ML20196J886

License Change Application 165 Requesting Amend to License NPF-1,modifying Tech Specs by Removing 3.5% U-235 Limit on Reactor Fuel Assemblies & Increase Enrichment Limit for New Fuel Storage Racks to 4.5%

ML20196J886
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	03/01/1988
From:	Cockfield D PORTLAND GENERAL ELECTRIC CO.
To:
Shared Package
ML20196J865	List: ML20196J861 ML20196J886 ML20196J903
References
NUDOCS 8803150086
Download: ML20196J886 (6)

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PORTLAND GENERAL ELECTRIC COMPANY EUGENE WATER & ELECTRIC BOARD AND ,

PACIFIC POWER & LIGHT COMPANY ,

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l Operating License NPF-1 l Docket 50-344 i License Change Application 165 j This License Change Application requests modifications to Operating License NPF-1 for the Trojan Nuclear Plant to remove the 3.5 weight percent Uranium-235 limit on reactor fuel assemblies, and to increase the enrichment limit for the new fuel storage racks to 4.5 weight percent.

PORTLAND GENERAL ELECTRIC COMPANY By.

D. W. ekfield Vice resident Nuclear subscribed and sworn to before me this 1st day of March 1988.

dieb f k Notary Public of Oregon My Comission Expires: < t v ,f [ / [ Y/ j j l l

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1 8803150086 G80301 i PDR ADOCK 05000344 l P DCD

4 LCA 165 Page 1 of 5 LICENSE CMANGE APPLICATION 165 Reason for Change Nuclear fuel cycle economics favor the use of high burnup fuel for once-through fuel cycles. High burnup is obtained by the use of higher enrichments and keeping the fuel in the core for more cycles of opera-tion, or operating with longer cycles. Allowing the higher enrichment will enable Portland General Electric (PGE) to extract more energy out of each fuel assembly with the benefits of decreased overall fuel fabrica-tion costs and an increase in the time available before the spent fuel storage facility is filled. For these reasons, it is desirable to use fuel of up to 4.5 weighc percent Uranium-235 (U-235) at Trojan.

Description of Change Increasing the enrichment of nuclear fuel used at Trojan requires two changes in the design features section of the Trojan Technical Specifications (TTS). The first change, in Section 5.3.1, is to eliminate ths 3.5 weight percent U-235 enrichment limit on the fuel assemblies. The second change, in Section 5.6.1.1, requires reanalysis of the suberiticality margin in the new fuel storage racks to verify that new fuel of up to 4.5 weight percent U-235 can be stored safely. The spent fuel storage racks have already been analyzed for 4.5 weight percent U-235 fuel.

Proposed replacement pages for the TTS are attached.

I Safety Evaluation Summary The portions of the TTS affected by this change are Design Features Sections 5.3.1 and 5.6.1.1. In addition, Final Safety Analysis Report (FSAR) Pages 9.1-1 and 9.1-2 will be changed to clarify and update the allowable limits for the neutron multiplication constant k ogg.

The two changes to the enrichment specifications are governed by different Nuclear Regulatory Commission (NRC) requirements and guidance.

The change to the new fuel design enrichment limit is administrative, and no specific regulatory requirements exist. Nuclear fuel used at Trojan is evaluated to verify that safety limits are maintained for each cycle of operation in the reload safety evaluation. The change in enrichment limits does not change the core power peaking f actors, burnup, or any other limits associated with power operation. The reload safety evalua-tion is the means for r, valuating cycle-specific safety parameters. The enrichment specifications serve as a limit for storage rack criticality control and an administrative limit on fuel design. Thus, this change only requires reanalysis of the new fuel storage rack criticality, since other parameters are verified acceptable with the reload safety

LCA 165 Page 2 of 5 evaluation. The deletion of the enrichment value in the Fuel Design Specification is justified by the fact that the enrichment value speci-fled does not directly affect Plant operating parameters or safety limits. There is no margin of safety or safety limit directly associated with fuel enrichment; rather, the safety margins are maintained by other limits such as power, power distribution, coefficients of reactivity, burnup, etc. Thus, tha deletion of the enrichment specification for fuoi assemblies does not affect the margin of safety, given that current safety limits are maintained.

The NRC guidance related to the new fuel storage rack enrichment change stems from Ceneral Design Criterion 62. This design criteria, entitled "Prevention of Criticaifty in Fuel Storage and Handling", states that

". . . criticality in the fuel storage and handling system shall be prevented by physical systems and processes, preferably by use of geometrically safe configurations". The acceptance criteria to satisfy this general design critorion is contained in NRC Standard Review Plan Section 9.1-1, "New Fuel Racks". This Standard Review Plan Section in turn references Ceneral Design Criterion 61 for fuel storage and handling and radioactivity control, and industry standards' contained in American

, National Standard (ANS) 57.1-1980, "Design Requirements for Light Water Reactor Fuel Handlin5 Systems", and draft ANS 57.3, "Design Requirements for New Light Water Reactor Fuel Storage Facilities". In order to verify the computer code analysis is performed correctly, the guidance of industry standard American National Standard Institute (ANSI) N16.9-1975, "Validation of Calculational Methods for Nuclear Criticality Safety", is used.

The change in enrichment specifications for the now fuel racks is justi-fled by the reanalysis summarired in the attachment. The FSAR descrip-tion of the new fuel storage racks indicates that drains and covers over the fuel (except when fuel is being moved) virtually eliminate the possi-bility of adding moderator to the new fuel storage racks. Nonetheless, this analysis shows that the now fuel racks are maintained suberitical for all moderator density conditions. The limits of Standard Review Plan Section 9.1-1 on the neutron multiplication factor k gg a are 0.98 for the optimum moderation case (the case which results in the highest kegg), and 0.95 for the fully flooded case. The results of the analysis described in the attachment indicate that optimum moderation is fully flooded, with a resulting k gg e of 0.9403, which is within acceptable limits.

The bench marking and validation were performed following the guidance of ANSI N16.9. To meet these requirements, a scoping study was performed using CASMO-3, a two-dimensional transport theory code, with 40 group microscopic cross-section data for various moderator densities. The peak values from this analysis were then analyzed using CASMO-3 with 70 group microscopic cross-sections. The CASMO Code has been bench marked with various critical experiments, using 70 group microscopic cross-sections.

The worst-case for Trojan is similar to those conditions covered by the

LCA 165 Page 3 of 5 bench marking and within the range of code and cross-section capability.

Uncertainty in the code results and code bias have also been accounted for and are included in the analysis results.

Based on the above discussion and the results and description provided in the attachment, it is concluded that the appilcable NRC requirements are met for the change in the fuel enrichment limit specification, for fuel assemblies and for the new fuel storage racks.

Significant Hazards Consideration Determination In accordance with requirements of Title 10, Code of Federal Regulations, Part 92 (10 CFR 50.92), this change to the fuel enrichment limit specifi-cations is judged to involve no significant hazards based on the following information:

1. Does the proposed license amendment involve a significant increase in the probability or consequences of an accident previously evaluated?

The change to the enrichment specifications has been reviewed and determined not to involve a significant increase in the probability or consequences of a previously analyzed accident. The change to the fuel design description is primarily administrative because other TTS serve to define the operating limits. In the rto ejection accident, for example, the analysis is based on tho ejected rod worth, not on enrichment. The reload safety evaluation examines each cycle of operation to verify that the fuel is operated within TTS limits. The enrichment limit is not used in the accident analysis. Because these other limits are not changed, the change in the enrichment limit specification has no effect on the results of the accidents analyzed.

An additional concern is f. hat the higher enrichment will be used to achieve higher fuel burnup wh -T may increase the radioactive source term. Extension of the current burnup limit of 44,000 megawatt days per metric ton of Uranium, analyzed in the FSAR, is described in LCA 161 by referencing the analysis in Westinghouse Topical Report WCAP-10125P. LCA 161 was submitted to the NRC on November 20, 1987, and its approval is expected prior to exceeding the current burnup limit.

The accidents analyzed for the new fuel storage racks have been evaluated and the results were determined to be within acceptable limits. The existing postulated accident of filling the new fuel racks with unborated water was reevaluated, and additional considera-tion was given t~ an event with the optinum moderation ratio. The mathod of evaluation used acceptabic methods and considered analysis and modeling unecrtainties in accordance with current standards.

This analysis shows there will be no accidental criticality, and the existing neutron multiplication factor limit is met, thus the proba-bility and consequences of the event are unchanged from the previ- '

ously analyzed case.

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2. Does the proposed amendment create the possibility of a new or different kind of accident from any previously evaluated?

The change to fuel enrichment does not affect any existing limits or conditions external to the fuel. The physical, chemical, thermal, and mechanical properties of the fuel are essentially unchanged for this small change in enrichment. The postulated criticality situa-tions are not changed by the increased enrichment, nor are the operating conditions of the fuel. Operating limits and accident assumptions remain the same for this change and are verified to be acceptable with each reload safety evaluation. It is concluded that the change to enrichment does not create any new or different types of accidents.

3. Does the proposed amendment involve a significant reduction in a margin of safety?

The fuel design description enrichment value is not related to a margin of safety, and is being deleted.

l The purpose of the enrichment specification is primarily to assure I criticality safety in the new fuel storage racks. The analyses performed demonstrate that the resulting neutron multiplication ['

factor ko rt is less than the limit of 0.95. The limit on k gg e provides the margin of safety, and assures that the new fuel rack is l maintained suberitical for the worst possible case. The margin of safety, which is the difference between the allowable limit of 0.95

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j and a critical configuration with k gr e of 1.00, is unchanged.

Therefore, this change does not reduce a margin of safety.

In the March 6, 1986 Federal Register, the NRC published a list of examples of amendments that are not likely to involve significant hazards considerations. The change to enrichment specifications occure in two '

places in the TTS. The change to TTS 5.3.1, Fuel Assemblies, is similar to Example i of the March 6, 1986 Federal Register list, which states:

1 i "A purely administrative change to technical specifications, for i example, a change to achieve consistency throughout the technical specifications, correction of an error, or a change in nomenclature."

The change to delete the enrichment specification ferr the fuel assembly description is administrative because the specification is not used for

any safety limits. The fuel assembly description provided by the FSAR is

more complete and useful than the one provided in TTS Section 5.3.1.

Based on this, pGE concludes that no significant hazards are associated with this change.

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LCA 165 Page 5 of 5 The chango to the allowable enrichment limit for the new fuel storage racks in TTS 5.6.1.1 is similar to Example vi of the March 6, 1986 Federal Register list, which states:

"A change which either may result in some increase to the probability or consequences of a previously analyzed accidcnt or may reduce in some way a safety margin, but whuro the results of the change are clearly within all acceptable criteria with restieet to the system or component specified in the Standard Review Plan, eg, a change result-ing from the application of a small refinement of a previously used calculational model or design method."

The change to the enrichment lir.it for the new fuel storage racks is shown in the attached analysis to meet the Standard Review Plan acceptance criteria, thus this change is similar to the Federal Register example cited above.

The change to the new fuel storage rack is not well represented by the l March 6,1986 Federal Register Item x, which involves an expansion to i the capacity of the spent fuel storage racks, because in this case the l existing racks are not altered. However, the Federal Register Item x does reflect that no significant hazards are involved in a change where the storage techniques and limits are the same, and that proven technology is used to analyze this change.

Based on the above examples, PGE concludes that there are no significant  !

hazards associated with an enrichment change to 4.5 weight percent U-235 l in the new fuel storage racks. I I

Environmental Evaluation Summary a

An environmental evaluation was performed as required by the Environ-mental Protection Plan (Appendix B to Operating License NPF-1). This review determined that the proposed changes do not involve a significant  :

adverse impact on the environment, and thus do not involve an unroviewed environmental question.

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