ML19347E359
| ML19347E359 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 04/20/1981 |
| From: | Eisenhut D Office of Nuclear Reactor Regulation |
| To: | SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| Shared Package | |
| ML19347E358 | List: |
| References | |
| NUDOCS 8104270123 | |
| Download: ML19347E359 (7) | |
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O 7590-01 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMISSION In the Matter of THE SACRAMENTO MJNICIPAL UTILITY DISTRICT Docket No. 50-312 (Rancho Seco Nuclear Generating
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Station)
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ORDER FOR MODIFICATION OF LICENSE I
The Sacramento Municipal Utility District (the licensee) holds Facility Operating License No. DPR-54, which authorizes the licensee to operate the Rancho Seco Nuclear Generating Station (the facility) at power levels *.ot in excess of 2772 megawatts thermal rated power. The facility, which is located at the licensee's site in Sacramento County, California is a pressurized water i
reactor (PWR) esed for the commercial generation of electricity.
II The Reactor Safety Study (RSS), WASH-1400, identified in a PWR an inter-system loss of coolant accident (LOCA) which is a significant contributor to risk of core melt accidents (Event V). The design examined in the RSS contained in-series check valves isolating the high pressure Primary Coolant l
System (PCS) from the Low Pressure Injection System (LPIS) piping. The scenario which leads to the Event V accident is initiated by the failure of these check valves to function as a pressure isolation barrier. This causes an overpressurization and rupture of the LPIS low pressure piping l
l which results in a LOCA that bypasses cc,7tainment.
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Oc 7590-01 In order to better define the Event V concern, all light water reactor ifcensees were requested bv letter dated February 23, 1980, to provide the following in accordance with 10 CFR 50.54(f):
1.
Describe the valve configurations and indicate if an Event V isolation valve configuration exists within the Class I boundary of the high pressure piping connecting PCS piping to low pressure system piping; e.g., (1) two check valves in series, or (2) two check valves in series with a motor operated valve (MOV);
2.
If either of the above Event Y configurations exist, indicate whether continuous surveillance or periodic tests are being performed on such valves to ensure integrity.
Also indicate whether valves have been known, or found, to lack integrity; and 3.
If either of the above Event V configurations exist, indicate whether plant procedures should be revised or if plant nodifications should be made to increase reliability.
In addition to the above, licensees were asked to perform individual check valve leak testing prior to plant startup after the next scheduled outage.
By letter dated Parch 12, 1980, the licensee responded to our February letter. Based upon the review of this response as well as the review of previously docketed information for the facility, I have concluded in con-
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sonance with the attached Safety Evaluation (Attachment 1) that one or more valve configuration (s) of concern exist at the facility. The attachea Tech-nical Evaluation Report (TER) (Attachment 2) provides, in Section 4.0, a tabulation of the subject valves.
The staff's concern has been exacerbated due not only to the large number of plants which have an Event Y configuration (s) but also because of recent Jnsatisfactory operating experience. Specifically, two plants have leak tested check valves with unsatisfactory results. At Davis-Besse, a pressure isolation check valve in the LPIS failed and the ensuing investigation found that valve internals had become disassembled. At the Sequoyah Nuclear Plant, two Residual Heat Removal (RHR) injection check valves and one RHR recirculation check valve failed because valves jammed open against valve over-travel limiters.
It is, therefore, apparent that when pressure isolation is provided by two in-series check valves and when failure of one valve in the pair can go undetected for a substantial length of time, verification of valve integrity is required. Since these valves are important to safety, they should be tested periodically to ensure low probability of gross failure.
- As a result, I have determined that periodic examination of check valves must be undertaken by the licensee as provided in Section III below to t
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verf TV that each valve is seated properly and functioning as a pressure isolation device. Such testing will reduce the overall risk of an inter-system LOCA. The testing mandated by this Order may be accomplished by direct volumetric leakage measurement or by other equivalent means t
j capable of demonst
' a that leakage limits are not exceeded in accord-ance with Section 2.2 of the attached TER.
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l 7590-01 4-In view of the operating experiences described above and the potential consequences of check valve failure I have determined that prompt action is necessary to increase the level of assurance that multiple pressure isolation barriers are in place and will remain intact. Therefore, the public health, safety and interest require that this modification of Facility Operating License No. DPR-54 be immediately effective.
III Accordingly, pursuant to Section 1611 of the Atomic Energy Act of 1954, as amended, and the Comission's regulations in 10 CFR Parts 2 and 50, IT IS HEREBY ORDERED THAT EFFECTIVE IMMEDIATELY, Facility Operating License No. DPR-54 is modified by the addition of the following requirements:
1 1.
Implement Technical Specifications (Attachment 3) which require periodic surveillance over the life of the plant and which specify limiting conditions for operation for PCS pressure isolation valves.
2.
If check valves have not been (a) individually tested within 12 months preceding the date of the Order, and (b) found to comply
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i with the leakage rate criteria set forth in the Technical Specifications described in Attachment 3, the MOV in ea.n line shall be closed within 30 days of the effective date of this i
Order and quarterly Inservice Inspection (ISI) MOV cycling ceased until the check valve tests have been satisfactorily i
accomplished.
(Prior to closing the MOV, procedures shall l
be implemented and operators trained to assure l
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I that the MOV remains closed. Once closed, the MOV shall be tagged closed to further preclude inadvertent valve opening).
3.
The MOV shall not be closed as indicated in paragraph 2 above unless a supporting safety evaluation has been prepared. If the MOV is in an emergency core cooling system (ECCS) the safety evaluation shall include a detennination as to whether the. requirements of 10 CFR 50.46 and Appendix K to 10 CFR Part 50 will continue to be satisfied with the MOV closed.
If the MOV is not in an ECCS. the safety evaluation shall include a deter-mination as to whether operation with the MOV closed presents an unreviewed safety question as defined in 10 CFR 50.59(a)(2).
If the requirements of 10 CFR 50.46 and Appendix K have not been satisfied, or if an unreviewed safety question exists as defined in 10 CFR 50.59 then the facility shall be shut down within 30 days of the date of this Order and remain shutdown until check valves are satisfactorily tested in accordance with the Techni-cal Specifications set forth in Attachment 3.
- 4. 'The records of the check valve tests required by this Order shall be made available for inspection by the NRC's Office of Inspection and Enforcement.
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7590-01 IV The licensee or any other person who has an interest affected hy this Order nay request a hearing on this Order within 25 days of its publication in the Federal Register. A request for hearing shall be submitted to the Secretary, U.S. Nuclear Regulatory Commissioa Washington, D.C. 20555.
A copy of the request shall also be sent to the Executive Legal Director at the same address, and to David S. Kaplan, Secretary and General Counsel, 6201 S Street, P. O. Box 15830, Sacramento, California 95814, attorney for the licensee.
If a hearing is requested hy a person other than the licensee, that person shall describe, in accordance with 10 CFR 2.714(a)(2), the manner in which his or her interest is affected by this Order. ANY REQUEST FOR A HEARING SHALL NOT STAY THE IMMEDIATE EFFECTIVENESS OF THIS ORDER.
If a hearing is requested by the licensee or other person who has an interest affected by this Order, the Commission will issue an order designating the time and place of any such hearing.
If a hearing is held, tlie issues to be considered at such a hearing shall be:
(a) Whether the licensee should be required to individually leak test check valves in accordance with the Technical Specifications set forth in Attachment 3 to this Order.
(b) Whether the actions required by Paragraphs 2 and 3 of Section III of this Order must be taken if check valves have not been tested within 12 months preceding the date of this Order.
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7590-01 i l
Operation of the f acility on terms consistent with this Order is not
,'j stayed by the pendency of any proceedings on this Order.
In the event that a need for further action becomes apparent, either in the course of i
i proceedings on this Order or any other time, the Director will take appropriate action.
FOR THE NUCLEAR REGULATORY COMMISSION d 10lA h 144 Darrell G. Fisenhut Director Division of Licensing Effective Date: April 20, 1981 Bethesda, Maryland Attachments:
1.
Safety Evaluation Report 2.
Technical Evaluation Report 3.
Technical Specifications l
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Sm urg'o UNITED STATES I
~g NUCLEAR REGULATORY COMMISSION n
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WASHINGTON, D. C. 20555
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SAFETY EVALUATION REPORT RANCHO SECO NUCLEAR GENERATING STATION PRIMARY COOLANT SYSTEM PRESSURE ISOLATION VALVES (WASH-1400, EVENT V) 1.0 Introduction The Reactor Safety Study (RSS), WASH-1400, identified in a PWR an intersystem loss of coolant accident (LOCA) which is a significant contributor to risk of core melt accidents (Event V). The design examined in the RSS contained in-series check valves isolating the high pressure Primary Coolant System (PCS) from the Low Pressure Injection System (LPIS) piping. The scenario which leads to the Event V accident is initiated by the failure of these check valves to function as a pressure isolation barrier. This causes an overpressurization and rupture of the LPIS low pressure piping which results in a LOCA that bypasses containment.
In order to better define the Event V concern, all light water reactor licensees were requested by 10 CFR 50.5?(f) letter, dated February 23, 1980, to identify valve configurations of concern and prior valve test results, if any. By letter dated March 12, 1980, the licensee responded to our request and this information was subsequently transmitted to our contractor, the Franklin Research Center, for verification that the licensee had correctly identified the subject valve configurations.
2.0 Evaluation In order to prepare the Technical Ev'aluation Report (TER) it was necessary that the contractor verify and evaluate the licensee's response to our February 1980 letter. The NRC acceptance criteria used by Franklin were based on WASH-1400 findings, probabilistic analyses and appropriate Standard Review Plan requirements. With respect to the verification of the licensee's response to our information request, the Franklin evaluation was based on FSAR information, ISI/IST site visit data, and other previously docketed infomation.
The attached Franklin TER correctly identifies the subject valve configurations.
3.0 Conclusion Based on our review of the Franklin TER, we find that the valve configurations of concern have been correctly identified. Since periodic testing of these PCS pressure isolation valves will reduce the probability of an intersystem LOCA we, therefore, conclude that the requirement to test these valves should be incor-porated into the plant's Technical Specifications.
l Dated: April 20,1981 Mk
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