ML20062E587
| ML20062E587 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 11/29/1978 |
| From: | Ippolito T Office of Nuclear Reactor Regulation |
| To: | Niav Hughes TENNESSEE VALLEY AUTHORITY |
| References | |
| NUDOCS 7812110029 | |
| Download: ML20062E587 (8) | |
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WASHINGTON, D. C. 20556
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November 29, 1978 Docket Nos. 50-259 50-260 and 50-296 l-I Mr. N. B. Hughes Manager of Power Tennessee Valley Authority 830 Power Building Chattanooga, Tennessee 37401
Dear Mr. Hughes:
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PE: CONTAINMENT PURGING DURING NORMAL PLANT OPERATION A number of events have occurred over the past several years which directly relate to the practice of containtrent purging during normal plant operation. During recent months, twc specific events have occurred which have raised several questions relative to potential failures of automatic isolation of the large diameter purge pene-trations which are used during power operation. On July 26, 1978, the Northeast Nuclear Energy Company reported to the NRC such an
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event at Millstone Unit No. 2, a pressurized water reactor located in New London County, Connecticut. On September 8, 1978, the Public Service Electric and Gas Company reported a similar event at Salem Unit No.1, a pressurized water reactor 1ccated in Salem County, i
During a review of operating procedures on July 25, 1978, the licensee discovered that since May 1,1978, intemittent containment purge 1
ocerations had been conducted at Millstone Unit No. 2 with the safety actuation isolation signals to both inlet and outlet redundant containment isolation valves (48 inch butterfly valves) in the purge inlet and outlet penetrations manually overridden and inoperable.
The isolation signals which are required to automatically close i
the purge valves for containment integrity were manually overridden to allow purging of containrent with a high radiation signal present.
The manual override circuitry designed by the plant's architect / engineer defeated the high radiation signal and all oth.r isolation signals to these valves. To manually override a safet,' actuation signal, the operator cycles the valve ontrol switch t, the closed position and then to the open pcsition. This action energized a relay which i
blocked the safety signal and allowed manual operation independent j
of any safety actuation signal.
This circuitry was designed to pemit reopening these valves after an accident to allow manual 4
operation of certain safety equipment.
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1 On September 8,1978, the staff was advised that, as a matter of l
routine, Salem Uni. No. I has been venting the containment through the containment nntilation system valves to reduce pressure.
In certain inst.,ces this venting has occurred with the containment high particulate radiation monitor isolation signal to the purge and pressure-vacuum relief valves overridden. Override of the containment isolation signal was accomplished by resetting the train A and B reset buttons.
Under these circumstances, six valves in t'a containment vent and purge systems could be opened with a hign particulate isolation signal present. This override was perfomed after verifying that the actual containment particulate levels were acceptable for venting. The licensee, after further investigation of this practice, detemined th&t the reset of the l
particulate alam also bypasses the containnent isolation signal to the purge valves and that the purge valves would not have auto-matically closed in the event of an emergency core cooling system (ECCS) safety injection signal.
l These events and infomation gained from recent licensing actions have raised several concerns relative to potential failures affecting the purge penetration valves which could lead to a degradation in containment integrity and, for PWR's, a degradation in ECCS perfomance. Should a loss-of-coolant accident (LOCA) occur during purging there could be insufficient containment backpressure to assure proper operation of the ECCS.
As the practice of containment purging during normal operation has become more prevalent in recent years, we have required that applicants for construction permits l
or operating licenses provide test resulcs or analyses to demonstrate l
the capability of the purge isolation valves to close against the i
dynamic forces of a design basis LOCA.
Some licensees have Technical Specifications which prohibit purging during plant operation pending demonstration of isolation valve operability.
In light of the above, we request that you provide within 30 days of receipt of this letter your commitnent to cease all containment purge during operation (hot shutdown, het stancby, startup and power operation) or a justification for continuing purging at your facilities. Specifically, provide the following information:
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. (1) Propose an amendment to the plant Technical Specifications based upon the enclosed model Technical Specification, or (2)
If you plan to justify limited purging, you must propose a Technica) Specification change Ifmiting purging during operation to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year as described in the enclosed Standard Review Plan Section 6.2.4, Revision 1.
Your justification must include a demonstration (by test or by test and analysis similar to that required by Standard Review Plan 3.9.3) of the ability of the containment isolation valves to close under postulated design basis accident conditions. Within thirty days of receipt of this letter, you are requested to provide a schedule for completion of your evaluation justifying continuation of limited purging durft:g power operation.
(3)
If you plan to justify unlimited purging you need not propose a Technical Specification change at this time.
You must, however, provide the basis for purging and a schedule for responding to the issues relating to purging during normal operation as described in the enclosed Standard Review Plan Section 6.2.4, Revision 1, and the associated Branch Technical Position CSB 6-4.
As discussed in these documents, purging during normal operation may be permitted if the purge isolation valves are capable of closing against the dynamic. forces of a design basis loss-of-coolant accident.
Also, basis for unlimited purging must include an evaluation of the impact of purging during operation on ECCS performance, an evaluation of the radiological consequences of any design basis accident requiring containment isolation occurring during purge operations, and an evaluation of containment purge and isolation instrumentation and control circuit designs. Within thirty days of receipt of this letter, you are reouested to provide-a schedule for completion of your evaluation justifying continuation of unlimited purging during power operation.
Pending completion of the NRC staff review of the justification for continued purging in (2) or (3) above, you shculd commit to either cease purging or limit purging to an absolute minimum, not to exceed 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year.
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4-The staff believes that both the Millstone and Salem events resulted from lack of proper management control, procedural inadequacies, and possible design deficiencies.
While the containment atmosphere was properly sampled and the purging (venting) discharges at both facilities were within regulatory requirements, the existing plant operating procedures approved by the licensee's management did not adequately address the operability of the purge valves and the need for strict limitations on (or prohibition of) overriding a safety actuation closure signal. The requirements for valve operability were not discussed and the related Technical Specifi-cations were not referenced in the procedures.
Design deficiencies probably contributed to the events as the safety actuation bypass condition is not annunciated nor is a direct manual reset of the safety actuation signal available.
Consequently, we have developed the position specified below to assure that the design and use of all override circuitry in your plant is such that your plant will have the protection needed during postulated accident conditions.
Whether or not you plan to justify purging, you should review the design of all safety actuation signal circuits which incorporate a manual override feature to ensure that overriding of one safety actuation signal does not also cause the bypass of any other safety actuation signal, that sufficient physical features are providad to facilitate adequate administrative controls, and that the use of each such manual override is annunciated at the system level for every system impacted. Within thirty days of receipt of this letter, you are requested to provide (1) the results of your review of override circuitry and (2) a schedule for the developnent of any design or procedural changes imposed or planned to assure correction of any non-conforming circuits. Until you have reviewed circuitry to the extent necessary to verify that operation of a bypass will affect no safety functions other than those analyzed and discussed on your dockets, do not bypass that signal. Our Office of Inspection and Enforcement will verify that
Mr. N. B. Hughes you have inaugurated administrative controls to prevent improper manual defeat of safety actuation signals as a part of its regular inspection program.
Sincerely, fC Thomalppolito, Chief x-s Operating Reactors Branch #3 Division of Operating Reactors
Enclosures:
1.
Model Technical Specification 2.
Standard Review Plan 3.
Branch Technical Position CSB 6-4 cc w/ enclosures:
See next page
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Tennessee Valley Authority cc:
H. S. Sanger, Jr., Esquire General Counsel Tennessee Valley Authority 400 Commerce Avenue E 118 33 C Knoxville, Tennessee 37902 Mr. D. McCloud Tennessee Valley Authority 303 Power Building Chattanooga, Tennessee 37401 Mr. William E. Garner Route 4, Box 354 Scottsboro, Alabama 34768 Mr. C. S. Walker Tennessee Valley Authority 400 Comnerce Avenue W 90199 C Knoxville, Tennessee 37902 Athens Public Library South and Forrest Athens, Alabama 35611 Robert F. Sullivan Nuclear Regulatory Comnission Office of Inspection and Enforcement 101 Marietta Street, Suite 3100 Atlanta, Georgia 30303