ML20138L989

Safety Evaluation Supporting Amends 91 & 85 to Licenses DPR-19 & DPR-25,respectively

ML20138L989
Person / Time
Site:	Dresden
Issue date:	12/12/1985
From:	Office of Nuclear Reactor Regulation
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ML20138L980	List: ML20138L978 ML20138L989
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NUDOCS 8512200164
Download: ML20138L989 (5)

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.prar UNITED STATES

.8 NUCLEAR REGULATORY COMMISSION

y WASHINGTON. D. C. 20555

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 91 TO PROVISIONAL OPERATING LICENSE NO. DPR-19 AND AMENDMENT NO. 85 TO FACILITY OPERATING LICENSE NO. DPR-25 COMMONWEALTH EDISON COMPANY DRESDEN NUCLEAR POWER STATION, UNIT NOS. 2 AND 3 DOCKET NOS. 50-237/249

1.0 INTRODUCTION

By letter dated August 13, 1985, Commonwealth Edison (the licensee) made application to amend the Licenses and Technical Specifications (TS) of Dresden Station Units 2 and 3 to permit storage of the Exxon Nuclear Company (ENC) 9x9 fuel assemblies in the spent fuel racks.

Changes to the TS include altering the basis for acceptance of assemblies for stor-age, movement of the present storage criteria in Section 5.5 of the TS to Section 3.10, placing new storage criteria in Section 5.5 and inclusion of 9x9 assemblies in the list of assemblies to be stored.

In addition to the above, License Conditions 3.N.1, 3.N.2 and 3.N.3 for Dresden 2 and 3.M.1, 3.M.2 and 3.M.3 for Dresden 3 have been transferred to the TS.

For Dresden 3 only, license conditions 3.M.4.a. 3.M.4.b 3.M.4.c and

.3.M.4.d, which have already been transferred intact to Section 10.1.2.2.

of the Updated FSAR, are deleted.

A Notice of Consideration of Issuance of Amendments to Licenses and Pro-posed No Significant Hazards Consideration Determination and Opportunity for Hearing related to the requested action was published in the Federal Register on October 23, 1985 (50 FR 43022). No public comments or requests for hearing were received.

2.0 EVALUATION The current basis for the storage of assemblies in the racks is defined in terms of the U-235 loading per unit length of assembly.

No credit is taken for burnable poison in the assembly.

This is unnecessarily conservative but is convenient to calculate.

The proposed criterion for storage in the racks is defined in terms of the K = value in reactor geometry at the assembly burnup for which this quantity is greatest rather than the more usual

" enrichment of U-235 axial loading density".

Use of this criterion has been previously approved for BWR racks (e.g. General Electric deligned racks) and we find its use for Exxon to be similarly acceptable.

l 8512200164 851212 PDR ADOCK 05000237 P

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The Technical Specification which defines the criterion for assembly storage in the spent fuel racks has been moved from'Section 5 of the Technical Spec-ifications (Design Features) te, Section 3/4 (Limiting Conditions for Operation and Surveillance Requirements).

Specifically, the criteria were moved to Section 3/4.10. The latter section location more properly describes the i

function of the specification and we find the change to be acceptable.

i The licensee submitted ENC report XN-NF-84-115, Rev. 1, " Criticality Safety Analysis, DRESDEN 2,3 Spent Fuel Storage Pool With Exxon Nuclear Company, Inc.

9X9 Reload Fuel," dated January 1985, in support of the proposed Technical Specification change. This report describes the calculations which were per-formed in order to obtain the proper K = value to be used for the 9.19 fuel.

The design case analysis was performed for a 9X9 assembly having an initial average enrichment of 3.50 weight percent U-235 with at least 7 gadolinia rods with a minimum 2 percent gadolinia concentration. This assembly was j

then burned to its point of maximum reactivity (6.0 GWD/MT) with the ENC fuel design code XFRYE. The residual U-235 average enrichment and Pu buildup were t

obtained for the burned up condition and a KENO (Monte-Carlo) calculation was performed for an asserbly having that uniform enrichment without the presence of residual gadolinium and built up fission products.

The results of that calculation for nominal rack condition is a K value of 0.8871.005.

TheK=valueoftheassemblyat6.0GWD/MTexposur$$ascalcu-lated by XFRYE to be 1.336 (no credit for gadolinia and fission products).

A five enrichment model was used for this calculation.

The corresponding K =

value calculated by the KENO single enrichment model was 1.370.

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Abnormal configurations considered in the analysis included movement of the l

racks (e.g., from seismic disturbance) so that the spacing between racks was reduced to zero (normal spacing = 1.75 inches), the absence of 1 boral absorber j

plate per 25 plates, and the cooling of the pool water to 40*F.

All three r

of these events would have to occur simultaneously to violate the 0.95 limit on pool K,ff value. This is not considered to be credible.

l The criticality analysis of the racks was performed with the KENO-NITAWL-XSDRNPM code package. This is the most widely used code set for spent fuel 4

I pool criticality analysis and is acceptable.

Exxon has provided the results of benchmark calculations which show that the calculations tend to slightly

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overpredict the reactivity of the experiments.

The experiments included i

the presence of boron absorber plates between assemblies. We conclude that adequate verification of the analysis methods has been provided.

As discussed above, the acceptance criterion for storage of fuel assemblies in the pool has been changed to the value of K = of the assembly at its most l

j reactive point. The acceptance criterion for. storage of ENC 9X9 assemblies has been established as 1.27.

This value is to be calculated by.the XFYRE code and is to include the effect of residual gadolinia and fission products.

j Comparison with the value calculated by XFYRE without consideration of

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' gadolinia and fission products shows that reduction of 0.066 in K = has been imposed. This margin is to include the reactivity effect of the gadolinia and fission products and to allow for variations that might occur due to different 9X9 fuel designs.

Although storage of 7X7 and 8X8 (both GE and ENC designs) in the racks is acceptable on other grounds (the current criterion), equivalent K = values have been established for these assemblies to provide consistency.

These values are similar to those which have been used by GE for similar rack designs and are acceptable.

Based on our review, we conclude that the proposed changes to the Technical Specifications of Dresden Units 2 and 3 are acceptable.

We further conclude that any amount of ENC 9X9 fuel may be stored in the racks so long as the K = value (in core germetry) does not exceed 1.27 when calculated at the point in assembly life wh re this quantity is a maximum.

These conclusions are based on the following (see review above):

1.

The K value for the racks has been calculated with acceptable methods which'b$vebeenverifiedbycomparisonwithcriticalexperiments.

2.

The K = value of the assemblies has been calculated by the standard ENC code which is used for core analyses and has been approved for this use.

3.

The K value for the racks has a significant margin to our acceptance crite$nforthisquantity.

4.

Significant margin has been provided between the Technical Specification value of the acceptance criteria and the design value.

Finally, we conclude that the complete deletion of license conditions 3N and 3M from the Dresden 2 and 3 licenses, respectively, is acceptable since the same information has been transferred either to the Technical Specifications or to the Updated FSAR.

3.0 ENVIRONMENTAL CONSIDERATION

i These amendments involve changes to 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 require-ments. The staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite and that there is no significant increase in individual or cumulative occupational radiation exposure.

The Commission has previously issued a proposed finding that these amendments involve no significant hazards consideration and there has been no public

O o comment on such finding.

Accordingly, these amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).

Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assess-ment need be prepared in connection with the issuance of these amendments.

4.0 CONCLUSION

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 proposed manner, and (2) such activities will be conducted in compliance with the Commission's regulations and the issuance of these amendments will not be inimical to the common defense and security or to the health and safety of the public.

5.0 ACKNOWLEDGEMENT This Safety Evaluation has been prepared by W. Brooks.

Dated: December 12, 1985 h

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. r Mr. Dennis L. Farrar DEC 121985 For administrative convenience we are enclosing a revised Page 6 of licenses DPR-19 and DPR-25 showing the changes made by these amendments.

-A copy of our related Safety Evaluation is also enclosed.

This action will appear in the Commission's biwaekly notice publication :in the Federal Register.

Sincerely, estgest slaped W John A. Zwolinski,. Director BWR Project Directorate #1 Division of BWR Licensing

Enclosures:

1. : Amendment No.91 to License No. DPR-19

'2.

Amendment No. 85 to License No.'DPR-25 3.

Safety Evaluation cc w/ enclosures:

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