ML20100Q376
| ML20100Q376 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 03/01/1996 |
| From: | Hill W NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20100Q380 | List: |
| References | |
| NUDOCS 9603110615 | |
| Download: ML20100Q376 (8) | |
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t Northem States Power Company Monticello Nuclear Generating Plant 2077 West Hwy 75 Monticello, Minnesota b6362-9637 March 1,1998 10 CFR Pad 50 Section 50.90 U S Nuclear Regulatory Commission A*'a: Document Controi Desk Washington, DC 20555 MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 Ucense No. DPR-22 Revision 1 to Ucense Amendment Request Dated December 11,1995 Removal of Surveillance Requirement Conceming Periodic Replacement of Containment Purae and Vent Valve Seat Seal Attached is a request for a change in the Technical Specifications, Appendix A of the Operating Ucense for the Monticello Nuclear Generating Plant. This request is submitted in accordance with the provisions of 10 CFR Part 50, Section 50.90. This submittal provides a revision and replaces in its entirety our December 11,1995 submittal with subject, " Removal of Surveillance Requirement Conceming Periodic Replacement of Containment Purge and Vent Valve Seat Seal." Significant changes between our December 11,1995 submittal and this revision are indicated by a side bar in the margin.
Changes are proposed to Section 4.7, Surveillance Requirements for Primary Containment Automatic isolation Valves. The proposed change to Monticello Technical Specifications surveillance requirement 4.7.D.4 revises the replacement frequency of the seat seats for the drywell and suppression chamber purge and vent valves from every five years to every six operating cycles.
Exhibit A contains a description of the proposed changes, the reasons for requesting the changes, a Safety Evaluation, a Determination of Significant Hazards Consideration, and an Environmental Assessment. Exhibit B contains the current Technical Specification pages marked up with the proposed changes. Exhibit C contains revised Monticello Technical Specification pages. Exhibit D contains a summary of the containment purge and vent valve leakage results.
Please contact Marvin Engen, Sr Ucensing Engineer, (612-295-1291) if you require further information related to this request.
[h/dh William J Hill Plant Manager I
Monticello Nuclear Generating Plant 9603110615 960301 PDR ADOCK 05000263 P
PDR 110008 p) i
1 a
e USNRC NORTHERN STATES POWER COMPANY March 1,1996 Page 2 c:
Regional Administrator-Ill, NRC NRR Project Manager, NRC Resident inspector, NRC State of Minnesota Attn: Kris Sanda Attachments: Affidavit to the US Nuclear Regulatory Commission Exhibit A - Evaluation of Proposed Changes to the Technical Specifications for Operating Ucense DPR-22 Exhibit B - Proposed Changes Marked Up on Existing Technical Specification Pages Exhibit C - Revised Monticello Technical Specification Pages Exhibit D - Measured Leakage of Monticello Primary Containment Purge and Vent Valves
UNITED STATES NUCLEAR REGULATORY COMMISSION NORTHERN STATES POWER COMPANY MONTICELLO NUCLEAR GENERATING PLANT DOCKET NO. 50-263 REQUEST FOR AMENDMENT TO OPERATING LICENSE DPR-22 REVISION 1 TO LICENSE AMENDMENT REQUEST DATED DECEMBER 11,1995 REMOVAL OF SURVEILLANCE REQUIREMENT CONCERNING PERIODIC REPLACEMENT OF CONTAINMENT PURGE AND VENT VALVE SEAT SEAL SUBMITTED BY LETTER DATED March 1,1996 Northern States Power Company, a Minnesota corporation, requests authorization for changes to Appendix A of the Monticello Operating License as shown on the attachments labeled Exhibits A, B, C and D. Exhibit A describes the proposed changes, describes the reasons for the changes, and contains a Safety Evaluation, a Determination of Significant Hazards Consideration and an Environmental Assessment. Exhibit B contains current Technical specification pages marked up with the proposed changes. Exhibit C is a copy of the Monticello Technical Specifications incorporating the proposed changes. Exhibit D contains a summary of the containment purge and vent valve leakage results.
This letter contains no restricted or other defense information.
NORTHERN STATES POWER COMPANY By
[sw f&
William J Hilf '
Plant Manager Monticello Nuclear Generating Plant On this
! SI day of NMcM l996 before me a notary public in and for said County, personally appeared William J Hill, Plant Manager, Monticello Nuclear Generating Plant, and being first duly sworn acknowledged that he is authorized to execute this document on behalf of Northern States Power Company, that he knows the contents thereof, and that to the best of his knowledge, information, and belief the statements made in it are true and that it is not interposed for delay.
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's-( A MARVW RICHARD ENGEN Marvin R Engen /
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Notary Public-Minnesota Sherbume County My Commission Expires January 31,2000
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EXHIBIT A Monticello Nuclear Generating Plant Revision 1 to License Amendment Reauest Dated December 11.1995 Evaluation of Proposed Changes to the Technical Specifications for Operating Ucense DPR-22 Pursuant to 10 CFR Part 50, Section 50.59 and 50.90, the holders of Operating License DPR-22 hereby propose the following change-i Proposed Chances Technical Specification 4.7.D.4 (found on page 171 of Appendix A of the facility operating license) specifies a surveillance requirement for the drywell and suppression chamber 18-inch purge and vent valves. The surveillance requirement states:
The seat seals of the dryweII and suppression chamber 18-inch purge and vent valves shall be replaced at least once every Rye years.
Surveillance requirement 4.7.D.4 was established in the Monticello Technical Specifications by Amendment Number 64, dated May 10,1989, to the Monticello facility operating license.
Technical Specification changes incorporated by Amendment 64, in part, provided resolution to Multi-Plant Action B-24 (purge and vent valve operability) for the Monticello Nuclear Generating Plant. Replacement of the drywell and suppression chamber 18 inch purge and vent valve seat seals on a five year interval was provided as an attemative to the NRC Staff position requiring accelerated local leakage testing of containment purge and vent valves. This Staff position was in response to the poor performance demonstrated for similar butterfly valves with resilient seals in service throughout the nuclear industry.
This submittal proposes to extend the interval for replacement of the drywell to suppression chamber vent and purge valve seat seats to six operating cydas, in addition, the change proposes an additional criterion for seat seal replacement. Surveillance requirement 4.7.D.4 is proposed to be changed such that the requirement states:
The seat seals of the drywell and suppression chamber 18-Inch purge and vent valves shall be replaced at least once every 6 operating cycles. If penodic Type C leakage testing of the valves performed per sutwillance requirement 4.7.A.2.b IdentiMes a common mode test failure attnbutable to seat seal degradation, then the seat seals of all drywell and supptossion chamber 18-inch purge and vent valves shall be replaced.
Reason for Chanaes The proposed change to extend the seat seal replacement interval would result in a reduction in the maintenance and engineering support resource assochted with this activity without any compromise in the level of protection provided to the health and safety of the public. The frequency of seat seal replacement is proposed to be changed to be consistent with the plant A-1
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conditions required to perform the activity. The added criterion for seat seal replacement provides for seat seal replacement upon identification of Type C leakage test failures caused by degradation of the elastomer seat seal attributable to a common mode failure with a.
potential for an adverse impact. This criterion maintains a high level of assurance that the ability of the purge and vent valves is maintained, thus providing an added level of conservatism.
Replacement of the seat seals and associated post maintenance testing for the 18 inch purge and vent valves requires plant conditions for which primary containment integrity is not required. These conditions exist during plant refueling outages. The proposed change places the activity on surveillance frequency consistent with the plant conditions required to perform the activity. The term operating cycle is defined in the Monticello Technical Specifications, Section 1.0, page 3. An operating cycle is defined as the interval between the end of one refueling outage and the end of the next subsequent refueling outage. Placing the seat seal replacement on a frequency of every six operating cycles equates to a seat seal replacement interval of nine years, considering an 18 month operating cycle, to a maximum of twelve years, should 24 month cycles ever be feasible. The extension of the surveillance frequency from five years to six operating cycles is supported by the operational performance of the valves,
- the operational performance of similar valves using the same seat material under similar service conditions, as well as the useful life of the seat seal material.
By letter dated November 22,1985; from David M Musolf to Director, Office of Nuclear Reactor Regulation; with subject, " Additional information to Support Proposed Technical Specifications for Containment Vent and Purge Valves," Monticello demonstrated that the T-shaped seal valve design for the Monticello purge and vent valves is relatively free of the valve leakage problems experienced at other facilities. Valve leakage test data for the period 1970 to 1985 was provided in our November 22,1985 letter to support the problem free performance of these valves. We have reviewed the maintenance history and the results of the leakage test program for the primary containment purge and vent valves for the period subsequent to 1985 to present. We have determined that the operational performance of these valves over the last ten years supports the extension of the seat seal replacement frequency of surveillance l
requirement 4.7.D.4.
The results of the leakage test program for the Primary Containment Purge and Vent Valves is provided in Exhibit D of this submittal. This data supports the conclusion that no significant improvement in valve leakage performance can be attributed to replacement of the valve's elastomer T-shaped seat seal. Furthermore, the results of leakage tests performed between the elastomer T-shaped seat seat replacement during the 1986 outage and the 1991 outage and subsequent to the 1991 outage indicate no adverse change in valve seat leakage performance.
Extension of the seat seal replacement frequency of surveillance requirement 4.7.D.4 is also l
supported by the leakage test results provided in Exhibit D for valves AO-2379 and AO-2380.
These valves are the Torus to Reactor Building Var" "m Breaker isolation valves. They are 20-inch air operated butterfly valves of the same muu.. ;nd design as the Primary Containment Purge and Vent valves. The Torus to Reactor Building Vacuum Breaker Isolation valves employ the same T-shaped elastomer seat seal as the Primary containment Purge and Vent valves and are not subject to the 5 year seat seal replacement requirement. The A-2 w
1 T-shaped elastomer seat seals of these valves were replaced in 1988. During the nine years i
of service of the Torus to Reactor Building Vacuum Breaker Isolation valves, there has been no degradation of valve seat leakage attributed to a failure of the T-shaped elastomer seat seal.
As stated above, due to Monticello's operational experience with the Primary Containment Purge and Vent Valves, Monticello proposed in our November 22,1985 letter the replacement of the T-shaped elastomer seat seal as an attemative to the NRC staff position requiring accelerated local leakage testing of containment purge Nd vent butterfly Valves. Regulatory Guide 1.163, " Performance-Based Containment Leak ' :st Program" (September 1995) indicates a modification of the earlier staff position requiring accelerated localleakage rate testing by stating the following:
...the interval for Type C tests for... containment purge and vent valves in PWRs and BWRs, should be limited to 30 months...with consideration given to operating exponence and satiety significance.
This submittal does not propose any change to the existing requirements contained in the Monticello Technical Specifications for the leak testing of the Primary Containment Purge and l
Vent valves per 10 CFR 50, Appendix J, " Primary Reactor Containment Leakage Testing For Water-Cooled Power Reactors."
The matenal of which the T-shaped elastomer seat is comprised has been found to withstand normal and accident thermal exposures for the design life of the plant based on a thermal aging analysis. The Purge and Vent valve elastomer seat material will provide acceptable seat 7
tightness when exposed to a total integrated radiation dose of 10 Rads based on information provided by the Electric Power Research Institute (EPRI) in technical report EPRI NP-2129, Radiation Effects on Organic Matenalin NuclearPlants, November 1981; and limited testing performed by the valve vendor. The radiation dose of 10' Rads bounds the design basis accident dose which these valves would be exposed to. The radiation dose the valves would be exposed to during normal operations is insignificant when compared to the accident dose.
Thus the radiation effects will not have an adverse impact on the elastomer seat material.
Safety Evaluation Purging of the primary containment is accomplished by use of an exhaust fan discharging to a purge line which goes to both the drywell and suppression chamber. The 18-inch purge line has 3 air operated isolation valves (AO-2377, AO-2378, and AO-2381) which will close on a Group 2 Primary Containment Isolation signal. The primary containment may be vented to the standby gas treatment system or the Reactor Building exhaust plenum. Venting is via the vent lines from the drywell and the suppression chamber. Each vent line has two 18-inch air operated isolation valves (AO-2386, AO-2387, AO-2383 and AO-2896). The vent line isolation valves close on the same isolation signal as the valves on the purge lines. The 18-inch purge and vent valves fail closed, are normally closed during plant operation when the reactor is at a temperature greater than 212*F, and provide primary containment isolction during design basis accidents requiring primary containment isolation.
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5 The 18-ir. 2 purge and vent valves are Fisher Controls Company-Continental Division, Type 9200, offset disc, T-shaped, butterfly valves; employing a replaceable T-shaped elastomer seat. The elastomer seat is pressure activated, prov: ding a tight shutoff seal. The pneumatic supply for the seal pressure is provided by the Instrument Nitrogen system with a backup pneumatic suriply from the safety grade Altemate Nitrogen system and installed accumulators.
h With the valve disc in the full closed position, the seal pressure is applied to the back of the
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elastomer ring giving the valve tight shutoff. Immediately upon an open signal, the seal J
pressure is released. After a short time delay the actuatoris permitted to open the valve allowing the disc to leave the seat without any force being exerted on the valve disc by the
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elastomer ring. When the valve disc is brought from its open position to 'he full closed position, a time delay is also used for pressurizing the seal. The valve disc is allowed to become fu3y closed (completely in the seat) after a short time delay the seal pressure is
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applied to a chamber behind the T-shaped seal.
An evaluation of the operational performance of the 18-inch r"rge and vent valves has concluded that a frequency extension from five yeais O six c ating cycles for the Monticello l
Technical Specification surveillance requirement to perform t.. ;placemerit of the T-shaped elastomer seat will have no adverse impact on the seat leakage performance of these primary containment imlation valves, and thus no adverse impact on the testing performed in k
accordance with 10 CFR 50, Appendix J. The operating experience of these valves has 3
demonstrated that the testing performed in accordance with 10 CFR 50, Appendix J provides a high level of confidence in the ability of these valves to perform their safety function with respect to valve leak tightness. The additional criterion to perform seat seal replacement of all 18 inch purge and vent valves upon Type C leakage test failures of any single valve due to degradation of the elastomer seat sealindicative of a potential common mode failure, maintains a high level of assurance of the capability of the purge and vent valves to perform the required safety function and provides an added level of conservatism.
The material of which the T-shaped elastomer seat is comprised has been found to withstand normal and accident thermal exposures for the design life of the plant based on a thermal aging analysis. Irradiation of the seat seal material under nomial and accident conditions has 1
been found to have 90 adverse impact on the elastomer seat material.
Determination of Sianificant Hazards Considerations The proposed change to the Operating License has been evaluated to determine whether it constitutes a signific. ant hazards consideration as required by 10 CFR Part 50, Section 50.91 using standards provided in St,ction 50.92. This analysis is provided below.
wg The proposed emendment will not involve a ionificant increase in the probability or consecuences of an accident previously evaluated.
M evaluatior. of the operational performance of the 18-inch purge and vent valves has concluded that a change in the seat seal replacement frequency specified in Montice!!o l
Technical Specification surveillance requirement 4.7.D.4 will have no adverse impact on the seat leskage performance of these primary containment isolation valves, no adverse impact on the testing performed in accordance with 10 CFR 50, Appendix J, y-=
and thus no adverse impact on the containe,', ant isolation function of thesa primary A-4
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containment isolation valves. The material of which the T-shaped elastomer seat is comprised of has been found to withstand normal and accident thermal exposures for the design life of the plant based on a thermal aging analysic. Radiation effects will not l
have an adverse impact on the elastomer seat material. Therefore, this amendment j
will not cause a significant increase in the probability or consequences of an accident previously evaluated for the Monticello plant.
The proposed amendment will not create the possibility of a new or different kind of accident from any accident oreviousiv analyzed.
The propose change to the Technical Specifications for the Primary Containment Purge i
and Vent valves does not alter the function of these components or their interrelationships with other systems. Therefore, this smendment will not create the 3
possibility of a new or different kind of accident from any accident previously analyzed.
The proposed amendment will not ir39lve a sianificant reduction in the maroin of i
AAfttL t
The operating experience of these valves has demonstrated that the testing performed in accordance with 10 CFR 50, Appendix J provides a high level of confidence in the l
ability of these valves to perform their safety function with respect to valve leak j
tightness. The proposed criteria for seat seal replacement provides added assurance that these containment isolation valves will perform the required safety function of containment isolation. The proposed amendment will not involve a significant reduction i
2 in the margin of safety.
l Environmental Assessment Northem States Power has evaluated the proposed changes and determined that:
1.
The change does not involve a significant hazards consideration.
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The changes do not involve a significant change in the type or significant increase in the amounts of any effluent that may be released offsite, or 3.
The changes do not involve a significant increase in individual or cumulative occupational radiation exposure.
Accordingly, the proposed changes met the eligibility criterion for categorical exclusion set forth in 10 CFR Part 51, Section 51.22(b), an environmental assessment of the proposed changes is not required.
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