ML20043C041
| ML20043C041 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 05/25/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20043C038 | List: |
| References | |
| NUDOCS 9006010232 | |
| Download: ML20043C041 (5) | |
Text
- i p urg j'k UNITED STATES c
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- j-WASHINGTON, D C. 20655
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 54 TO FACILITY OPERATING LICENSE NO. NPF-30 s
UNION ELECTRIC-COMPANY CALLAWAY PLANT, UNIT 1 l 0CKET NO. SIN 50-483
1.0 INTRODUCTION
1 By letter dated December 28, 1989, the Union Electric Company (UE), the licensee, proposed changes to Technical Specifications (TSs) for the Callaway Plant Unit 1.
The proposed changes would revise TSs 5.3 and 5.6.1.1 to allow storage of spent fuel with maximum initial enrichments of 4.45 weight percent (w/o) U-235'in Region 1 of the spent fuel pool.
TS 5.6.1.1 would be further revised to reference a requirement that the reference k-infinity of fuel assemblies stored in Region 1 be less than or equal to 1.455 in unborated water at 68 degrees F.
In addition, the licensee estimates an associated pro-jected average burnup of 52,000 meg'awatt-days per metric ton uranium (MWD /MTU) due to the higher enrichments.
4 2.0 DISCUSSION The amendment request concerns only the storage of Vantage 5 (VS) fuel containingintegral-fuelburnableabsorbers(IFBAs)withmaximuminitial enrichments of 4.45 w/o U-235. The proposal limits storage of this type of spent fuel in Region 1 of the Callaway spent fuel pool only. The licensee L
estimates that a license amendment proposal requesting storage of V5 fuel with maximum initial enrichments greater than 4.25 w/o U-235 per TS Figure 3.9-1 in Region 2 of the spent fuel pool will not be required until the Callaway-Plant Refueling 6.
Plant operation using specific fuel enrichments is normally demonstrated to be acceptable by a cycle-specific reload safety evaluation prior to each I
fuel loading. The licensee has modified a previous analysis evaluating the heat load on the spent fuel pool cooling system to address the increased heat load due to the 4.45 w/o U-235 fuel and increased burnup.
l The following evaluation provides an assessment of the use of V5 fuel containing IFBAs with a maximum enrichment of 4.45 w/o U-235 and its impact l.
on currently installed equipment by including reactivity analyses, spent fuel pool heat load analyses, and an audit of the licensee's dose estimates for a spectrum of postulated design basis accidents.
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. -3.0 QALUATION The Callaway spent fuel pool is divided into two separate and distinct regions.
Region 1 is designed to accommodate fresh (unirradiated) fuel assemblies and a full core off-load, if necessary.
Therefore, from a criticality viewpoint, any type of fuel not exceeding a maximum initial enrichment of 4.45 w/o U-235 from the Callaway core can be stored in Region 1.
Region 2 is designed to store only irradiated fuel assemblies which have attained sufficient burnup.
The spent fuel is normally stored in pool water containing at least 2000 ppm of soluble boron which results in a significant reduction in reactivity.
However, for conservatism the spent fuel rack reactivity is calculated assuming no soluble boron in the water.
The Callaway spent fuel pool was previously anal Westinghouse 17 x 17 optimized fuel assemblies (yzed for the storage of 0FA) and standard fuel assemblies (SFA)~with enrichments up to 4.25 w/o U-235.
The current analysis, which supplements the previous analysis, analyzes the storage of V5 fuel with enrichments up to 5.0 w/o U-235 containing IFBAs. The fuel assembly IFBAs consist of a thin boron coating on the outside of the fuel pellet, thus making it an integral part of the fuel assembly. Callaway plans to utilize only the V5 fuel design for Cycle 5 and future cycles. The analytical methods and models used in the reactivity analysis have been benchmarked against experi-mental data and have been found to adequately reproduce the critical values.
~The staff has found these methods and models to be acceptable.
The design basis for preventing criticality outside the reactor ensures that, including uncertainties, there is a 95 percent probability at a 95 percent confidence level (95/95 probability / confidence) that the effective multiplication factor (k-eff) of the fuel assembly array will be no greater than 0.95.
Two analytical techniques are used to ensure the criticality criterion for the storage of IFBA fuel'in the Callaway storage racks. The first method uses reactivity equivalencing to establish the poison material loading required to meet the criticality limits. The second method uses the fuel assembly infinite multiplication factor (k-infinity) to establish a reference reactivity.
l l-The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with the addition of IFBA fuel rods. Series of reactivity l
calculations are performed to generate a set of IFBA rod number versus enrich-ment ordered pairs which all yield the equivalent k-eff when the fuel is stored in the spent fuel racks.
From the licensee's evaluation, it is evident that the rack reactivity of fuel with 80 IFBA rods with an initial enrichment of 5.0 w/o U-235 is equivalent to the rack reactivity of fresh (unirradiated) fuel having an initial U-235 enrichment of 3.85 w/o and containing no IFBA rods. This equivalence relationship assures the maximum k-eff will be calcu-lated since depletion calculations performed by the licensee have shown that l
the maximum reactivity of the Westinghouse fuel assemblies occurs at zero
w
- o burnup for any number of IFBA rods per assembly. The licensee will incorporate I
this in the Callaway Updated FSAR. This method of reactivity equivalencing has been used by other licensees for fuel storage' analyses and has been accepted lby the staff.
The resulting k-eff for the Callaway Region I spent fuel storage racks was 0.9476' including all appropriate biases and uncertainties at a 95/95 probability / confidence level. This meets the NRC acceptance criterion and is, therefore, acceptable.. The value of k-eff was determined by a:suming the fuel is stored in a two-out-of-four (checkerboard) arrangement in Region 1, as de-scribed in Section 9.1 of the FSAR.
In addition, those storage locations that are required to be empty are physically blocked to prevent inadvertent fuel assembly placement.
In order to simplify verification of acceptability for storage of fuel'in the spent fuel racks, a k-infinity for a fresh 3.85 w/o U-235 fuel assembly was determined. As mentioned earlier, this is equivalent to the reactivity of a 5.0 w/o U-235 fuel assembly with 80 IFBA rods. When k-infinity is used as a reference reactivity point, the need to specify an acceptable enrichment versus number of IFBA rods correlation is eliminated. Calculation of k-infinity
.for a fuel array of 3.85 w/o fuel in the Callaway reactor geometry resulted in a reference value of 1.455. The licensee has shown that fuel with a reference k-infinity of 1.455 results in a maximum k-eff of less than 0.95 when stored in a checkerboard arrangement in Region 1 of the Callaway s]ent fuel storage racks. Therefore, the only requirements needed to ensure t1at the fuel racks are maintained at a k-eff below 0.95 are to verify that for each assembly, the k-infinity is no greater than 1.455 at 68 degrees F in the core geometry ar.d to store the fuel in a. checkerboard configuration in Region 1 of the spent fuel a
racks.
It is possible to postulate events which could lead to an increase in storage rack reactivity, such as not maintaining a checkerboard configuration.
However, for such events, credit may be taken for the approximately 2000 ppm of boron in the spent fuel pool water by application of the double contingency principle of ANSI N16.1-1975. This states that one is not required to assume two unlikely, independent, concurrent events to provide for protection against a criticality accident. The staff finds this acceptable since 7.dministrative L
procedures require that the boron concentration be verified to be no less than l
2000 ppm in the spent fuel pool once a week. The reduction in k-eff caused by the borated water more than offsets any reactivity addition caused by credible accidents. Based on the above evaluation, the staff concludes that the storage racks in Region 1 of the Callaway spent fuel pool can accommodate Westinghouse V5 fuel assemblies with maximum enrichments of 4.45 w/o U-235 provided that the fuel is stored in a checkerboard (two-out-of-four) array and that fuel with enrichment greater than 3.85 w/o U-235 contains sufficient IFBAs such that the L
maximum core geometry k-infinity of these assemblies is no greater than 1.455 at 68 degrees F.
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From the perspective of increased heat load on the spent fuel cooling system, calculations show that the increased burnup of the V5 fuel would result in a maximum 5'F temperature rise in the spent fuel pool for both normal and 1
off-normal (fuel core offload) discharge conditions. The increased heat load would not result in a bulk pool temperature in excess of the current limits for both-above conditions as addressed-in the Standard Review Plan, Section 9.1.3.
The revised analysis utilized a heat load calculation method which is consistent with BTP ASB 9-2 and was previously reviewed and approved-by the staff.
Based on the above review, the staff concludes that the increased heat load from the proposed increased enrichment and burnup of spent fuel is small and can be adequately handled by the spent fuel pool cooling system without exceeding the temperature limits of the Standard Review Plan.
The staff finds the proposed technical specification change acceptable, In reviewing the dose estimates provided by the licensee, the staff agrees with the licensee's conclusion that the effect of increasing fuel enrichment to 5.292 w/o U-235 and burnup to 60,000 MWD /MTV, respectively, would be to increase calculated thyroid doses for a postulated fuel handling design basis accident by about 20%. There would be no effect on the estimated consequences of other postulated fuel damage design basis accidents, which scale with power level rather than with enrichment and/or burnup. The licensee's reanalysis of the fuel handling accident reflects this small increase.
The licensee also references an NRC public notice " Extended Burnup Fuel For Use in Commercial LWRs:
Environmental Assessment and Findings of No Significant Impact" (Fed. Ry., February 23,1988), in which the NRC staff.
concluded that no significant impacts are expected for fuel enrichments up to 5.0 w/o U-235 and burnups to 60,000 MWD /MTU.
Thus, the staff finds that the proposed revisions to the Technical Specifications are acceptable.
4.0 ENVIRONMENTAL CONSIDERATION
Pursuant to 10 CFR 51.21, 51.32, and 51.35, an environmental assessment and finding of no significant impact has been prepared and published in the Federal Register (55 FR 19375). Accordingly, based upon the environmental assessment, the Commission has determined that the issuance of this amendment will not have a significant effect on the quality of the human environment.
5.0 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
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'will not be endangered by operation in the pro)osed manner; and (2) such a
activities will be conducted in compliance witi-the Commission's regulations AL and the issuance of this amendment will not be inimical to the common defense and security or to.the health and safety of the public.
Principal Contributors:
L. Kopp, SRXB/ DST r
S. Sanders, SPLB/ DST J. A. Martin, PRPB/ DST 1
S.V. Athavale Dated:. May 25, 1990-e L
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