ML20126H321

Forwards Summary of 921209 Meeting Between BWROG Regulatory Guide 1.97 Committee & NRC to Discuss BWROG Recent Assessment of Adequacy of Rod Position Indication for post-accident Monitoring

ML20126H321
Person / Time
Issue date:	12/28/1992
From:	Newberry S Office of Nuclear Reactor Regulation
To:	Tully C SOUTHERN NUCLEAR OPERATING CO.
References
RTR-REGGD-01.097, RTR-REGGD-1.097 NUDOCS 9301050142
Download: ML20126H321 (1)

Text

,

DEC 2 81992 l

Ms. Cynthia L. Tully, Chairperson BWR Owners Group c/o Southern Nuclear Operating Company P.O. Box 1295, Bin BOS2 Birmingham, Alabama 35201

SUBJECT:

BOILING WATER REACTOR OWNERS GROUP (BWROG) ASSESSMENT OF ADEQUACY OF R0D POSITION INDICATION FOR POST-ACCIDENT MON 110 RING This letter forwards a copy of the summary of the December 9, 1992, meeting between the BWROG Regulatory Guide 1.97 Committee and the Nuclear Regulatory Commission (NRC) to discuss the BWR0G's recent assessment of the adequacy of rod position indication (RPI) for post-accident monitoring.

We appreciated the opportunity to comment on the assessment methodology prior to the report being finalized.

The NRC staff concluded that the event analysis methodology described by the BWROG was reasonable.

However, we could not comment on the assessment results or conclusions without completing a detailed review of the report.

We understand that the BWROG's report on the assessment of the adequacy of RPI for post-accident monitoring will likely be provided to the NRC staff in late February 1993.

We look forward to receiving this report and appreciate the BWROG's assistance in providing input for our consideration in addressing an important NRC staff action.

Sincerely, Scott F. Newberry, Chief Instrumentation and Controls Branch Division of Reactor Controls and Human Factors Office of Nuclear Reactor Regulation

Enclosure:

Meeting Summary Distributiog.

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December 21, 1992 BOILING WATER REACTOR OWNERS GROUP MEETING

SUMMARY

OF DECEMBER 9, 1992. MEETING WITH BOILING WATER REACTOR OWNERS GROUP (BWROG) REGULATORY GUIDE 1.97 COMMITTEE TO DISCUSS ADEQUACY Of ROD POSITION INDICATION DESIGN The subject meeting was held on December 9, 1992, at the Nuclear Regulatory Commission (NRC) Headquarters at One White Flint Norta in Rockville, Maryland.

The meeting was requested by the BWROG to discuss their recent assessment of the adequacy of rod position indication (RPI) for post-accident monitoring. 1: a list of attendees and Enclosure 2 is a copy of the handout material provided by the BWROG.

The BWROG representattves initially discussed the events that resulted in their assessment of RPI.

Specifically, all RPI was lost as a result of the

'ailure of a nonsafety-related uninterruptible power supply (UPS) during the incident at Nina Mile Point Unit No. 2 on August 13, 1991.

The NRC incident Investigation Team (IIT) noted that loss of RPI required the operators to enter the anticipated transients without scram contingency procedures and complicated their response to the incident.

The Ili also noted that RPI is vulnerable to single failures such as the loss of a single UPS.

NRC staff actions resulting from the llT's investigation of the incident were identified in a memorandum from the Executive Director for Operations dated January 6, 1992.

Item 2.c of the NRC Staff Action Plan was related to the IIT's RPI observations and required the Office of Nuclear Reactor Regulation to evaluate the need for alternate RPI or for providing safety-grade power to RPI systems.

The BWR0G agreed in discussions with NRC management to independently assess the adequacy of RPI for post-accident monitoring and provide the results of this assessment to the NRC for the agency's use in addressing item 2.c.

The BWROG completed this assessment and requested the subject meeting to solicit NRC staff comments on their methodology prior to providing the staff with a final report.

The BWROG representatives subsequently provided an overview of RPI designs, cperator uses of RPI, and of the event analysis methodology used in the BWROG assessment of the adequacy of RPI for post-accident monitoring.

In essence, the BWROG examined a broad spectrum of events within and somewhat beyond design basis.

Events examined included transients with scram, accidents with scram, transients without scram, and other occurrences without scram.

The importance of RPI to the operator was evaluated for each event by determining the difference in plant response if RPI was or. was not available.

The assessment used Revision 4 of the Emergency Planning Guidelines (EPGs) as the bases for operator actions.

The assessment also considered the impact of the aveilability or unavailability of the neutron monitoring system (NMS) on the importancc of RPI.

The results and conclusions of the assessment of RPI were subsequently presented by the BWROG.

The BWROG determined that RPI is most important for events which appear to involve a failure to scram when in fact a scram did

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BWR OWNERS GROUP MEETING December 21, 1992 occur.

The RPI was also found to be important for events in which operators have an opportunity to manually insert control rods.

The assessment showed that RPI is not important for events where automatic response occurs very rapidly, where it is obvious that a scram did occur, or where it is relatively apparent that power is in the decay heat range.

The BWROG concluded that loss of RPI is not a safety concern, the EPGs adequately address indeterminate control rod position, and there is no basis for requiring either an alternate RPI or safety grade power to RPI systems.

At the conclusion of the meeting the NRC staff indicated that the overall methodology described by the BWROG seemed reasonable. The staff also stated that they could not comment on the assessment results and conclusions without completing a detailed review of the report.

The NRC staff also suggested that the BWROG consider quantifying the risks of losses of RPI and NHS and including these values in the final report.

The BWROG acknowledged the staff's comments and indicated that the final report would likely be provided to the NRC staff in late february 1993.

The BWROG also stated that they did not expect to receive a NRC staff evaluation of the rsport since they would be providing the report for the staff's internal use in addressing item 2.c.

E.

John E. Monning, P ject Manager Project Directorate 1-1 Division of Reactor Projects - 1/II Office of Nuclear Reactor Regulation

Enclosures:

1.

Attendance List 2.

Handout Material l

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ENCLOSURE 1 QECEMBER 9,_19R B0llit4G WATER REACTOR OWNERS GROUP MEETING R00 POSITION INDICATION DESIGN ATTENDANCE LIST Altendees Ornanization H. Garg NRC/NRR/HICB A. Marinos NRC/NRR/HICB S. Newberry HRC/NRR/HICB J. Menning NRC/NRR/PDI-l S. Marek Detroit Edison F. Kenny GPU Nuclear G. Stranovsky NYPA R. Patterson Entergy Operations J. Wolcott TVA C. Tully Southern Nuclear Co.

J. Post General Electric A. Attard NRC/NRR/SRXB L. Lois NRC/NRR/SRXB

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Meeting Between t

the BWROG Reg Guide 1.97 Committee i

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-Rod Position Information System (RPIS) Issues i

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Agenda JD Wolcott (TVA) 8:30 Introductions / Purpose 9:00 BWROG Approach and Analysis JS Post (GE) 10:30 Discussion / Staff Feedback BWROG/NRC 11:30 Adjourn l

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JD Wolcott-1 12/9/92

Introduction o

Loss of power event at NMP-2, August 13,1991, led to several Staff concerns regarding reactivity monitoring instrumentation o

BWROG/NRC Management discussions led BWROG to agree to assess adequacy of RPIS for post-accident monitoring as input to Staff o

Concern being addressed by this meeting is NRR Staff Action Plan Item 2c:

" Evaluate the need to provide an alternate Rod Position Indication (RPI) or safety grade power [to RPI] for BWRs."

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BWROG is soliciting Staff comments on the BWROG approach o

Current BWR RPIS designs fully comply with RG1.97 requirements for post-accident monitoring (Type B, Category 3 instrument)

JD Wolcott-2 12/9/92 L

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Purpose of Meeting.

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o Inform the Staff of the BWROG approach: Outline the bases,

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assumptions, scope, results, and conclusions V

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. Obtain Staff comments on' the BWROG approach g

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Discuss Staff schedule and BWROG plans for submittal of the report f

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BWROG Approach and Analysis i

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Summary of Approach l

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lo RPIS Description L

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o Use During Normal Plant' Operation L

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Basis for Event Analysis i

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o Events Analyzed 1

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o-Results-o I

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Conclusions.

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BWROG Approach and-Analysis - Summary of Approach -

' Document the RPIS description, design bases, and regulatory o

j requirements Examine RPIS use by the operator for normal operation and o

post-accident monitoring i

Perform three step event analysis process:

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Determine the impact of RPIS failure on the plant and operator response-2.

Use the impact assessment to determine RPIS importance for post-accident monitoring 3.

Use the importance to judge'if the existing RPIS system design e

is adequate i

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BWROG Approach and Analysis - Summary of Approach (continued)

Same event analysis method as used for the NMS evaluation in o

NEDO-31558, March 1988:

Examine a broad spectrum of events within and somewhat beyond the plant design bases Evaluate importance of RPIS to the operator for each event by determining the difference in the plant response if RPIS is available or fails Use EPG Revision 4 as bases for operator actions Consider the impact of NMS availability / failure on the RPIS importance JS Post-3 12/9/92

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-BWROG Approach and Analysis - RPIS Description t

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BWR/2-5 Designs:

RPIS is part of the Reactor Manual Control System (RMCS) f l

Meets plant power generation requirement to know control rod position-j e

i Controllers (Rod Worth Minimizer and Rod Sequence Control System) used to set / limit control rod positions - RPIS provides i

input'to controllers j

BWR/6 Designs:

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RPIS is part of the Rod Control & Information System (RC&IS) l Meets plant power generation requirement to know control rod i

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position.

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..Two channel Rod Pattern Controller used to set / limit control

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rod positions - RPIS designed as a two channel system to p_rovide input to the two RPC cht.nnels -

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.BWROGl Approach and Analysis - RPIS Description (continued)

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.o RPIS Position probe:

Each position probe is a sealed tube that fits inside the CRD r

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t Tube contains 53 magnetically operated reed switches i

i Switches at each increment (48; every three inches), extra switch t

at full-out, one at beyond full-out, two at full-in-(Notch 00), and L

one at beyond full-in (53 total) s The control rod locks at the even numbered (Notch) positions I'

The magnet is affixed to the hydraulic drive mechanism f

i BWR/6 has two independent sets of reed switches within the l

position probe for its two channel system j

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BWROG' Approach and Analysis - RPIS Description (continued)

I Variety of rod position displays across BWRs:

o Full core display with numeEical position of each rod and lights to indicate full-in and full-out

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. Full core display with indicating lights only Four-rod display to show'the position of a selected rod and the j

other rods in its immediate vicinity Process. computer, SPDS displays, etc.

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Power supplyis typically an UPS UPS has a backup power supply of a diesel, station battery, and/or

.o secondary power supply;

- RPIS power for.BWR/6 is typically from a Class 1E bus, but power lL o.-

for the operator display may be from an instrument UPS L

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BWROG Approach and Analysis - Use During Normal Operations RPIS used repeatedly during normal operations:

o Every time a rod is being moved to a new location j

As input for core burnup, peaking, and core performance calculations To perform various Tech Spec sun'eillances (e.g. control rod j

operability, coupling integrity, rod pattern requirements) 1 Provides an alarm if a rod drifts o

RPIS is input to the systems which restrict rod movements to set o

patterns Any system faults that occur would likely be discovered and o

corrected during normal operations The locking control rod drive mechanism makes a rod unable to o

withdraw once it is locked JS Post-7 12/9/92

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BWROG' Approach and Analysis - Basis for Event Analysis -

p rI Examine operator and plant response if reactivity monitoring l

o instrumentation is available 'or has failed:

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Both RPIS and NMS instruments work f

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RPIS fails, but NMS functions correctly J

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RPIS and NMS both fail p

o Events selection criteria:

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RPIS information is most useful to the operator i

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Full spectrum of operator actions related to post-accident l

shutdown are exercised i

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- Spectrum of conditions the operator must evaluate occur

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Impact on plant and operators if RPIS fails are maximized 4

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BWROG Approach and Analysis - Basis for Event Analysis (conte) i i

Use generic BWROG EPG Revision 4 as basis for operator actions o

Possible post-accident monitoring uses of RPIS by the operator:

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Determine that all rods are fully inserted Determine that control rods are sufficiently inserted so that the reactor will remain shutdown as reactor state conditions change Determine if the reactor is critical, or the reactor is shutdown 4

Determine candidate control rods for rod insertion' actions following scram failures

- Monitor the effectiveness of rod insertion attempts JS Post-9 12/9/92

BWROG Approach and Analysis - Events Analyzed

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Consider events within and somewhat beyond plant design basis:

Transients with scram s

o Feedwater centroller failure - maximum demand o Turbine trip with bypass failure

Accidents with scram o Large break LOCA with ECCS division failure o Small break LOCA with high pressure makeup failure o Control rod drop accident.

Transients without scram -

o MSIV closure with complete scram failure o Inadvertent open SRVwith partial scram failure i

Other occurrences without scram -

s o L Recirc pump seal leakage with manual scram which fails l

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o : Loss of drywell coolers, failure to scram L

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BWROG Approach and Analysis - Events Analyzed (continued)

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Impact of Impact of Add'nl Event Use of RPIS RPIS Failure NMS Failure FWC-Max Confirm all Enter ATWS EOP, Delay RPV Demand rods in few actions reg'd cooldown TT with ditto ditto ditto Bypass Failure Large ditto ditto Possible boron LOCA.

injection Small ditto Enter ATWS EOP, Expected boron LOCA terminate and injection and prevent injection waterlevel prior to ADS reduction CRDA ditto None None JS Post-11 12/9/92

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BWROG Approach and Analysis - Events Analyzed (continued)

Operator Impact of Impact of Add'nl Event Use of RPIS RPIS Failure NMS Failure MSIV Determine None None Closure rod pattern ATWS SORV Determine Less effective Accelerate boron Partial rod pattern, in driving rods injection ATWS prioritize rods to drive Recire ditto ditto None - boron pump seal injection not leakage required ATWS Loss DW ditto ditto ditto Coolers ATWS JS Post-12 12/9/92

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BWROG Approach and Analysis - Results o

RPIS most important for events which may appear to have a scram failure when in fact a scram did occur i-o RPIS also important for events with an opportunity to drive control rods o

RPIS not important for events where the automatic response occurs very rapidly, where it is obvious a scram did not occur, or where it is relatively apparent that power is in the decay heat range I

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JS Post-13 12/9/92

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BWROG Approach and Analysis - Conclusions o-Loss of RPIS is not a safety concern 4

EPGs adequately address indeterminate control rod position o.

I oi No basis for requiring either an alternate RPIS or safety grade power to RPIS 1

JS Post-14

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