ML18005B038
| ML18005B038 | |
| Person / Time | |
|---|---|
| Site: | Harris  |
| Issue date: | 08/31/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18005B037 | List: |
| References | |
| NUDOCS 8909110216 | |
| Download: ML18005B038 (5) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON. D. C. 20555 SAFETY. EVALUATION.BY THE OFFICE-OF. NUCLEAR REACTOR. REGULATION SUPPORTING AMENDMENT.NQ.. 12-TO-FACILITY-OPERATING LICENSE NO.. NPF-63 CAROLINA.POWER. 8 LIGHT.COMPANY
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SHEARON.HARRIS NUCLEAR POWER PLANT.UNIT 1 DOCKET-N0..50-40Q
1.0 INTRODUCTION
By letter dated April ll, 1989, as supplemented June 29, 1989, the Carolina Power Im Light Company (the licensee) requested changes to the Shearon Harris, Unit 1, (Harris) Technical Specifications (TS).
The June 29, 1989, letter provided clarifying information that did not alter the action noticed, or change the initial determination of no significant hazards consideration as published in the Federal Re ister.
The proposed changes would revise TS 5.3.1 by increasing the~max mum a
owe enrichment of stored fuel to 5.0 weight percent U-235 from 4.2 weight percent U-235.
In addition, a requirement for storage would be added to TS 5.6.1 to require that a maximum core geometry k-infinity for PWR fuel assemblies be less than or equal to 1.470 at 68'F.
The licensee's submittal includes a Westinghouse report, "Criticality Analysis of Shearon Harris Spent Fuel Racks with IFBA Fuel," November 1988, which supports the requested amendment.
Plant operation using the higher enriched fuel will be demonstrated to be acceptable by a cycle specific reload safety evaluation performed prior to each fuel loading.
Also, in this amendment
- request, the numbering sequence of Section 5.6.1, Criticality, has been revised to eliminate duplicate specification numbers.
The reactivity analysis and administrative change associated with this amendment are delineated below.
- 2. 0 EVALUATION The Harris spent fuel storage racks consist of square stainless steel cans having an inside dimension of 8.75 inches and a 0.75 inch wall thickness.
On the outer surface of each side of the cans, Boraflex sheets having a minimum area density of 0.02 grams per square centimeter of Boron-10 (B-10) are held in place by a thin-walled stainless steel wrapper plate.
The rack structure maintains these cans'n a 10.5 inch center-to-center spacing.
The spent fuel is normally 'stored in pool water containing about 2000 ppm of soluble boron which results in about a 30 percent reduction in reactivity.
However, for conservatism the spent fuel rack reactivity is calculated assuming no soluble boron in the water.
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The Harris spent fuel pool was previously analyzed for the storage of Westinghouse 17xl7 optimized fuel assemblies (OFA) and standard (STD) fuel assemblies with enrichments up to 4.2 weight percent U-235 and no contained burnable absorbers.
The current analysis, which supplements the previous
- analysis, analyzes the storage of 5.0 weight percent 17xl7 OFA and STD fuel assemblies with integral fuel burnable absorbers (IFBAs).
The fuel assembly IFBAs consist of a neutron absorbing material such as gadolinium or boron which is homogeneously mixed with the fuel pellet or applied as a thin coating on the outside of the fuel pellet.
The analytical methods and models used in the reactivity analysis have been benchmarked against experimental 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 is that, including uncertainties, there is a
95 percent probability at a 95 percent confidence level (95/95 probability/confidence) that the effective multipli-cation factor (k-effective) 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 Harris 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.
The concept of reactivity equivalencing is predicated upon the reactivity decrease associated with the addition of IFBA fuel rods and fuel depletion.
A series of reactivity calculations are performed to generate a set of IFBA rod numbers versus enrichment-ordered pairs which all yield the equivalent k-effective when the fuel is stored in the spent fuel racks.
This is shown in the enclosed Figure which appeared in the supporting Westinghouse report noted above.
From the Figure, it can be seen that the rack reactivity of fuel with 48 IFBA rods with an initial U-235 enrichment of 5.0 weight percent is equivalent to the rack reactivity of unirradiated fuel having an initial U-235 enrichment of 4.2 weight percent.
The method of reactivity equivalencing has been widely used by other licensees for fuel storage analyses and has been accepted by the staff.
The resulting k-effective for the Harris spent fue'l storage racks was 0.9448 including all appropriate biases and uncertainties at a 95/95 probability/
confidence level.
This meets the NRC acceptance criterion and is, therefore, acceptable.
In order to store fuel assemblies that may have a non-standard IFBA rod pattern and, therefore, cannot use the IFBA versus enrichment Figure, an infinite multi-plication factor for a nominal fresh 4.2 weight percent U-235 fuel assembly was determined.
As mentioned earlier, this is equivalent to the reactivity of a 5.0 weight percent U-235 fuel assembly with 48 IFBA rods.
When k-infinity is used as a reference reactivity point, the need to specify an acceptable enrich-ment versus number of IFBA rods correlation'is eliminated.
Calculation of the infinite multiplication factor for a fuel array of 4.2 weight percent fuel in
the Harris reactor geometry resulted in a reference k-infinity of 1.470.
The licensee has shown that fuel with a reference k-infinity of 1.470 results in a maximum k-effective of less than 0.95 when stored in the Shearon Harris spent fuel storage racks.
Therefore, the only requirement needed to ensure that the fuel racks are maintained at a k-effective below 0.95 is to verify that for each
- assembly, the k-infinity is no greater than 1.470 at 68'F in the core geometry.
The IFBA rods versus enrichment Figure is, of course, an acceptable way for the licensee to verify that the k-infinity limit is met if a particular fuel assembly design meets the assumptions under which the enclosed Figure was generated.
It is possible to postulate events which could lead to an increase in storage rack reactivity, such as misplaced fuel assemblies.
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 administrative procedures require that the boron concentration be verified to be n'o less than 2000 ppm in the spent fuel pool once a week.
The reduction in k-effective caused by the borated water more than offsets the reactivity.addition caused by credible accidents.
Based. on the above evaluation, the staff concludes that the spent fuel storage racks at Harris can accommodate Westinghouse 17x17 standard or optimized fuel assemblies with maximum enrichments of 5.0 weight percent U-235 provided, that fuel with enrichments greater than 4.2 weight percent U-235 contain sufficient integral burnable absorbers such that the maximum core geometry k-infinity of these assemblies is no greater than 1.470 at 68'F.
The current TS have two Sections numbered 5.6.1.
The licensee requests revising the identification sequences so that the two p5rts will become 5.6.la and 5.6.1b.
In addition, the subparts of 5.6.la would be changed from alphabetic to numeric.
The revised numbering is an administrative change that clarifies the TS and, therefore, is acceptable to the staff.
- 3. 0 ENVIRONMENTAL CONS IDERATION Pursuant to 10'FR 51.21, 51.32, and 51.35, an. environmental assessment and finding of no significant impact have been prepared and published in the Federal Re ister on August 30, 1989 (54 FR 35953).
Accordingly, based upon the
~env ronmenta assessment, the Commission has determined that the issuance of this amendment will not have a significant impact on the quality of the human environment.
4.0 CONCLUSION
The Commission made a proposed determination that this amendment involves no significant hazards consideration which was published in the Federal Re ister (54 FR 25370) on June 14, 1989, and consulted with the State oOt~or h
aro dna.
No public comments or requests for hearing were received, and the State of North Carolina 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 proposed
- manner, and (2) such activities will be conducted in compliance with the Commission's regulations 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 R. Becker Dated:
August 31, 1989
.Enclosure to Safety Evaluation Supporting Amendment No. 12, Shearon Harris Nuclear Power Plant, Unit 1
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I 4.9 5.0 Figure 2.
Shearon Harris Fuel Assembly Minimum Number of IFBA Rods vs.
Initial U' 'nrichment for Storage in Region 1 Spent Fuel Racks "Criticality Analysis of Shearon Harris Spent Fuel Racks with IFBA Fuel," 'llestinghouse,
- November, 1988.