low pressure reactors
DESCRIPTION
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LOW PRESSURE REACTORS
OVERVIEW
I’ll discuss here:What is nuclear energy?Nuclear reactorNuclear power plantTypes of nuclear reactors andNuclear reactor hazards
What is nuclear energy?
Nuclear energy produces electricity from heat through a process called fission. Nuclear power plants use the heat produced by fission of certain atoms.
1. Nuclear fission
nucleus of atom is split into parts, produces free neutrons and
energy
Nuclear Reactors
Nuclear Reactor device built to sustain a controlled nuclear fission chain reaction
www.pbase.com/pbrakke/image/44279993
http://en.wikipedia.org/wiki/Image:Crocus-p1020491.jpg
Main Components of Nuclear Reactor: - reactor vessel- tubes of uranium- control rods- containment structure
control rods control radioactivity, absorbs neutrons
Containment structure contains the reaction in at least 3 feet of concrete!
The Nuclear Power Plant
Fission occurs in the reactor
vessel. Heat is produced.
The heat is used to heat water to
create steam
The steam is used to turn the
turbine in the generator to
produce electricity
The steam is cooled in the condenser to return to the liquid phase.
Nuclear power plant consists of all the parts needed to create electricity by using nuclear energy
Types of Nuclear Reactors:
Thermal Reactors and Fast Reactors Homogeneous and Heterogeneous Reactors Low Pressure and High Pressure and Reactors
Low Pressure Reactors: Pressure is normally 7MPa Water boils in the core of the reactor Low pressure reactors are working in a “DIRECT CYCLE”
Most common low pressure reactors are:
Boiling Water Reactors BWR Advanced BWR, ABWR Economical Small Boiling Water Reactor (ESBWR) RBMK Reactor
Boiling Water Reactors BWR:
• Direct Boiling• 10% Coolant = Steam• 3.2% U-235 Fuel• Lower Power Density
than PWR• Corrosion Product
Activated in Core• Higher Radiation Field
• UO2 Fuel
• 60 – yr Service Life• Internalized Safety and
Recirculation Systems
Basic Diagram of a BWR
http://www.nrc.gov/
ABWR (Advanced Boiling Water Reactor)• 1350 MWe• 77% more compact
than BWR design• 39 month construction
period
TOSHIBA, Kashiwazaki-Kariwa Unit 6, Japan
GE
ABWR – Less Pieces
ABWR-IIEarly 1990s - TEPCO, 5 other utilities, GE,
Hitachi and Toshiba began development1700 MWeGoals
30% capital cost reductionReduced construction time 20% power generation cost reduction Increased safety Increased flexibility for future fuel cycles
Commercialize – latter 2010s
ESBWR (Economic Simplified Boiling Water Reactor)
1550 MWe (4500 MWt)Passive Condenser
Systems for Heat Transfer
Standard Seismic Design
Improved EconomicsShorter Construction
TimeReduced Plant Staff
and Operator Requirements Raised Suppression
Pool
Decay Heat Heat Exchangers Above Drywell
All Pipes/ Valves Inside Containment
High Elevation Gravity Drain Pools
Raised Suppression Pool
Decay Heat Heat Exchangers Above Drywell
All Pipes/ Valves Inside Containment
High Elevation Gravity Drain Pools
RBMK Reactor High Power Channel-type Reactor Graphite-moderated 1986 Chernobyl disaster Reactor pit is made of reinforced concrete Pit Dimensions 21.6×21.6×25.5 meters Vessel of the reactor, made of a cylindrical wall and top and bottom metal
plates Moderator blocks are made of nuclear graphite of dimensions 250×250×500
mm There are holes with 11.4 cm (4.5 in) diameter Cylindrical core 14 m (45 ft 11 in) in diameter and 8 m (26 ft 3 in) high Maximum allowed temperature of the graphite is less or equal to 730 °C (1,350
°F) Top of the reactor is covered by the upper biological shield, called "Schema E" Fuel channels consist of welded zircaloy pressure tubes 8 cm (3.1 in) in inner
diameter with 4 mm (0.16 in) thick walls There are 1661 fuel channels and 211 control rod channels in the reactor core UO2 pellets 1.15 cm (0.45 in) in diameter and 15 mm (0.59 in) long Emergency Core Cooling System (ECCS)
Nuclear Reactor Hazards Radiation effects to the workers of plant Radiation effects on environment and atmosphere Power plant is a major threat for public in case of a disaster like
Chernobyl Ageing process of nuclear reactors produces:
Small leakages Cracks Short-circuits due to cable failure Gradual weakening of materials Embrittlement of the reactor pressure vessel
There is also a threat of terrorism attack That attack may be from air, water or firing on plant from a
distance Spent fuel pool disaster Radioactive waste storage disaster Two major nuclear reactor disasters are Three miles island and
Chernobyl
