ML20205N815
| ML20205N815 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 10/26/1988 |
| From: | Robert Williams PUBLIC SERVICE CO. OF COLORADO |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| IEB-88-008, IEB-88-8, P-88357, TAC-71380, NUDOCS 8811040362 | |
| Download: ML20205N815 (4) | |
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e G. rubiicservice-a-'
P.o. Box 640 Denver,Co 80201 C640 2420 W. 26th Avenue, Suite 1000 Denver, Colorado 80211 October 26, 1988 Fort St. Vrain Unit No. 1 P-88S57 U. S. Nuclear Regulatory Commission ATTN:
Document Control De:;k
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Washington, D.C.
20555 Docket No. 50-267
SUBJECT:
Thermal Stresses in Piping Con-aected to Reactor Coolant Systems
REFERENCE:
NRC Bulletin No. 88-08, dated June 22, 1988 (G-88250)
Gentlemen:
The purpose of this letter is to provide Public Service Company of Colorado's (PSC's) response to NRC Bulletin No. 88-08, the Reference letter.
The subject bulletin requested that all holders of operating licenses or construction permits for light-water-cooled nuclear power reactors:
(1) review their reactor coolant systems (RCSs) to identify any connected, unisolable piping that could be subjected to temperature distribution' which would result in unacceptable thenaal stresses and (2) take action, where such piping is identified, to ensure that the piping will not be subjected to unacceptable thermal stresses.
Even though the subject bulletin was not addressed to high-temperature-gas-cooled nuclear power reactors, PSC has reviewed the RCS in the Fort St. Vrain (FSV) nuclear generating station to ensure tha? failures similar to the thennal fatigue related failures of unisolable piping connected to the RCS of LWRs will not occur at FSV.
Conditions similar to those reported in the subject bulletin, leading to thermal fatigue of unisolable piping in LWRs, do not exist in the FSV piping systems.
8811040362 831026 DR ADOCK 0000 67
P-88357 Page 2 October 26, 1988 No action is considered necessary to preclude thermal fatigue failure of piping that is connected to the RCS at FSV. This is based upon:
a, There are no unisolable piping systems containing water thct penetrate any RCS pressure boundary.
The RCS presure boundary in the FSV plant is principally the steel liner of the Prertressed Concrete Reactor Yessel (PCRV) with connecting auxiliary piping systems that contain helium rather than water.
It is noted that the steam generatort have feedwater and steam tubes that are considered RCS pressore boundaries.
- However, these tubes have been analyzed by tm designer for both normal and abnormal operating cond' t ion,
tubes are continuously monitored for leaks and are isolbble, and further analysis per NRC Bulletin 88-08 is considered unnecessary, b.
There are no RCS piping systems containing helium that fluctuates in flowrate and/or temperature to the extent that resultant fluctuating thermal stresses would contribute significantly towards thermal fatigue failures of any unisolable RCS pressure boundary piping, t
c.
Thermal fatigue of the unisolable RCS pressure boundary caused by abnormal fluctuating temperatures or flowrates of the helium is also unlikely because of the reactor coolant thermal and physical property dif Terences between helium and water.
That is, unacceptable thermal stresses in RCS pipe i
walls result from dif ferenet:s in pipe wall temperatures produced by the fluctuating taperature of the fluid in contact with the pipe walls and the fluid's heat input or j
removal capacity.
This capacity is a function of the fluid's thermal and physical properties 3f density, thermal conductivity, and specific heat, alonf with the fluid's boundary layer velocity.
In conclusion, a m ous helium is much less capable of creating thermal e sses in a RCS 1
pressure boundary than is water.
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l UNITED STATES OF AMERICA NUCLEAR REGULATORY COMri!SSION In the Matter
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Public Service Company of Colorado Docket No. 50-267 Fort St. Vrain Unit No. 1 AFFIDAVIT et.
O.
Williams, Jr.
being first duly sworn, deposes and says:
That he is Senior Vice President, Nuclear Operations, of Public Service Company of Colorado, the Licensee herein, that he has read the information presented in the attached letter and knows the contents thereof, and that the statements and matters set forth therein are true and correct to the best of his knowledge, information and helief.
N R. O. Williams, Jr.//
Senior Vice Pr2sident Nuclear Operations STATE OF h
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COUNTY OF h,a v Subscribe and sworn to before me, a Notary Public on this 2L A day of r, clew
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P-88357 Page 3 October 26, 1988 If you have any questions concerning PSC's response, please contact Mr. M. H. Holmes at (303) 480-6960.
Very truly yours, M
R. O. Williams, Jr.
Senior Vice President Nuclear Operations R0W:AHW/pjb s