ML20116D562
| ML20116D562 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 07/25/1996 |
| From: | Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-95-07, GL-95-7, NUDOCS 9608020222 | |
| Download: ML20116D562 (7) | |
Text
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Stzthn Support Depcrtmtnt i
G.L 95-07 A
PECO NUCLEAR ecco e"e'uv co-neov Nuclear Group Headquarters A UMi of PECO EMscr 9
esteyy9 v 'd p
July 25,1996 Docket Nos. 50-277 50-278 License Nos. DPR-44 DPR-56 U. S. Nuclear Regulatory Commission A1TN: Document Control Desk Washington, DC 20555
SUBJECT:
Peach Bo' tom Atomic Power Station, Units 2 and 3 Response to NRC Request for Additional Information Regarding 180 Day Response to Generic Letter 95-07, " Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves."
REFERENCE:
1)
Letter from G. A. Hunger, Jr. (PECO -
Energy Company) to NRC dated February 13,1996 2)
Letter from J. W. Shea (NRC) to G. A. Hunger dated June 26,1996
Dear Sir:
The NRC issued Generic Letter (GL) 95-07, " Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves," on August 17,1995. In the GL the NRC requested that addressees perform, or confirm that they previously performed, evaluations of operational configurations of safety-related, power-operated gate valves for susceptibility to pressure locking and thermal binding.
In Reference 1, PECO Energy provided its 180 day response to GL 95-07. In Reference 2, the NRC requested additional information regarding that response This letter provides the requested additionalinformation. Restated below are the NRC questions followed by the PECO Energy response.
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'O 960802o222 96o725 PDR ADOCK 050oo277 g
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July'25,1996 Page 2 1
If you have any questions concerning this submittal or require additional information i
please contact us.
Sincerely, l
3 G. A. Hunger, r.
Director-Licensing Attachment cc:
T. T. Martin, Administrator, USNRC, Region 1
)
W. L Schmidt, Senior Resident Inspector, PBAPS i
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l'
' COMMONWEALTH OF PENNSYLVANIA I
- SS.
COUNTY OF CHESTER l
D. B. Fetters, being first duly sworn, deposes and says:
l That he is Vice President of PECO Energy Company; the applicant herein; that
-he has read the attached response to the NRC request for additionalinformation i
regarding Generic Letter 95-07, and knows the contents thereof; and that the l
statements and matters set forth therein are true and correct to the best of his knowledge, information and belief, g
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m
- Vice President Subscribed and sworn to before me this day of 1996.
1
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th Noyry Public Notarial Seal Lou Skrocki. Notary Public At Ced4s Eh b 9c4 t
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1 ATTACHMENT NRC Ouestion 1 l
Regarding the high pressure coolant injection (HPCI) and reactor core isolation cooling (RCIC) suppression pool suction gate valves, are these valves solid wedge gate valves? If not, were they evaluated for potential thermally-induced pressure locking from heatup of the suppression pool? If applicable, please i
provide any analysis or evaluation which was completed for staff review.
PECO Enerav Resconse The HPCI and RCIC torus suction valves are solid wedge gate valves.
NRC Ouestion 2 Regarding valve 23-14, HPCI steam isolation, does this valve exist in an orientation such that condensation could collect in the bonnet and experience a heatup during a design basis event leading to thermally-induced pressure locking? Also, has this valve been evaluated for potential thermal binding?
Please provide any analysis or evaluation which was completed for staff review.
PECO Enerav Resoon.sg HPCI Turbine Steam Admission Valve MO-2/3-23-014 was previously evaluated for thermally-induced pressure locking caused by condensate collection as well as for thermal binding (TB) prior to our Reference 1 submittal.' It was found not susceptible to either thermally-induced pressure locking (TIPL) caused by condensate collection or thermal binding. As a result, it was not included in that submittal.
The evaluation concluded that the valve is not susceptible to TIPL for the following reasons: 1) the steam line is sloped away from the valve toward the drain pot and the valve stem is oriented vertically, both of which prevent steam line condensate from collecting in the valve bonnet, and 2) the valve is kept at a relatively constant temperature by reactor pressure steam against the valve wedge which prevents thermally-induced pressurization of any condensate present in the bonnet due to steam leakage.
The evaluation also concluded that the valve was not susceptible to thermal binding since it is heated by condensing steam at all times. The absence of thermal binding has been, and will continue to be, proven by system surveillance tests.
The possibility of TB due to cooldown as part of a normal reactor 1
l d: pressurization was consid: red. Howsvar, HPCI is only required to be operable above 150 psig reactor pressure. Considering the difference in saturated steam temperature between normal operating pressure and 150 psig, 4
j and the insulation on the entire HPCI line, the typical reactor depressurization rate will not produce a significant temperature change of the MO-23-014 valve body. Therefore, this scenario is not a concern.
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The possibility for TB following a system outage was also evaluated. The l
potential concern is as follows:
the valve was last closed hot during surveillance testing, 1
4 the HPCI steam line was isolated for a system maintenance outage, when returning the system for service, the steam line is un-isolated and
- warmed, a time period may exist for TB until the MO-23-014 valve body temperature stabilizes.
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This scenario is not a concern for the MO 23-014 valve since HPCI operability runs are typically performed following these out of service periods, verifying j
i valve operability under these conditions. In addition, successful valve stroking following complete cooldowns have been performed for GL 89-10 periodic verification testing.
NRC Ouestion 3 i
i in Attachment 1 to GL 95-07, the NRC staff requested that licensees include consideration of the potential for gate valves to undergo pressure locking or thermal binding during surveillance testing. During workshops on GL 95-07 in each Region, the NRC staff stated that, if closing a safety-related power-operated gate valve for test or surveillance defeats the capability of the safety system or train, the licensee should perform one of the following within the scope of GL 95-07:
1 (a)
Verify that the valve is not susceptible to pressure locking or thermal binding while closed, (b)
Follow plant technical specifications for the train / system while the valve is
- closed, (c)
Demonstrate that the actuator has sufficient capachy to overcome these
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j phenomena, or (d)
Make appropriate hardware and/or procedura' mod 4ications to prevent 1
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i pressure locking cnd th:rmal binding.
j The staff stated that normally open, safety-related power-operated gate valves which are closed for test or surveillance but must return to the open position should be evaluated within the scope of GL 95-07. Please discuss if valves l
which meet this criterion were included in your review, and how potential j
pressure locking or thermal binding concerns were addressed.
PECO Enerav Resoonse Valves which are normally open and are closed for test or surveillance and which must return to the open position were evaluated within the scope of GL 95-07. PECO Energy has concluded that these valves are not susceptible to pressure locking or thermal binding while closed except as noted below.
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Valve applications, with the exception of MO-2/3-14-011 A/B, the Core Spray outboard injection valves, were found not susceptible while in this configuration due to the absence of system pressure or temperature transients as a result of,
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- 1) other system blocking during plant operation or,2) plant conditions during j
testing (e.g., surveillance testing performed during cold shutdown conditions).
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Valves MO-2/3-14-011A/B may be susceptible to pressure locking during short l
durations of the surveillance test sequence to support stroking of the inboard j-injection valves. The evaluation considered MO-2/3-14-011 A/B acceptab!e as-is based on the following reasons:
j numerous concurrent circumstances must occur to create conditions j
favorable for pressure locking, MO-2/3-14-011 A/B are IST Category B valves with no seat leakage requirements, and therefore, are not maintained to achieve leak tight j
performance, there is significant plant operating experience under current surveillance test conditions which demonstrates that these valves are capable of opening following de-pressurization of the piping between the inboard 1
and outboard valves, valves MO-2/3-14-011 A/B are out of their normal standby position for short durations.
Note: In response to NRC Routine Integrated inspection report 50-277/96-03 and 50-278/96-03, PECO Energy is currently re-evaluating valves MO-i 2/3-14-011 A/B with regard to our Generic Letter 89-10 program scope.
The results of the re-evaluation, which will be included in PECO Energy's
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response to the inspection report, may affect how these valves are addressed with regard to Generic Letter 95-07.
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, NRC Ouestion 4 I
Through review of operational experience feedback, the staff is aware of instances where licensees have completed design or procedural modifications to preclude pressure locking or thermal binding which may have had an 4
adverse impact on plant safety due to incomplete or incorrect evaluation of the potential effects of these modifications. Please describe evaluations and
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training for plant personnel that have been conducted for each design or l
procedural modification completed to address potential pressure locking or thermal binding concerns.
j PECO Energv Resoonse l
PECO Energy has performed several design modifications involving wedge relief holes or external bypass lines to preclude pressure locking of susceptible gate
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vanes at PBAPS.
A comprehensive design evaluation was performed in accordance with PECO l
Energy's modification process including the following considerations as appropriate:
bi-directional seating capability and other system operating modes, ANSI B31.1 requirements l
ASME B&PV Code Section lil requirements, 1
ASME B&PV Code Section XI Pressure Isolation Valve leakage, 10CFR50 Appendix J leakage, seismic design requirements, high energy / moderate energy line break requirements.
As part of its modification process, PECO Energy also issued modification Training Bulletins to Operations and Training personnel as required, evaluated operator / plant procedure impact, defined test requirements, specified modification acceptance criteria, and identified documents for configuration control.
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