ML20056E091

SE Re Util 930614 Response to Bulletin 93-03, Resolution of Issues Related to Reactor Vessel Water Level Instrumentation in Bwrs. Util Justification for Not Implementing Addl Short Term Actions Acceptable

ML20056E091
Person / Time
Site:	Oyster Creek
Issue date:	08/04/1993
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20056E087	List: ML20056E086 ML20056E091
References
IEB-93-003, IEB-93-3, NUDOCS 9308190321
Download: ML20056E091 (2)

Text

.

ar%g nM 0 )

n G UNITED STATES i$ g g/ i NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 N .'.ss ... 4 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RESPONSE TO BULLETIN 93-03. " RESOLUTION OF ISSUES RELATED TO BEACTOR VESSEL WATER LEVEL INSTRUMENTATION IN BWRs" GPU NUCLEAR CORPORATION OYSTER CREEK NUCLEAR GENERATING STATION DOCKET NO. 50-219

1.0 INTRODUCTION

By letter dated June 14, 1993, GPU Nuclear Corporation (GPUN/ licensee), for Oyster Creek Nuclear Generating Station (OCNGS), submitted a 15 day response to Bulletin 93-03, " Resolution of Issues Related to Reactor Vessel Water Level Instrumentation in BWRs," issued May 28, 1993. This report explains why the licensee did not take the short term corrective actions requested by the bulletin.

2.0 EVALUATION The areas of concern addressed by Bulletin 93-03 involve water level instrumentation errors during normal reactor cooldown and the adequacy of operator guidance during an associated event. In particular, the bulletin addresses reactor pressure vessel (RPV) drain-down initiated during low pressure conditions. Automatic isolation signals based on low RPV level are normally credited for terminating these events. If there are large level errors in multiple instruments, automatic isolations may not occur.

In their response, the licensee summarized the water level measurement capability at 0CNGS and the associated protective functions. The plant uses both hot leg (Yarway) and cold leg (GEMAC) instruments. Yarway instruments provide water level signals used for emergency core cooling system (ECCS) and reactor protection system (RPS) actuation and reactor isolation. The Yarway instruments are not susceptible to errors resulting from non-condensible gases coming out of solution during depressurization. Since the isolation valves for the shutdown cooling system and the reactor water cleanup system are actuated by Yarway instrumentation, the concern that a drain-down scenario could occur during cooldown conditions without automatic isolation, as addressed by Bulletin 93-03, is not applicable to OCNGS.

Cold leg instrumentation, which is susceptible to the non-condensible gas concern, is used at Oyster Creek to sense the water level setpoint used for Automatic Depressurization System (ADS) actuation and control room indication.

The licensee cited the BWROG generic report which states that safety system actuations occur prior to the introduction of errors associated with non-9308190321 930804 PDR ADDCK 05000219 Q PDR

i condensible gases coming out of solution in cold leg instrumentation.

Therefore, ADS initiation occurs before the errors arise. With regard to operator guidance following an event, an NRC inspection (Ref. 5) found the '

licensee's implementation of recommendations made in Generic Letter 92-04, regarding emergency procedures and operator training on water level errors, to be satisfactory. Since the procedures currently in place at OCNGS apply equally to full power and cooldown conditions, no further procedural changes are needed.

Reactor Building Closed Cooling Water (RBCCW) also receives an isolation signal from cold leg instruments. However, since this system does not directly interface with the reactor coolant system, failure to isolate does not increase the potential for core damage from drain-down events.

3.0

SUMMARY

AND CONCLUSIONS The NRC staff has reviewed the licensee's interim response to Bulletin 93-03.

The instruments which would signal the automatic isolation of any systems with the capability to drain the RPV at Oyster Creek are not affected by the degassing phenomenon. In addition, emergency procedures and operator training implemented previously in response to NRC Generic Letter 92-04 applies to potential water level errors occurring during normal cooldowns. The licensee's justification for not implementing additional short term actions is therefore acceptable.

4.0 RffERENCES

1. Oyster Creek response to NRC Generic Letter 92-04, "BWR Reactor Vessel Water Level Instrumentation," September 29, 1992.

2. BWROG letter to William T. Russell (NRC), BWROG Report, " Supplementary Information regarding RPV Water Level Errors Due to Non-condensible Gas in Cold Reference legs of BWRs," May 20, 1993.

3. NRC Bulletin 93-03, " Resolution of Issues related to Reactor Vessel Water Level Instrumentation in BWRs," May 28, 1993.

]

4. Oyster Creek response to NRC Bulletin 93-03, June 14,1993.

5. NRC Inspection Report 50-219/93-09. ],

Principal Contributor: B. Korona ,

1 Date: August 4, 1993 l

I J

i