full scale component test facility kopra – qualification ...the test facility kopra is designed...

IYNC 2008 Interlaken, Switzerland, 20 – 26 September 2008

Paper No. 136

136.1

Full Scale Component Test Facility KOPRA – Qualification Test of EPR Control Rod Drive Mechanism

Alexander Sykora, Wolfgang Herr1, Francois Champomier2

1AREVA NP GmbH, P.O. Box 3220, 91050 Erlangen, Germany; 2AREVA NP SAS, Tour AREVA – CEDEX 16, 92084 Paris-La Défense, France

[email protected]

ABSTRACT

The test facility KOPRA is designed for full scale-tests on nuclear components under operational conditions. One part of it is the component test loop for developing and qualifying nuclear core components respecting temperature, pressure and mass flow of pressurized water reactor conditions.

The KOPRA test facility and its measuring equipment is presented through qualification tests for the control rod drive mechanism and the control rod driveline of the new European Pressurized Water Reactor (EPR).

The control rod drive mechanism qualification test program is split into three different test phases. At first, performance tests are conducted to verify the adequate performance of the new equipment, e.g. measurement of rod cluster control assembly drop time under different thermal hydraulic conditions, impact velocity of drive rod on CRDM latch tips and drive rod acceleration during stepping operation by means of strain gauges or through direct measurement.

After these functional tests follow the stability tests to ensure that proper functioning is reliably achieved over an appreciable amount of time and the endurance tests to quantify the amount of time and/or the number of steps during which no appreciable wear, that could possibly alter the correct behaviour, is to be expected.

1 INTRODUCTION

It is necessary for developing and qualifying nuclear components to conduct extensive tests under reactor conditions respecting temperature, pressure and mass flow. Beyond that, for tests regarding long term behaviour and wear effects it is also required to adapt the water chemistry so that it is comparable to reactor conditions.

The component test facility KOPRA is developed to fulfil these requirements for pressurized water reactors. It is a multifunctional high-pressure test facility containing four test loops, three pressurizers and three main pumps. Figure 1T displays the design principle of the test facility with the four test loops being described subsequently. Table 1 shows the possible test parameters.

The test pressurizer serves as a test station for the qualification of pressurizer main safety valves under full flow conditions. Furthermore, it is also used for the hot adjustment of pilot valves and the recording of valve characteristics under different conditions.

Functional testing and qualification of various valves in closed and open test loops is the domain of the valve test section, consisting of four different horizontal pipes with diameters up to DN 200.

Control Rod Drive Mechanisms (CRDMs) can be tested in the CRDM test section, where the focus lies on the CRDM which makes it possible to simplify the test assembly by omitting the fuel assembly (FA) and the control rod guide assembly (CRGA). The rod cluster control assembly (RCC-A) is represented by a dummy with the corresponding weight and flow behaviour. This test section is

Proceedings of the International Youth Nuclear Congress 2008

136.2

mainly used for acceptance and functional tests of CRDMs after manufacturing or repair as well as for new developments.

Figure 1: Principle Diagram of the Component Test Facility KOPRA

Table 1: Test Parameters of the Component Test Facility

pressure [bar]

temperature [°C]

flow rate [kg/s]

test fluid material of test facility

steady state 5 – 160 50 0 – 400

Cold Water transient < 194 50 0 – 100 steady state 10 – 160 50 – 340 0 – 300

Hot Water transient < 185 < 360 0 – 30

Saturated Steam transient < 185 100 – 360 0 – 30

Two Phase Flow transient < 185 < 360 0 – 30

(water)

Pure demineralised water to which chemicals can be added to

meet the specific PWR requirements

austenitic stainless steel

With the core test section that will be described in this paper by means of the qualification test

of the CRDM and control rod driveline of the EPR, it is possible to test FA and primary-system components.


136.3

An outline of the possible tests in the core test section is mentioned below:

• Functional tests of entire FA and CRDM configurations • Investigations of FA and control assembly behaviour under normal and abnormal

operating conditions • Control assembly insertion tests • FA pressure drop measurements • Testing of flow-induced vibration of core components, especially fuel rods

2 TEST CONFIGURATION

2.1 Test Set-up

The main pump, heater, pressurizer and test channel are the main circuit components (Figure 2) and are providing the required temperature, pressure and main flow.

Storage Tank

Pressurizer

Feed Pump

Main Pump

Test Channel

Bypass

main mass flow

CRDM

Figure 2: Core Test Section with Main System Components


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It is necessary to degas the water to meet the specified requirements. Therefore, a permanent leakage is piped through the storage tank and pumped back into the main circuit by the feed pump. The conditions in the storage tank are optimized to limit the amount of solved gases in the water.

The core test section, or more precisely the test channel, had to be adapted to satisfy the geometric specifications of the EPR driveline components. After the adaptation of the test channel it is possible to place the complete driveline of the EPR into the channel, as illustrated in Figure 3.

Different flow conditions, up and down streams, depending on the location of the driveline prevail in the upper part of the core, between upper support plate and reactor vessel hat. An additional bypass is realized at the top of the test channel to enable the simulation of different driveline positions on the reactor vessel hat.

Test Channel Assembly of the CRGA

Top of Fuel Assembly

Figure 3: Test Set-Up and Test Components

2.2 Measuring Technique

The measuring equipment has to fulfil the different requirements imposed on the test, which are: • control of proper interaction of all components • control that the design fulfils the mandatory requirements • investigation of the long term behaviour • data collection for verifying and adjusting computer based models • additional measuring equipment for determining drop times of the RCC-A

The complex measuring tasks and the conditions in the test loop regarding temperature and

pressure made it necessary to divide the sensors into two groups. One group is assembled for all tests whereas the other group is only applied for specific tests. The first group is the subject of this chapter, the other one will be characterized later in the test description.


136.5

The following list gives an overview of the measured physical values:

• system parameters like temperature, pressure and mass flow (main mass flow and bypass mass flow) at different positions in the test loop to record the status of the entire test set-up

• differential pressures over the FA to determine the pressure drop over its entire length; this information is important for the validation of computer based models investigating the behaviour or the driveline

• differential pressure over the pressure housing, for detailed analysis of the RCC-A drop times and drop behaviour

• structure-borne sound to detect component movements in the test channel, i.e. for verifying the proper functioning of the CRDM and determination of RCC-A drop times.

3 SET-UP AND FUNCTION OF THE CRDM

It is necessary to explain the components and functions of the CRDM to ease the description of the different conducted tests. Figure 4 displays the CRDM main components. The driving coils and the funnel build the outer shell of the CRDM. Within the funnel, the positioning coils are located. These parts are mounted on the pressure housing. The pressure housing is part of the pressure vessel, i.e. within the pressure housing prevail reactor conditions. The latch unit, which moves the drive rod, is located in the pressure housing. The drive rod is connected with the Rod Cluster Control Assembly (RCC-A), these two components together are called the mobile set.

Drive Rod Driving Coils and Funnel

Positioning Coils Pressure Housing

Latch Unit

Figure 4: Control Rod Drive Mechanism (CRDM) – Dismantled

The latch unit has two groups of latches, with three latches each, on different levels, the holding latches and the lifting latches. The holding latches are activated by the stationary gripper armature.


136.6

The lifting latches are shifted with the lifting armature and activated by the moveable gripper armature. The three armatures have corresponding driving coils, stationary gripper coil (SGC), moveable gripper coil (MGC) and lifting coil (LC).

The magnetic field emitted by the coils acts through the pressure housing and moves the armatures of the latch unit and with them the latches. The movement of the RCC-A is performed by a sequence of movements of the armatures and latches. When the mobile set is idle, the MGC is activated and, hence, the lifting latches are engaged. To perform an upward movement, the LC is activated and the LC armature performs a 10 mm shift upwards. When the armature reaches the uppermost position the SGC is activated and the holding latches engage. The holding latches take over the load from the lifting latches which are disengaged by deactivating the MGC. This is followed by the deactivation of the LC and the LC armature moves down to its origin position. This sequence of steps is finished by engaging the lifting latches (MGC is activated) and disengaging the holding latches (SGC is deactivated).

Figure 5 shows the currents and voltages of the driving coils for one step (the step starts at the blue vertical line and ends at the red one). The red graphs are the currents of the coils and the green ones are the voltages. The signal of the attached acceleration sensor measuring structure-born noise is the lowermost graph. This signal helps to define the ends of the armature movements. Figure 6 shows the latch unit.

Figure 5: Current and Voltage of the Driving Coils during one Step up

LC I TLS1 -42,91 mA2 -84,12 mA

10,00 Ampere

1,00 e0 Amper

LC U Coil A1 279,0 mVo2 -1,696 Vo

t

-500,0 Volt

400,0 Vol

MGC I TLS1 4,082 Am2 4,350 Am

6,000 Ampere

2,00 e0 Amper

MGC U Coil A1 245,5 Volt2 245,7 Volt

400,0 Volt

-500,0 Volt

SGC I TLS1 43,71 mAm2 63,74 mAm

6,000 Ampere

2,00 e0 Amper

SGC U Coil A1 -24,71 Vo2 -24,15 Vo

lt

-500,0 Volt

400,0 Vo

S031 99,65 mg2 118,5 mg

40,00 g

-40,00 g

100,0 ms/div00:00:03.8180000 00:00:04.8180000

100:00:03.8842526 200:00:04.6844596-2 1 =

00 00:00.8002070:

active

active

active

active

SG

C

MG

C

LC


136.7

holding latches

LC armature

MGC armature

SGC armature

lifting latches

Figure 6: Latch Unit

4 CRDM TESTS

The focus of the qualification tests for the CRDM and the control rod driveline of the EPR lies, firstly, on verifying the proper functioning of the components and, secondly, on the investigation of the long term behaviour. The first test series, the so called functional test, is a number of different tests concentrating on the interaction of the different components, whose origin lies on French and German NPP developments. Following list is an outline of the conducted tests:

• Measurement of the loads in the RCC-A and drive rod during stepping operation. • Measurement of position and velocity during drop of the RCC-A. • Measurement of drag forces of the mobile set during movement. • Measurement of drop and system behaviour with oscillating pressure housing.

These functional tests are followed by the long term tests of the driveline which aim on investigation of the long term and wear behaviour. During these tests, the CRDM is continuously moving the RCC-A to simulate long term operation in NPPs. 4.1 Functional Tests

4.1.1 Load Measurement during Stepping Operation

The movement of the mobile set is, as described previously, a discontinuous movement. This kind of stepping operation implies different loads during one step and by means of these loads it is possible to draw conclusions about the component movement of the latch unit and mobile set. The task for this test sequence lies on the determination of the loads acting in the mobile set during


136.8

stepping operation. This is realized by strain gauges applied on the drive rod. The design of the test channel allows the leading out of the signal cable and thus to run tests up to certain pressure levels limited by the strain gauges. The measured strain can be converted into to the acting force.

The force which acts in the drive rod during one upward step is displayed in Figure 7. The step starts with activating the lift coil, driving the lifting armature. After establishing the magnetic field the armature and with it the mobile set starts to move upwards which leads to a tension force in the drive rod caused mainly by the inertia of the mobile set, marked with “A” in Figure 7. A sudden decrease of the force is the result when this movement ends (position “B”). The force level at position “D” represents the force acting in the drive rod when it rests on the latches. This means that the mobile set looses contact with the latches after position “B”. The following oscillation of the force is generated by the natural oscillation of the mobile set (mark “C”) and the load transfer to the holding latches. The mobile set rests during the time span marked with “D” when the lifting armature moves back to its origin position. The step ends with the engaging of the lifting latches and the disengaging of the holding latches which leads to the oscillation force on position “E”.

This test provides the opportunity to study the movement of different components of the CRDM in interaction with the mobile set under varying conditions.

Forces Drive Rod

-6

-4

-2

0

2

4

6

0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8

Time

Forc

e

B A C D E

Figure 7: Drive Rod Loads during one Upward Step

4.1.2 Position and Velocity Measurement during RCC-A Drop

In this test series the position and the velocity of the RCC-A during a drop from the uppermost position is measured by an independent measuring device. The measurement of the position and velocity during the drop is necessary for rating the drop behaviour and for determination of the drop time. This measurement is a direct measurement of the RCC-A drop and serves to adjust and control the indirect drop time measuring devices.

The position and velocity is measured by a draw wire sensor which is connected to the drive rod and is mounted at a fixed point outside of the test channel. The wire of the sensor is led out of the test channel through a special sealing on top of the pressure housing. The mounted acceleration sensors measuring the structure borne noise are also used to detect the start and end of the drop.

Figure 8 shows the velocity of the mobile set and the differential pressure over the pressure housing. After the release of the mobile set (Figure 8 “A”) the speed increases up to a maximum velocity (Figure 8 “B”) which is nearly constant for most of the drop. When the RCC-A enters the dashpot of the fuel assembly (Figure 8 “C”) the velocity decreases suddenly until the mobile set reaches its lowermost position (Figure 8 “D”). After the end of the drop an oscillation of the mobile set can be seen caused by the spring absorbing the impact of the RCC-A on the fuel assembly. The


136.9

differential pressure reflects the characteristics of the velocity and can therefore be used for determination of the velocity for tests without positioning coils, measuring position and velocity of the mobile set.

Drop CR Uppermost Position

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Time

Velo

city

-1

0

1

2

3

4

5

6

Pres

sure

RCC-A Drop

Pressure over Pressure Housing

Drop Velocity

B C

D

A

drop dashpot

Figure 8: RCC-A Drop – Drop Velocity and Pressure over Pressure Housing

The position of the mobile set and the measured structure-borne noise are displayed in Figure 9, the indications “A” to “D” have the same meaning as in Figure 8. There are two events visible in the acceleration signal. The first one (Figure 9 “A”) is the end of the motion of the LC armature. The second one is the contact of the RCC-A with the fuel assembly and represents the exact end of the drop. These events are used for controlling and verifying the drop time measurements.


136.10

Drop CR Uppermost Position

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Time

Posi

tion

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Acc

eler

atio

n

Acceleration

Position

dashpot drop

A

D

C

B

Drop RCC-A

Figure 9: Drop DR – Drop Position and Structure Born Noise

4.1.3 Drag Force Measurement

This test is focused on the determination of the drag force between the mobile set and the surrounding internals while the mobile set completes an entire up and down movement under different flow conditions, reaching from 0% to 100% nominal mass flow. The drag force is measured by a load cell connected to the drive rod and located within the test loop. Since the movement has to be controlled from outside of the test loop a tie rod is connected to the load cell and the mobile set is moved by means of this tie rod. An adapter on top of the pressure housing enables the movement of the tie rod and simultaneously seals the test loop.

The measured forces for 0%, 80% and 100% nominal mass flow are displayed in Figure 10. Each curve represents a complete up and down movement, whereas the upper part of the graph is the extracting of the mobile set, the lower part the insertion. The measured force Fmeas depends on various influencing variables, including the weight force of the mobile set FW, the buoyancy force of the mobile set in water FB, the Coulomb’s friction FC and the hydraulic resistance force FH caused by the main flow. The balance of forces reads as follows:

CHBWmeas FFFFF ±−−= (1)

The hydraulic resistance force increases with rising mass flow and this causes the decrease of

the measured force in Figure 10 for the tests with 80% and 100% mass flow whereas the weight force and the buoyancy force keep constant during the test. The friction force is half the difference between the upper and lower parts of the curves. The elevated friction force at the begining of the movement is caused by the dashpot of the fuel assembly. The hydraulic friction force decreases with the up movement of the mobile set, since less area is affected by the main mass flow. This explains the rising of the measured force during the displacement of the mobile set.


136.11

dashpot

2xFC

Figure 10: Drag Force under Different Flow Conditions

4.1.4 Displacement and Snap Back Test

The drop times and the behaviour of the oscillating pressure housing with funnel are the subject of the displacement and snap back test. The focus lies on two issues, firstly, the eigenfrequency depending on the drive rod position and, secondly, drop times of the mobile set with displaced pressure housing. The pressure housing has to be adapted to attach a device for displacing it. The oscillation is measured with two draw wire sensors applied horizontal at 90° to each other to measure the oscillation in the horizontal plane.

The eigenfrequency is determined by displacing the pressure housing and measuring the periodic time after releasing the deflected pressure housing. Figure 11 shows the displacement of the top of the pressure housing during a snap back test. After releasing the pressure housing, it oscillates until it reaches is original position.


136.12

release of pressure housing

Figure 11: Oscillation top of Pressure Housing

The drop times of the mobile set are important for the safety performance of NPPs. The influence of the displacement of the pressure housing on the drop times are the subject of this part of the test. Drops are performed with different displacements. The test leads to the conclusion that the drop times are not influenced by the oscillating pressure housing because drop times keep constant despite different displacements. The drops are repeated with statically displaced pressure housing and lead to the same result.

4.2 Long Term Tests

The aim of the functional test is to verify the proper functioning of the components. The long term tests, on the other hand, are to test the long term behaviour of the components under nominal reactor conditions. These tests simulate the number of steps that theoretically occur during the operation of the NPP. The boundary conditions of the test are:

• Nominal temperature, pressure and mass flow • Oxygen concentration < 100µg/l • pH-Value 7,6 (T=300°C) • Lithium concentration = 1,5 ppm

The test loop is designed to adjust the water chemistry in such a way that it fits the

requirements based on reactor water conditions. No boric acid is added to the water in the test loop. The complete test program is divided into three parts, which means 5 weeks of continuous

stepping operation for each part. Additional to the required steps, drops have to be performed. The evaluation of the components condition takes place by a comprehensive inspection of components after every part of the test. Additional to the inspections, measurements of all armature opening and releasing times as well as of the drop times are conducted in order to recognize alterations of the components early. The armatures move the latches by means of articulated levers. Therefore, the opening and releasing times are important for the evaluation of the condition of the latch unit.

Figure 12 shows the armature opening and releasing times during the long term test. The times are nearly constant over the period. At the beginning of each part of the test a run-in effect is visible, marked with an arrow.


Upward Movement

0

20

40

60

80

100

120

140

160

180

200

0 0.5 1 1.5 2 2.5 4 4.5 5 5.5 6 6.5

Clo

sing

/Rel

easi

ng T

imes

LC closing time LC releasing timeMGC closing time MGC releasing timeSGC closing time SGC releasing time

s

Figure 12: Armature Closing a

The drop time of the mobile set is areleasing times. Two times are measured, tdashpot of the fuel assembly and the time bethe fuel assembly. The drop times are consta

5 CONCLUSION

This paper describes the possibilitiesfacility by means of the qualification test of tvariable design of the test loop a number applied on the described qualification testrequirements. Therefore, the test loop can alinvestigate their behaviour under full operatitest loop for additional measurement instrumthe test loop provides the possibility to run extended instrumentation to analyse and imp

.53 3Number of Step

136.13

o. of StepsN

nd Releasing Times – Upward Movement

nother important value beside the armature closing and he drop time between start of drop to entrance into the tween start of drop and contact of the RCC-A spider with nt over the complete period of the test.

which offer the core test section of the component test he control rod drive mechanism of the EPR. Through the of different test set-ups are possible which were not all . The test loop can be adapted to meet different test so be used for developing primary components in order to onal conditions. This is supported by the capability of the entation which it is not possible to install in NPPs. Thus, test under full operational conditions in combination with rove primary components under real reactor conditions.

full scale component test facility kopra – qualification ...the test facility kopra is designed...

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