ML20097F861
| ML20097F861 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 02/12/1996 |
| From: | Hill W NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-95-07, GL-95-7, TAC-M93487, NUDOCS 9602200206 | |
| Download: ML20097F861 (13) | |
Text
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Northem States Power Company Monticello Nuclear Generating Plant 2807 West Hwy 75 Monticel!o, Minnesota 55362-9637 i
February 12,1996 NRC Generic Letter 95-07 US Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 i
MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 180 Day Response to Generic Letter 95-07: Pressure Locking and Thermal Bindina of Safetv-Related Power-Operated Gate Valves (TAC M93487)
The purpose of this letter is to provide the 180 day response required by NRC Generic Letter 95-07 for the Monticello Nuclear Generating Plant.
Generic Letter 95-07 (dated August 17,1995) was issued by the NRC requesting licensees to provide information conceming (1) the evaluation of operational configurations of safety-related, power-operated gate valves for susceptibility to pressure locking and thermal binding; and (2) analyses, and needed corrective actions, to ensure that safety-related power-operated gate valves that are susceptible to pressure locking or thermal binding are capable of performing the required safety function.
Generic Letter 95-07 contained the following required response:
- 1. Within 60 days from the date of(Generic Letter 95-07), a wntien msponse indicating whether or not the addressee willimplement the action (s) requested [by the generic letter). If the addressee intends to implement the requested action (s), provide a schedule forcompleting implementation. If an addressee chooses not to take the requested action (s), provide a descnption of anyproposed altemative course of action, the schedule forcompleting the attemative course of action (if applicable),
and the safety basis for determining the acceptability of the planned altemative course of action.
- 2. Within 180 days from the date of[Genenc Letter 95-07), a wntten response to the information request specified[by the genenc letter].
By letter dated October 16,1995, with subject, " Response to Generic Letter 95-07: Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves," Monticello responded to item 1 above. Attachment 1 to this letter provides the information requested by item 2 above.
2/9/96 NsP HsDATA\\NRCCoRRCL9507sR. Doc Ig h 9602200206 960212 PDR ADOCK 05000263 P
PDR R
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USNRC NORTHERN STATES POWER COMPANY February 12,1996 Page 2 This letter contains the following new NRC commitments:
- 1. MO-2006 and MO-2007 are to be modified by drilling an anti-pressure locking hole in the pump side of the disc to prevent pressure locking due to potential high ambient i
area temperatures after an accident. MO-2007 is to be modified prior to completion of the 1996 refueling outage. MO-2006 is to be modified prior to completion of the 1998 j
refueling outage. (M96002A) 1 Please contact Marv Engen, Sr Licensing Engineer, at (612) 295-1291 if you require further information.
]
/) 4 Y6 6 w 0 $ 4 William J Hill Plant Manager Monticello Nuclear Generating Plant c: Regional Administrator-Ill, NRC NRR Project Manager, NRC Sr Resident inspector, NRC State of Minnesota, Attn: Kris Sanda Attachments: Affidavit to the US Nuclear Regulatory Commission (1) Monticello Nuclear Generating Plant,180 Day Response to Generic Letter 95-07 (2) Pressure Locking and Thermal Binding Criteria I
UNITED STATES NUCLEAR REGULATORY COMMISSION NORTHERN STATES POWER COMPANY MONTICELLO NUCLEAR GENERATING PLANT DOCKET NO. 50-263 180 DAY RESPONSE DATED February 12,1996 TO GENERIC LETTER 95-07:
PRESSURE LOCKING AND THERMAL BINDING OF SAFETY-RELATED POWER-OPERATED GATE VALVES Northem States Power Company, a Minnesota corporation, hereby provides response to NRC Generic Letter 95-07, Pressure Locking and Thermal Binding of Safety-Related Power-Operated Gate Valves. This letter contains no restricted or other defense information.
NORTHERN STATES POWER COMPANY
/d*k By William JHitf' '
Plant Manager Monticello Nuclear Generating Plant On this 120 day of Iekrao N l 99(o before me a notary public in and for said County, personally appeared Willi 6m J Hill, Plant Manager, Monticello Nuclear Generating i
Plant, and being first duly swom acknowledged that he is authorized to execute this document on behalf of Northem States Power Company, that he knows the contents thereof, and that to the best of his knowiedge, information, and belief the statements made in it are true and that it is not interposed for delay.
l MARVIN RICHARD E MaNin R $ngen /
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c s,
Notary Public-Minnesota Sherbume County My Commission Expires January 31,2000
February 12,1996 Page 1
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l Monticello Nuclear Generating Plant l
180 Day Response to Generic Letter 95-07 I
i Reauested Action I
Within 180 days of the date of(Generic Letter 95-07), each addressee of(the) generic letteris requested to implement and complete the guidance providedin Attachment 1 \\of Generic Letter 95-07} to perform the following actions 1.
Evaluate the operational configurations of safety-related power-operated (i.e., motor-operated, air-operated, and hydraulically operated) gate valves in its plant to identify valves that are susceptible to pressure locking or thermal binding; 2.
Perform further analyses as appropnate, and take needed corrective actions (orjustify longerschedules), to ensure that the susceptible valves identiMedin 1 are capable of performing theirintended safety function (s) under all modes of plant operation, including test configuration.'
' Reauested Information AII addressees, including those who have already satisfactorily addressed pressure locking and thermal binding forMOVs byimplementing the guidance in Supplement 6 to GL 89-10 (or equivalent industry methods), are requested to provide a summary description of the following:
1.
The susceptibility evaluation of operational configurations performed in response to (or consistent with) 180-day Requested Action 1, and the further analyses performedin response to (or consistent with) 180-day Requested Action 2, including the bases or criteda fordetermining that valves are or are not susceptible to pressure locking or thermalbinding; 2.
The results of the susceptibility evaluation and the further analyses referred to in 1 above, including a listing of the susceptible valves identified; l
3.
The corrective actions, or otherdispositioning, forthe valves identified as susceptible to pressure locking or thermal binding, including: (a) equipment orprocedural modifications completed and planned (including the completion schedule for such actions); and (b) justification for any determination that particular safety-related power-operated gate valves susceptible to pressure locking or thermal binding are acceptable
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as is.
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1 February 12,1996 Page 2 4
Monticello Response Summary Description of Susceptibility Evaluation The following provides a summary description of our susceptibility evaluation performed in response to Requested Action 1 of the generic letter 180 day action items, in accordance with item 1 of the information requested by NRC Generic Letter 95-07.
All Motor Operated Valves (MOVs), Air Operated Valves (AOVs), and Hydraulically Operated Valves (HOVs) were reviewed to determine applicability of this issue. The initial screening consisted of a review for the following.
- 1. Safety related power operated (electric, air or hydraulic) gate valves which have a t
safety function to open.
- 2. Normally open valves which do not have a safety function to cycle open, but which are closed for surveillance testing were evaluated for pressure locking and thermal binding unless the technical specification limiting condition for operation is entered l
during the time that the valve is closed.
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- 3. Mispositioning was not considered.
The initial screening results for each valve type are provided below.
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- 1) Air Operated Valves All safety related air operated valves were reviewed. The majority of air operated valvas were found to be not of a gate valve design. Of the gate valves which are air operated, none had a safety function to open, or the valves were not required to be in the open position for system operability. Therefore, the pressure locking / thermal binding issue identified in Generic Letter 95-07 was determined to be not applicable to Monticello's population of air operated valves.
- 2) Hydraulically Operated Valves Monticello has three hydraulically operated, safety related valves; two in the High Pressure Coolant injection (HPCI) system (HO-7 and HO-8) and one in the Reactor Core Isolation Cooling (RCIC) system (HO-8). All three of these valves are globe type valves and are therefore not susceptible to pressure locking or thermal binding. The pressure locking / thermal binding issue identified in Generic Letter 95-07 was determined to be not applicable to Monticello's population of hydraulically operated j
valves.
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l Attachment i February 12,1996 i
Page 3
- 3) Motor Ooerated Valves (MOVs)
Evaluation of pressure locking and thermal binding of MOVs was most recently performed per Generic Letter 89-10 supplement 6 and received favorable NRC review as part of Monticello's Generic Letter 89-10 closeout inspection. Although Generic l
Letter 95-07 states that if satisfactory implementation of supplement 6 guidance was l
performed the licensee need not perform any additional action for MOVs, a thorough review of all safety related motor operated gate valves was re-performed for this 1
response.
Each valve identified as being within the scope of this evaluation was further evaluated
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to determine susceptibility based on the criteria set forth in Attachment 2 of this submittal. Procedural practices as well as surveillance testing, hydrostatic pressure testing, accident environments, and industry and plant historical events were considered for each valve.
Summary of Susceptibility Evaluation Results The following provides the susceptibility evaluation results in accordance with item 2 of the information requested by NRC Generic Letter 95-07.
The following table lists those valves which were identified as having operational configurations such that the valves are potentially susceptible to pressure locking or thermal binding. As a result of actions taken to address valve pressure locking and thermal i
binding prior to issuance of NRC Generic Letter 95-07, few potentially susceptible valves were identified. The bases for determining that a valve is not susceptible to pressure locking or thermal binding is provided in the table notes. Va!ves identified as potentially susceptible based on the Generic Letter 95-07 review are indicated with bold text in the table. For those valves which were identified to be potentially susceptible, an evaluation was performed to ensure each valve can perform its intended safety function. All valves were found to be capable of performing the intended safety function.
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1 AttachmInt 1 February 12,1996 Page 4 Valvet identified for Evaluation Based on Operational Configurations and identified as Potentially Susceptible to Pressure Lockina and/or Thermal Bindina Phenomena l
]
! c MOV No.1
- Discy
[Normaly y Openi
- Potential Potential Walve Description;
?Typef iPosition; JSafety.
... l fori.
. (forf.
~ ' ', '
,a j
(Function ?
? Pressure 1 Thermal; y.,
- Locking 2 L Bindino -
MO-1741 Solid Open No No (1)
No (3)
Core Spray Pump Suction 1
MO-1742 Solid Open No No (1)
No (3)
Core Spray Pump Suction MO-1761 Flex Open Yes Yes No (3)
Core Spray Outboard injection valve j
MO-1762 Flex Open Yes Yes No (3)
Core Spray Outboard injection valve MO-1753 Flex Closed Yes No (2)
No (3)
Core Spray Inboard injection valve MO-1754 Flex Closed Yes No (2)
No (3)
Core Spray Inboard injection valve MO-1986 Solid Open No No (4)
No (3)
RHR Torus suction MO-1987 Solid Open Yes No (4)
No (3)
RHR Torus suction MO-2006 Flex Closed Yes Yes No (3)
RHR Torus Coolin0/ Spray j
MO 2007 Flex Closed Yes Yes No (3)
RHR Torus Cooling / Spray MO-2014 -
Flex Closed Yes No (2)
No (3)
A RHR LPCl Injection inboard i
MO-2015 Flex Closed Yes No (2)
No (3)
B RHR LPCI Injection inboard MO-2020 Flex Closed Yes No (5)
No (3)
A RHR Drywell Spray Inboard i
MO-2021 Flex Closed Yes No (5)
No (3)
B RHR Drywell Spray Inboard MO-2022 Flex -
Closed Yes No (5)
No (3)
A RHR Drywell Spray Outboard MO-2023 Flex Closed Yes No (5)
No (3)
B RHR Drywell Spray Outboard MO-2033 Flex Open No No (6)
No (6)
RHR Crosstle MO-2034 Flex Open No Yes No (5)
HPCI Steam isolation inboard MO-2036 Flex Open No Yes No (5)
HPCI Steam isolation Outboard MO-2036 Flex Closed Yes No (2)
Yes HPCI Steam Supply MO-2061 Solid Closed Yes No (4)
No (3)
HPCI Torus Suction i
MO-2062 Solid Closed Yes No (4)
No (3)
HPCI Torus Suction MO-2063 Solid Open No No (4)
No (3)
HPCI CST Suction MO-2067 Flex Closed Yes No (2)
No (3)
HPCI Injection MO-2068 F1ex Closed Yes No (2)
Yes HPCI Injection MO-2075 Flex Open No No (7)
No (5) -
RCIC Steam Isolation inboard MO-2076 Flex Open No No (7)
No (5)
RCIC Steam isolation Outboard MO-2100 Solid Closed Yes No (4)
No (3)
RCIC Torus Suction MO-2101 Solid Closed Yes No (4)
No (3)
RCIC Torus Suction MO-2102 Solid Open No No (4)
No (3)
RCIC CST Suction MO-2106 Flex Closed Yes No (2)
No (3)
RCIC Injection i
MO 2107 Flex Closed Yes No (2)
Yes RCIC injection NOTES:
(1) Normally open valve, does not need to open to perform it's safety function. Also, during surveillance testing when the valve is closed, the Tech Spec limiting condition for operation (LCO) is entered and the valve is re-opened prior to exiting the LCO.
(2) Anti-Pressure locking hole has been drilled in disc.
(3) Placed in closed position while valve is cool therefore will not thermally bind.
(4) This valve has a solid disc design and is therefore not susceptible to pressure locking.
(5) Operational practices preclude pressure locking or thermal binding.
(6) This valve remains open whenever LPCI is required and is not stroked during surveillance testing.
(7) Normally open valve, not required to open for pressure locking scenario.
February 12,1996 Page 5 I
An: lysis of Safety Function Capability and Corrective Actions The following provides a summary description of our evaluation performed per Requested Action 2, in accordance with items 1 and 2 of the information requested in NRC Generic Letter 95-07. The potentially susceptible valves are identified, the basis for determining susceptibility and when appropriate, a 1
summary of the further analysis performed to confirm that the valves are capable of performing the required safety function. In accordance with item 3 of the information requested in NRC Generic Letter j
95-07, the corrective actions are provided for the potentially susceptible valves.
MO-1751/1752.11/12 Core Sorav Outboard Inloction 1
Analysis Summary During the surveillance test these valves are placed in the closed position and are left closed during the run of the Core Spray pumps. While these valves are closed they are potentially susceptible to pressure j
locking.
Corrective Action The surveillance test and system operating procedures have been revised to declare the affected system train inoperable during the time that these valves are in the closed position. If valve maintenance arises which would allow performance of a modification to provide a valve disc anti-pressure locking hole, then installation of an anti-pressure locking hole will be considered such that declaring the affected system train inoperable would no longer be necessary.
MO 2006/2007.11/12 RHR Torus Coolina/Sprav
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Analysis Summary Temperature profiles from the equipment environmental qualification analysis shows that the area temperature surrounding MO-2006 and MO-2007 would increase following a postulated accident to 6*F and 93*F respectively. Pressure locking could occur due to valve bonnet pressurization as a result of the elevated area temperatures. A calculation has been performed which demonstrates that sufficient margin exists such that the valves are capable of performing their intended function should bonnet pressurization occur. A long term solution to drill anti-pressure locking holes in the discs of these valves is planned and committed to with this response. The magnitude of the temperatures involved and the existing calculation provide appropriate justification until these modifications can be performed in a controlled, planned manner.
Corrective Action MO-2006 and MO-2007 are to be modified by drilling an anti-pressure locking hole in the pump side of the disc to prevent pressure locking due to high area temperatures after an accident. MO-2007 is to be modified prior to completion of the 1996 refueling outage. MO-2006 is to be modified prior to completion of the 1998 refueling outage.
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Uebruary 12,1996 Page6 1
MO-2034/2035. HPCI Inboard / Outboard Steam Line Isolation
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Analysis Summary The inboard and Outboard containment isolation valves for the High Pressure Coolant injection (HPCI) 1 turbine steam supply are normally open. During surveillance tests these valves are placed in the closed J
position. When these valves are closed they are potentially susceptible to pressure locking in the event of a rapid depressurization of the reactor vessel. For a large depressurization event, the HPCI system would not be required to mitigate the consequences of the accident, nor would it be capable of i
responding as sufficient steam pressure would not be available from the reactor system.
J Corrective Action i
The surveillance test and system operating procedures have been revised to declare the affected system train inoperable during the time that these valves are in the closed positjon. If valve maintenance arises f
which would allow performance of a modification to provide a valve disc anti-pressure locking hole, then j
installation of an anti-pressure locking hole will be considered such that declaring the affected system train inoperable would no longer be necessary.
MO-2036. HPCI Turbine Steam SuDDIV Analysis Summary 1
The HPCI turbine inlet valve will be affected by a decrease in the reactor steam temperature during plant shutdown. At 150 psig reactor pressure the steam saturation temperature will be 358 F, as compared to i
544*F at 1000 psig reactor pressure, or a 184*F change in temperature. Since HPCI must be operable over the range of steam pressure of 150 psig to 1000 psig, MO-2036 must be able to open at the lower j
temperature. MO-2036 is normally left in the closed position until after plant shutdown, therefore it is not 1
re-opened until after it has cooled to HPCI room ambient temperature (which is equivalent to a temperature differential of approximately 450*F).
c Thermal binding has occurred on a similar valve in the industry, however MO-2036 has not had a thermal binding event. Since MO-2036 is normally opened when cool after the plant has been shutdown, and this represents a much greater temperature differential than that required for HPCI operability, the potential for thermal binding is considered low.
Corrective Action The plant shutdown procedure has been revised to require cycling of MO-2030 during plant shutdown as the valve body temperature decreases. The periodic cycling will be performed during that portion of the shutdown when valve operability is required.
MO-2068. HPCI Pumo Inlection I
Analysis Summary l
The HPCI injection valve to feedwater will be affected during plant shutdown by a decrease in feedwater temperature. This valve is normally closed and is only cycled during valve surveillance testing or to mitigate accident consequences. At full power the feedwater temperature is approximately 375'F, however at 150 psig reactor pressure the feedwater temperature will have decreased to approximately
_ = -. - - -. _ - -
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l February 12,1996 l
l Page 7 however at 150 psig reactor pressure the feedwater temperature will have decreased to approximately 1
140*F. Measured valve body temperature of MO-2068 at full power operation was found to be 279'F.
Thermal binding has not occurred on MO-2068 even though it is routinely opened when cool after being l
closed hot. Based on the recent temperature measurements of MO-2068 and on the fact that no plant or i
l industry events have been reported for this valve, the potential for thermal binding is considered low.
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Corrective Action l
The plant shutdown procedure has been revised to require periodic cycling of MO-2068 during plant l
shutdown as the valve body temperature decreases. The periodic cycling will be performed during that portion of the shutdown when valve operability is required.
MO-2107. RCIC Pumo inlection Analysis Summary The RCIC Injection valve, will be affected during plant shutdown by a decrease in feedwater temperature, l
similar to MO-2068 as described above. Similar to MO-2068, the valve is normally closed and is only l
cycled during valve surveillance testing or to mitigate accident consequences. Measured valve body temperature of MO-2107 at full power operation was found to be 140 F. Based on the recent temperature measurements of MO-2107 and on the fact that no plant or industry events have been reported for this valve, the potential for thermal binding is considered low.
Corrective Action l
The plant shutdown procedure has been revised to require cycling of MO-2107 during plant shutdown as the valve body temperature decreases. The periodic cycling will be performed during that portion of the shutdown when valve operability is required.
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Pressure Lockina and Thermal Bindina Criteria In order to review the susceptible population of power operated gate valves the following criteria was used.
A. Screenina for Thermal Bindina T1. Valves with solid, split or flexible wedge type discs. Parallel wedge type designs may be excluded since they cre not susceptible to thermal binding.
T2.The valve is closed hot and must re-open when cooled to perform it's safety
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function. Operational configurations, including normal operating practice and surveillance procedures will be considered to determine if the valve is left in a position which may cause the valve to be susceptible (i.e. closed hot during surveillance test and allowed to cool). Based on current industry thinking the following temperature decreases will not cause the disc to become thermally bound.
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=> Solid Disc Design 50 F
=> Flexible Disc Design 100 F AND/OR T3. Valves found to have a history of thermal binding through a review of industry events (Generic LeMer 95-07 and NUREG 1275) and/or plant operational i
experience (NCR's, NPRDS & Maintenance History) should be reviewed for evidence of thermal binding.
B. Screenina for Pressure Lockina P1. Flexible or double disc gate valves which have not had a hole drilled into the disc to prevent pressure locking. Solid disc gate valves are not susceptible.
M P2. Valves whose bonnet cavity is susceptible to a higher pressure than the disc upstream and downstream pressure, this can occur through rapid system pressure decreases (allowing the disc to seal without relieving bonnet pressure).
Considered in this evaluation are running system pumps with the valve closed then shutting the pump down, relieving system pressure after a hydrostatic pressure test, line break scenarios and stroking of other system valves which could relieve system pressure. Upstream or downstream check valves cannot be assumed to hold pressure.
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.o February 12,1996 Page 2 M
P3. Valves whose bonnet cavity can become heated by either intemal system fluid, or by extemal environmental temperature prior to the valve opening to perform it's safety function. This can allow the fluid in the bonnet to increase in temperature and pressure possibly leading to pressure locking. Normal operating ambient temperature swings can be ignored.
M P4. Valve found to have a history of pressure locking through a review of industry 1
events (Generic Letter 95-07 and NUREG 1275) and/or plant operational experience (NCR's, NPRDS & Maintenance History) should be reviewed for evidence of pressure locking.
M P5. Valves which are left with the possibility of high bonnet pressure after inservice hydrostatic pressure testing per ASME Section XI, without further stroking of the j
valve to relieve pressure prior to returning the valve to service, should be considered susceptible.
M P6. Valves which are left with the possibility of high bonnet pressure after surveillance testing, without further stroking of the valve to relieve pressure prior to retuming the valve to service, should be considered susceptible. Valves that are closed during a surveillance test when the plant technical specification LCO is entered and the valve is stroked prior to retum to service will not be classified as susceptible.
1 C. Review of Industry Events According to Generic Letter 95-07 and NUREG 1275 the following valves have been involvod in oressure lockino events:
o Low Pressure Coolant injection valves (LPCI)
Low Pressure Core Spray injection valves o
o RHR System Hot Leg Crossover Isolation Valves o Containment Spray Valves e RHR Shutdown Cooling isolation valves o RHR Containment Sump and Suppression Pool Suction valves o High Pressure Coolant injection (HPCI) Steam Admission valves RHR Heat Exchanger Outlet valves
=r o Emergency Feedwater Isolation valves
=> RCIC Steamline Isolation Valves
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February 12,1996 Page 3 According to Generic Letter 95-07 and NUREG 1275 the following valves have been involved in thermal bindino events:
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= Reactor Depressurization System isolation valves i
= RHR Inboard Suction isolation valves
= HPCI Steam Admission valves
= Power-Operated Relief valve (PORV) Block valves
= Reactor Coolant System Letdown isolation valves
= RHR Suppression Pool Suction valves
= Containment Isolation valves (sample line, letdown heat exchanger, inlet header)
= Condensate Discharge valves
= Reactor Feedwater Pump Discharge valves D. Review of Plant Events A review was performed of Monticello nonconformance reports, the Nuclear Plant Reliability Data System (NPRDS), and maintenance history, l
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