ML20116M500
| ML20116M500 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 08/15/1996 |
| From: | Diprofio W NORTH ATLANTIC ENERGY SERVICE CORP. (NAESCO) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-95-07, GL-95-7, NYN-96058, NUDOCS 9608200178 | |
| Download: ML20116M500 (7) | |
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North North Atlantic Energy Service Corporation 1
'# Atlaritic P.O. Box 300 Seatroet, Nii o3874 I
(603) 474-9521 The Northeast Utilities System A E I 5 1996 4
Docket No. 50-544 NYN-96058 j
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United States Nuclear Regulatory Commission j
Attention:
Document Control Desk Washington, D.C. 20555 Seabrook Station Resoonse to Reauest for Additional Information for Gene.ic Letter 95-07 Enclosed is Nonh Atlantic Energy Service Corporation,(North Atlantic) response to the NRC request for additional information, dated July 17,1996' Should you have any additional questions regarding this response, please contact Mr. Anthony M.
Callendrello, I,icensing Manager, at (603) 474-9521, extension 2751.
j Very truly yours, NORTH ATLANTIC ENERGY SERVICE CORP.
h-W. A. DiProfio l
Station Directo 1
cc:
H. J. Miller, Regional Administrator A. W. De A azio, Sr. Project Manager E
J. B. Macdonald, NRC Senior Resident Inspector 1
l NRC Letter dated July 17,1996," Request for Additional Information-Generic Letter 95-07," Pressure Locking and Thermal Binding c.f Safety-Operated Gate Valves", Seabrook Station Unit 1"
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9608200178.960815 PDR ADOCK 05000443 P
REQUEST FOR ADDITIONAL INFORMATION GENERIC LETTER 95-07," PRESSURE LOCKING AND TIIERMAL BINI)ING OF SAFETY-RELATED POWER-OPERATED GATE VALVES," SEABROOK STATION, UNIT I (TAC NO. M93517)
BACKGROUND On August 17, 1995, the NRC issued Generic Letter (GL) 95-07, " Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves," which requested licensees to take certain 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. As requested by the NRC, North Atlantic provided a 180 day response in letter NYN-96007, dated February 13,1996.
DISCUSSION The NRC staff is evaluating Seabrook's 180-day response to GL 95-07.
However, additional information is required for the staff to complete its review. Each additional information item requested by the NRC is stated below with Seabrook's response to the requested information.
NRC RAI No. I Regarding valves Ril-V-22 and RH-V-21, RHR Train "A" and "B" Discharge X-Connect, in Table 2, North Atlantic's submittal does not identify these valves as potentially susceptible to pressure locking.
However, these valves may be potentially susceptible to thermally-induced pressure locking from heat transfer from the RHR system during a design basis event. Please address the potential susceptibility of 1
these valves to thermally induced pressure locking.
Seabrook Response Seabrook had previously identified a concern with these valves which was most likely the result of thermally induced pressure locking. The condition arose prior to commercial operation of the plant. When on RHR shutdown cooling, the crossconnect isolation valve closest to the RHR header that was in service l
was closed to isolate one train of RHR. Subsequently, when the valve was attempted to be re-opened the motor operator tripped and the valve remained closed. Procedure changes were instituted to close the valve in the non operating train (i.e. farthest away from the operating train) and keeping the valve closest to the operating train open. Since this procedure change was made valve performance has been satisfactory. The distance from the operating train provides an acceptable heat sink so that conditions at the closed valve that would make it susceptible to thermally induced pressure locking r.re not created. Accordingly, since the procedure change was instituted, these valves have not been impacted by thermally induced pressure locking. These valves were evaluated for susceptibility to pressure locking and thermal binding in Engineering Evaluatien 95-07 that was performed to support North Atlantic's 180-day response. The pertinent excerpt from this engineering evaluation follows:
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1 RII-V21. RII-V22 - RHR Crossconnect Valves These valves are Westinghouse Dexible wedge gate valves located in the cross connect between RHR pump A and RHR pump B discharge headers. The valves are normally open during power operation. During plant cooldowns when the unit is in Mode 4 and the RHRS is in service, one valve is closed to provide accurate Dow measurement and control for the RHR train that is in operation. To prevent thermal binding l
ar.d pressure locking for this condition, station operating procedures direct the valve furthest from the operating train to be closed. The valves are located in the RHR equipment vaults in environmental zones EV-6B and EV-6A, respectively. The normal environmental temperature in this area is 50 - 104 F. The j
valves are closed during the Recirculation phase of ECCS operation ifit is necessary to isolate a leak in a passive component. Once closed, the valve remains closed to perform its safety function. During a plant cooldown, the opposite train's crossconnect valve is closed. This practice isolates the valve from the hot process Guid and precludes the possibility of liquid entrapment pressure locking. Since the valves are closed cold, they are not subject to thermal binding. The valves are designed to close against the RHR pump head, therefore they are not subject to differential pressure locking. During ECCS operation one valve may be closed when the RHR Cuid temperature is approximately 210 F to isolate a leak in a passive component. At that time the adjacent RHR train would be taken out of service and the valve would not be re-opened during the ECCS Recirculation phase of operation. Closing the valve at 210 F may subject the valve to the potential for thermal binding. For these conditions, however, the valve is not required to re-open.
These valves can be closed to locate a LOCA outside containment, refer to ECA-1.2, LOCA Outside Containment. For this condition, the valves are closed and remain closed once the leak location is identiDed or the valve is immediately re-opened. For this operating condition the valves would not be subject to pressure locking or thermal binding.
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Based on this evaluation which took into account that the operating procedures had been changed, these valves were not identiDed as being sumeptible to pressure locking in North Atlantic's 180 day response to Generic Letter 95-07.
NRC RAI No. 2 Regarding valves SI-V-138, -139, Charging Pumps Supply to RCS Cold Legs, in Table 1, North Atlantic's submittal does not identify these valves as potentially susceptible to pressure locking.
However, these valves may become pressurized from the reactor coolant system (RCS) and appear to be susceptible to pressure locking during a design basis depressurization of the RCS. Please address the potential susceptibility of these valves to depressurization-induced pressure locking.
Seabrook Response These valves are normally closed valves that isolate the Charging System from the Reactor Coolant System. These valves are located outside the containment in the Mechanical Penetration Area, Environmental Zone MPA-2, which has a normal temperature range of 50 F to 104* F. These valves automatically open in response to a safety injection actuation signal. During normal power operation the upstream piping is pressurized to approximately 2600 psig by the charging pump. The downstream piping assuming check valve leakage is at Reactor Coolant System pressure, approximately 2250 psia.
There are two check valves in series for each Cow path; these valves function as pressure isolation valves 0
and are leak tested in accordance with Seabrook's Technical Specifications. Accordingly, the bonnet pressure of the valve could approach the discharge pressure head of the Charging System. If the RCS System was rapidly depressurized as a result of a LOCA, these valves would be required to open under CVCS discharge pressure, an assumed 0 psig downstream pressure (RCS fully depressurized) and a valve bonnet pressure of approximately 2600 psig. In response to Generic Letter 89-10, Seabrook Station's MOV Program dynamically tested SI-V138 under the following operating conditions. A charging pump was running on recirculation, a differential pressure across the valve was 2730 psig and the RCS was depressurized with the vessel head removed. The successful dynamic test of SI V138 showed positive results with an acceptable margin. The test conditions were more severe than the NRC l
postulated RCS depressurization condition. SI-V139 is scheduled to be dynamically tested during the next refueling outage.
These valves were evaluated for susceptibility to pressure locking and thermal binding in Engineering Evaluation 95-07. The pertinent excerpt from this engineering evaluation follows:
SI-VI38. SI-V139 - High Head Inicction 11ne Isolation Valves t
Description of Valve Function These valves are normally closed valves that are opened to provide a flow path for the charging pumps to l
the RCS cold legs during the injection phase of ECCS operation. These valves are Westinghouse flexible gate valves.
Evaluation I.iquid Entraoment Pressure Lockin2 These valves are located in the mechanical penetration area and are subject to the ambient temoeratum conditions in this area. These valves operate at the initiation of a transient; therefore, no significant temperature transient is experienced by these valves prior to their operation. These valves are isolated from the RCS by redundant check valves, and long pipii.g runs. Therefore, no*heatup of the valves will be experienced due to the interfacing system. No mecha.nism exists to increase the valve temperature, therefore liquid entrapment pressure locking is precluded for these valves.
Differential Pressure Locking These valves are e:. posed to charging pump discharge head, with a maximum pressure of approximately i
2600 psig. The design differential pressure of these valves is 2750 psid; differential pressure locking is therefore precluded by design.
The valves are not exposed to any significant temperature transients. The valves are required to open during j
a LOCA, at which time systems temperatures would equal or exceed those experienced during valve closure. Thermal binding is therefore not a concern for these valves.
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Conclusion These valves are not subject to either liquid entrapment pressure locking, or differential pressure locking, or to thermal binding. Therefore, these valves will remain capable of fulfilling all required safety functions.
NRC RAI No. 3 Regarding valves RC-122, -124, PORV Block Valves, North Atlantic's submittal discusses the potential susceptibility of these valves to thermal binding involving low temperature over pressure protection (LTOP) and states that LTOP protection can also be provided by the RiiR suction relief valves or by providing an RCS vent path. Please address the potential susceptibility of these valves to thermal binding. In addition, if North Atlantic has any testing or analysis, or has operational experience tojustify the acceptability of these valves as-is, please provide this information for our review.
In addition, North Atlantic's submittal does not identify these valves as potentially susceptible to
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pressure locking. Ilowever, these valves may be potentially susceptible to pressure locking if they are closed to isolate a leaking PORV and subsequently required to open during a design basis depressurization, such as during a steam generator tube rupture event. Please address this potential susceptibility to pressure locking.
Seabrook Response 1
RC-V122 and RC-V124, the PORV Block Valves, are normally open valves that could be closed to j
isolate a leaking PORV. These 3 inch Westinghouse gate valves have a Limitorque SB-00 motor operator that closes under limit switch control. The motor operator is equipped with a compensatin'g.
spring pack. Both limit controlled closure and the compensating spring pack will limit the magnitude of the closing thrust from the previous close stroke or from stem growth. The valve is a flexible wedge gate i
valve that is less susceptible to thermal binding than a solid wedge gate valve. The valve body material for these valves is SA-182-F304 and the disc material is SA-182 F316. These materials are nearly identical and accordingly their thermal expansion coefficient is similar.
Since the thermal expansion / contraction of these materials are similar and the operator has a compensating springpack which will minimize thrust buildup due to stem growth, small thrust loads due to thermal binding would 1
be anticipated. Seabrook has the following operating experience for the potential thermal binding condition:
During November 1990 the Train "A" PORV was declared inoperable, then isolated by closing and deenergizing the associated block valve while the plant was at normal operating pressure and normal operating temperature (RCS at approximately 2250 psia,650 F). The plant was cooled down and depressurized (127 F, Pressurizer vent open) and then the block valve (RC-V122) was reopened. The block valve fully opened; no adverse valve operating conditions were noted.
Even with a reduced voltage assumption, the motor capability of the motor operators for these valves has l
considerable margin for open operation (see discussion below regarding pressure locking).
Despite the design considerations and operating experience which indicates that the susceptibility of these valves to thermal binding is low, precaution 3.19 and procedure step 7.1.4 were added to Operations Procedure OS1000.04," Plant Coofdown From flot Standby to Cold Shutdown" to address the i
potential for thermal binding. The precaution identifies that if the PORV block valve is closed at normal
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. operating temperature and a subsequent cooldown is required the block valve (s) is to be considered inoperable. It further states that if a block valve is closed and a subsequent cooldown is undertaken,
t!.en if possible, the valve should be opened prior to commencing the cooldown. This precaution provides flexibility to operations personnel to open the block valve if it was closed to isolate minor PORV leakage. Procedure step 7.1.4 provides direction to Operations personnel if either of the block valves are closed and will remain closed for the duration of the cooldown.
North Atlantic has reviewed the PORV block valves for their susceptibility to thermally induced pressure locking and differential pressure locking. These valves are located in the containment in Environmental Zone CS-11. The maximum normal operating temperature for Zone CS-11 is 120 F. These valves were not identified as being potentially susceptible to pressure locking. These valves had not been specifically evaluated for pressure locking for the specific steam generator tube rupture conditions postulated by this RAl. This evaluation has now been completed as follows:
In order to mitigate a stear generator tube rupture condition, RCS depressurization is required. Normal RCS depressurization would be performed using the pressurizer spray valves. If the pressurizer spray valves are not available, RCS depressurization would be accomplished using either the PORV (s) or using auxiliary sprays. Since the PORV block isolation valves are normally open, depressurization could commence by manually opening one or both of the PORVs. However, if the PORV block valve is closed to isolate a leaking PORV, it would subsequently be required to be opened so that the PORV is available to support RCS depressurization. Emergency Response Procedure E-3, " Steam Generator Tube Rupture", step 5 requires that at least one PORV block isolation valve be opened, if closed. The RCS pressure at the time of block valve opening is dependent on the magnitude of the tube rupture. The WOG Background Document for the Emergency Response Guidelines assumes that the RCS pressure would be approximately 1500 psia when a PORV would be opened assuming pressurizer spray is unavailable. However, the RCS pressure could be less based on the size of the leak. The thrust required for valve operation has been calculated assuming an RCS pressure of 1000 psig, a bonnet pressure of 2250 psig (assuming the valve is closed at normal RCS pressure) and a downstream pressure of 0 psig.
The required thrust to open the block valves under these conditions has been determined to be 10,800 pounds (using a 4500 pound unseating load, the maximum as-tested unseating load for these valves was measured as 4254 lbs). The calculated thrust value was based on the Commonwealth Edison methodology. The PORV block isolation valve capability was determined considering derated conditions (motor torque due to ambient temperature and reduced voltage), and using the pullout efficiency. Comparing the motor operator capability to the calculated thrust revealed a margin of 74%.
Therefore, RC-V122/V124 are capable of opening against these conditions.
NRC RAI No. 4 Through review of operational experience feedback, the staffis aware ofinstances 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 dee to incomplete or 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 modification completed to address potential pressure locking or thermal binding concerns.
J Ssabrook Respanic During Refueling Outage 04, Seabrook modified ten valves to eliminate the potential for pressure locking. The valve modification packages were prepared in accordance with the North Atlantic design control procedures. Minor Modi 6 cation (MMOD)95-509 addressed the potential pressure locking concern for the Containment Sump Isolation Valves, CBS-V8N14. Design Coordination Report (DCR)95-023 modified the following eight Westinghouse valves: Low liead 110t Leg Recirculation Valves (Ril-V32N70) the Intermediate llead liot Leg Recirculation Valves (SI-V77N102), and the RCS to RilR Suction Isolation Valves (RC-V22N23N87N88). The design packages for both the MMOD and DCR provided detailed design descriptions and analysis, and each package included a detailed safety evaluation.
Licensed operators received either classroom training on both of these design changes as part of Lesson Plan Ll655C or were required to perform required reading on the lesson plan. Additionally, MMOD 95-509 was included as part of L5034C, required reading for licensed operators.
Operations procedure OS1000.04," Plant Cooldown from liot Standby to Cold Shutdown," was changed to address the Pressure Operated Relief Valve (PORV) Block Isolation Valves, RC-V122N124 potential for thermal binding and was considered to be self explanatory and no additional training was determined to be required.
Procedure changes to preclude thermally induced pressure locking of Rii-V21N22, RiiR Crossconnect Valves, during both startup and shutdown were made prior to commercial operation. Closing the opposite train RilR cross connect isolation valve is included in lesson plan LIS03C which is the operator requaliGcation lesson plan for the RIIR System.
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