ML20116B773
| ML20116B773 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 07/25/1996 |
| From: | Cruse C BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20116B777 | List: |
| References | |
| GL-95-07, GL-95-7, TAC-M93444, TAC-M93445, NUDOCS 9607300265 | |
| Download: ML20116B773 (7) | |
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CHARLES H. CRUSE Baltimore Gas and Electric Company Vice President Calvert Cliffs Nuclear Power Plant Nuclear Energy 16.50 Calvert Cliffs Parkway Lusby, Maryland 20657 410 495-4455 July 25,1996 U. S. Nuclear Regulatory Commissior Washington, DC 20555 ATTENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50-317 & 50-318 Response to Request for Additional Information - Generic Letter 95-07,
" Pressure Locking and Thermal Binding of Safety-Related, Power-Operated Gate Valves."(TAC Nos. M93444 & M93445)
REFERENCES:
(a)
Letter from Mr. D. M. Crutchfield (NRC) to Mr. R. E. Denton (BGE),
datec Augus. 17,1995,"NRC Generic Letter 95-07: Pressure Locking and Thermal Binding of Safety-Related, Power-Operated Gate Valves" (b)
Letter from Mr. C. H. Cruse (BGE) to Document Control Desk (NRC),
dated r ebruary 13, 1996, "180-Day Response to NRC Generic Letter 95-07: Pressure Locking and Thermal Binding of Safety-Related, Power-Operated Gate Valves" (c)
Letter from Mr. A. W. Dromerick (NRC) to Mr. C. H. Cruse (BGE),
dated June 18,1996, " Request for Additional Information " Generic Letter 95-07, Pressure Locking and Thermal ' Binding of Safety-Related Power-Operated Gate Valves," Calvert Cliffs Nuclear Power Plant, Units 1 and 2 (TAC Nos. M93444 and M93445)
On August 17,1995, the NRC issued Reference (a) to request that licensees take actions to ensure that safety-related, power-operated gate valves that are susceptible to pressure locking or thermal binding are capable of performing their safety functions. Reference (b) was our initial response to the request. As a result of their review and evaluation of our initial response to Generic Letter 95-07, the NRC staff has requested additional information (Reference c) in order to complete their review. This letter forwards our response to the request for additional information. In addition, this letter includes a written response to a number of questions that were posed during telephone conferences that were held on July 2 and
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11056 9607300265 960725 PDR ADOCK 05000317
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Document Control Desk July 25,1996 Page 2 July 15 with the NRC staff. Attachment (1) contains our response to each of the questions. During the July 15 telephcr.e conversation, Baltimore Gas and Electric Company was granted a seven-day extension to the Reference (c) requested response date.
Should you have questions regarding this matter, we will be pleased to discuss them with you.
Very truly yours, N
/ 141-CHC/JMO/ dim
Attachment:
(1)
Baltimore Gas and Electric Company's Response to Request for Additional Information on Generic Letter 95-07: Pressure Locking and Thermal Binding of Safety-Related, Power-Operated Gate Valves cc:
(Without Enclosure)
D. A. Brune, Esquire T. T. Martin, NRC J. E. Silberg, Esquire Resident inspector, NRC Director, Project Directorate I-1, NRC R.1. McLean, DNR A. W. Dromerick, NRC J. H. Walter, PSC i
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A1TACIIMENT J,1)
BALTIMORE G AS AND ELECTRIC COMPANY'S RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION ON GENERIC LETTER 95-07:
PRESSURE LOCKIN9 AND TIIERMAL BINDING OF SAFETY-RELATED, POWER-OPERATED GATE VALVES ADDITIONAL INFORMATION REOUESTED 1.
Regarding Motor-Operated Valves (MOVs) 4144 and 4145, Emergency Sump Recirculation Valves, the licensee's submittalstates that calculations that ver# the actuator can overcome the bonnet pressure have been completed verifying the valve will not pressure lock. Please provide these calculations for our review. In addition, please provide these thrust requirement and actuator capability calculationsfor our review.
Also, the licensee's submittal states that, to provide additional margin, plant startup procedures will be revised to fill the piping between valves MOV-4144 and 4145 prior to plant startup.
Based on a review ofplant piping and instrumentation drawings [P&lDs], it is unclear that 1
filling the piping between these valves willprovide a thermal barrier to prevent heatupfrom water in the containment sumpfollowing a postulated accident. Further, the NRC staff believes that reliance on water-filledpiping to preclude thermally-inducedpressure locking is uncertain.
Please provide a detailedjustificationfor the planned modification.
Response
The calculations requested are Enclosure (1). The enclosure also includes the thrust requirement and actuator capability calculations. The pressure locking calculation shows that the valves will operate under the scenario where the pressure in the bonnet increases due to heat-up caused by fluid entering the containment emergency sump following a loss-of-coolant accident. The calculation assumed that the piping was dry, which increased the potential to heat each of the MOVs.
We have determined that additional margin is provided by filling each of the containment emergency sump pipe lines between the emergency sump and the respective MOV (MOVs-4144 and 4145) to form a thermal barrier between the MOVs and the emergency sump. The lines are 24-inch diameter piping and embedded in concrete up to the containment wall. Outside of containment, the MOVs and the lines are encapsulated. The MOVs are approximately 45 feet downstream of the sump and approximately 2 feet outside of containment. There is normally no now in these lines unless a recirculation actuation signal is initiated following a loss of coolant accident. The Updated Final Safety Analysis Report analyzes a range of break sizes and concludes the recirculation actuation signal will actuate at approximately 36 minutes for the maximum safety injection containment design basis (i.e., two high pressure safety injection pumps, two low pressure safety injection pumps, and two containment spray pumps). For the minimum safety injection containment design basis (i.e., one high pressure safety injection pump, one low pressure safety injection pump, and one containment spray pump), the recirculation actuation signal will actuate at approximately 71 minutes. The Updated Final Safety Analysis Report also shows that the maximum sump temperatures are 270 F for minimum safety injection and 250 F for maximum safety injection (Figures 14.20-4, -5, and -6).
It is our judgment that the proposed changes to procedures to fill the piping between the MOV and the sump would prevent any signi0 cant heat up of the bonnet caused by these sump 1
i ATIACHMENT (1) 1 BALTIMORE GAS AND ELECTRIC COMPANY'S l
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION ON GENERIC LETTER 95-07:
l PRESSURE LOCKING AND TilERMAL BINDING OF SAFETY-RELATED, POWER-OPERATED GATE VALVES temperatures. Since the calculation showed the valves to be capable under increased pressure in the bonnet, the valves would be more capable with the proposed procedure changes.
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2.
Regarding valves MOV-403 and -405, Power-Operated Relief Valve (PORV) Block Valves, the licensee's submittal states that these valves are limit seated and the limits on the valves will be adjusted to reduce / prevent wedging to provide additional marginforpreventing thermal binding i
l The NRC staff agrees that prevention ofexcessive closingforces on the valve disk is an effective l
method in reducing susceptibility to thermal binding. Please discuss the licensee's planned actions to provide assurance that the adjustments to the valve limit switch settings will reduce or prevent wedging.
Respnsiac Valve Operation Test and Evaluation System (VOTES) testing was performed on 1-MOV-403 and 1-MOV-405 on April 29,1996. The limit switch was adjusted such that seat contact is achieved. Excessive wedging is prevented since the final force was only 191 lbs above the packing load on 1-MOV-405, and 95 lbs above the packing load on 1-MOV-403. The same methodology will be used to adjust 2-MOV-403 and 405. They are currently scheduled to be adjusted during the 1997 refueling outage.
3.
In Attachment 1 to Generic Letter (GL) 95-07, the NRC staff requested that licensees include
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consideration of the potentialfor gate valves to undergo pressure locking or thermal binding during surveillance testing. During workshops on GL 95-07 in each Region, the NRC staffstated that, if closing a safety-related, power-operated gate valvefor test or surveillance defeats the l
capability of the safety system or train, the licensee shouldperform one of thefollowing within the scope ofGL 95-07:
1)
Verify that the valve is not susceptible to pressure locking or thermal binding while i
closed; 2)
Followplant TechnicalSpecificationsfor the train / system while the valve is closed; 3)
Demonstrate that the actuator has sufficient capacity to overcome thesephenomena; or 4)
Make appropriate hardware and/or procedural modifications to prevent pressure locking and thermalbinding.
The staffstated 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 which meet this criterion were included in your review, and howpotentialpressure locking or thermal binding concerns were addressed.
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j KIIACHMENT (1) l BALTIMORE GAS AND ELECTRIC COMPANY'S RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION ON GENERIC LETTER 95-07:
I PRESSURE LOCKING AND TIIERMAL BINDING OF SAFETY-RELATED, POWER-OPERATED GATE VALVES Resnesisc j
We reviewed the safety-related Motor-Operated Gate Valves that fell under the scope of the GL for pressure lockirg and thermal binding (PLTB) during surveillance testing as requested in GL 95-07. This evaluation included the 17 valves per unit that were identified as having a l
safety-related function to open or remain open during or after an accident.
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Our original evaluation did include consideration of the potential for PLTB occurring in normally open valves which can be closed for surveillance testing. However, since we concluded that this level of detail exceeded the level of summary description requested by the GL, we did not include it in our original response (Reference a). There are nine valves per unit that fall into this category. Pressure locking and thermal binding during surveillance testing for these valves was evaluated as follows:
Power-Operated Relief Valve Block Valves (MOVs-403 and 405) are stroked Qued quarterly as part of the Inservice Test Program. The valves are closed, anc inen immediately reopened. Even if these valves were susceptible to PLTB, there would not be sufficient time between the closed and open strokes to create a condition for PLTB.
High Pressure Safety Injection Header Isolation Valves (MOVs-654 and 656) do not receive an automatic signal to open on an accident initiator. If these valves are closed for testing in modes where they are required to be operable, the applicable action statement will be entered until the valve is opened.
Safety injection / Containment Spray minimum flow isolation valves (MOVs-659 and 660) cannot be closed for surveillance testing in modes where they are required to be operable.
Refueling Water Tank Outlet Isolation Valves (MOVs-4142 and 4143) do not receive an automatic signal to open on an accident initiator. If these valves are closed for testing in modes where they are required to be operable, the applicable action statement will be entered until the valve is opened.
The Instrument Air Containment Isolation Valve (MOV-2080) is only tested in cold shutdown and refueling to ensure instrument air is not isolated to containment during power operations.
4.
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 adverse impact on plant safety due to incomplete or l
Incorrect evaluation of the potential effects of these modifications. Please describe evaluations and training for plant personnel that have been conducted for each design or procedural
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modification completed to address potentialpressure locking or thermal binding concerns.
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ATTAClIMENT (1) l BALTIMORE GAS AND ELECTRIC COMPANY'S l
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION ON GENERIC LETTER 95-07:
PRESSURE LOCKING AND TIIERMAL BINDING OF SAFETY-RELATED, l
POWER-OPERATED GATE VALVES l
Resannse Motor-Operated Valves-4144 and 4145: Plant Start-up and operating procedures were revised to ensure the containment emergency sump piping is filled prior to starting up following a refueling l
outage. Appropriate training to support the procedure changes will be conducted.
Motor-Operated Valves-651 and 652 were evaluated as not susceptible to pressure locking; l
however, they have minimal margin and are difficult to test. They will be modified to prevent pressure build up in the bonnet. Training and evaluations will be completed as part of the modification process.
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The Unit 1 PORV block valves (1-MOV-403/405) torque and limit adjustments were discussed with the MOV test engineers prior to the 1996 VOTES tests. The VOTES test procedure is being revised to include the following:
1 1)
A requirement to contact the MOV Engineer prior to adjusting limit or torque switches of susceptible valves; and 2)
A warning that improper adjustment of the closed limit or torque switch may cause the MOV to bind into the seat under certain conditions.
No special training is expected to be required.
l Questions and Responses from the July 2 and 15.1996 Telephone Conferences with NRC Staff 1.
What documentation or evidence does Baltimore Gas and Electric Company have to show that either of the Unit 2 containment emergency sump recirculation lines are filled with water between the isolation valves (MOVs-4144 and 4145) and the containment emergency sump?
Response
We reviewed recent Surveillance Test Procedures to determine if there is any documented inspection that verifies that one or both Unit 2 containment emergency sump recirculation lines are filled. Surveillance Test Procedure M-661, conducted on May 5,1995, contains an inspection comment that the " north most pipe is full of water."
Subsequent interviews with the inspector confirmed the statement is correct. We have not located any documentation that the other line is filled with water. The inspector stated that because of his sight line to the sump, he could not confirm whether there was water in the other line.
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i-ATTACIIMENT (1) l l
BALTIMORE GAS AND ELECTRIC COMPANY'S RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION ON GENERIC LETTER 95-07:
PRESSURE LOCKING AND TilERMAL BINDING OF SAFETY-RELATED, i
POWER-OPERATED GATE VALVES l
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Determine if the containment emergency sump area is reasonably accessible during power operations to visually confirm that the lines arefilled.
Response
l The containment emergency sump is in a 6 rem /hr field. We estimate that an inspection at power is not reasonable since workers would receive approximately 0.5 to 1.0 rem.
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What are Baltimore Gas and Electric Company's plansfor installing a modification to ensure the Unit 2 containment emergency sump recirculation lines are currentlyfilled?
Response
A modification was developed to allow filling each of the Unit 2 lines at power. The l
modification has been approved and has been installed for Unit 2. We expect to fill the lines by July 31,1996.
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