P E R F O R M A N C E T E S T P R O G R A M O F D A S H P O T F O R F F T F C O L D L E G C H E C K V A L V E

D. K. SHARMA, R. HENSCHEL 8¢, M. KRAWCHUK

Foster l~77eeler Energy Corporation, John Blizard Research Center, Litingvton, New Jersey 07039, USA

(Received: 28 November, 1976)

A BSTRA CT

This paper describes and evaluates the performance tests that were carried out on the prototypical dashpot for the Fast Flux Test Facility Cold Leg Check Valve ( F F T F - C LCV). The study consisted of acceptance testing in freon, argon and air, and final testing in liquid sodium. Based upon this work it was concluded that the dashpot performance was acceptable. This dashpot was previously developed through a test program that was primarily conducted in water.

INTRODUCTION

Check valves are included in the Cold Legs of Fast Flux Test Facility (FFTF) primary loops to prevent reverse flow in the loops in the event of a pump failure. This permits the maximum possible flow of liquid sodium through the reactor core to be maintained. A dashpot is included in each check valve to limit the surge pressure (sodium hammer) resulting from the rapid closure of the valve disk due to the reverse flow.

A prototypical dashpot design was developed through a series of tests in water. Water was chosen as an initial test medium for reasons of safety, economy and expediency. Subsequently, a full-size prototypical dashpot unit was fabricated. This unit is shown in Figs. 1 and 2 and was described in previous publications.1- 3

There is no published information regarding dashpot performance in a high- temperature liquid sodium environment. Therefore, the latter full-size prototypical dashpot unit was subjected to extensive sodium testing to evaluate its characteristics. This was done after the unit met its preliminary acceptance test requirements. The acceptance tests were performed in freon, argon and air to check the structural integrity, as well as the filling, recocking and damping characteristics of the dashpot

41 Int. J. Pres. Ves. & Piping (6) (1978)---© Applied Science Publishers Ltd, England, 1978 Printed in Great Britain

42 D.K. SHARMA, R. HENSCHEL, M. KRAWCHUK

Fig. I.

Spring Cylinder ~ Cover P ate

", '~ ~ ~ . StelMe Sleeve

I ,'1 i t , ~1 '1 '~

[, . . . . . . . ~ , ,~ . . . . . . . . . ~

i Bushing

18 Orifices I I 0 0

H3 i

260 i

Prototypical dashpot with exception of stacked orifices in piston. Approximate dimensions (mm).

Fig. 2. Photograph showing prototypical dashpot.

PERFORMANCE TEST PROGRAM OF DASHPOT FOR FFTF COLD LEG CHECK VALVE 43

prior to its final testing in sodium. Freon TF Solvent (TCTFE) was chosen for the damping acceptance test since this test required a liquid medium which could be completely removed from the dashpot crevices prior to the sodium testing. It was also chosen since it is safe, economical, detectable and relatively easy to use, and is allowed prior to sodium testing by the Reactor Development Technology (RDT) Standard F5-1 T, for degreasing austenitic stainless steels where crevices are present.

The sodium test was designed to evaluate the dashpot performance and its reliability under long term exposure to FFTF-CLCV operating conditions. Specifically, its purpose was to determine the filling, recocking, damping, wear and endurance characteristics of the dashpot as well as the corrosive effects of sodium on the dashpot material.

This paper presents the details of the acceptance and sodium tests which showed that the dashpot performance was acceptable.

DASHPOT CYLINDER AND SLEEVE ASSEMBLY PROOF TEST ACCEPTANCE TEST

All dashpot components, including the cylinder and sleeve, were designed by means of a 'Design by Analysis' approach in accordance with the rules of the ASME Boiler and Pressure Vessel Code, Section III, Class I Nuclear Component as modified by Code Case 1331-5t for elevated temperature service. 4'5

The primary objective of the proof test was to check the structural integrity of the dashpot cylinder and sleeve assembly using the rig shown in Fig. 3. This test began by

Stainless Sleel Flange

Argon supply

Prege Gage

Fig. 3. Dashpot cylinder and sleeve assembly proof test rig.

t Code Case 1331-5 was the case version applicable to this dashpot design. Since then Code Case 1331-5 has been revised to 1592-1.

44 D. K. SHARMA, R. HENSCHEL, M. KRAWCHUK

measuring the outside cylinder diameter at three different locations. Subsequently, all radial orifices in the dashpot cylinder wall were closed. A pressure of 10,342 kPa was then applied to the cylinder utilising a regulated argon gas supply. This pressure was subsequently released and a visual inspection was made for any cracks. Furthermore, the diametral measurements presented in Table 1 indicate no measurable change in the cylinder diameter. Therefore, the cylinder and sleeve assembly strength was considered acceptable.

T A B L E 1 RESULTS OF CYLINDER AND SLEEVE ASSEMBLY PROOF TEST

Test Pressure time in dashpot

(hours) cylinder (kPa)

Outside diameter of dashpot cylinder along axis A - A t (mm)

Axis Axis Axis 1 1 2-2 3 3

Remarks

14:00 0 120.637 120.343

14:30 10342 14:40 10342 15:30 0 120.637 120.548

120.596 Pressurisation of cylinder begins

120.596 Pressure was bled off

2

1 3

3 1

2

t See enclosed figure for reference axes,

DASHPOT THERMAL CYCLE TEST ACCEPTANCE TEST

This test was conducted to determine the dashpot performance in air at room and elevated temperature by utilising the rig shown in Fig. 4. The rig consisted of a stainless-steel vessel, a furnace for heating the dashpot assembly and an argon gas supply for purging. A rod was extended through the clearance hole in the vessel to actuate the dashpot piston by an applied force. A chromel-alumel thermocouple was used to measure the dashpot temperature.

PERFORMANCE TEST PROGRAM OF DASHPOT FOR FFTF COLD LEG CHECK VALVE 45

Stainless Steel Fixture Argon Supply

--Heating Furnace d ~Thermocouple /Vent

_ //

Actuation Rod t. / x / /Load Celt

Dashpot \

, . . . . . , . . . . . . . . .

Rod

External Force

Fig. 4. Dashpot thermal cycle test rig.

At ambient temperature a measured force was first applied, three times, to the dashpot piston utilising the actuation rod. Subsequently, argon gas was introduced into the vessel and the piston was stroked three times to replace the air in the dashpot cylinder with the argon gas. The furnace was then turned on to heat the dashpot assembly to 427°C at a maximum rate of 10°C per hour, as required. The 427°C temperature is slightly higher than the CLCV's highest operating temperature of 422 °C. At the 427 °C condition, the dashpot piston was again actuated three times and the measurements mentioned above were made. This procedure was repeated after turning off the furnace, when the assembly reached the steady state ambient temperature.

The performance of the dashpot at room and elevated temperature was satisfactory. No sticking or mechanical interference was observed during the forward and recock stroke of the piston. This also proved that in both these conditions, the spring force was greater than the frictional forces to recock the dashpot piston.

DAMPING TEST IN FREON ACCEPTANCE TEST

The main objective of this test was to check the dashpot damping behaviour before its testing in sodium. As discussed by Sharma e t a l . , ~ Dashpot Damping Factors (DDF) characterise the hydraulic resistance imparted by the dashpot piston to the closing simulated or actual valve disk. Specifically, the objective of this test was to see if DDF values were in the same range as those obtained from the water and freon testing of the prior developmental unit. The testing of the developmental unit showed that its damping performance in water and freon was similar.

4(3 D. K. SHARMA, R. HENSCHEL, M. KRAWCHUK

FAI Port Dashpot S~de RaLIS

Load Cell Vessel Buna-n Bellows ,Adaptor

]

Doshpot Piston Actuator Rod Load Cell

Fig. 5. F reon test rig.

Hydraulic Actuotton Cylinder

Fig. 6. F r eo n test rig.

PERFORMANCE TEST PROGRAM OF DASHPOT FOR FFTF COLD LEG CHECK VALVE 47

The damping test of the prototypical dashpot was conducted utilising the rig shown in Figs. 5 and 6. It consisted of a stainless-steel vessel, cover plates, a hydraulic cylinder, with a hydraulic supply and control system, and their supporting structures. A load cell was installed to measure the applied force on the dashpot piston whereas a linear variable differential transformer (LVDT) gauge was mounted to measure the displacement of the dashpot piston. Two chromel alumel thermocouples were utilised to measure the dashpot body and freon temperatures.

The test began by pressurising the hydraulic cylinder to approximately 690 kPa. The resulting hydraulic force was then applied to the dashpot piston. The resulting pressure in the dashpot cylinder and the piston displacement were recorded. Subsequently, the pressure in the hydraulic cylinder was increased and the above test procedure was repeated. This procedure was continued to a dashpot cylinder pressure of approximately 6205 kPa. Three test runs were generally made at each pressure level in the hydraulic cylinder. A second damping test was then performed in a similar manner to verify the results of the first test.

The dashpot damping for the final 4.5 degrees of disk travel, when only the stacked orifices in the piston were open, is shown in Fig. 7. The dashpot cylinder

D

D

F

130"

120"

I10"

I00"

90"

BO"

70"

60"

50"

40"

30"

20"

I0"

0 0

o

8

• • I I

• • O • o W o 8 o e

t :Test no. I

® :Test no. 2

! I i I | I I !

I 2 3 4 5 6 7 8 x l O a D a s h p o t C y l i n d e r P r e s s u r e - k P a

Fig. 7. DDF values versus cylinder pressure-dashpot damping test in freon.

48 D.K. SHARMA, R. HENSCHEL, M. KRAWCHUK

pressure was obtained by dividing the recorded force on the dashpot piston by its area. The DDF values ranged from 75 to 130 for the dashpot cylinder pressure range of 0 to 6205 kPa. These values were consistent with those obtained from testing of the previous developmental unit.

SODIUM TEST

Following the tests in freon, the dashpot was removed from its test rig. It was disassembled, cleaned, dried and reassembled for its final testing in liquid sodium under simulated F F T F ~ L C V normal, upset and emergency operating conditions. This test included 3485 cycles and soaking of the dashpot for almost 168 hours. These 3485 cycles represent a conservatively greater number than that specified by the operating conditions for 20 years of plant life. One cycle was achieved every time the dashpot piston was actuated to its full stroke and allowed to recock. During the first 350 cycles, the test rig did not perform satisfactorily. Hence, the rig was modified. Furthermore, the dashpot spring was replaced. The sodium test was then successfully completed, using the modified rig discussed herein. The 3135 remaining cycles were divided into the following two categories:

Class 1 There were 3110 of these cycles. They consisted of starting with the disk arm

nearly touching the dashpot piston. When an external force was applied, the arm rotated and actuated the dashpot piston. The disk arm rotation continued for 7.5 degrees which forced the dashpot piston to complete the forward portion of its stroke. The piston was then allowed to recock to its initial position for the start of the next stroke. These cycles were performed to simulate the normal and upset operating conditions of the FFTF ~CLCV.

Class II There were 25 of these cycles. Each cycle operated so that the disk arm swung 10.5

degrees before contacting the dashpot piston. It then rotated an additional 7.5 degrees to force the dashpot piston forward.' These cycles were performed to simulate emergency valve disk closures. This operating condition is the most severe in that it produces the highest surge pressure.

DESCRIPTION OF TEST RIG AND INSTRUMENTATION

The rig used during this test consisted of a sodium facility, a hydraulic pumping system and a test fixture. The sodium facility is a complete closed-loop supply and

PERFORMANCE TEST PROGRAM OF DASHPOT FOR FFTF COLD LEG CHECK VALVE 49

purifying system. It is capable of supplying high purity liquid sodium at a rate up to 0-011 m3/min at a controlled temperature up to 538 °C for a prolonged period of time.

A schematic of the sodium test fixture along with its associated instrumentation is shown in Fig. 8. As seen from Fig. 8, a stainless-steel vessel was used to contain the sodium and the mountings for the simulated valve disk arm. This disk arm and the piston of the hydraulic cylinder were connected through a rod. A knocker was mounted to the lower portion of the disk arm to actuate the dashpot piston which controlled the final 7-5 degrees rotation of the disk. This knocker was a duplicate of the actual part used in the FFTF-CLCV. The load nut, which was located between the hydraulic piston and the pull rod, was used to measure the applied hydraulic force which was needed to actuate the dashpot piston. An LVDT gauge and a strain gauge pressure transducer, in conjunction with an oscillograph recorder, were used to measure the hydraulic piston displacements and dashpot cylinder pressures, respectively. Chromel-alumel thermocouples monitored the dashpot, body and sodium temperatures.

A sensing system in conjunction with an automatic data acquisition system, and an automatic relay control system, were used to determine the recocking of the dashpot piston. The sensing system consisted of an air cylinder, linear potentiometer and recock indicator arm, as shown in Fig. 8. During each cycle, the dashpot was actuated and allowed to recock for 20 seconds before the indicating arm of the sensing system made contact with the dashpot piston, to determine if the piston had recocked completely.

Autom~ic Relay Hydraulic Air Cylinder Control System Supply I "

Hydr~lUlrlC Linear Potentiometer

I I t , 0o,o ..... .... , Acq,,i, I TT" o o System -[ , , LL ~ ! .L Temp. ,

~ ~ u I I [ ~ Recoraer

Recorder

Pres s/u re R cock Transducer Indicator Arm

Fig. 8. Sodium test fixture.

5 0 D. K. SHARMA, R. HENSCHEL, M. K R A W C H U K

TEST PROCEDURE

The test began by purging the vessel and associated piping system with argon gas. Subsequently, the vessel was filled with liquid sodium at approximately 204 °C which is the initial F FTF-CLCV fill temperature. The sodium temperature was then raised to 427 °C. It was circulated through the sodium loop and vessel. Its oxygen and carbon contents were brought to within 2.5 and 2.0 ppm.

Upon completing the initial fill procedure, the dashpot piston was repeatedly actuated. Each cycle was actuated by the automatic relay control system at a rate of three per minute. A cycle consisted of applying a hydraulic force to the simulated valve disk arm which in turn actuated the dashpot piston, under one of the two different conditions previously discussed. After completion of the dashpot piston forward stroke, the hydraulic loading was reversed which caused the disk arm to return to its initial position. This also permitted the dashpot piston to recock due to its spring force. By changing the hydraulic cylinder pressure, the loading on the simulated valve disk arm was regulated to simulate the reverse flow forces encountered by the valve disk in actual operation. After performing 3052 cycles at 427 °C, the sodium temperature was reduced to 315 °C. A total of 27 cycles were conducted at 315°C. Subsequently 32 cycles were performed at 177°C. These temperature levels were chosen to represent the operating range of the CLCV dashpot.

Measured quantities of sodium carbonate (Na2CO3) and sodium cyanide (NaCN) were next added to the vessel to intentionally contaminate the sodium by raising its oxygen and carbon contents to 100 and 50 ppm, respectively. The dashpot was then soaked in this sodium for approximately 168 h. Following this, 15 cycles of Class 1 and 8 cycles of Class I1 were performed to complete the sodium test.

During each of the 3485 cycles that were performed using the improved sodium test rig, the parameters recorded were: applied hydraulic force, dashpot cylinder pressure, hydraulic piston displacement, all versus time, piston recock position, dashpot body and sodium temperatures.

RESULTS AND DISCUSSION

A total of 3485 cycles were performed during the sodium test. There were 3460 cycles performed in sodium having an oxygen and carbon content of approximately 2.5 and 2 ppm, respectively, at temperatures of 427, 315 and 177 °C. The remaining 25 cycles were performed in intentionally contaminated sodium having oxygen and carbon contents of 100 and 50 ppm, respectively.

The first few cycles of test data were used to determine the dashpot filling ability by observing the cylinder pressure versus time curve. The dashpot was considered to be completely filled during each stroke since a constant pressure level was observed during these cycles.

PERFORMANCE TEST PROGRAM OF DASHPOT FOR FFTF COLD LEG CHECK VALVE 51

The dashpot piston did not completely recock during the first 350 cycles. This incomplete recocking was probably due to a low spring preload, higher frictional forces in high temperature sodium and the external resistance applied to the piston from the recock indicator. Once the rig was modified and the spring replaced with a higher preload in its installed position, the piston completely recocked during all subsequent cycles. The piston always recocked within 20 sec, which is less than the maximum acceptable recock time of 30 sec.

The pressures in the dashpot cylinder, during the disk closure under various simulated reverse flow forces, were measured in the range of 348-2413 kPa. The dashpot damping factor (DDF) values for approximately 150 cycles, which were distributed throughout the sodium test, are shown in Fig. 9. They represent the dashpot damping for the final four degrees of disk rotation, in which only the stacked orifices in the piston were open. The values at 427 °C are the average of three observations. The values at 315 and 177 °C are the average of two observations. By comparing Figs. 7 and 9 it is seen that the majority of DDF values in sodium are in the same general range as those in freon, for the dashpot cylinder pressure range of 348-2413 kPa.

D

D

F

150-

120-

I10-

I00-

90 -

80-

70-

60-

50-

40-

:50-

20-

I0-

0 0

t O •

(3 • 0

e: 427°C

e:515°C A:177°C

i i I l i

500 I000 1500 2000 2500 Dashpot Cylinder Pressure- kPa

Fig. 9. DDF values versus cylinder pressure-dashpot damping test in sodium.

52 D. K. SHARMA, R. HENSCHEL, M. KRAWCHUK

The performance of the dashpot during the acceptance tests in freon, argon and air and the test in sodium was considered satisfactory. The post-test inspection of the dashpot, its components and the simulated valve disk arm, showed no evidence of wear, mechanical interference or corrosion. Hence, the design was accepted for the FFTF-CLCV. The production units of this design were tested in freon to verify their characteristics, specifically against the standards for filling, recocking and damping behaviour.

ACKNOWLEDGEMENTS

The authors would like to thank I. Berman for his review of the paper and helpful comments; G. Rabe for his recommendations used to redesign the dashpots; J. Apice and M. McKeeby for graphical work; N. Marshall for typing the manuscript; Westinghouse Advanced Reactor Division, Pittsburgh, Pennsylvania, who sponsored the development work, and the FWEC for permission to publish this paper.

REFERENCES

1. SHARMA, D. K., HENSCHEL, R. and KRAWCHUK, M. Dashpot Development Test/or FFTFCold Leg Check Valve, Int. J. Pres. Ves. and Piping, 6 (1978) pp. 23-39.

2. N ULTON, J. D. Large Sodium Valve Design and Operating Experience in the United States, Summary Report, International Working Group on Fast Reactors Specialist Meeting on Operating Experience and Design Criteria of Sodium Valves, National Technical Information Service, U.S. Department of Commerce, Springfield, Virginia, 1974, pp. 424-31.

3. RABE, G. B. and NASH, C. F. Fast Flu): Test Facility Primary Sodium Check Valve, ASME Paper Number 76-PVP-70, presented at the Joint Petroleum Mechanical Engineering and Pressure Vessels and Pipirig Conference, Mexico City, Mexico, September 19 24, 1976.

4. American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section Ill. Nuclear Power Plant Components, 1971 edition, including Winter 1971 Addenda.

5. ASME Boiler and Pressure Vessel Code, Case 1331-5, Nuclear Components in Elevated Temperature Service.