ML20247R596
| ML20247R596 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 08/01/1989 |
| From: | Hairston W GEORGIA POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-89-10, IEB-88-008, IEB-88-8, NUDOCS 8908080064 | |
| Download: ML20247R596 (3) | |
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August 1, 1989 U.S. Nuclear Regulatory Commission f
ATTN: Document Control Desk
.I Washington, D.C.
E0555 PLANT HATCH - UNI H 1, 2 NRC DOCKETS 50-321, m-366 l
OPERATING LICENSES DPR-Si, NPF-5 RESPONSE TO BULLETIN 88-08, SUPPLEMENT 3 PIERMAL STRESSES IN PIPING Gentlemen.
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On September 8, 1988, Georgia Power Company (GPC) responded. to NRC Bulletin 88-08, " Thermal Stresses in. Piping-Connected to Reactor Coolant j
Systems (RCS)".
The Bulletin requested licensees to review their RCS to j
identify any connected, unisolable piping that could be subjected to 1
temperature distributions which would result in unacceptable thermal l
stresses.
It was issued as a result of a. leak detected in an unisolable section of the Emergency Core Cooling System (ECCS) piping at a PHR. The Bulletin stated that, " thermal fatigue of unisolable piping connected to the RCS can occur when connected piping is isolated by a leaking block
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valve,..the pressure upstream from the block valve is higher than RCS:
pressure, and the temperature upstream is significantly cooler.than the RCS temperature." Our response was made after a comprehensive review of
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the affected systems by the BHR Owner's Group and GPC.
It concluded that this was not a problem at Plant. Hatch (BHR).
Supplements.1-and 2 to Bulletin = 88-08 contained no new requirements but reported a.similar event i
j' in another PHR, and emphasized the need for enhanced ultrasonic testing.
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requirements.
However, it Supplement 3 did not contain any new reported an event in which leakage from the RCS through a leaking valve-l (either through the
- packing, or past the - valve). caused thermal j
stratification.
A crack occurred on the RCS side (upstream) of. the' i
isolation valve due to thermal cycling.
The stagnant fluid. on - the RCS j
side of the isolation valve cooled due to heat loss which contracted the valve disk.
The upstream pressure pressed the disk leaving a gap, allowing' leaking through -the packing and drawing hot water from the RCS.
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U.S. Nucle?r Regulatory Commission August 1, 1989 Page Two The hot fluid expanded the valve and stopped the leakage, and the process was repeated continuously.
This scenario no longer requires the system connected to the unisolable RCS piping to be at a higher pressure than the RCS, and another review of the RCS was necessary.
Our review of the RCS has concluded that the only unisolable suction piping with a normally closed isolation gate valve connected to the vessel fluid system is inboard of the RHR shutdown cooling valve (E11-F009 in Unit 1 and 2 Ell-F009 in Unit 2).
For the following reasons, GPC believes that significant cyclic thermal stresses similar to that reported in the Bulletin Supplement will not occur at Plant Hatch.
The RHR shutdown cooling valve in Unit 2 (2 Ell-F009) closes on a preselected torque, which is one of the approaches suggested in Bulletin 88-08, Supplement 3 to alleviate the concern.
(The closure of the subject RHR isolation valve reported in Supplement 3 was controlled by limit switches which moved the valve disk into a preselected position.
With the valve closed, a small gap existed between the valve seat and disk, permitting the cyclic fatigue phenomenon.)
The closing circuit in the RHR shutdown cooling motor-operated valve in Unit 1 (E11-F009) has both a torque and limit switch in series.
The two switches function as an anti-pumping circuit, to prevent re-energizing the motor.
Because the torque and limit switches are in series, either switch could de-enert,1ze the motor.
However, the valve disk does close tightly in the seat; a
review of local leak rate tests for the last several years has indicated no failures and no upward trend in leakage.
Tight closure of this isolation valve is required since it (and the outboard valve) are a high/ low pressure interface between the vessel and the RHR system.
In addition, the valve is live-load packed (as is the Unit 2 valve) and the l
1eak-off line has been cut and capped.
Note that the RHR shutdown cooling valve will fall under the scope of Generic Letter 89-10. " Safety i
Related Motor-Operated Valve Testing and Surveillance".
Detailed valve diagnostics (including verification of switch settings) will be elements of our program to respond to this Generic Letter.
U.S. Nuclear Regulatory Commission August 1, 1989 Page Three The information provided herein is true to the best of my knowledge and belief.
If you have questions, please advise.
Respectfully submitted,
/A/..
M H. G. Hairston, III Sworn to and subscribed before me this f day of O RlxA 1989.
& burm baw M N Y pr00#2Nh[ dabs"ttPik nn GKM/eb c: Georaia Power Comoany l
Mr. H. C. Nix, General Manager - Nuclear Plant Mr. J. D. Heidt, Manager Engineering and Licensing - Hatch GO-NORMS l
l U.S. Nuclear Regulatory Commission. Washington. D.C.
Mr. L. P. Crocker, Licensing Project Manager - Hatch l
U.S. Nucir*r Reaulatorv Commission. Reaion II Mr. S. D. Ebneter, Regional Administrator Mr. J. E. Henning, Senior Resident Inspector - Hatch