ML18038B730

Responds to RAI Re GL 95-07, Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves.

ML18038B730
Person / Time
Site:	Browns Ferry
Issue date:	07/30/1996
From:	Salas P TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GL-95-07, GL-95-7, TAC-M93437, TAC-M93438, NUDOCS 9608060089
Download: ML18038B730 (14)

Text

II CATEGORY 1 REGULAT a INFORMATION DISTRIBUTlON YSTEM '(RIDS)

ACCESSION. NBR:9608060089 DOC.DATE: 96/07/30 NOTARIZED: NO DOCKET FAC1L:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 50;.-296 'Browns Ferry Nuclear Power Station, Unit 3, Tennessee 05000296 AUTH. NAME ~ AUTHOR AFFILIATION SALAS,P. Tennessee Valley Authority RECIP.NAME RECIPIENT 'AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Responds to RAI re GL 95-07, "Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves."

DISTRIBUTION 'CODE: A056D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: Generic Ltr 95-07 Pressure Locking & Thermal Binding of Safety Rela T NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL NRR/DRPE/EATON 1 1 PD2-3-PD 1 1 WILLIAMSgJ. 1 1 INTERNA FILE CENTER 01 1 1 NRR/EMEB/B 1 1 EXTERNAL: NOAC 1 1 NRC PDR 1 1 NUDOCS ABSTRACT 1 1 D

0 NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM OWFN 5D-5(EXT. 415-2083) TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON T NEEDI TOTAL NUMBER OF COPIES REQUIRED: LTTR 8 ENCL 8

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Tennessee Valley Authority, Post Office Box 2000, Decatur. Alabama 35609 July 30, 1996 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:

In the Matter of Docket Nos. 50-260 Tennessee Valley Authority 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) UNITS 2 AND 3 GENERIC LETTER (GL) 95-07'RESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER-OPERATED GATE VALVES RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION (TAC NOS. M93437 AND M93438)

This letter provides TVA's reply to a request from the NRC Staff, dated June 17, 1996, for additional information regarding BFN's response to GL 95-07.

NRC issued GL 95-07 on August 17, 1995, requesting licensees to take actions, as necessary, to ensure that safety-related power-operated gate valves susceptible to pressure locking or thermal binding are capable of performing their required safety function. TVA provided BFN's response to NRC in letters dated October 16, 1995, December 15, 1995, and February 13, 1996. In its February 13, 1996 letter, TVA described;the BFN GL 95-07 valve population, evaluation methodology, and provided a schedule for completion of corrective actions.

Xn the Staff's request for additional information, BFN was requested to describe evaluations and training for plant personnel that have been conducted for each design or procedural modification that was completed to address each potential pressure locking or thermal binding concern. The enclosure to this letter provides TVA's response to the Staff's request for additional information. Xn summary, TVA considers that the corrective actions taken for BFN 9608060089 960730 fog(p r,'.,'PDR> "ADQCK 05000260 tl >I; ',

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U.S. Nuclear Regulatory Commission Page 2 July 30, 1996 Units 2 and 3, including training, are adequate to prevent thermal bind'ing and pressure locking of safety-related power-operated gate valves without adversely impacting plant safety.

There are no new commitments contained in this letter. If you have any questions, please contact me at (205) 729-2636.

Sincer l ro Salas Manager of Site Licensing Enclosure cc: See page 3

U.S'. Nuclear Regulatory Commi'ssion.

Page 3 July 30, 1996 Enclosure cc (Enclosure):

Mr. Mark S. Lesser, 'Branch Chief U,.S. Nuclear Regulatory Commission Region 101 II Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Browns Ferry Nuclear Plant 10833 Shaw Alabama 35611 Road'thens, Mr. J. F. Williams, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852

ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS'ERRY NUCLEAR PLANT (BFN)

UNITS' AND 3 GENERIC LETTER (GL), 95-07'RESSURE. LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER-OPERATED GATE VALVES RESPONSE TO'EQUEST FOR ADDITIONAL INFORMATION BACKGROUND In a letter dated June 17,, 1996, NRC requested additional information regarding BFN's response to GL 95-07. The Staff requested that TVA describe evaluations and training for plant personnel that have been conducted for each design o'r procedural modification completed to. address potential pressure locking or thermal binding. TVA's response to the Staff's request i;s provided below.

BFN VALVE MODIFICATIONS During the BFN Units 2 and 3 GL 95-07 evaluations, several valves were eliminated from consideration as being susceptible to the pressure locking phenomenon since modifications had been previously performed .to prevent pressure locking from occurring.

These valves are the Residual Heat Removal (Flow Control Valves

[FCV],-74-53 and -67) and Core Spray (FCV-75-25 and -53) inboard injection valves. Each Unit at BFN has a complete set of these flex wedge gate valves that are included: in the scope of the GL 89-10 program. These valves are normally closed with a check valve located between the subject valve and the reactor vessel.

During normal operation, the valves may 'be exposed to full reactor pressure due to leakage across the check valve. During a design basis Loss of Coolant Accident, the reactor is rapidly depressurized causing normal reactor pressure to become entrapped in the bonnets of the subject valves, which may cause them to become pressure locked.

The subjec't valves were modified as part of the GL 89-10 program by drilling a hole in the downstream (reactor side) face of the valve disc, which allows the bonnet pressure to remain equalized with the reactor pressure. Consequently, when these valves are called upon to open for their required'afety function, the highest bonnet pressure the valves would experience is the same as the downstream pressure of approximately 450 pounds per square inch gage (psig) based on the reactor permissive signal for the low pressure Emergency Core Cooling System injection systems.

The subject valves are operated for quarterly stroke time testing

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to satisfy the American Society of Mechanical Engineers Boiler

~ and Pressure Vessel Code,Section XI, and Technical Specification operability testing during normal operations and for 10 CFR 50, Appendix J, leakage testing during outage conditions. The stroke testing remains unaffected by these valve modifications, since the bonnet pressure and the downstream system pressure remain equalized through the hole drilled in the downstream face of the valve disc.

For Appendix J leakage testing during outage conditions, the subject valves are tested with 50 psig of hydrostatic pressure from the downstream (containment/reactor) side of the valve. The valve bonnet will be exposed to this test pressure and seat leakage across the upstream disc face which is measured to represent containment leakage rates. Maintenance procedures that cover the disassembly and'eassembly, of the valves include specific steps to ensure the valve disc will remain in the correct orientation. As a result, there are no operational considerations. adversely affected by the modification to these valves. Thus, no additional training was required.

BFN PROCEDURE MODIFICATIONS The results of the GL 95-07 evaluation showed that BFN has'ne valve in each unit that is susceptible to thermal binding. This valve was identified as the High. Pressure Core Injection .(HPCI) steam admission valve (FCV-73-16). The: valve is a solid wedge gate valve that is normally closed and must open to perform its required safety function. When the valve is opened, steam from the reactor vessel passes through and heats the valve. After the valve is closed, binding.

it cools and may become susceptible to thermal Temperatures of the subject valve body were measured before HPCI system operation on .Unit 2. The data indicated that and'fter at steady state conditions (prior to system operation) the temperature differential between the upstream (reactor/steam) side and the downstream side of the valve was approximately 75 degrees fahrenheit (F), with the upstream side of the valve remaining close to saturation temperature of 1000 psig steam (approximately 526 degrees F). When the valve was opened, the average valve body temperature at the downstream side was raised to within '20 degrees F of the upstream side of the valve. The temperature cooling rate was monitored and it was determined that if the valve was stroked, at any ti;me during the second half hour period following system operation, the differential temperature experienced by the valve would not be sufficient to cause thermal binding. The above Unit 2 temperature data is considered applicable to Unit 3 due to the configuration similarity of the Units 2 and 3 HPCI systems and plant operating parameters.

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Based on the above, plant operating and survei.llance instructions were revised to requi're stroking of .the subject Un'its 2 and 30 to 60 minutes following HPCI system operation to ensure 3'alves the valve will not become thermally bound. Licensed operators were made aware of these procedure changes by "required reading" training. Other Operations personnel were notified of the procedure changes through the plant Operations Daily Instructions. The procedure revisions ensure that the valve will open when required and will not adversely affect the normal operation of the subject valves.

CONCLUSION TVA has performed the evaluations required by GL 95-07 for BFN Units 2 and 3. The evaluations were conducted using the guidance provided in the GL. TVA considers that the corrective actions taken, including training, are adequate to prevent and pressure locking of .safety-related power-operated thermal'inding gate valves wi.thout adversely impacting plant safety.

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