NRC Generic Letter 1984-23
| ML031180067 | |
| Person / Time | |
|---|---|
| Issue date: | 10/26/1984 |
| From: | Eisenhut D G Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| GL-84-023, NUDOCS 8410290050 | |
| Download: ML031180067 (2) | |
o UNITED STATESNUCLEAR REGULATORY COMMISSIONWASHINGTON, D. C. 20555October 26, 1984TO ALL BOILING WATER REACTOR (BWR) LICENSEES OF OPERATING REACTORS(EXCEPT LACROSSE, BIG ROCK POINT, HUMBOLDT BAY AND DRESDEN-1)Gentlemen:
SUBJECT: REACTOR VESSEL WATER LEVEL INSTRUMENTATION IN BWRs(GENERIC LETTER NO. 84-23 )The water level instrumentation in a BWR is relied upon for controllingfeedwater, actuating emergency systems, and for providing the operatorsinformation which is used as basis for actions to assure adequate corecooling. Many of the actions in the emergency procedures guidelines arekeyed to reactor water level.The NRC staff has reviewed the S. Levy, Inc. report SLI-8211, "Review ofBWR Reactor Vessel Water Level Measurement System," which was commissionedby the BWR Owners Group. The report provides a generic evaluation of waterlevel instrumentation adequacy of BWR/2 through BWR/6 plants and identifiesseveral improvements in BWR water level measurement and instrumentationsystems which will improve the reliability and accuracy of those systems.The staff has concluded that changes identified in the emergency procedureguidelines are adequate for the short term, but permanent physical improve-ments should be made on a deliberate schedule to reduce the burden on theoperator. Three potential improvement categories are presented below:O Improvements to plant(s) that will reduce level indication errorscaused by high drywell temperature. These improvements includeprevention of reference leg overheating or reduction of the verticaldrops in the drywell. (Vertical drop should be measured from thecondensation pot to the drywell exit point. Maximum drop would allowan indicated level at the bottom of the normal operating range whenactual level is just above lower tap for worst flashing condition.)Those plants for which the vertical drop in the drywell has alreadybeen minimized will not have to make additional changes for thedrywell heating effect.o Review of plant experience relating to mechanical level indicationequipment. Plant experience shows mechanical level equipment is morevulnerable to failure or malfunction than analog equipment. A numberof plants have already connected analog trip units to their leveltransmitters to improve reliability and accuracy. Those plants thatuse mechanical level indication should replace the mechanical levelindication equipment with analog level transmitters unless operatingexperience confirms high reliability. '~9OO
--2 -° Changes to the protection system logic that may be needed for thoseplants in which operator action may be required to mitigate theconsequences of a break in a reference leg and a single failure in aprotection system channel associated with an intact reference leg.Changes will generally result in additional transmitters to satisfythe single failure criterion. This improvement, under evaluation byNRC, may be needed in plants where an analysis has demonstrated avulnerability.Implementation of the first two categories of improvements will giveIncreased assurance that the level instrumentation will provide theinadequate core cooling instrumentation required by NUREG-0737, Item II.F.2and thereby safisfy this requirement. Please submit within 30 days adescription of your plans to implement these improvements and your proposedschedule.The last improvement is still being evaluated by the staff; hence it is nota requirement at this time. However, should the continuing evaluation showthat there is a significantly high priority. It will be identified as a newgeneric letter.This request for information was approved by the Office of Management andBudget under clearance number 3150-0065 which expires September 30, 1985.
Sincerely,Franki Miraglia/forDarrell G. Eisenhut, DirectorDivision of LicensingOffice of Nuclear Reactor RegulationDL: ORB #5CJamersonp /tp/84DL:ORB #5pJShea Y,6 //DL i #5WPaulson19 />3/84kDL~ii utDSI: DI ?RBerner6$/o /ZS/84DL.WADCrut hfield1o/t484