ML17254A840
| ML17254A840 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 06/21/1984 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML17254A839 | List: |
| References | |
| NUDOCS 8406280420 | |
| Download: ML17254A840 (8) | |
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UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION ROCHESTER GAS AND ELECTRIC CORPORATION R;E.
GINNA NUCLEAR POWER PLANT DOCKET NO. 50-244
1.0 INTRODUCTION
In November
- 1978, a generic letter was sent to all operating reactor licensees.
The letter identified certain events relating to containment purging during nor-mal plant operation of concern to NRC.
Specifically, events at Millstone 2 and Salem 1 were described wherein containment isolation valves were opened to purge containment by using override features.
These override features were found to be designed such that a legitimate automatic closure would not have occurred, if needed.
The generic letter requested that each licensee provide a commitment to either cease all containment purging or justify con-tinuing to to purge.
In response to the gener'ic letter, Rochester Gas and Electric Corporation (RG&E) (licensee),
submittals made on January 2, 1979, February 16,
- 1979, March 30, 1979 and July 2, 1979.
On October 23, 1979, the staff notified the licensee that certain types of containment isolation valves might not close against the ascending differen-tial pressure and resultant dynamic loading of the design basis LOCA.
The licensee was requested to commit to an interim position pending staff review of the long term measures.
The'licensee responded by letter dated October 8, 1980.
For staff review purposes, the long term measures were divided into four cat-egories.
Each category will be addressed in this Safety Evaluation.
2..0 VALVE OPERABILITY REVIEWS By letter dated February 23, 1983, the staff informed the licensee that infor-mation concerning the operability of large-diameter Pratt butterfly valves (of the generic family RlA or NRIA) in the event of a DBA-LOCA raised concern whether the licensee's justification for operability provided the required assurance that the valve will close.
The licensee was requested, pursuant to 10 CFR 50.54(f), to:
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1.
Provide an assessment of the operability of the Ginna large-diameter Pratt purge and vent valves in light of the information conveyed in the
- letter, and 2.
Inform the staff whether or not the licensee intended to maintain the purge and vent valves sealed closed in accordance with Standard Review Plan Section 6.2.4, II.6.f and to verify them to be closed every 31 days whenever the reactor is not in the cold shutdown or refueling mode until such time as'acceptable information that demonstates that the large-diameter Pratt purge/vent valves will operate in the event of a DBA-LOCA is submitted.
The licensee responded by letter dated March ll, 1983.
In that letter the licensee stated that after reviewing the staff information, RGSE believed that a conservative position was to commit, on an interim basis, to maintain the purge valves closed while the reactor is critical.
In addition, the valves would not be opened until the reactor had been subcritical for at least one hour.
This position was based on:
1.
The conservatism in the Pratt analysis completed in 1982.
2.
The fact that there are two valves in series each with mechanical stops which prevent the valve from going to the full open position.
There is no active failure which could cause the valve to go to the full open position.
3.
The probability of a LOCA occurring while the purge valves are open but the plant has not been brought to cold or refueling conditions is very small.
4.
The radiological consequences of a LOCA at hot zero power (HZP) are substantially below the 10 CFR Part 100 limits with primary coolant activity at the Technical Specification l.imit.
5.
Maintaining personnel radiation exposure to as low as reasonably achievable while minimizing costs to the RGSE rate payers.
The licensee stated that the commitment would remain in effect until acceptable information demonstrating operability is submitted.
The staff considers that the commitment should remain in effect pending completion of our review and approval of the information.
The staff and its technical assistance contractor, Brookhaven National Labora-tory have examined the March ll, 1983 submittal and determined that the licensee addressed quantitatively the issued raised by the staff.
The staff will complete the review as a plant specific review.
Until the plant specific review of the March ll, 1983 submittal is completed, the licensee's commitment to the interim position with respect to valve operability is still acceptable.
3.0 ELECTRICAL, INSTRUMENTATION AND CONTROL ASPECTS OF THE OVERRIDE OF This portion of the review was completed per NRC letter of March 19, 1982 to the licensee.
4.0 CONFORMANCE WITH STANDARD REVIEW PLAN SECTION 6.2.4 REVISION 1
AND H
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P R TING PR CTICES Enclosure 3 to staff letter of December 15, 1981, transmitted a draft Safety Evaluation Report (SER) to the licensee.
The draft SER identified several areas where further information was needed before the staff could complete its review.
These areas included:
1.
The provisions to protect structures and safety-related equipment located downstream of the purge/vent system isolation valves against a loss of function from the environment created by the escaping air and steam; 2.
The provisions made to ensure that isolation valve closure will not be prevented by debris which could potentially become entrained in the escaping air and steam; 3.
Licensee response to the staff recommendation that purge/vent system operation during operating modes other than refueling or cold shut-down be limited to safety-related needs since the plant is inherently safer with closed purge/vent valves than with open lines to the envi-ronment which require valve action to provide containment integrity; and 4.
Licensee response to the staff recommendation that leak testing of the purge/vent butterfly isolation va1ves be done at three-month intervals to provide for early 'detection of valve seat deterioration.
The licensee responded to the open issues identified in the staff's letter of December 15, 1981 in its letter dated February 4, 1983.
A.discussion of each of the issues identified in the December 15, 1981, letter, follows.
4.1 Protection of Downstream Structures and E ui ment A ainst Loss of Function The staff requested an analysis of the provisions made to protect structures and safety-related equipment located downstream of the purge isolation valves againt loss of function due to the environment created by the escaping air and stream.
In response, the licensee stated that there was no safety-related equipment downstream or in the vicinity of the ductwork outside the containment.
The staff finds this response to be acceptable.
4.2 Prevention of Valve Closure b
Debris The staff requested the licensee to provide measures to ensure that isolation valve closure would not be prevented by debris which could potentially become entrained in the escaping air and steam.
The infor-mation supplied by the licensee has demonstrated that the Ginna design satisfies this staff recommendation.
Both of the purge valve inlets inside containment have 4-inch mesh screens and are located approxi-mately 17 feet above the nearest floor elevation.
The purge exhaust line is covered 'by a combination of an exhaust hood and mesh screen.
A few feet below the bottom of the hood is an open grating, which will further reduce the chance of debris reaching the isolation valves.
The staff concludes that the present design features at Ginna are sufficient to prevent the entry of debris into the purge/vent lines and, therefore, meet the design objectives of. this issue.
4.3 Limit Pur e and Vent 0 erations to Safet Related Needs In response to the staff's request to limit purge/vent operations to safety-related
- needs, the licensee has committed to limit purging to as low as reasonably achievable and only for safety-related reasons.
In addition, the licensee will inform the NRC whenever the total time of purging in any calendar year exceeds 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> along with the actions planned to minimize purging.
Based on the above commitments by the
- licensee, and because the purging system at Ginna has been used, typ-ically, less than 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year in the past, the staff finds the planned purge operations meet the objectives of this issue
- and, therefore, are acceptable.
However, Technical Specifications are necessary in accordance with enclosure 4 to NRC letter dated December 15, 1981.
4.4 Earl Detection of Deterioration of Seat Naterial To assure early detection of deterioration of the resilient seat mate-rial used in purge butterfly isolation valves, the staff requested the licensee to perform leak integrity tests on these valves at three-month intervals.
The Ginna Technical Specifications (TS) currently require that the purge/vent valves be leak tested within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after each usage and within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> after multiple usages of'he purge/vent system.
While the staff believes that this test procedure is a valuable test, it does not by itself assure early detection of seat deterioration, particularly for long periods of plant operation with no purge operation.
In lieu of testing the purge/vent isolation valves at three months intervals, the staff would find acceptable the current leak test procedure in the plant's TS if an additional require-ment to test the purge/vent valves at intervals not to exceed six months is also included in the plant's Technical Specifications.
The basis for finding this alternative test frequency acceptable is that the purge t
4.5 valves can be considered to be passive between usages of the purge system and, therefore, fall under the six month test interval recom-mendation the staff applies to passive purge isolation valves.
There-fore, the licensee should request a change to the TS which would include the staff's recommendations or propose an acceptable alternative.
Effect of Fuel Clad Peak Tem erature Durin a
LOCA Resultin From a
Reduced ECCS Back ressure In addition to the items discussed
- above, the staff has performed an evaluation of the effect on fuel clad peak temperature of initially open purge/vent valves during a
LOCA resulting from a reduced ECCS backpressure.
Using conservative values for valve closure time and containment pressure during the time it takes the valves to close, the staff calculated a maximum pressure drop of 1.5 psi.
Experiments and sensitivity studies performed for other Westinghouse plants have shown that a 1.5 psi drop in ECCS backpressure will result, at most, in a 10-20'F rise in peak clad temperature.
This increase is insig-nificant when compared with the temperature margins available at the Ginna facility (greater than 200'F).
5.0 RADIOLOGICAL CONSEQUENCES
.The release of radioactivity through vent or purge valves from a potential large LOCA at power has been considered to assure that such events do not constitute an undue hazard to the people residing around operating reactor sites.
A large number of staff evaluations of the radiological consequences of LOCA's were performed for construction permit, operating license, operating license amendment, and Systematic Evaluation Program reviews for a number of plants.
In addition, a generic assessment of the amount of radioactivity that could be released while venting and purging from a spectrum of pipe breaks through the range of purge valve sizes utilized by industry was made.
The evaluations were made utilizing the following bases:
1.
Vent and purge valve isolation signals, circuitry and purge valve actuation were reliable; 2.
If purge system isolation valve closure times were sufficient (less than 10 seconds) to prevent the release of activity associated with fuel failures that could follow a large break (a total accident elapsed time of about 15 seconds or less);
- 3. If maximum allowable coolant iodine equilibrium and spiking activity limits did not exceed those contained in Standard Technical Specifications (STS);
4.
Fission products generated by pipe breaks were reflective of coolant activity and fuel failures estimated using 10 CFR Part 50, Appendix K, analysis techniques; and 5.
Radiological consequences of accidents while purging or venting would be bounded by those produced by a large break.
In virtually all cases, the contribution through vent or purge valves was estimated to be of the order of 2 percent, or less, of the Exclusion Area Boundary (EAB) and outer boundary of the Low Population Zone (LPZ) doses that would occur from a large break LOCA in which a source term indicative of a substantial melt of the core with subsequent release of appreciable quantities of fission products is assumed (estimates based on SRP analysis techniques and 10 CFR Part 100.11).
For dose assessment in which only activ-ity in primary coolant systems would be released, or for events in which fuel fail.ures indicative of 10 CFR Part 50, Appendix K, LOCA analyses are indicated, EAB and LPZ dose estimates are substantially less than dose estimates made for a large break LOCA assuming a substantial fuel melt.
Since the magnitude of the vent or purge contribution to severe LOCA dose estimates is small compared to other LOCA scenarios within design
- bases, the staff concludes that the consequences of such accidents are within applicable dose guidelines.
A generic assessment of the radiological consequences of large break acci-
- dents, including a resulting severe LOCA of the type hypothesized for site suitability purposes, while venting or purging at power indicates that the dose contribution through open valves is small.
Therefore, the staff finds total radiological consequences of such accidents would be less than the dose guidelines of 10 CFR Part 100.
The basis used in the foregoing generic analyses applies to Ginna.
Conse-quently the radiological consequences of venting or purging from a spectrum of pipe breaks are within applicable dose guidelines and are, therefore, acceptable
- 6. 0 CONCLUSIONS The staff has evaluated the licensee's submittals describing the purge and vent system at Ginna, and the commitments made by the licensee. regarding limited time of'peration.
Based on the evaluation, the staff concludes that the purge and vent system design and operating practices for Ginna, with the exception of the interval for performing leak integrity testing on the purge/vent isolation valves (Section 4.4) are acceptable.
The licensee should submit a requested for a TS change consistent with the staff recommendations for testing intervals or propose an acceptable alternative.
7.0 ACKNOWLEDGMENT M. Fields, R. Wright and K. Dempsey contributed to this Safety Evaluation.
Dated:
June 21, 1984
Mr. Roger W'. Kober June Zl, 1984 periods of plant operation with no purge valve operation.
In lieu of testing the purge/vent isolation valves at our proposed three month intervals, the staff would accept the current leak test intervals in the plant's TS if the test of the purge/vent valves leakage was also done at intervals not to exceed six months.
Consequently, you are requested to submit, within 60 days of receipt of this
- letter, a request for a change in the Ginna TS which would include all of the staff's recommendations or an alternative TS acceptable to the staff.
We will review such a request for amendment on a plant specific basis.
The reporting and/or recordkeeping requirements, contained in this letter affect fewer than.ten respondents; therefore, OMB clearance is not required under P.L.96-511.
Sincerely, Original signed by Thomas V. Wambach for
Enclosure:
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