NRC Generic Letter 1981-18
| ML031080572 | |
| Person / Time | |
|---|---|
| Issue date: | 03/30/1981 |
| From: | Eisenhut D G Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| GL-81-018, NUDOCS 8106220468 | |
| Download: ML031080572 (5) | |
UNITED STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON, D. C. 20555March 30, 1981TO ALL LICENSEES OF OPERATING BWRs AND APPLICANTS FOR BWR OPERATING LICENSES(GENERIC LETTER No. 81-18)Gentlemen:
SUBJECT: BWR SCRAM DISCHARGE SYSTEM; CLARIFICATION OF DIVERSE INSTRUMENTATIONREQUIREMENT (Generic Letter 81-18)Reference: NRC Staff Safety Evaluation Report (SER) on BWR Scram DischargeSystem dated December 1, 1980We are aware that efforts are underway to implement permanent modificationsto the BWR Scram Discharge Systems that will comply with the criteriaproposed by the staff in the referenced SER.As a result of our continuing review, the staff has revised its positionon the requirement for diverse instrumentation. The following informationis being provided to enable our revised position to be factored into yourdesign modification efforts.Safety Criterion 3 of the staff SER (Reference) states:"The scram discharge system instrumentation shall be designed toprovide redundancy, to operate reliably under all conditions, andshall not be adversely affected by hydrodynamic forces or flowcharacteristics."The "acceptable compliance" section of the staff SER expanded this criterionto consider not only redundancy but also diversity. Two alternatives foracceptable compliance to meet the diversity requirement were given. Thesewere:"Alternative 1:(a) Provide additional (or substitute) level-sensing instrumentationfor the automatic scram function to include diversity as wellas redundancy. The diversity should, as a minimum, be achievedby level sensors that employ different operating principles formeasuring the water level;(b) For the instrumentation selected, demonstrate how common-causefailures; such as those identified by operating history andthose identified in the Forward to IEEE 379-1977 will beconsidered."81 0622 0oL/(
a --2-/"Al ternativxe-2(a) Utilize the existing type level sensors, i.e., float level switches;(b) Provide a demonstration that the cause of the damaged floats hasbeen identified and will be corrected or compensated for;(c) Provide a periodic test procedure (for on-line at power testingas well as for testing during and after shutdown) which helpsensure that testing-induced human error and adverse environmentalfactors will be minimized (requirement under surveillance criteria);and(d) Provide either:i. Additional (or substitute) level switches for automatic scramwhich are made by a different manufacturer; orii. Demonstrate that the diverse indication of SDV water accumulationprovided to the operator by an alarmed continuous monitoringsystem can provide adequate backup protection if the levelsensors (providing auto scram) should fail (note that operator'sresponse to a fast SDV fill event must be considered, i.e.,automatic air dump on loss of air)."We have reevaluated these methods of complying with the criteria and find themto be appropriate with the exception of alternative 2. with option (d)ii, andwith the clarification that option (d)i includes the overall float assembly,not merely the switch.We are deleting the option that allows credit for operator action on the basisof an ATWS consideration that allows no credit for operator action for aminimum of 10 minutes.Accordingly, Alternative 2.(d) for Safety Criterion 3 should be revised asfollows:(d) Provide additional (or substitute) float assemblies (includinglevel switches) for automatic scram which are made by adifferent manufacturer.We consider diverse instrumentation for the automatic level sensing systemon the Scram Discharge Volume to be a necessary and important provision thatwill enhance the overall reliability of the BWR Scram Syste
- L- --3 -We have concluded that the two compliance alternatives, as revised, allowsufficient flexibility to enable operation BWR licensees to implement thecriterion within the time allowed for permanent modifications (end of 1982).Please contact this office if we can be of further assistance.
Sincerely,cc: Service List 6401*BOILING WATER REACTOR LICENSEESDocket No. 50-293Pilgrim Unit 1Docket No. 50-245Millstone Unit 1Docket No. 50-325Brunswick Unit 1Docket No. 50-263MonticelloDocket No. 50-324Brunswick Unit 2Docket No. 50-133Humboldt BayDocket No. 50-10Dresden 1Docket No. 50-277Peach Bottom Unit 2Docket No. 50-237Dresden 2Docket No. 50-278Peach Bottom Unit 3Docket No. 50-249Dresden 3Docket No. 50-333FitzPatrickDocket No. 50-254Quad-Cities Unit 1Docket No. 50-259Browns Ferry Unit 1Docket No. 50-265Quad-Cities Unit 2Docket No. 50-260Browns Ferry Unit 2Docket No. 50-155Big Rock PointDocket No. 50-296Browns Ferry Unit 3Docket No. 50-409Lacrosse :-' c,Docket No. 50-321Edwin I. Hatch Unit 1Docket No. 50-366Edwin I. Hatch Unit 2Docket No. 50-331Duane ArnoldDocket No. 50-219Oyster CreekDocket No. 50-220Nine Mile Point Unit 1Docket No. 50-298Cooper StationDocket No. 50-271Vermont Yankee I .43 UI c~i-Lb tun ._ ( n1+/-; go-335oz37Th_ __- --_____uAC.4Ase X 5o1-0abe dA- OlA1A IS -qt ,- So,- ...-- 5 AJA 5va-3s 36 t0_3E* -* s h y~e2. -so-_5 -~ ~~ 57-3 5_ _ 7_ _ _ _0oi* A __ ... ._ _ .. ..X.. /5On, .--.I.4-A .-.LL( _1+ y 5a_ 4SS 350--1-<* 5, -35Ns+ 5c-355-~~ ~ ~ _c- '-V2