ML20062G641
| ML20062G641 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 01/05/1979 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7901110089 | |
| Download: ML20062G641 (3) | |
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k NSP NORTHERN STATES POWER COMPANY M I N N E A PO L.l e. M IN N r s otA 55408 January 5, 1979 Director of Nuclear Reactor Regulation U S Nuclear Regulatory Comnission Washing, ton, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PIX:T Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Containment Purging During Normal Plant Ooeration In a letter dated i:ovember 29, 1978 f rom Mr A Schwencer, Chief, Operating Reactors Branch #1, Division of Operating Reactca, USNRC, we were informed of a number of events occurring at other f acilities which reduced the ef fectiveness of automatic isolation of containment purge valves. This letter requested that we respond within 30 days with our plans for dealing with this concern at the Prairie Island Nuclear Genrating Plant. Specifically, we were requested to:
a.
Review the design of safety actuation signal circuits which incorporate a manual override f eature to ensure that ove rridi ng of one safety actuation signal does not also cause the bypass of any ether safety actuation signal, that sufficient physical features are provided to f acilitate adequate adminis trative controls, and that the use of each such manual override is annunciated at the system level for every system impacted.
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b.
Agree to one of the following courses of action with respect to containment purging:
1.
Agree to cease purging, or 2.
Agree to linit purging to less than 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> / year.
Provide proof of ability of the containment isolation valves in the purge path to close under postulated accident conditions, or 3.
Provide the basis for continued unlimited purging and a schedule for demonstrating purge isolation valves can close unde r pcs tulated accident conditions, an evaluation of the impact of purging during operation en ECCS perfor-mance, an evaluation of the radiological consequences of any design basis accident requiring containment iso la tion during purging, and an evaluation of containment purge isolation instrumentation and control circuit designs.
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NORTHERN GTATES POWER COMPANY 91 rector of Nuclear Reactor Regulation Page 2 January 5, 1979 Review of Safety Actuation Signal Circuits All emergency safety features equipment control circuits have been reviewed for manual override features. The results of this review indicated that no individual equipment control circuits contain overrides of any safety actuation inputs other than local /renot e selectors. These selectors are provided on certain equipment to provide for shutdown from outside the control room.
Selection of local control is individually annunciated in the control room to assure appropriate adminis t rat ive control.
Safety actuation systems reviewed included Reactor Protection, Safeguards, and Radiation Monf toring. The Safeguards System includes saf ety injection, containment isolation, containment ventilation isolation, containment spray, feedwater isolation, and main steam isolation functions. llanual override of any of these systems, their subsystems, or individual circuits can only be accomplished by placing the circuitry in the test mode utilizing built-in test circuitry. Test circuit actuation only affects one of the redundant trains or channels within the system; it does not impair operability of its redundant counterpart nor does it affect operation of the other two systems. Test circuit use is annunciated in the control room at least at the individual train or channel level. This facili-tates adminis trat ive control.
Containment Purging Three aystems are used at Prairie Island for containment venting and purging:
a.
Cont ai nne nt purge system utilizing 36-inch supply and exhaust b.
_ Con t a in me nt inservice purge system utilizing 18-inch supply and exhaust S sten (a) in a high volume purge and ventilation system (33,000 cf m) used to f
vent ila te cont ainment followiag reactor shutdown to permit access for inspection and maint enance. Two containment isolation valves are provided on each supply and exhaust line which receive an automatic closure signal on receipt of a safety inj e c t ion (SI) or high radiation signal. These valves are of the butterfly type designed tc close against calculated peak accident pressure in 3 seconds.
A System (b) is a low volume (4,000 cie) purge system which provides charcoal absorption and particulate filt ration of containcent air prior to release. This system is used to assist the internal cleanup system in permitting containment access when airbornes rsdioactivity levels preclude entry.
It may also be used as a low volume normal purge and vent system. Two containment isolation valves arc
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i NORTHERN STATES POWIIR COMPANY 7 01 rector of Nucleah Reactor Regulation Page 3 January 5, 1979 provided on each supply and exhaust line which receive an automatic closure signal on receipt of an Si or high radiation signal. These valves are of the butterfly type designed to close against calculated peak accident pressure in 3
$PCondS.
L A 90 hour0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> / year limitation on operation of either the containment purge system or the cont ai nme nt in-service purge system when the reactor coolant system is above 200 F could severely af fect p la nt availability if more than the average number of containment entries are required for inspection and maintenance. For this have contacted the Westinghouse Electric Corporation with a request for reason we technical as;istance to evaluate the impact of purging during operation on ECCS pe rf o r ma nce. As noted above, the purge valves can, by design, close rapidly unde r pos tulated accident conditions. The radiological consequences of an accident occurring during purging are believed to be inconsequential due to the rapid closure of the purge valves. The Prairie Island containment purge and isolation instrumentation and contrcl circuit designs are also believed to be adequate.
If, after discussing the requirements established by the NRC Staf f for allowing unlimited purging with Westinghouse, we find the required ECCS analysis is practical, we will provide the Commission with a schedule for submitting the necessary analysis results. This will include confirmation of acceptable radio-logical consequences and adequate isolation instrucentation and control design.
A followup to this letter will be submitted by March 30, 1979 which will address this issue.
In the in t e rim, use of the containment purge system and inservice purge system will continue to be mininized consistent with plant inspection and maint ena nce requirements and prudent plant operating practices.
P le as e contact us if you have additional questions related to this matter or if our schedule for conf orming to your reques t is not satisfactory.
Yhurs ve ry truly, Yw fcm L 0 Mayer, PE Manager of Nuclear support Se rvic es LOM/ D."Ji/ ak cc: J G Keppice G Charnoff 1
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