ML19312C711
| ML19312C711 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 09/26/1977 |
| From: | Schwencer A Office of Nuclear Reactor Regulation |
| To: | Parker W DUKE POWER CO. |
| References | |
| NUDOCS 7912190918 | |
| Download: ML19312C711 (3) | |
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3 UNITED STATES NUCLEAR REGULATORY COMMISSION g
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WASHINGTON. D. C. 20555
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.o SEP 2 61977 Docket tio's'. 50-269 50-270 and 50-287 Duke Power Conpany ATTN:
Mr. William 0. Parker, Jr.
Vice President - Steam Production Post Office Box 2178 422 South Church Street Charlotte, North Carolina 28242 Gentl emen:
RE:
OCONEE NUCLEAR STATION, UNITS 1, 2 & 3 Recently at an operating PWR facility, a limited boron oilution incident occurred due to tne inadvertent injection of a portion of the contents of the NaOH tank into the reactor coolant system while the reactor was in the cold shutdown condition. '4hile performing surveillance testing (valve cycling) of the NaOH tank isolation valve, with the Decay Heat Removal (DHR) systeu lined up for reactor coolant recirculation, a portion of the tank's contents drained into the DHR system.
Upon resumption of coolant recirculation this Na0H was injected into the reactor coolant systen.
In the above-mentioned case, only a limited amount of Na0H (approximately 600 gallons) was injected and the reactor remained subcritical by a large margin. However, this event highlighted the fact that a postulated single failure at this facility (i.e., misposition of the isolation valve for the NaOH tank when the DMR system is lined up for recirculation or operating in the recirculation mode) could result in a moderator dilution incident which had not been previously considereo.
Subsequent analysis by the licensee and his vendor revealed that, for certain conservative assumptions (e.o., reactor in the cold shutdown condition, vessel temperature less than 1007, beginning of core life characteristics, vessel drained to a level approximately equal to the height of the outlet nozzle, lowest inital boron concentration allowed by Technical Specifications, the maximum worth control rod stuck in the fully out position, and no credit assumed for operator action), the injection of the Na0H tank contents into the reactor coolant system due to the misposition of a single isolation valve could result in reactor criticality with the control rods inserted.
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Duke Power Company Based upon our review of this particular incident, we concluded that the assumption that operator action would not be taken in suf-ficient time to teminate the event prior to reactor criticality would be overly conservative. This detemination was influenced by the length of the dilution t,ime necessary before return to criticality and by the nunber of indications and alarms available to the operator at this facility.
Due to plant-specific system design and instrumen-tation cifferences, we are not able at this time to reach a similar con-clusion for all PWR's. Furthemore most PWR boron dilution analyses have been limited to addressing a malfunction in the makeup and purification systec (chenical and volume control system). The incident discussed above is an example of a boror dilution accident not covered by these analyses. Therefore we are requesting that each licensee of a PWR facility provide an analysis of the potential for and consequences of boron ailution accidents at his facility.
You are requested to perfom and submit the results of such an analysis within 90 days of receipt of this letter.
Your analysis should be based upon conservative assumptions consistent with the design of your facility and your Technical Specifications and should include the assumption of the most limiting single failure. The analysis should also include an assess-ment of the factors which affect the capability of the operator to take corrective action which would teminate the postulated events prior to achieving reactor criticality.
If, based on the results of this analysis, you detemine that corrective actions (design or procedural) are required to preclude the occurrence or mitigate the consequences of postulated boron dilution accidents, your response should include proposals for such actions.
Sincerely ' '
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f QW$6 V A. Sc'Ewencer, Chief Operating Reactors Branch #1 Division of Operating Reactors cc:
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Duke P wer Company 3-SEP 2 61977 cc:
Mr. William L. Porter Duke Power Company P. O. Box 2178 422 South Church Street Charlotte, North Carolina 28242 J. Michael McGarry, III, Esquire DeBevoise & Liberman 700 Shoreham Building 806-15th Street, NW.,
Wasilington, D.C.
20005 Oconee Public Library 201 South Spring Street Walhalla South Carolina 29691 4
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