ML20245C301
| ML20245C301 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 09/14/1977 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Dunn C DUQUESNE LIGHT CO. |
| References | |
| TAC-8372, NUDOCS 8710220086 | |
| Download: ML20245C301 (3) | |
Text
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9' pa mic UNITED ST ATES
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,,g NUCLE AR REGULATORY COMMISSION g-I'*"
g WASHINGTON. D. C. 20555
% %,'4,8 September 14, 1977
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Docket No.:
50-334 Duquesne -Light Company I
ATTN:
Mr. C. N. Dunn, Vice President Operations Division 435 Sixth Avenue Pittsburgh, Pennsylvania 15219 Gentl emen:
RE:
BEAVER VALLEY POWER STATION UNIT NO. 1 Recently at an operating PWR facility, a limited boron dilution incident occurred due to the 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 coVition. While perfonning surveillance testing (valve cycling) of the Na0H tank isolation valve, with the Decay Heat Removal (DHR) system 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 i
system.
In the above-mentioned case, only a limited amount of NaOH (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., disposition of the isolation valve for the NaOH tank when the DHR system is lined up for recirculation or operating in the recirculation mode) could result in a moderator dilution incident which had not been previously considered.
Subseauent analysis by the licensee and his vendor revealed that, for certain conservative assumptions (e.g., reactor in the cold shutdown condition, vessel temperature less than 100 F, 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 NaOH tank contents into the reactor coolant system due to the disposition of a single isolation valve could result in reactor criticality with the control rods inserted.
8710220086 770914
/
PDR ADOCK 05000334 p
E I
Duquesne Light 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 tenninate the event prior to reactor criticality would be overly conservative.
This determination was influenced by the length of the dilution time necessary before return to criticality and by the number of indications and alarms available to the operator at this facility.
Due to plant-specific system design and instrumen-tation differences, we are not able at this time to reach a similar con-clusion for all PWR's. Furthermore most PWR boron dilution analyses have i
been limited to addressing a malfunction in the makeup and purification system (chemical and volume control system). The incident discussed l
above is an example of a boron 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 dilution accidents at his facility.
You are requested to perform 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 terminate the postulated events prior to achieving reactor criticality.
If, based on the results of this analysis, you determine 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, 5D C kbertW.Re1d, Chief Operating Reactors Branch #4 Division of Operating Reactors cc:
See next page i
m
i Duquesne Light Company cc: Gerald Charnoff, Esquire Jay E. Silberg, Esquire Shaw, Pittman, Potts and Trowbridge 91 0 17th Street, N.W.
Washington, D.C.
20006 Karin Carter, Esquire Special Assistant Attorney General Bureau of Administrative Enforcement I
5th Floor, Executive House Harrisburg, Pennsylvania 17120 Marvin Fein Utility Counsel City of Pittsburgh 313 City-County Building Pittsburgh, Pennsylvania 15219 Mr. J. M. Cumiskey 3
Stone & Webster Engineering Corporation P. O. Box 2325 Boston, Massachusetts 02107 Mr. M. H. Judkins Westinghouse Electric Corporation P. O. Box 355 Pittsburgh, Pennsylvania 15230 1
Beaver Area Memorial Library 100 College Avenue Beaver, Pennsylvania 15009 Mr. Jack Carey Technical Assistant Duquesne Light Company P.O. Box 4 Shippingport, Pennsylvania 15077 Mr. R. E. Martin Duquesne Light Company 436 6th Avenue Pittsburgh, Pennsylvania 15219