ML20116J488

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Responds to NRC RAI Re GL 95-07, Pressure Locking & Thermal Binding of Safety-Related Power-Operated Gate Valves
ML20116J488
Person / Time
Site: Sequoyah  Tennessee Valley Authority icon.png
Issue date: 08/06/1996
From: Shell R
TENNESSEE VALLEY AUTHORITY
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20116J490 List:
References
GL-95-07, GL-95-7, TAC-M93519, TAC-M93520, NUDOCS 9608130238
Download: ML20116J488 (6)


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Bl4 Tennessee Valley Authonty. Post Ottee Box 2000. Soddy-Da sy Tennesse'e 37379 August 6,1996 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:

In the Matter of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 SEQUOYAH NUCLEAR PLANT (SON)- UNITS 1 AND 2 - RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION - GENERIC LETTER (GL) 95-07,

, " PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER- 3 OPERATED GATE VALVES" (TAC NOS. M93519 AND M93520)

The purpose of this letter is to provide the response to NRC's request for additional information dated July 9,1996. The enclosure provides TVA's response to NRC's request for SON. 3 No commitments are identified in this letter. Please direct questions concerning this a issue to D. V. Goodin at (423) 843-7734.  !

1 Sincerely, i Y.

R. H. Shell Manager SON Site Licensing ,

t so daya / 1996 ff]Q4 Y U Notary'Vublic /

My Commissi_sn Expires 88I k Nf Enclosures cc: See page 2 /_l(fh 13'079 9608130238 960806 PDR ADOCK 05000327 P PDR

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, U.S. Nuclear Regulatory Commission Page 2 August 6,1996 l

cc (Enclosures):

Mr. R. W. Hernan, Project Manager i Nuclear Regulatory Commission One White Flint, North l 11555 Rockville Pike Rockville, Maryland 20852-2739 l NRC Resident inspector l Sequoyah Nuclear Plant

! 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379-3624

! Regional Administrator U.S. Nuclear Regulatory Commission Region ll 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323-2711 l

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ENCLOSURE a

SEQUOYAH NUCLEAR PLANT (SQN) UNITS 1 AND 2 GENERIC LETTER (GL) 95-07 REQUEST FOR ADDITIONAL INFORMATION NRC letter dated July 9,1996, requested additional information regarding TVA's response to GL 95-07 for SON. The following provides responses to the NRC ,

requests:  !

Question 1 "Regarding valves FCV-63-156, Safety injection Pump (SIP) A to Hot Leg (HL) 1&3 Injection isolation, and FCV-63-157, SIP A to HL 2&4 Injection Isolation, TVA's submittal states that analysis for the pressure locking condition due to the pressure increase indicates these valves are capable of performing their safety function. Please provide this analysis for our review. Please include thrust requirement and actuator capability calculations completed as part of this analysis, if capable."

Response 1 The thrust requiremcnts were performed in accordance with the methodology developed by Grand Gulf Nuclear Station, as presented in NUREG/CP-0146. The l results of these evaluations are attached (see EPM-RJP-022691, EPM-RJP-022791, l 2-FCV-63-156 [GL 89-10], and 2-FCV-63-157 [GL 89-10]). I Note that in addition to the evaluations performed in accordance with the Grand Gulf methodology, contract 96N4E-176161 has been awarded to Velan Engineering to determine whether pressure locking would occur at the conditions experienced by these motor-operated valves (MOVs) and, if so, the thrust required to overcome the pressure locked condition. The Velan determinations are required to be based on I actual test data and are expected to be provided to TVA by September 6,1996.

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Question 2 l "The TVA submittal discusses the susceptibility of valves FCV-63-25 and -26, High Pressure injection isolation, to depressurization induced (hydraulic effects) pressure  ;

locking. The submittal states that these valves have a bonnet bypass line that is maintained closed. Please discuss why the bypass line is maintained closed.

In addition, these valves may be potentially susceptible to depressurization induced pressure locking during a loss of coolant accident coincident with a loss of offsite power in which the centrifugal charging pumps trip. Please address this scenario.

Provide thrust requirement and actuator capability calculations that have been completed to address pressure locking concerns for these valves."

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Resoonse 2 Valves in the bonnet bypass lines were closed to ensure double isolation of the four l

1 1/2-inch safety-injection lines from the charging pumps. This action was a result of NRC Bulletin 88-08 and was performed to improve system reliability by eliminating the potential for thermal stress in the injection lines. The bypass lines, which were a part of the original Westinghouse design, were required to prevent pressure locking of the valves due to the affects of heat tracing. Heat tracing was disconnected with the plant modification that eliminated SON's Boron Injection Tank. With the elimination of heat tracing, the temperature changes of the valves would not develop a pressure locking condition.

During a subsequent review performed for GL 95-0+*. iowever,it was realized that pressure locking due to pressure differential betw ee e valve bornet and piping could occur. This condition has been analyzed and a vetermination was made that adequate capability to overcome pressure locking was available. The evaluations are attached (see 1&2-FCV-63-25 [GL 89-10) and -26 [GL 89-10]).

The calculations discussed above assume the centrifugal charging pumps to be running. The scenario mentioned in Question 2, (i.e., loss of offsite power coincident

, with a loss of coolant accident [LOCA]), would result in no upstream pressure (at the valve) for a maximum of seven seconds (by design, at two seconds the pump receives a " start" signal and is up to speed in five additional seconds). Based on the expected temperature rise (i.e., 75 degreos Centigrade), the seven second delay is considered an insignificant impact on valve operability for depresurization induced pressure locking and no additional analysis is deemed nece::sary.

Question 3 j I

" Valves FCV-68-332 and -333, Pressurizer PORV Block Valves, may be potentially i susceptible to depressurization induced pressure if shut to isolate a leaking PORV and l later required to open following an RCS depressurization, such as during a steam i generator tube rupture. Please address this issue. Also provide thrust requirement and actuator capability calculations completed to address potential pressure locking concerns for our review.

In addition, the TVA submittat discusses previous operating experience in which these valves were shut at high temperature and later opened at low temperature. The NRC staff agrees that previous operating experience can provide usefulinformation in determining the susceptibility of valves to thermal binding. For the purposes of '

closure of the NRC staffs review of GL 95-07:

a. Please describe any available information involving the thrust requirement for the valves when they were shut in a high temperature condition and later opened in a low temperature condition, which might include diagnostic test results or analysis. Note: This is to ensure that the motor actuators were not degraded by

' the previous hot-to-cold scenarios described in the licensees submittal.

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b. Do the actuators for these valves have design features to prevent excessive closing forces on the disk such as a compensating spring pack or limit switch seating logic?"

Resoonse 3 The potential for these valves to be susceptible to depressurization induced pressure locking was realized in TVA's GL 95-07 review. The thrust to overcome this condition was evaluated and it was determined that adequate thrust capability is available to overcome pressure locking. The evaluations are attached (see EPM-RJP-041091, EMP-RJP-031191,2-FCV-68-332 [GL 89-101, and 2-FCV-68-333 [GL 89-10]).

No diagnostic data is available that would identify the thrust requirement for the valves when they were shut at a high temperature and later opened at a low ,

temperature. Additionally, no data associated with normal maintenance / periodic l verification activities is currently available since no diagnostic testing has been performed since the occurrence of these events. These MOV's are in SON's GL 89-10 program, however, and will be periodically monitored and the data trended to determine whether any degradation has occurred.

The PORV block valves at SON do not have any special design features to prevent excessive closing forces.

Question 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 incorrect evaluation of the potential effects of these modifications. Please describe evaluations and training for the plant personnel that have been conducted for each design or procedural modification completed to address potential pressure locking or thermal binding concerns."

Resoonse Modifications performed at SON Units 1 and 2 are limited to two flow control valves (FCV-63-172) for both units. The modification involved the addition of a bypass line, with a manualisolation valve.

These valves are 12 inch flex-wedge, Velan gate valves. They serve as the emergency core cooling system residual heat removal (RHR) hot-leg recirculation flow path isolation vaives. They are normally closed and are required to open remotely, from the main control room,12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> after initiation of the event. These modifications were performed by design change notices (DCNs) M08573 and M08574.

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The following was considered in TVA's Safety Evaluation-l

increased due to addition of the bypass line which runs from the valve body to the RCS side of the valve.

  • Potentialleakage through the bypass line during post-LOCA cold leg injection is addressed by considering a penalty of a 6-degree Fahrenheit increase in the peak clad temperature (this was coordinated with Westinghouse Electric Corporation).
  • The manual bypass valve is normally open to protect against pressure locking of the l main valve. However, due to operational concerns, the manual valve is closed during normal plant cooldown, after the RCS reaches 380 psi (decreasing) and prior to placing RHR in service. Closure of the manual valve will prevent leakage past FCV-063-172 and resulting flow through the RHR recirculation primary and l secondary check valves.

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  • During startup, the manual valve must be opened prior to the RCS exceeding l 380 psig.
  • The evaluation clearly recognizes that the valve becomes uni-directional when the bypass valve is open.
  • The valve vendor (Velan Engineering) was consulted prior to modifying the valve.

System Operating Instruction 0-SO-74-1," Residual Heat Removal System," addresses closure and reopening requirements for the manual bypass valve (VLV-63-800) associated with FCV-63-172. This procedure states that, "lF placing Unit in shutdown cooling, THEN CLOSE VLV-63-800." Reopening is addressed by stating, "lF placing RHR in ECCS Standby injection Mode, THEN OPEN VLV-63-800."

The addition of the bypass line is also addressed from a training standpoint in Operator Lesson Plan OPL2739414, Revision 0, pages 8 and 9, which states:

. . . this bypass line contains a 1/2" Kerotest, or equal, manual globe valve (VLV-63-800). The purpose of this bypass line is to provide a relief path for potentially trapped fluid inside FCV-63-172 to vent and prevent pressure locking. This valve will be normally open, but can be closed during normal plant cooldown after the RCS reaches 380 psig (decreasing) and < 350 degrees F and prior to placing RHR in l

service. During Startup, VLV-63-800 must be opened prior to the RCS exceeding 380 psig and 350 degrees F and off RHR."