ML20035G253

Requests Assistance in Resolution of Concerns Re Removal of Manual Scram Criteria for Power Oscillations from Plant Operating Procedures,W/Respect to NRC Bulletin 88-007, Suppl 1

ML20035G253
Person / Time
Site:	Limerick
Issue date:	02/04/1993
From:	Hodges M NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
To:	Varga S Office of Nuclear Reactor Regulation
References
IEB-88-007, IEB-88-7, NUDOCS 9304270048
Download: ML20035G253 (18)

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KING OF PRUSSIA, PENNSYLVANIA 19406-1415 FEB 41993 Docket Nos. 50-352 50-353 MEMORANDUM FOR:

Steven Varga, Director of Reactor Projects - I/II, NRR FROM:

Marvm W. Hodges, Director, Division of Reactor Safety, Region I

SUBJECT:

REQUEST FOR TECHNICAL ASSISTANCE ON POWER OSCILLATION ISSUES AT LIMERICK GENERATING STATION (TIA NO. RIDRS-934)l)

This memorandum requests NRR assistance in resolution of concerns about the removal of the manual scram criteria for power oscillations from the Limerick operatmg procedures. It does not appear to the inspectors that the Limerick procedures meet the criteria stated in NRC Bulletin No. 88-07, Supplement 1, " Power Osediation in Boiling Water Reactors (BWRs)." However, the licensee believes their procedures do meet the criteria.

Limerick removed the average power range monitor (APRM) peak to peak oscillation and periodic local power range monitor (LPRM) upscale or downscale alarms as procedure criteria for the recognition of thermal hydraulic instabilities requiring a manual reactor scram. 'Ihe facility representatives stated that the procedure revision was based on information contained in BWROG letter No. BWROG-92030, dated March 18, 1992, (Attachment 1). The deletion of the APRM and LPRM information could result in plant operation within a thermal hydraulic instability region and subsequent MCPR safety limit violation. Region I issued a deviation from Limerick's commitment to NRC Bulletin No.

88-07, Supplement 1, Core Thermal Hydraulic Instabilities (50-352/353/92-21-02, ).

Limerick's response stated that there was no deviation from commitments made in response to NRC Bulletin No. 88-07, Supplement 1. Their reply was provided to NRC in a letter dated October 16,1992, (Attachment 3). The response stated that Limerick adopted the recommendation contained in BWROG letter No. 92030, " Implementation Guidance for Stability Interim Corrective Actions." Region I contends that the BWROG letter did not require or suggest that facilities remove the existing APRM and LPRM criteria. It should be noted that other BWR plants in Region I, responding to the same information, added the new guidance contained in BWROG-92030 to the existing APRM/LPRM criteria committed to in NRC Bulletin No. 88-07, Supplement 1. Our view is that the Limerick action was not l

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fEB 46 also revised their recirculation pump trip procedure to initiab a manual reactor scram if both recirculation pumps trip. This action will place the plant in a safe condition before power oscillations could occur. Based on the above information, the Region will wait for the TIA response to resolve the issue.

To resolve and provide for NRC documentation of the acceptability of the preceding, Region I proposes that a Task Interface Agreement (TIA) be established lietween Region I and NRR. Specifically, we request that, for Limerick, the TIA encompass an NRR safety evaluation on the licensee's procedure change to resolve the procedure deviation issue.

Region I will support a meeting with the licensee, if necessary, to discuss the issue and assure NRR has all the facts in the case prior to writing the above requested safety evaluation.

The Region I point of contact is Sam Hansen, Operations Engineer, Boiling Water Section (FTS 215-337-5236). The NRR point of contact was Larry Phillips, NRR/SRXB.

N W-Marvin W. Hodges, Director Division of Reactor Safety Attachments:

1. BWROG Letter No. 92030

2. Report Excerpt No. 50-352/353/92-21

3. Limerick Deviation Reply

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F. arch 18. 1992 Page 2 the and the AT'!S issue, Solutions ial performance identified several potentlikelihood of en Ter:

stability work associated vith Long and GE have also During the are the Stability co==itteewhich nay reduceand after I.ons Ters solutions stability, are items related to are applicable improvementregion both in the near ter: benefits beyond thoseall Attachment 2 ts and Group which may have 2

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ifferences between Group I p an the to c:eet briefly summarized in Attachmenttypes, as there are d These items, necessary d solely to these items is not This information is being provide owners may of to all plant Implementation which individual II plants.

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improvements objectives of Bulletin 8 -of possible aware each owner reviewed by all owners for make find cost effective.

Atta:hment and 1 be training programs.

recoc= ended that88-07 51 procedures is In s'.:==ary, it Eulletin r infor=ation only.

their to applicationAttach=ent 2 is pro ided for you v

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SPECIFIC GUIDANCE The ICAs and Power / Flow regions defined in Bulletin 88-07 S1 were based upon operating and analytical experience available in late 1988 and remain appropriate for use as written until Long Term Solutions are in place (for those units requiring Long Term Solutions).

Implementing the following five additional items of specific guidance in training and procedures (as appropriate) will enhance the effectiveness of the Interim Correctiva Actions.

1.

ACTION WHEN OSCILLATIONS OBSERVED Bulletin 88-07 51 ICA #5 states:

"If at any time during operation in Region A, B or C, core thermal hydraulic instability occurs, the plant operator shall manually scram the reactor.

Evidence of thercal hydraulic instability consists of APRM peak to peak cscillations of greater than 10% or periodic LPRM upscale or downscale. alarms in addition to the guidance provided in SIL 380, Revision 1."

The Stability Committee recommends that operators be trained and retrained to scram the reactor when thermal-hydraulic oscillations are observed (see 2.

OSCILLATION RECOGNITION below).

The training should emphasize that a scram is required, even if the magnitude is below 107. on the APRMs and LPRM upscale or downstale alarms have not occurred.

Such training minimizes the potential for a safety limit violation (see REASONS FOR GUIDANCE 1.b).should a regional oscillation occur, and is censistent with a proactive reactivity management philosophy.

The requirement to scram upon recognition of an oscillation should also be c?ontained in station procedures.

Bulletin 88-07 S1 was clarified by the BWROG in Reference 4 as follows:

"Our interpretation o' Interim Corrective Action #5 was t

intended to identify the occurrence of multiple LPRM upscale or downscale alarms as only one of the possible indications of thermal hydraulic oscillations that would then cause subsequent verification of instability.

The BWROG agrees that the methods used to investigate the possible occurrence of instability include the evaluation of both APRM and LPRM noise and that EVIDENCE OF INSTABILITY REQUIRES AN IMMEDIATE SCRAM AT ANY TIME.

We wish to clarify that the BWROG recommendations place primary emphasis on exiting the restricted region (s) without delays to perform formal surveill ances.

In addition, operators are directed to manually scram the reactor if core thermal-hydraulic instabilities are observed while exiting the region (s)."

(emphasis added)

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SPECIFIC GUIDANCE (continued) 2.

OSCILLATION RECOGNITION (continued) i (continued) b.

The period meters (with the SR}is in the fully withdrawn position) have also been observed to show strong positive / negative swings during thermal hydraulic osciliations.

These swings will be of the same characteristic period describeo above.

Additionally, if four period meters are available frcm different quadrants (e.g. using four SRti locations), a regional oscillation can be discerned by cbserving whether each SM period is swinging positive then negative together (core wide oscillation), or if one or two SRMs are going positive the same time that others are going negative (regional or "out-of-phase" oscillation).

It should be emphasized that determining the type of oscillation is less important than recognizing that an oscillation exists.

c.

The LPRMs that are displayed during control rod withdrawal or insertion can provide early indications of potential thermal hydraulic oscillations.

Fcr additional corroboration or whenever conitoring or verification is needed, LPRMs should be c!oser selected and monitored from several different-areas of the reactor.

Cne way is to select control rods in each quadrant or octant of the core in a sequential manner. When the control rod is selected, the l

surrounding LPRMs will be displayed and can be monitored.

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remaining areas can then be monitored by selecting the remaining i

identified control rods.

I 3.

EXCLUSION REGION AND UNCERTAINTIES The stability exclusion region power / flow boundaries defined in the i

recent BWROG analysis results and bulletin have been reviewed against against oscillaticn events since the bulletin's issuance and determined to still be appropriate.

The Stability Committee now recommends that operator training and retraining programs include the following:

Caution should be used whenever operating near the region boundary, and it is best to minimize the amount of time spent operating near a.

the stability exclusion region.

The stability exclusion region bcundaries are not exact, but rather an approximate region where oscillations have been known to occur.

Furthermore, at lower powers and flows or when cperating in single ' loop, the uncertainties in measuring power and flow can increase.

Whenever exiting the stability exclusion region (i.e., whenever in b.

Regions A, B, or C of Bulletin 88-07 S1 and a scram is not otherwise required), carefully monitor L?RMs and APRMs.

Also monitor the LPRMs and APRMs whenever control rods are being withdrawn near the stability exclusion regionc 1-4

ATTACHMENT 2 POSSIBLE PERFORMANCE IMPROVEMENTS h

INTR 000CTION In addition to the Interim Corrective Action (ICA) guidance provided in Attachcent 1, the SWROG Stability Committee and GE have identified several potential stability-related performance improvements.

These potential The performance improvements are based on lesson learned type information.

goals of these performance improvements are to:

1.

Reduce the frequency of operational and transient entries into the stability exclusion region, 2.

Reduce the likelihood and severity of oscillations if a stability exclusion region is penetrated, and 3.

Avoid stability-related scrams.

The recommendations proviced below will provide stability performance improvements by reducing operational challenges prior to implementation of stability Long Term Solutions (LTS) and by providing a scram frequency reduction after a stability LTS has been implemented. All the recommendations provided herein are not applicable to e'ach plant.

They are provided for utility evaluation to determine if they are appropriate for specific plant implementation, including cost / benefit evaluations.

Much of this information has been previously expressed in various forms including EWROG stability related meetings, License Topical Reports for the BWROG, NRC meeting presentations, GENE Service Information Letters (Sits) and GENE Rapic Information Communication Service Information Letters (RICS!Ls) including the following:

SIL No. 380, Revision 1, February 10, 1984 (Reference 6),

o RICSIL No. 006, June 13, 1986 (Reference 7),

o RICSIL No. 005, Supplement 1, March 11, 1988 (Reference 8), and o

RICSIL No. 006, Supplement 2, April 12,1991 (Reference 9).

o The compiled and collated information provided below is' intended to facilitate each utilities' evaluation of their own possible plant specific stability performance improvements.

BACKGROUNQ Since the two recirculation pump trip event at LaSalle Unit 2 in March 1988, which resulted in a reactor scram from neutron flux oscillations, there has j

The been significant interest in-stability phenomena in the BWR industry.

BWROG is involved in an extensive program to respond to Bulletin No. 88-07 S1 i

by defining stability Long Term Solutions. There have also been extensive 2-1

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3;RC0 92030 1992 March 15, Page 2 j

the and the AI"JS issue.

f mance Term Solutions identified several potential per or work associated with Long stability likelihood of entering theimplemented.

l and GE have also During the are the Stability Co=mitteewhich may reduced after Long Term Solutionsrelated tolicable stability, are l

items region both in the near term anwhich may have benefits improve ent beyond thoseall Attachment 2 items are app d Group briefly su==ari:ed in Attachment differences between Group Not to meet the These ite=s.

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necessary lely to items is not types, as there are information is being provided so of these individval owners =ay all plant Implementation co 07 Sl.

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objectives of Bulletin 88of possible improvements each owner aware find cost-effective.

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is reco== ended that Attachmentprocedures and 88-07 Si In su:::ary, it Sulletinour information only.

their to applicationAttachment 2 is pro ided for y v

Sincerely.

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0 ifNITED STATES NUCLEAR REGULATORY COMMISSION 8

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KING OF PAUSSIA, PENNSYLVANtA 19406 3415 cy Docket Nos. 50-352 50-353 Mr. D. M. Smith Senior Vice President - Nuclear Philadelphia Electric Company Nuclear Group Headquarters Correspondence Control Desk P. O. Box 195 Wayne, PA 19087-0195

SUBJECT:

EXAMINATION REPORT NO. 50-352/353/92-21 (OL)

During the weeks of July 20,1992, and July 27,1992, the NRC administered initial examinations to employees of your company who had applied for licenses to operate the Limerick Unit 1 & 2 facilities. The evaluation addressed areas important to public health and safety and were conducted in accordance with Revision 6 (1/1/91) to NUREG-1021,

" Operator Licensing Eraminer Standards." The purpose of the evaluation is the examination of the individual operators to determine if they would satisfy the regulatory requirement of passing an NRC administered examination prior to license issuance. At the conclusion of the exammations, the preliminary findings were discussed with those members of your staff identified in the enclosed report.

The test results indicate that twelve of thirteen applicants passed the examination and were well prepared for the examinations. One Limited Senior Reactor Operator also passed a retake of the operating examination section B. Your staffis commended for their cooperation during the examination preparation and administration. Sections 3 and 4 of the enclosed' report contain additional details of the applicants' performance and the NRC Eraminers' observations.

As a result of this examination, we identified an apparent deviation from commitments made in response to NRC Bulletin No. 88-07 Supplement 1, which dealt with core thermal hydraulic instabilities. A revision to two plant procedures removed any reference to APRM peak to peak oscillations and periodic LPRM upscale or downscale alarms. These indications are used to monitor for thermal hydraulic instabilities. If they exceed certain criteria, a manual reactor scram must be inserted in order to prevent violating the Minimum Critical Power Ratio (MCPR), a safety limit. You are requested to respond to the enclosed Notice of Deviation (Appendix A), and you should follow the instructions in the attached notice.

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l APPENDIX A NOTICE OF DEVIATION, l

Docket Nos. 50-352/353 Philadelphia Electric Company Licensee Nos. DPR-39/85 Limerick Units 1 and 2 During an NRC examination conducted from July 20 through July 29,1992, a deviatio your written commitments made in response to NRC Bulletin No. 88M/, Supplement identified. In accordance with the, " General Statement of Policy and Procedure for NRC Enforcement Actions," 10 CFR Part 2, Appendix C (1992), the deviation is listed below:

In response to NRC Bulletin No. 88-07, Supplement 1, licensee letter dated March 7,1989, states that Philadelphia Electric Company committed that the General Electric interim stability recommendations were completed and implemented for Limerick Unit I and would be used for the operation of Unit 2. The following conditions for evidence of thermal hydraulic instabilities were incorporated into the approved plant procedures:

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" Average power range monitor (APRM) peak to peak oscillations greater than 10% or periodic local power range monitor (LPRM) upscale or downscale alarins in addition to the guidance provided in SIL 380, Revision 1."

Contrary to the above, Procedures OT-104, " Unexpected / Unexplained Reactivity Insertion," and OT-112, " Recirculation Pump Trip," were revised on June 12, 1992, such that it substantially changed so APRM peak to peak oscillations greater than 10%

or periodic LPRM upscale or downscale alarms are not now considered evidence instability.

Document Control Please provide to the U.S. Nuclear Regulatory Commission, ATTN:

j Desk, Washington, DC 20555 with a copy to the Regional Administrator, Region I and a copy to the NRC Resident Inspector within 30 days of the date of this Notice, the re the deviation, the corrective steps which have been taken and the results achieved and the corrective steps which will be taken to avoid further deviations, and the date when your corrective action will be completed. Where good cause is shown, consideration will be given to extending the response time.

Dated M/W @%ne, A' this /N day ofS2199-

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3.

Period meters display strong positive to negative swings (with approximately 1 to 2 second oscillation period).

I The facility representatives stated that the procedure revision was based on information contained in BWROG - 92030, dated March 18,1992, " Implementation Guidance for Stability Interim Corrective Actions."

In response to NRC bulletin No. 884)7, Supplement 1, in a letter dated March 7,1989, Philadelphia Electric Company committed that the GE interim stability recommendations were implemented for Limerick Unit I and would be implemented for Limerick Unit 2. The committed conditions (interim corrective action 5) for evidence of thermal hydraulic instabilities are, in part, as follows:

"APRM peak to peak oscillations greater than 10% or periodic LPRM upscale or downscale alarms in addition to the guidance provided in SIL 380, revision 1."

The procedure change of June 12,1992, appears to have been made without consideration of the previously made written commitments to the NRC staff. 'Ihis is an apparent deviation from a licensee written commitment (352/353//92-21-01).

Further, it appears to the NRC staff that, when compared to the written commitment, the new procedure no longer contains discreet, easily identifiable criteria for the operator to determine when thermal hydraulic instabilities exist. This lack of clear criteria could lead to a subjective identification of conditions that require a manual reactor scram to prevent a Minimum Critical Power Ratio (MCPR) safety limit violation.

The facility representatives have independently identified potential implementation problems through Licensed Operator Requalification traming feedback. The facility is currently evaluating the concerns for usefulness of the revised procedure.

4.2 Drywell Spray - Low Pressure Injection Interlock During enmimtion development, NRC examiners noted a situation where the Residual Heat Removal (RHR) system could be operated outside its design limits. Such operation could occur if drywell spray was in service at the same time that the low pressure coolant injection (LPCI) system began injecting into the vessel. The effect of this spray-with-injection scenario (in contrast to just spray or just injection) is that with two flowpaths available, RHR pump runout could likely occur, with the loss of the RHR pumps on an overcurrent trip as the ultimate result.

The scenario leading to a two flowpath situation most likely would begin as a result of executing T-225, "Startup and Shutdown of Suppression Pool and Drywell Spray Operation."

Per T-225, if no loss of coolant accident (LOCA) signal exists at the time when sprays are directed, then jumpers are installed to override the LOCA logic requirement. By overriding

l PHILADELPHIA ELECTRIC COMPANY LIMERICK GENERATING STATION P. O. BOX 2300 SANKIDGA, PA 19464-2300 October 16, 1992 (215) 327-1200, EXT. 3000 Docket Nos.

50-352 50-353 DAVID R. HELWiG License Nos. NPF-39 vce entsiocur NPF-85 LiuCRCK CENERATING $TATION U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555

SUBJECT:

Limerick Generating Station, Units 1 and 2 i

Reply to a Notice of Deviation NRC Inspection Report Nos.

i 50-352/92-21 and 50-353/92-21 i

Attached is Philadelphia Electric Company's reply to a Notice of Deviation for Limerick Generating Station (LGS) Units 1 and 2, which was contained in the NRC Inspection Report Nos. 50-352/92-21 and 50-353/92-21 dated September 18, 1992.

The Notice of Deviation identified an apparent deviation from commitments made in response to NRC Bulletin No. 88-07 Supplement 1,

" Power Oscillations in Boiling Water Reactors

( BWRs), " dated December 30, 1988, which dealt with core thermal hydraulic instabilities.

The attachment to this letter provides a restatement of the deviation followed by our response.

If you.have any questions or require additional information, please contact us.

Very truly yours,

/'

l JLP:cah Attachment cc:

T. T. Martin, Administrator, Region I, USNRC j

T. J. Kenny, USNRC Senior Resident Inspector, LGS

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Attachment-Page 2 of 2 l

• 1. 1 Docket Nos. 50-352/92-21 50-353/92-21 for Stability Interim Corrective Actions."

Procedures OT-104 and i

OT-112 were revised to incorporate the follqwing BWROG-92030 recommended conditions for evidence of thermal hydraulic instabilities:

1 1.

Any LPRM or APRM noise signal grows by two or more times its initial noise level.

2.

The characteristic of the LPRM and APRM signals change from random to a regular periodic variation (with approximately 1 to 2 second oscillation period).

3.

Period meters display strong positive to negative swings (with approximately 1 to 2 second oscillation period).

I I

As a result of the revision to procedures OT-104 and OT-112, operators are expected to initiate a scram well before APRM peak l

to peak oscillations exceed 10% or LPRM upscale or downscale alarms are received.

Furthermore, the NRC staff has reviewed BWROG-92030, which is the basis for the current procedural guidance.

In a September 17, 1992, Nuclear Reactor Regulation staff presentation to the Advisory Committee for Reactor Safeguards the staff discussed the imminent issuance of an Information Notice which will endorse

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BWROG-92030 precautions.

i In summary, no deviation from commitments made in response to NRC Bulletin No. 88-07, Supplement 1 exists because the commitments made are bounded by the guidance in the current revisions to plant operating procedures, including OT-104 and OT-ll2.

APRM peak to peak oscillations greater than 10% or periodic LPRM i

upscale or downscale alarms are still considered evidence of instability-.

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