage to zero. Due to unpredictable life of the bellow, the use of a secondary seat is a must in order to hold the leakage from the metal bellow. The secondary seal is usually of white asbestos packing and serves as a back up seal.

Pressure relief devices:

Applications safety valves are used to prevent excessive pressure in process piping and piping system and thus protect equipments from failure. They are of three major types:

Relief type

Safety type

Pop type

Relief valve:

Relief valve are primarily used to relieve excessive pressure in the liquid service. Pop valve are used in compressible fluids like steam, air and gases.

Relief valves are must to use in the outlet of every positive displacement pump. They are usually spring loaded and the valve opening pressure is adjusted by tightening or loosing the spring. The valve is activated by static pressure under the disk. When the line pressure exceeds the present pressure of the spring the valve is opened and excess fluid goes out of piping to the suction tank.

Safety relief valve:

The essential element in a safety relief valve is a disk, which is held against the seat by a heavy spring and so called HUDDING CHAMBER. The huddling chamber is so constructed that when the valve is slightly opened static pressure is build up in the chamber, which immediately forces the valve open. The pressure below the valve must drop a few units below the opening pressure before the valve closes. This is known as blow down and is often from 2-4% of the opening pressure.

Spring loaded safety valve:

The valve is designed to give a positive lift when the set pressure is reached. The positive lift is achieved by the design of the valve disk known as THERMO DISK. As the valve commences to open, the area of the disk exposed to the steam greatly increases, this causes the valve to lift, further forcing the valve disk upward inside the valve guide.

Setting involved:

( Set pressure: The set pressure of the valve can be increased or decreased by tightening or loosening the compression screw. Moving the head of the compression screw by one flat, approx. alters the set pressure by 1%.

( Adjusting blow down: This is altered by moving the upper adjusting ring clockwise or anticlockwise. Moving the ring clockwise will increase the blow down and vice versa. The ring should be moved 8 to 10 slots at a time to have some noticeable change in blow down.

( Simmering: This is the state of safety valve when it reaches to the opening pressure then instead of neatly opening it remains in that state for a long time and it leaks. This can cause steam cuts on the disk and seat faces. This can be removed by raising the lower adjusting ring.11. CONCLUSION The practical training at R.A.P.S. has proved to be quite faithful. It proved an opportunity for encounter with such huge components like 220MW generators, turbines, transformers and switchyards etc. The architecture of the NPP (Nuclear Power Plant):

The way various units are linked and the way working of whole plant is controlled make the students realize that engineering is not just learning the structure description and working of various machines, but the greater part is of planning, proper management.

It also provides an opportunity to learn technology used at proper place and time can save a lot of labor for example almost all the controls are computerized because in running condition no any person can enter in the reactor building.

But there are few factors that require special mention. Training is not carried out into its tree spirit. It is recommended that there should be some projects specially meant for students where the presence of authorities should be ensured. There should be strict monitoring of the performance of students and system of grading be improved on the basis of the work done.

However training has proved to be quite faithful. It has allowed as an opportunity to get an exposure of the practical implementation to theoretical fundamental.

DILRAJ MEENAII-YEAR

GOVT. POLY. COLLEGE

BANSWARA

Principle Of Heat Generation

Fission Reaction

n1

Sr90

In the above equation, (1) the total mass before fission, is the sum of the masses of U235 and the neutrons. Mass after fission is the sum of fission fragments and neutrons.

Since loss of mass of 1 a.m.u is equivalent to an energy release of 931 MeV. Therefore energy release in the above reaction could be calculated as follows. Since

Xe144

n1

( - Ray

U235

U236

EMBED Unknown

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