ML20155B607

Responds to NRC Bulletin 88-008 Re Thermal Stresses in Piping Connected to Rcs.Seven Piping Sections Unisolable from RCS Identified to Be Potentially Susceptible to Previously Unanalyzed Thermal Stress

ML20155B607
Person / Time
Site:	Seabrook
Issue date:	09/30/1988
From:	George Thomas PUBLIC SERVICE CO. OF NEW HAMPSHIRE
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
IEB-88-008, IEB-88-8, NYN-88130, NUDOCS 8810060363
Download: ML20155B607 (4)

Text

4 George'S. Thomas I Vice Presk$en! Nuclect Production l

NYNb8130 ruise s.*. om sampe*.

New Hampshire Yankee Division 88Ptember 30, 1988 United States Nuclear Regulatory Commission Washington, DC 20555 Attention: Document Control Desk

References:

(a) Facility Operating License NPF-56, Docket No. 50-443 (b) NRC Bulletin 88-08, dated June 22, 1988, "Thermal Stresses in Piping Connected to Reactor Coolant Systems'

Subject:

Response to NRC E'alletin 88-08 Dear Sir In response to Reference (b), this letter describes the actions taken to date at Seabrook Station to ensure that unisolable piping connected to the Reactor Coolant System (RCS) is not subjected to unacceptable thermal stress from either temperature stratification or temperature oscillations that could be caused by valve seat leakage.

In response to action item number one in the Bulletin, each system connected to the RCS was reviewed to determine whether any sections of piping unisolable from the RCS could be subjected to stress from temperature stratification or temperature oscillations induced by a leaking isolation valve. The system review determined that the charging pumps are the only pumps capable of providing the necessary head to drivo assumed leakage flow through a closed isolation valve toward an unisolable piping section connected to the RCS. At Seabrook Station, the seven piping lines shown in Figure 1 are pressurized by the charg.tng pumps and connect to the RCS. Four of these lines are High Head Safety Injection lines and the remaining three are Charging System lines (t.he normal and alternate loop charging lines and the pressurizer auxiliary spray line). The unisolable sections of piping in each of these seven lines have therefore been identified as potentially susceptible to previously unanalyzed thermal stress from a leaking isolation valve.

With respect to action item number two in the Bulletin, it has been determined that non-destructive examination of the potentially susceptible areas of the four High Head Safety Injection lines will be performed prior to initial criticality. Non-destructive examination of the three potentially susceptible piping sections identified in the Charging System is not meaningful because these piping sections have not been subjected to excessive thermal stress. In the Charging System, the temperature differences imposed upon the unisolable piping sections during normal power operation are limited to acceptable values because any leakage would first pass through the regenerative heat exchanger and become significantly heated. 0 Additionally, to date, the RCS has been operated at temperatures exceeding 200 F for less than eighty days. In each of the potentially susceptible lines, the closed isolation valves are new valves designed to moet a specification that limits

" "E** 8910060363 0G0930 PDR G

ADOCK 05000443 PNU h

t P.O. Box 300 . Seabrook, NH 03874 . Telephone (603) 474 9574 8 t

Unitsd States Nuclear Regulatory Commission Septembsr 30, 1988 Attention: Document Control Desk Page 2 In response to action item number three in the Bulletin, a temperature monitoring program for the High Head Safety Injection System lines is currently being developed and will be implemented prior to initial criticality. This program will place temperature monitoring instrumentation on each of the four i High Head Safety Injection unisolable piping sections to detect adverse temperature distributions. The program will specify appropriate temperrture limits, define requirements for ptaiodic review of temperature measurements and set forth action to be taken in the event cf exceeding a temperature limit.

It has been determined that the scope of the program will not include the three Charging System lines. Assumed leakage through a closed isolation valve in either the normal charging, alternate charging or pressurizer auxiliary spray line would be heated to acceptable levels by the heating action of the regenerative heat exchanger. Each of these Charging System lines is fully

insulated downstream of the regenerative heat exchangers thus the loss of heat from the piping to the containment is minimal. Therefore, the maximum expected temperature difference that could occur in each of these unisolable piping sections resulting from assumed leakage through a closed isolation valve could not induce a level of cyclic thermal stress exceeding the material endurance limits thus the material could withstand additional thermal stress cycles without failure due to fatigue.

In summary, as a result of the requested evaluation of Reference (b),

seven piping sections unisolable from the RCS were identified to be potentially susceptible to previously unanalyzed thermal stress that could be induced by a leaking isolation valve. Non-destructive examination of the four unisolable piping sections in the High Head Safety Injection System will be performed and a temperature monitoring program to detect deleterious valve leakage in these piping sections will be implemented prior to initial criticality.

Should you have any questions regarding this information, please contact Mr. Geoffrey Kingston at (603) 474-9574, extension 3371.

Very truly yours, f

G orge . Thomas l

Enclosure l

cci Mr. William T. Russell Mr. David G. Ruscitto l Regional Administrator Senior Resident Inspector l U. S. Nuclear Regulatory Commission P. O. Box 1149

Region I Seabrook, NH 03874 475 Allendale Road King of Prussia, PA 19406 Mr. Victor Nerse', Project Manager Project Directe. ate I-3 Division of Reactor Projects U. S. Nuclear Regulatory Commission Washington, DC 20555

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. United States Nuclear Regulatory Comission September 30, 1988 Attention: Document. Control Desk Page 3 STATE OF NEW HAMPSEIRE Rockingham, ss. September 30, 1988 Then personally appeared before me, the above-named George S. Thomas who, being duly sworn, did state that he is Vice President - Nuclear Production of Public Service Company of New Hampshire, that he is duly authorized to execute and file the foregoing information in the name and on the behalf of Public Service Company of New Hampshire, and that the statements therein are true to the beat of his knowledge and belief.

1. A b& UttoU Marilyn R/ Sullivan, Notary Public Hy Commission Expires: April 29, 1992

, ENCLOSURE I TO NYN- 88130 Figure 1 Piping Containing Unisolable Sections Potentially Susceptible to Thermal Stress from a Leaking isolation Valve 7 IRC Regenerative

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Pzr Spray Vatves IRC V139

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HIGH HEAD SAFETY INJECTION [ / f Same Layout and Diameters for i a!! Leops i 7

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