LD-83-073, Forwards Proposed Rev to CESSAR-F Section 5.4.13 & App 5A, Reflecting Revised Pressurizer Relief Valve Blowdown Analysis.Proposed Changes Will Be Incorporated Into CESSAR-F in Future Amend

Forwards Proposed Rev to CESSAR-F Section 5.4.13 & App 5A, Reflecting Revised Pressurizer Relief Valve Blowdown Analysis.Proposed Changes Will Be Incorporated Into CESSAR-F in Future Amend

ML20077J429
Person / Time
Site:	05000470
Issue date:	08/11/1983
From:	Scherer A ABB COMBUSTION ENGINEERING NUCLEAR FUEL (FORMERLY
To:	Eisenhut D Office of Nuclear Reactor Regulation
References
LD-83-073, LD-83-73, NUDOCS 8308160394
Download: ML20077J429 (8)

Text

o e

C E Power Syct ms Tel. 203/688-1911 Cornbustion Engineenng. Inc. Telex: 99297 1000 Prospect Hill Road Windsor, Connecticut 06095 POWER H SYSTEMS Docket No. STN 50-470-F August 11,1983 LD 073 Mr. Darrell G. Eisenhut, Director Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

CESSAR-F Revised Pressurizer Relief Valve Blowdown Analysis

Reference:

Letter RWW-82-70, R. Wells to H. Bernard, dated December 20, 1982

Dear Mr. Eisenhut:

The reference letter provided a report prepared by Combustion Engineering (C-E) for the C-E Owners Group entitled, " Summary Report on the Operability of Pressurizer Safety Valves in C-E Designed Plaats". As a result of the EPRI testing which served as the basis for this report, C-E has determined that the safety valve blowdown settings for its System 80' design will be necessarily higher than the valve settings assumed in the CESSAR-F overpressure protection report provided in Appendix 5A.

Enclosed is our proposed revision to CESSAR-F Section 5.4.13 and Appendix 5A, which documents the results of the analysis performed to justify the increased primary system blowdown. The analysis concludes that the maximum expected blowdown resulting from the higher Pressurizer Safety Valve (PSV) blowdown settings will not cause the specified PSV design bases or Chapter 15 acceptance criteria to be exceeded. The proposed changes will be incorporated into CESSAR-F in a future amendment.

If I can be of any further assistance in this matter, please contact either myself or G. A. Davis of my staff at (203) 285-5207.

Very truly yours, COMBUSTION ENGINEERING, INC.

Director Nuclear Licensing l

j AES:las Enclosure Eco3 8308160394 830811 II4 PDR ADOCK 05000470 A PDR

p l

5.4.13.4 Tests and Inspection The valves are inspected during fabrication in accordance with ASME III Code  !

requi rements. i 5.4.13.4.1 Pressurizer Safety Valves l

< The-inlet and outlet portions of the valves are hydrostatically tested with water at the appropriate pressures required by the applicable section of the ,

i ASME Code. Set pressure and seat leakage tests are performed with steam using a prorated spring. Final set pressure tests are performed with the final springs using either high pressure air or low pressure steam with an hydraulic assist device. Final seat leakage tests are performed with the final springs

.using either hot air or hot nitrogen. Valve adjustment shall be made to a valve ring setting combination selected to provide stabl9 yalve operation on the basis of the EPRI Safety Valve Test Program results.i le 5.4.13.4.2 Main Steam Safety Vavles The inlet portion of the valve is hydrostatically tested with water in accordance with the ASME Code. Set pressure and seat leakage tests are performed using steam. Adjustment is made to provide a valve blowdown meeting the requirement specified in Table 5.4.13-2.

I' (1) CEN-227 " Summary Report on the Operability of Pressurizer Safety Relief

.. Valves in C-E Designed Plants", December 1982.:

5.4-42

4 o

TABLE 5.4.13-1 PRESSURIZER SAFETY VALVE PARAMETERS Property Parameter Design pressure, Ib/in.2 a 2500 Design temperature. *F 700 Fluid Saturated Steam, 4400 ppm boron pH=4.5 to 10.6 Set pressure, 1b/in.2 a 2500 + 1%

Min. capacity,1b/h at accumulation pressure,each 460,000 Type Spring loaded safety-balanced bellows.

Enclosed bonnet.

Orifice area, in.2 4,34 Accumulation, % 3 Backpressure Max. buildup / max superimposed,1b/in.2 9 700/340 Minimum blot!down pressure, psia 2040 Typical materials Body ASME SA 182, GR. F316 Disc ASTM A637, GR. 688 Nozzle ASME SA 182, GR. 347

. . . = . -- .. . _.

TABLE 5.4.13-2 MAIN STEAM SAFETY VALVE PARAMETERS Property Parameter D2 sign pressure, Ib/in.2g 1375 Design temperature, *F 575 Fluid Saturated Steam Set pressure, 1b/in.2g 1255, 1290, 1315 6

Min. capacity, lb/h at accumulation pressure 19 x 10 Total (20 Valves)

Type Spring loaded Orifice area, in.2 16 Accumulation, % 3 Backpressure Max, buildup / max superimposed, lb/in.2g 125/0

Approx. dry weight, lbs. 1545 Minimum blowdown pressure, psig. 1175 Typical materialc Body ASME SA 105 Disc ASTM A565, GR. 616 Nozzle ASME SA 182, GR. F316 w

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APPENDIX 5A OVERPRESSURE PROTECTION FOR COMBUSTION ENGINEERING SYSTEM 80 - PRESSURIZED WATER REACTORS TABLE OF CONTENTS SECTION TITLE PAGE NO.

1.0 INTRODUCTION

5A-1 2.0 AH&LYlls 5A-1 2.1 METHOD 5A-1 2.2 ASSUMPTIONS 5A-1 2.2.1 SECONDARY SAFETY VALVE SIZING 5A-2 2.2.2 PRIMARY SAFETY YALVE SIZING, 5A-3 2.2.3 ACCEPTABILITY OF SAFETY VALVE BLOWDOWN 5A-4

3.0 CONCLUSION

S SA-5

. i

~

gesperaturecoeffic'entcanvarybetweenzeroand-3.5.x10 Therefore, a coefficient for various phases of core life.

of zero is chosen to maximize the power / pressure transient.

, c. Doppler coefficient of .8 x 10 -5 AK/K/F is used in the loss-of-load analysis. Actual opgrating coefficients can be exggeted to range from -1.4 x 10 at zero power to -1. x 10 AK/K?F at full power. By choosing a relatively small Doppler coefficient, the reduction in reactivity with increasing l fuel temperature is minimized, thereby maximizing the rate of power rise,

d. No credit is taken for letdown, charging, pressurizer spray, I turbine bypass, or feedwater addition after turbine trip in the loss-of-load analysis. Letdown and pressurizer spray both act to reduce primary pressure. By not taking credit for these systems, the rate of pressurization is increased.

t Including these systems in the analysis will delay tripping the reactor on high primary pressure by 1.1 seconds. The peak primary pressure is not affected. By not taking credit for the addition of feedwater, the steam generator secondary inventory will be depleted at a faster rate. This in turn i

reduces the capability of the steam generator to remove heat from the primary loop, thereby maximizing the rate of primary pressurization.

e. The analysis reflects consideration of plant instrumentation 4 error and safety valve setpoint errors. For example, all safety valves are assumed to open at their maximum popping 4

pressure. This extends the period of time before energy can be removed from the system. The reactor trip setpoint errors are always assumed to act in such a manner that they delay reactor trip, again resulting in maximum pressurization.

i

f. Pressurizer pressure at the onset of the incident is 2200 psi. By using the lower limit of the normal plant operating pressure, the time required to trip the plant on high pressure is increased.

2.2.1 SECONDARY SAFETY VALVE SIZING i

i The discharge piping serving the secondary safety valves is designed to

&ccommodate rated relief capacity without imposing unacceptable backpressure on the safety valves. ,

The secondary safety valves are conservatively sized to pass excess steam flow. This limits steam generator pressure to less than 110% of steam gInerator design pressure during worst case transients. A plant's secondary safety valves consist of three banks of valves with staggered set pressures.

The vavles are spring loaded type safety valves procured in accordance with ASME Boiler and Pressure Vessel Code,Section III.

SA-2 '

1

___ _ __. _ . _ _ _ _ _ .._ . _ . . _ , . . . . . . . . _ _ _ . - _ _ . . . _ . , _ . , _ _ _ . . _ . . . . . _ , . _ . . . _ . ..m... _,

In the event that a complete loss of load occurs without a simultaneous reactor trip, the protection provided by the high pressurizer pressuire trip, primary safety valves and secondary safety valves is sufficient to assure that the integrity of the RCS and main steam system is maintained and that the minimum DNB ratio is not less that 1.19.

2.2.3 Acceptability of Safety Valve Blowdown 2.2.3.1 Background Full scale, full pressure prgtypical performed by EPRI in 1981.

testing of settings The blowdown pressurizer safety required valves was to insure stable valve operation during the blowdown from the set pressure were above the 5% setting specified in the ASME Code. In order to insure that the extended blowdown would not adversely affect overpressure protection or plant operation, analyses were performed to evaluate the HSSS response. The analyses described below demonstrate that a blowdown setting, including associated uncertainties, of 18.5% is acceptable.

2.2.3.2 Results of Evaluation An extended blowdown of the safety valves could result in swelling of the pressuizer liquid level due to flashing and possible liquid carryover through the safety valves. Since the safety valve design specification specifies dry saturated steam flow conditions, it is desirable to show that these conditions are maintained during the extended blowdown. It is also desirable to verify that the RCS remains in a subcooled condition in order that steam bubble formation in the RCS is precluded.

A computer analysis was performed of the Loss-of-load event with delayed reactor trip, similar to that used in safety valve sizing, except that a conservative 20% safety valve blowdown and initial conditions biased to maximize pressurizer liquid level were assumed. The purpose of this analysis was to determine the pressurizer liquid level response and the RCS subcooling under these conservative conditions. For additional conservatism, an additive adjustment was made to the computer-calculated pressurizer levels on the basis of a very conservative pressurizer model. This model assumed that the initial saturated pressurizer liquid did not mix with the cooler insurge liquid, that the initial liquid remained in equilibrium with the pressurizer steam space, and that the steam which flashed during blowdown remained dispersed in the liquid phase and caused the liquid level to swell I water level vs time curve showed a maximum of 98%(2)The adjusted (1730 pressurizer ft3), below the 4 safety valve nozzle elevation of 107%, so that dry saturated steam flow to the safety valves is assured throughout the blowdown. The computer analysis also showed that adequate subcooling was maintained in the RCS caring the blowdown, so that steam bubble formation is precluded. l l

In addition, the System 80 safety analysis pressurization events were re. l evaluated to determine the impact of assuming an 18.5% blowdown below nominal set pressure for the pressurizer safety valves in lieu of the 5% specified by 5A-4

l .

l the ASME Code. The evaluation indicated that, for the FWLB event analysis, which produces the greatest increase in pressurizer level, the increased blowdown would not result in the pressurizer liquid level reaching the safety

' valve nozzle elevation and thus normal safety valve operation would be assured. Further subcooling in the RCS was maintained during the blowdown. In summary, analyses show that adequate plant overpressure protection and RCS l subcooling are ensured during a blowdown of 18.5% below the nominal pressurizer safety valve settings.

3.0 CONCLUSION

S C-E's System 80 pressurized water reactor, steam generators, and Reactor Coolant System are protected from overpressurization in accordance with the guidelines set forth in the ASME Boiler and Pressure Vessel Code,Section III. Peak Reactor Coolant System and Secondary System pressures are limited to 110% of design pressures during worst case loss of turbine-generator load. Overpressu re protection is afforded by primary safety valves, secondary safety valves, and the Reactor Protection System.

(1) CEN-227, " Summary Report on the Operability of Pressurizer Safety Relief Valves in C-E Designed Plants", December 1982.

(2) Water. level expressed as the percentage of the distance from the lower level nozzle to the upper level nozzle.

5A-5

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