ML19319B487
| ML19319B487 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 09/16/1977 |
| From: | Stolz J Office of Nuclear Reactor Regulation |
| To: | Roe L TOLEDO EDISON CO. |
| References | |
| TAC-8378, NUDOCS 8001220896 | |
| Download: ML19319B487 (3) | |
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e SEP 16 1977 Cociet No. 50-346 Toledo Edison Conpany ATIN:
Hr. Lowell E. Roe Vice President, Facilities OO Develos:ent D
D Edison P1aza O V[ 'j 300 Madison Avenue Toledo, Ohio 43 tis 2 0
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RE: CAYIS 3 ESSE tlNIT NO.1 Recently at an operating P'A facility, a linited baron dilution incider t occurred due to tee inadvertent injection of a portion of the contents of the haGu tank into the reactor coolant system while the reactor was in the cold snutdown condition. While performino surveillance testicq (valve cycling) of the NaOH tank isolation valyc, wi 6 the C: cay beat Pencv31 (DnR) system lined up for reactor c::olar t recirculation, 3 partien of the tank's contents drained into tne DhR systec. lipon resumotion of cooldr.t recirculation this HaOH was injected into the reactor coolant systen.
In the aoove-eentioned case, only a limited anount of M3CH (accrcximately 600 callons) was injected and the reactor remained subcritical by a lar';e nargin. homver, this event highlighted the fact that a postulated single failure at this facility (i.e., nisposition of the isolation valve for t;e NaGH tant w+:en the GUR systen is lined up for recirculation or operating in the recircul3 tion ucce) could re, ult in a : odernor dilution incident wnich had riot been previously considered. SUDsequent Jealysis oy tne licensee and his vendor revealed that, for cortain conservative asstr.ptions (e.g., reactor in the cold shutdown condition, vessel ter:;erature less than 100 F, beginning of core life characteristics, vessel drained to a level approxinately equal to the height of the outlet nczzle, lowest inital 3cron concentration allowed by Technical Specifications, the maxinun wortt control rod stuck in the fully out position, and no credit assu'1ed for oparatar action), the injection of.the NaOH tcnk contents into the reactor coolant system due to the misposition of a single isolation valve could result in reactor criticality with the control roos inserted.
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Toledo Edison Company
-2 SEP 16 1377
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Based upon our review of this particular incident, we concluded that the assumption that operator action would not be taken in st.f-ficient tice to teminate the event prior to reactor criticality would be overly conservative. This determination ww influenced by the lengtn of the dilution the necessary before return to criticality and by the number of indications and alarms available to tne cperator at this facility. Due to plant-soecific systemi design and instru'ren-tation dif ferences, we are not able at this time to reach a similar con-clusion for all PWR's.
Furthemore nest PWR boron dilution analyses have been linited to addressing a malfunction in tr.e nakeup and purification systen (chemical and volume contr 1 systen). The incicent discussed above is an example cf a boron dilution accident not covered by these analyses. Therefore we are requesting that eacn licensee of a N't facility provice an analysis of the potential for and consecuences of Doron dilution accidents at his facility.
You are recuested to perfom and suunf t the results of such an analysis uithin 90 cays of receipt of In1s letter.
Your analysis shoulq oc nascd epon conservative assumptions consistent sith the design of your facility and your Technical Specifications and shculd include the assu:nction of the most limiting sinqle failure. The analysis should also include an assess-cent of the factors which affect the capability of the operator to take corrective action which would teminata the postulated events prior to achieving reactor Criticality.
If, based on the results of this analysis, you detamine that corrective actions (design or procedural) are required to precluoe the occurrence or itigate the consequences of ocstulated boron dilution accidents, yow response should incluce croposals for such actions.
mmm Sincerely, D
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Orldnni Signed bf n
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John F. Stolz U
John Stolz. Chief Light Water Reactors Branch fl Division of Project Management cc: See ext page DISTRIBUTIO DocketY LWR #1 Rdg EHylton OELD-JRBuchanan NRC PDR Glear PWagner 0I&E (3)
ACRS (16)
Local PDR JStolz LEngle DEisenhut File ORB #3 Rdg CParrish CNelson TBAbernathy ORB V LWRO A LWlHil ORB #3 i
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.-[oledo Edison Company g r_,- t.; 07 cc:
Donald H. Hauser, Esquire Cleveland Electric Illuminating Company P. O. Box 5000 Cleveland, Ohio 44101 Gerald Charnoff, Esquire Shaw, Pittman, Potts & Trowbridge 1800 M Street, fl. W.
Washington, D. C.
20036 Leslie Henry, Esquire Fuller, Seney, Henry and Hodge 300 Madison Avenue Toledo, Ohio 43604 l
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