ML20032D518
| ML20032D518 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 11/06/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20032D512 | List: |
| References | |
| NUDOCS 8111170206 | |
| Download: ML20032D518 (4) | |
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'o UNITED STATES 4 NUCLEAR REGULATORY COMMISSION ss CASHINGToN, D. C. 20555
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S5FETY EVALUATION BY.THE' 0FFICE OF NUCLEAR REACTOR REGULATION g
1 SUPPORTING ' AMENDMENT NO. 26 TO PROVISIONAL OPERATING LICENSE NO. DPR-45 i
DAIRYLAND POWER COOPERATIVE LA CROSSE BOILQWATER RZACTOR
'O DOCKET NO.'50-409 I
.).0 INTRODUCTION i.
By 16tte'r dated June 1,1981, Dairyland Power Cooperative (DPC)(the licensee),
proposed changes to' Appendix A of the Technical Specifications for the La' Crosse Boiling Water Reactor (LACBWR). The changes involve revision to fuel exposure (b~ rnup) limitations for fuel assemblies not located on the periphery of the u
Core.-
2.0 BACKGROUND
The la Crosse Boiling Water Reactor (LACBWR), owned'and operated by the Dairyland Power Cooperative (DPC) in Wisconsin, is a 165 megawatt (thermal) plant, built by Allis Chalmers.
It is the only Boiling Water Reactor that utilizes ' fuel rods with stainless steel cladding, and it has had a history.
of fubl failure problems associated with stress corrosion cracking (SCC) df the stainless steel.
For exanple, as many as 26 of the ? fuel assemblies ccnstituting the LACB;'R r e. tere found to have some dcgree of fuel damage, including leaking rods and missing sections of rods (57 inches in one case),
at the end of Cycle 4 (Refs.1, 2).
As a result of a lengthy and comprehensive stRy of the contribu*i'- factors to the failures, a technical specif' cation on fuei assenciy bur:.,. a. 4.2.4.2.5) was imposed in March 197S as part of Amencment 11 to the license.
The burnup linitation was 15,000 Mh'D/MTU on all i
assemblies in the core. Subsequently, the maxinum allowable average exposure li-it (of any fuel assembly) was raised to 15,603 "Q/MTU.
To concensate for "e
W re ne in axi
.m alle. cable ex;cs se.
.e<< and cre restrictive limits were imposed on reactor coolant and off-gas' radioactivity (Ref. 3).
In Amend-
. ment 20 (Ref. 4), the burnup limitation was removed from fuel assemblies loca.ted on the periphery of the core in recognition of fact that operating experience had shown that the 28 outer fuel assemblies had had a much lower rate'of failure than the 44 interior fuel assemblies. This trend has been attributed to the lower power density along with reduced effects of control rod movements at the peripheral locations.
Amendment 20 to the LALBWR license was adopted in May 1980, during the middle of Cycle 6 operation.
At the end of that cycle, the assemblies with more than one cycle of operation were' examined visually and by dry sipping.
Only one
" probable" leaker was found, thus demons'trating that the combination of voluntary cperating restruction:, burnup limits, and some fuel design changef was resulting in improved fuel performance.
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3.0 DISCUSSION AND EVALUATION The current license change request (Ref. 5) is to delete the maximum exposure (burnup) limitation on LACBWR fuel (Technical Specification 4.2.4.2.5).
An associated technical specification (No. 5.2.17.5),.which addresses periodic evaluation of the maximum average exposure of each fuel assembly not on the---
periphery of the corc, would also be removed.
DPC's rationale.for. the removal of these technical specifications is that the fuel damage problems encountered in previous cycles of operation were confined to Type I and II (Allis-Chalmers) design fuel, which has been replaced (except for two previously exposed Type I A-C assemblies) with Type III Exxo.n fuel. Since 58 of the 72 assemblies irradiated during Cycle 6 were Exxon Type III assemblies, since only one of the 46 assemblies sipped was a " probable" leaker, and since that one assembly
' was a Type II (A-C) assembly, the implication is strong that the improved fuel performance is primarily attributable to the new design (which has a thicker cladding and larger as-fabricated pellet-to-cladding gap). ' Mechanistically, the thicker cladding and larger gap are design features that should reduce pellet / cladding interaction stresses, and this should improve the stress corrosion cracking resistance of-the stainless steel-clad rods.
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It is clear, however,_ that the changed fue1 design is not the sole factor in the improved fuel performance.
During Cycle 6 operation,14 of the 72 fuel assemblies were previously irradiated Allis-Chalmers designs, yet only one was identified as a " probable" leaker at E0C 6.
Based on prior operation statistics, larger numbers of failures might have been expected if fuel design alone were important.
As noted by DPC in the most recent license amendment request (Ref. Sa), "the restrictions on rate of power escalation and rate of control rod withdrawal... and judicious reload planning to limit power density increases in the fuel, also contribute to good fuel performance." We agree with that assessment and we understand that DPC will continue to implement the restrictions on rate of power increases and control rod movement listed in Table I of LAC-TR-096 (Ref. Sb) and to continue the policy of attempting to locate previously irradiated assemblies in positions in 'the core (generally on the periphery) where the power level will not exceed the peak power achieved during the previous cycle of operation While we,are encouraged by the greatly improved perfonnance of LACBWR fuel during Cycle 6 and 7 we believe it would be imprudent to completely remove all burnup limitations since the reduction in peak burnup (of assemblies not ia the pe-iphery of the core) may also have been a key factor in the observed improvement in fuel performance.
It is well known that certain stainless steel components are susceptable to stress corrosion cracking in BWR environments, so it seems advisable to increase the burnup limit gradually on a step-by-step basis. We, therefore, coiclude that Technical Specification 4.2.4.2.5 should be amended to permit the maximum average exposure of any fuel assembly not on the periphery of the core to reach 16,800 MWD /MTU,
Technical Specification 5.2.l'.5 concerning the calculation of exposure is also amended accordingly.
s.
'l The increase of 1200 MWD /MTU in the'burnup limit is exactly.twice that approved in-Amendment 19 (Ref. 3). To. assure that an. increase of this magnitude does not result in increased number of fuel failures, the licenree will continue to_ closely monitoring of the off-gas and reactor coolant activity levels in accordance with the provisions of-the Technical Specifications, and if there is an activity increase of a magnitude commensurate.with the. onse.t of_ additional fue.l..failu.re.s,. a,n.
estimate-of the number of ' failures will be made and' provide to NRC. We further understand that the licensee will examine all fuel assemblies at the next-refueling outage, both vis'ually and by dry sipping, to confirm t' at additional leakers have not occurred or to identi.fy the.
2
" location of suspected 21eakers. ~ Examinations of fuel assemblies ~ at future refuelings will be dependent upon fuel.per.formance during #
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hubsequenti cyclesk E - -
'We therefore concidds'that 't!hde 'is reasonable as's'urance'i.h'aY t'he
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extension of the burnup limit on LACBWR stainless steel fuel rods to 116;800 MWD /MTU will not result in a danger to the health and safety of the public.
Further extensions of the burnup. limit may be possible,,,
provided that there is rio unacceptable increase in th'e incidence of fuel fai. lures during future cycles _of operation.
4.0 ENVIRONMENTAL CONSIDERATION
We have determined that this amendment does.not authorize a change in effluent types or total' amounts-nor an increase in power level and will not result in any significant environmental impact.
Having made this determination, we have further concluded that the amendment involves-an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR 551.5(d)(4), that an environmental impact statement, or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this amendment.
5.0 CONCLUSION
We have concluded, based on the consideration discussed above, that:
(1 )
because the amendment does not involve a significant increase in the pro-bability or consequences of accidents previously considered and does not involve a significant decrease in' a safety margin, the amendment does not involve a signific3nt hazards consideration, (2) there is reasonable ass'urance that the health and safety of the public will not endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commis'sion's regulations and the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
6.0 REFERENCES
l.
R. R. Riggs, " Analysis of LACBWR Fuel Failures,""USNRC, February 1978, attachment to Amendment 11 to Operating License No. DPR-45, March 3, 1978.
22i ~ Paul S'. ~ Check (NRC), Memorandum to Dennis L. Ziemann.2"Motionlo Suspend
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DPR-45..(LACBWR) License (TAC #11839), July 19,1978.
- 3.. Dennis Z. Ziemann (NRC), Letter to Frank Linder (DPCI), with.Amendmer.t 19 to License No. DPR-45, February 4,1980.
. ' 4.:
Dennis' M.~ Crutchfield '(NRC)', Le'tter to' Frank Linder (DPC), with
. Amendment 20 to License, No. DPR_-45, May 13,1980.
5(a) Frank Linder (DPC), Letter to Dennis M. Crutchfield (NRC), No. LAC-7572,
- June 1,1981. '.
(b)S. J. Rafferty, "LACBWR ' Cycle 5 Fuel Performance and Finalized Refueling Plan for Cycle 7," Enclost.re 1 to DPC Letter LAC-7572, DPC Report
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LAC-TR-096 (Undated).
u Dated:
November 6,1981 O
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