ML20195H889

Forwards Response to NRC 990315 RAI Re GL 95-07, Pressure Locking & Thermal-Binding of SR Power-Operated Gate Valves, 180-day Response Submitted by District on 960213

ML20195H889
Person / Time
Site:	Cooper
Issue date:	06/14/1999
From:	Swailes J NEBRASKA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-95-07, GL-95-7, NLS990058, TAC-M93453, NUDOCS 9906180027
Download: ML20195H889 (7)

Text

r NLS990058 June 14,1999 H

Nebraska Public Power District -

Nebraska's Energy Leader i

U.S. Nuclear Regulatory Commission

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Attention: Document Control Desk '

Washington, D.C. 20555-0001

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Gentlemen:

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Subject:

Generic Letter 95-07180-day Response to Request for Additional Information I Cooper Nuclear Station, NRC Docket No. 50-298, DPR-46

Reference:

1. Letter to G.R. Horn (NPPD) from L.J. Burkhart (USNRC) dated March 15, 1999, " Request for Additional Information - Generic Letter 95-07, Pressure-Locking and Thermal-Binding of Safety-Related Power-Operated Gate Valves",

Cooper Nuclear Station (TAC No. M93453).

By letter dated March 15,1999 (Reference 1), the Nuclear Regulatory Commission requested the Nebraska Public Power District (District), to provide additional information regarding the Generic Letter 95-07180-day response submitted by the District on February 13,1996.

Attachment I to this letter provides the additional information requested.

Should you have any questions concerning this matter, please contact me.

Sinc y, h NY m Jo 1. Swailes .

ice President of Nuclear Energy

/rar Attachment cc: Regional Administrator w/ attachment USNRC - Region IV jlj

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Senior Project Manager w/attachmen:

USNRC - NRR Project Directorate IV-1 Senior Resident Inspector w/ attachment USNRC NPG Distribution w/o attachment 0

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Cooper Nudear Station P.o. Box 98/ Brownville. NE 68321D098 Telephone: (402) 825 3811/ W: (402) 825 5211 "p#*** nnpd om 990618002'7 99b614 PDR- ADOCK 05000298 P PDR

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Attachment 1 i to NLS990058  ;

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i Response to NRC RAI on Cooper Nuclear Station GL 95-07180-Day Submittal The following is the Nebraska Public Power District's (District's) response to the Nuclear I Regulatory Commission's Request for Additional Information (RAI) dated March 15,1999. The RAI questions concern the District's 180-day submittal for GL 95-07," Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves" dated February 13,1996.

The questions from the RAI have been restated in italics with the individual responses stated in non-italics format. Additionally, as requeste'd by the NRC staff on February 4,1999 in a conference call with NPPD personnel, short and long term mitigating actions, where necessary are clearly delineated.

The District recognizes that certain questions contained in the RAI were not specifically addressed in the 1996 GL 95-07.180-day response. The District has evaluated these questions based on current industry information. This information will also be considered in the review of any generic applicability to other safety related power operated gates valves in accordance with the District's corrective action program.

Question 1. Are there an" conditions when high pressure coolant injection (HPCI) valve, HPCI-M014, would t. ~ quired to open when pressure in the valve 's bonnet is greater than upstream or downstream pressure? Ifso, is this valve susceptible to pressure locking and are other valves in the HPCIsteam lines susceptible topressure locking during surveillance testing?

Response

The following response has been formatted to address each of the separate issues raised in

. Question 1. 1 (1) A review of applicable Cooper Nuclear Station (CNS) accident, transient, special and normal events revealed that there are plant conditions in which valve HPCI-M014 would be required

~ to open when pressure in the valve's bonnet is greater than upstream or downstream pressure.

- (2) Based on identified plant conditions in which valve HPCI-M014 would be required to open i

.when the pressure in the valve's bonnet is greater than upstream or downstream pressure, j opening thrust requirements have been evaluated using the MPR Associates methodology for predicting opening thrust requirements under postulated conditions ofincreased bonnet l

pressure. Under postulated conditions ofincreased bonnet pressure, HPCI-MOV-M014 i

~ opening thrust and motor torque margins remain positive based on the use of as-tested valve  !

performance parameter values versus bounding design basis parameter values. Although less than design basis margin exists, adequate opening thrust and motor torque margin remains to y provide assurance that HPCI-M014 safety functions will be accomplished. Thus, HPCI-M014 is not susceptible to pressure locking. As a long term fix to restore HPCI-M014  ;

design basis margin, the District will implement an appropriate modification to equalize D

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bonnet cavity pressure and upstream pressure prior to startup from refueling outage 20 (RE20) currently scheduled in 2001. This schedule enables sufficient investigation and planning of an appropriate modification.

(3) Other valves in the HPCI steam line are HPCI-M015 (inboard isolation) and HPCI-MOl6 (outboard isolation). HPCI-MOIS and HPCI-MOl6 are reopened quickly following closure during surveillance testing to avoid a significant transient on the Augmented Off Gas (AOG) system, which receives its steam supply downstream of HPCI-M015 and HPCI-MOl6.

Since these valves are closed only momentarily, a significant change in downstream pressure is not credible thus, the conditions which result in potential pressure locking are not created.

Question 2. The 180-day Generic Letter 95-07 submittalstates that testing demonstrated that HPCI suppression pool suction valve, HPCI-A10V-A1058, is not susceptible to pressure locking due to increased ambient room temperatures. Please describe the test, how the test demonstrates the valve is not susceptible topressure locking, accident room temperatures, and room temperatures during the test. Testing and operational experience are not generally acceptable corrective actionsforpressure locking because valve leakage rates are not predictable. Also discuss how this testing demonstrates that the valve will operate during pressure locking conditions with reduced voltage to the actuator.

Response

The following response has been formatted to address the issues raised in Question 2.

(1) The referenced HPCI-MOV-MO58 (HPCI-MO58) test was conducted in July 1993. The test was specifically scheduled to obtain information (opening thmst) to disposition a potential pressure locking issue associated with the CNS Generic Letter 89-10 Motor Operated Valve (MOV) program. Specifically, the HPCI-MO58 valve opening thrust was measured afler HPCI toom heatup (and subsequent HPCI-MO58 heatup) following plant restart from refueling' outage RE15. A current review of this test reveals that the information provided by the District in its GL 95-07180-day response contains two basic weaknesses. The first weakness involves the failure to adequately demonstrate how the temperature rise of the HPCI-MO58 valve which preceded the test bounded the postulated worst case valve temperature rise. Secondly, the results of this test did not adequately justify why valve seat leakage did not contribute to the absence of measured pressure locking loads. The District agrees with the NRC that valve seat leakage rates are not consistently predictable and cannot be relied upon as a conservative long term operability basis. As such, the District has analytically re-evaluated the effect ofincreased ambient room temperatures on the HPCI-MO58 valve temperature and corresponding bonnet pressure assuming no valve seat leakage and no trapped bonnet non-condensibles. The results indicated that HPCI-MO58 is susceptible to pressure locking due to increased bonnet pressure during certain postulated events. Therefore, a modification was implemented to install insulation on HPCI-MO58.

Under worst case postulated HPCI room temperature, calculations show that the installed

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. Attachment I to NLS990058

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insulation will limit valve heatup and corresponding bonnet pressure such that positive operability margin exists: Although less than design basis margin exists, adequate opening thrust and motor torque margin remains to provide assurance that HPCI-MO58 safety

, functions will be accomplished. Thus, HPCI-MO58 is not susceptible to pressure locking.

As a long term fix to restore HPCI-MO58 design basis' margin, an appropriate modification will be implemented to prevent bonnet pressurization due to the effects of room heatup. This modification will be completed prior to startup from RE 20. This schedule enables sufficient investigation and planning of an appropriate modification.

(2) The July 1993 HPCI-MO58 test indicated that the valve opening thrust was within MOV program limits. As such, the valve was determined to be not susceptible to pressure locking.

This conclusion was considered valid for reduced voltage conditions as well; the MOV program limits account for the effect of reduced voltage. However, as discussed above, the test did not adequately bound the postulated worst case temperature rise nor did it account for the effect of potential seat leakage on test results. The current operability evaluation of HPCI-MO58 does include consideration of design basis low voltage conditions and concludes that HPCI-MO58 will perfomi its required safety functions.

Question 3. Explain ifsuppression pool cooling loop isolation valves, RHR-Af0V-Af039A and RHR-Af0V-Af039B,^ are susceptible to pressure lockingfollowing operation ofthe residual heat removal (RHR)/ low pressure safety injection (LPSI) system in the shutdown cooling, pump testing, or injection modes. Are the bonnets ofthese valves pressurizedfrom the'RHR/LPSI pump then required to open later at a lowerpump pressure?

Response

The following response has been fomutted to address each of the separate issues raised in Question 3.

(1) In certain scenarios, the bonnets of RHR-MO39A and RHR-MO39B are rcessurized from the Residual Heat Removal (RHR) pumps and then are required to open later at a lower pump discharge pressure. The specific scenarios are discussed as follows.

. Shutda ,.%oling Mode In the shutdown cooling mode of operation the RHR-

- MO39A or RHR-MO39B bonnets could be pressurized by the operation of the RHR pumps. In this configuration, reactor vessel pressure and elevation head contributes to RHR' pump discharge head and resultant RHR-MO39A or RHR-MO39B bonnet pressurization. However, the RHR-MO39A and RHR-MO39B valves are interlocked closed whenever the RHR shutdown cooling suction valves are not fully closed, to prevent reactor vessel drain down. Subsequent manual realignment to the Low Pressure Coolant Injection (LPCI) injection mode could result in the need to L open either RHR-MO39A or RHR-MO39B for suppression pool cooling. The required opening thrusts resulting from this scenario have been evaluated using the

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MPR Associates methodology for predicting opening thrust requirements under j

postulated conditions ofincreased bonnet pressure. The results indicate that, based on as-tested valve performance parameter values and a scenario specific voltage value, opening thrust and motor torque margin remains positive for RHR-MO39A and RHR-MO39B. Although less than design basis margin exists, adequate opening thrust and motor torque margin remains to provide assurance that RHR-MO39A and RHR-MO39B safety functions will be accomplished. Thus, RHR-MO39A and RHR-MO39B are not susceptible to pressure locking. Prior to startup from RE20, an appropriate modification will be implemented to prevent bonnet pressurization and restore RHR-MO39A and RHR-MO39B design basis margins.

This schedule enables sufficient investigation and planning of an appropriate

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modification. RHR-MO39A is scheduled to be dynamically tested during RE19

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under a commitment associated with Generic Letter 96-05 and the Joint Owners l Group. The testing associated with this commitment involves dynamic testing of

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RHR-MO39A once per cycle for three cycles in order to determine if any valve j

' degradation is occurring.

RHR Pump Surveillance Testing: Existing CNS surveillance procedures for RHR pump testing contain steps which direct operations personnel to open RHR-MO39A or RHR-MO39B prior to pump start, and to close these valves following securing j the RHR pumps. Therefore, the RHR-MO39A and RHR-MO39B bonnets are not

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pressurized during surveillance testing, thus the valves are not susceptible to pressure locking during this activity.

'RHR Pump Injection (LPCI): Operation of the RHR pumps in the LPCI mode could  ;

result in RHR-MO39A and RHR-MO39B bonnet pressurization in certain scenarios. The required opening thrusts for these scenarios have been evaluated i using the MPR Associates methodology for predicting opening thrust requirements during postulated conditions ofincreased bonnet pressure. Based on these results, both RHR-MO39A and RHR-MO39B opening thrust and motor torque margins i remain positive based on as-tested valve performance parameter values. Although i less than design basis margin exists, adequate opening thrust and motor torque margin remains to provide assurance that RHR-MO39A and RHR-MO39B safety functions will be accomplished. Thus, RHR-MO39A and RHR-MO39B are not susceptible to pressure locking. As stated above, an appropriate modification to prevent bonnet pressurization on these valves will be implemented prior to startup from refueling outage RE20 to restore design basis margins.

' Question 4. Discuss ifLPSIinjection valves, RHR-MOV-MO25A and RHR-MOV-MO25B. are susceptible to thermal bindingfollowing operation ofthe RHR system in the plant heatup mode ofoj>eration. Are these valves closed after securing RHR during heatup of the unit and then requirea to automatically open after the valves have cooled down?

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- Attachment 1 to NLS990058 l Page 5 of 5 i l Response . l The following response has been formatted to address each of the separate issues raised in Question 4.

'(1) Valves RHR-MOV-MO25A and'RHR-MOV-MO25B could be required to automatically open following closure at elevated temperatures caused by operation of the RHR system in the heatup mode of shutdown cooling, normal shutdown cooling mode, and LPCI mode.

Thus these valves could potentially be susceptible to thermal binding due to closure of these valves at an elevated temperature followed by cooldown to ambient temperature. As a long term solution to prevent a thermal binding event, the District will use the MPR Associates prediction methodology for thermal binding to establish appropriate proceduralized criteria to ensure that RHR-MOV-MO25A and RHR-MOV-MO25B do not become susceptible to thermal binding. In the interim the control switches for RHR-MOV-MO25A and RHR-MOV-MO25B have been caution tagged with appropriate operator guidance to ensure that these valves do not become susceptible to thermal binding.-

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. . -l' ATTACHMENT 3 LIST OF NRC COMMITMENTS l

Correspondence No: NLS990058 l-- - The 'following table identifies those actions committed to by the District in this

document. Any other actions discussed in the submittal represent intended or planned actions by the District. They are described to the NRC for the NRC's information and are not regulatory commitments. Please notify the NL&S Manager at Cooper Nuclear Station of-any questions regarding this document or any associated

regulatory commitments.

COMMITTED DATE COMMITMENT OR OUTAGE CNS will implement modifications as required to eliminate Prior to Start-up the potential of bonnet pressurization of Motor Operated from RE20 Gate valves discussed in this submittal.

CNS will establish ~proceduralized temperature criteria to ensure affected valves are not susceptable to thermal Prior to RE19 binding.

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.] PROCEDURE NUMBER 0.42 l REVISION NUMBER 6 l PAGE 9 OF 13 l j

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