ML20247A555

Safety Evaluation Supporting Amend 62 to License NPF-29

ML20247A555
Person / Time
Site:	Grand Gulf
Issue date:	08/31/1989
From:	Office of Nuclear Reactor Regulation
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NUDOCS 8909120143
Download: ML20247A555 (7)

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- ~g UNITED STATES NUCLEAR REGULATORY COMMISSION n-j i-WASHINGTON, D. C. 205S5 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT.NO. 62 T0-FACILITY OPERATING. LICENSE.NO. NPF-29 SfSTEM ENERGY RESOURCES. INC.-

GRAND GULF NUCLEAR. STATION. UNIT.1 DOCKET NO.-50-416

1.0 INTRODUCTION

By letter dated December 19, 1988 (Ref. 1), as revised February 24, 1989 System Energy Resources, Inc., (SERI or the licensee) requested an amendment to Facili v Operating License No. NPF-29 for the Grand Gulf Nuclear Station, Unit 1, (GGNS-1.

The proposed amendment would change the Technical Specifications (TS) by deleting TS 3/4.3.10, Neutron Flux Monitoring Instrumentation, and modifying TS 3/4.4.1, Recirculation System. Figure 3.4.1.1-1, Power Flow Operating Map, would be changed to redefine flow stability regions. TS 3/4.4.1 would be changed to reflect the redefined regions of Figure 3.4.1.1-1.

The Bases for TS 3/4.3.10 and TS 3/4.4.1 would be changed to reflect the changes in TS. The proposed changes would alter some of the boundaries of, and allowed or required operation or' surveillance within re ions of the power-flow map with potential for thermal hydraulic stability THS problems. The submittal included a report (Ref. 2) describing methodology used to determine decay ratios (DR) associated with BWR THS, benchmarks of the methodology and sensitivity studies done for GGNS-1 comparing THS characteristics of General Electric Company (GE) and Advanced Nuclear Fuels (ANF) fuel assemblies. Discussions hatween the staff and SERI representatives, and the publication of NRC Bulletin 88-07, Supplement 1 (Ref. 3) resulted in SERI's letter dated February 24, 1989 (Ref. 4) submitting several changes to the proposed TS to comply with the Supplement, and additional information. The staff review of these submittals, particularly the report discussing methodology, has been assisted by NRC consultants at Oak Ridge National Laboratory (ORNL).

The proposed changes to TS 3/4.3.10, which is deleted, and to TS 3/4.4.1 and corresponding Bases bring surveillance and operations relating to THS more directly in line with the GE " Interim Recommendations for Stability Actions" (IRSA),whicharepresentedintheBulletinSupplement(Ref.3). These recom-mendations, along with other staff requests presented in the Supplement and in the initial Bulletin (Ref. 5), constitute current NRC recommendations for BWR THS related operations. They are the result of calculations and reviews by the NRC, the BWR Owner's Group (BWROG) and associated consultants following the LaSalle instability event of March 9, 1988. The Supplement requested that licensees implement the IRSA (and other associated requests) by modifying relevant procedures. Modification of TS was not specifically requested since it is expected that long-term solution implementation will begin within about 8909120143 890S?1 PDR ADOCK 05000416 P

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j a year. SERI has responded to the initial Bulletin and to the Supplement, and has indicated that the requested changes to operator training and procedures have been made for GGNS-1. They have also proposed the changes to the TS under ruiew here to provide a more direct correspondence between TS and procedures and to increase effectiveness of operator actions.

2.0 EVALUATI'ON The IRSA specify three regicns (A, B, C) on the power-flow map involving different degrees of allowed or prohibited operation. These are bounded by constant fiow lines or control rod lines (lines of flow variation with all otner reactor parameters, particularly control rod position, held constant).

Region A is above the 100 percent rod line (intercepts 100 percent rated power at 100 percent rated flow) and beluw 40 percent flow. Region B is between the 80 and 100 percent rod lines and below 40 percent flow. Region C is above the 80 percent rod line and between 40 and 45 percent flow. Deliberate entry into regions A and B is not permitted, and if it occurs immediate exit is required.

For a group 2 plant (such as GGNS-1) immediate scram is required in region A, while Mr region B control rod insertion or flow increase may be usec to exit.

Operations may be cor 1:ted in region C, with suitable surveillance, if required during "stai ups" to prevent fuel damage.

If during operations in B or C instability occurs, the reactor shall be scrammed, with evidence for instability coming from Average Power Range Monitor (APRM) oscillation greater than 10 percent or Local Power Range Monitor (LPRM) upscale or downscale alarms.

lamentation of the IRSA, the Bulletin Supplement requested In :ddition to imp (1) reactors in IRSA group 2 (such as GGNS-1) to initiate an licensees with:

immediate scram for a trip of both recirculation pumps, (or "no pump operating")

when in the RUN tode, and (2) reactors with fuel other than that supplied by GE to evaluate and justify the A, B, C region boundaries to be used based on operating experience, calculations and/or DR me surements.

The latter request was because the IRSA boundaries were based primar ?ly on experience with reactors using GE fuel,,

The present SERI submittal:

(1) proposes changes to the THS TS so that the specified power-flow map THS boundaries, operations and surveillance correspond to IRSA, and add the NRC requested scram for "no pumps operating," (2) shows by analyses and operating tests and experience that IRSA boundaries, based on GE fuel experience, are suitable for the ANF supplied GGNS-1 fuel, and (3) describes and justifies the methodology, primarily RETRAN, used in sensitivity studies to compare DRs for ANF and GE fuel loadings.

The proposed TS changes consist of the deletion of TS 3/4.3.10 and extensive changes to the THS sections of 3/4.4.1 (and Figure 3.4.1.1-1).

Currently TS 3/4.3.10 provides requirements for using the APRM and LPRM noise levels as a monitor of instability.

It requires establishment of a base noise level for those detector systems and provides limits on the magnitude of noise. increase allowed (or departure from the region) when operating in region I of current figures 3.4.1.1-1.

Stability monitoring in the proposed TS is provided in TS 3/4.4.1, and corresponds more closely to the IRSA indicated monitoring.

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. l Proposed changes to TS 3/4.4.1 affect only the sections relevant to THS (although the order of some other sections is changed). The primary changes are to Figure 3.4.1.1-1 altering the current region boundaries and designations so that they correspond to the IRSA regions. This changes the boundaries of current region I sometvhat (and changes the designation to region C) and separates current region IV into IRSA regions A and B.

The Specification prohibits operation in region A and B, and to some extent in region C.

It requires, if the regions are entered, departure by scram in region A and by control rod insertion or flow increase (if a recirculation pump is operating at fast speed) in region B ard C.

(Bulletin, Supplement 1, allows entry into, and through, region C for flow increase depcrture from B.)

Operation in region C is permitted for control rod withdrawals during startup for required fuel conditioning.

(This would include restart or power increase from zero or low power conditions, but not other types of operations in region C, e.g., rod pattern exchange.) The TS also requires immediate scram, when the l

reactor mode switch is in the RUN position, when both recirculation pumps are not operatin (This does not include deenergizing during pump speed transfers.)g.This is in compliance with the staff request in the Bulletin Supplement.

During operation in region B or C, while departing from the region, and for region C during allowed operations, the TS require surveillance of significant oscillation potential via monitoring of APRM neutron flux level. A 10 percent (of rated power) peak-to-peak nt,ise level (typical steady-state normal noise level is about 2 to 6 percent) requires immediate scram.

In addition procedures require monitoring of LPRM upscale /down W e alarms as recommended by IRSA.

These TS changes and additions and procedures appropriately implement the reconnendations and requests of the Bulletin Supplement for operations within the specified regions of the power-flow map. The proposed TS are acceptable.

The Bases for TS 3/4.3.10 have been removed and for TS 3/4.4.1 have been changed and extensively augmented to describe the regions, operations and requirements. These changes are also acceptable. The acceptance Jf the region boundaries used in these TS assumes that the boundaries are applicable to the ANF fuel loading currently used in GGNS-1. That assumption is considered next.

GGNS-1 has changed from a first cycle all GE 8x8 fuel loas ng (via approximately equal increases of ANF fuel each cycle) to an all ANF 8xf fuel loading in l

Cycle 4.

(There are 4 ANF 9x9 Lead Test Assemblies in Cycle 4, but these should have no significant influence on THS.) Current GGNS-1 region I boundaries are based on ANF calculations using COTRAN and (previous) NRC criteria on DR limits for region boundaries. SERI has proposed in the submittal that the COTRAN calculations are too conservative because they did not include significant parts of the reactor system. They propose that stability characteristics of the ANF and GE fuels, and other core THS parameters are very similar, and thus the overall DR characteristics of the reactor are essentially the same for the GGNS-1 ANF 811 fuel cores or for a GE 8x8 core.

Thus the IRSA region boundaries, based or JE fuel experience, are also applicable to GGNS-1. As the basis for the proposec similarity in THS characteristics, SERI has discussed (1) the physical similarity of the ANF and GE fuel and core design

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. and normal vakiations, (2) calculation sensitivity studies (Ref. 2) using the RETRAN-frequency domain methodology and the resulting comparisons of the ANF and GE fuel.and core THS ci.aracteristics and DR (including the DR for the four>

GGNS-1 cycles with varying ANF/GE fuel ratios), and (3) the stability measurements made at GGNS-1 (by ORNL for the NRC).

2 The staff and' ORNL consultants have reviewed these stability calculations, as well as the methodology used for the calculations and the justification for I

the methodology, the sensitivity studies and ANF/GE comparisons, and the experimental tests (by ORNL) at GGNS-1. This review has concluded that the relevant fuel assembly and core reload parameter characteristics and variations are sufficiently similar to expect similar reactor DR, and fuel and core calculations confirm that expectation.

Furthermore, parametric calculations over a range of reactor conditions performed at ORNL with the LAPUR stability code support the SERI position that there is no significant overall difference in reactor stability for GE and ANF 8x8 fuel loadings. Differences between GE aad ANF fuel DR for specific fuel parameters are small and generally tend to cancel out when combined. The stability tests at GGNS-1, while not conclusive (because of the restricted range of the tests), provide additional evidence for margin to instability with a significant loading of ANF fuel. The review has thus concluded that the stability characteristics of the ANF fuel currently used in GGNS-1 are sufficiently similar to GE 8x8 fuel that the IRSA region boundaries may be used for 6GNS-1. This conclusion applies only to the ANF 8x8 fuel and not, for exanple to ANF 9x? fuel, which has not been reviewed here.

Reloads with other fuel will require reevaluation.

The staff and ORNL consultants have also re;iewed the RETRAN methodology (Ref.

2) used for the stabili!y calculations and the benchmarking of the methodology.

It is based on the RETRAN ti4 mal hydrau'ics, using point kinetics fci the neutronics. The THS calculation examire the transients following an inposed pressure decrease and use a Fast Fourier Transform to the frequency domain frcm which a DR can be obtained. The code Sas been benchmarked against noise analysis stability data from GGNS-1 during Cycle 2.

The agreement is reasonable, but the range of DR is limited. Results from the code have also been compared to results from GE and ANF calculations with reasonable agreement. The review has indicated that, while there are several modeling assumptions that can adversely affect stability calculation accuracy, the overall methodology is reasonable and acceptable within limits. The staff did not directly att~empt to consider more than the methodology role in the present TS review, and for that role concludes that the code is useful for scoping calculations and for comparative analysis such as ul involved in the ANF/GE comparisons, and is thus acceptable as used in the present submittal.

Based on its the review, the staff concludes that the propused TS changes and the material submitted to support the changes are acceptaale.

It should be noted, however, that the NRC staff, its consultants, BWR0G, GE and others are continuing the review of THS concerns.

The BWROG is developing several long term solutions for the problem.

It is expected that a selection will be announced by the end of 1989. Any new requirements resulting from the continuing generic review of THS concerns and BWP0G long-term solutions will be applicable to GGNS-1 and may impact some of the operations, systems, surveillance or TS found to be acceptable in this review.

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, In summary, we have reviewed the reports submitted t;y SERI for GGNS-1 proposing TS changes relating.to THS requirements for power-flow map operating restraints and surveillance. We have also reviewed the plant THS experience and tests, and the sensitivity studies, comparative core DR calculation and the accompanying methodology description and benchmarking. Based on this review, we conclude that appropriate documentation was submitted, staff questions were

appropriately responded to and the proposed TS changes satisfy staff positions E

and requirements in these areas. Operations with GE or ANF 8x8 fuel in the regions and in the modes proposed by SERI are acceptable.

(Other fuels are not included in this review.) This conclusion may be subject to future review based Jon results from the staff continuing generic review and conclusions on long term solutions. We further conclude that the RETRAN-frequency domain methodology described in Reference 2 is sufficiently justified for use in DR-sensitivity and

'GE/ANF core stability comparisons as used in this submittal. However, we have not concluded at this time that the methodology has been justified for use in any wider _ area.

3.0 ENVIRONMENTAL CONSIDERATION

This amendment. changes a requirement with respect to the installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and changes to the surveillance requirements.. The staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the ty' pes, of any effluents that may be released off site; and that there is no significant increase in individual or cumulative occupational radiation exposure. The Connission has previously issued a propt sed finding that this amendment involves no significant hazards consideratici and there has been no public comment on such finding. Accordingly, this amendment meets the eligibility criteria for categorical exclusion set forth in 10 CrR 51.22(c)(9).

Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of this amendment.

4.[~ CONCLUSION The Commission made a proposed determination that this amendment involves no significant hazards consideration, which was published in the Federal Register (54 FR 23324) on May 31, 1989, and consulted with the State of Mississippi. No j

public comments or requests for hearing were received, and the State of Mississppi did not have any comments.

The staff has concluded, based on the considerations discussed above, that:

(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the p oposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations and the l

issuance of this amendment will not be inimical to the connon defense and the security, or to the health and safety of the public.

Principal Contributor:

H. Richings Dated:

August 31, 1989

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.4.

v. L Referency-1.-

Letter and enclosurt;, from W. Cottle, SERI, to NRC, dated December 19,1988, " Reactor Core Stability, Proposed Amendment to Operating License."

2.

NESDQ-88-005, " Boiling Water Reactor Core Reactivity Stability Methodology,- Sensitivity and Benchmark Analyses," dated

' December 1988.

3.-

NRC Bulletin'No. 88-07 ' Supplement 1. " Power Oscillations in BoilingWaterReactors(BWRn"datedDecember 30, 1988.

4.

Letter and enclosures from W. Cottle, SERI, to NRC, dated February 24, 1989, " Response to RAI in Support of Proposed

' Amendment on Core Stability."

5.-

NRC Bulletin No. 88-07, " Power Oscillations in Boiling Water Reactors (BWR)," dated June 15, 1988.

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