ML20244D403
| ML20244D403 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 04/13/1989 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20244D399 | List: |
| References | |
| NUDOCS 8904210326 | |
| Download: ML20244D403 (5) | |
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UNITED STATES
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L SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED.T0 AMENDMENT N01130 TO FACILITY OPERATING LICENSE NO. NPF-3
-TOLEDO [DISON COMPANY AND THE CLEVELAND ELECTRIC ILLUMINATING COMPANY DAVIS-BESSE NUCLEAR POWER STATION, UNIT NO. 1 DOCKET NO. 50-346-
1.0 INTRODUCTION
By letter dated April 11. 1988, Toledo Edison Company (TE), the licensee, requested a change to Facility Operating License NPF-3 which would change n
Sections 3.9,' 5.3.1 and 5.6.1.2 of the Technical Specifications for the Davis-Besse-Nucle u Power Station Unit 1 (DB1). The proposed changes wnuld armit the reload of fuel assemblies with enrichments up to 3.8 weight percent J-235 and the storage of such assenblies prior to and subsequent to loading in the reactor.
y 2.0 DISCUSSION The current 0B1 spent fuel storage racks are of the flux trap design and have a 13' inch center-to-center assembly spacing with a fuel assembly capacity of 735.. They are licensed to' store fresh fuel.having enrichments up to 3.3 weight percent U-235'without any restrictions on the location of the fuel in the racks. The storage of fuel with greater enrichment requires either that it have a burnup greater than some value which is dependent on initial enrichment or that it be stored in a checkerboard pattern in the racks. The submittal provides analyses to show that checkerboard storage is sefe and presents the results of the analysis of the required burnup as a function of initial enrichment.
3,0 EVALUATION The ' analysis of the reactivity effects of the increase in fuel enrichment was perfGrmed with the KENO-IV Monte Carlo ccmputer code. This code is widely used in the analysis of fuel rack criticality v.d has been verified by the R
fuel. vendor, Babcock and Wilecx (B&W), against critical experiments conducted at the B&W Research Center in Lynchburg, Virginia. Neutron crosu sections for
' KENO-IV were obtained from either the standard 123 energy group MDP.N cross E
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section. library or from the NUOF/NUTAN111 energy group library. The latter
.was used to model irradiated fuel. The staff concludes that the analysis.
methods. used for DBI' are' acceptable.
The analyses were performed with several. assumptions which tend to maximize
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.the rack reactivity. These include:
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Unborated pool water at a temperature yielding the highest reactivity.-
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The absorption effect of burnable poisons, control rods, and fuel assembly grid spacers is neglected.
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Assumptions of infinite extent in the' lateral directions.
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Dimensional tolerances on fuel assenblies and racks which yield the highest reactivity.
'The staff concludes that appropriately conservative assumptions were made.--
T..a codes mentioned previously were used to obtain a curve of required burnup as a function l of initial' enrichment for. unlimited storage in the racks of fuel having enrichment between 3.3 and 3.8 weight percent U-235. These codes are.also used to obtain the required burnup as a function of initial enrichment for fuel that may be used to fill the checkerboard when fresh fuel with enrichment of 3.8 weight percent U-235 or lower is stored in the racks.~The
- ' method:used for obtaining-the constant' reactivity curve for required burnup as a function of. enrichment is'the' standard one used for rack criticality
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3' evaluations and is acceptable. The application of this method to the evaluation of checkerboard loading is also acceptable. The required
' burnup curve is obtained by first evaluating the rack multiplication factor
- for a checkerboard array ccnsisting of fresh 3.8 weight percent and 1.4 weight percent.U-235 fuel in alternating'(checkerboard) locations. The value obtained for the multiplication' factor was 0.891. Next, burned fuel having an initial enrichment greater than 1.4' weight percent was substituted for the 1.4 weight percent fuel and the burnup of'that fuel was varied until the same multiplica-tion-factor was obtained.- This process was repeated for several initial enrichment values up to 3.8 weight percent U-235. A curve of required burnup as a function cf. initial enrichment was then constructed and is included in the proposed Technical Specifications.
The multiplication factor values cited above are nominal values and do not include any uncertainties.
Biases and uncertainties due to the method, off-center loading of fuel, a dropped assembly lying horizontally on top of
.the' vertical stored fuel assemblies, and assembly burnup predictions were, therefore, added. -The final value for the multiplication factor was 0.948 at the 95% probability, 95% confidence level which is required by the staff.
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A separate calculation was performed for the case of the fresh 3.8 weight L percent fuel loaded into the racks without any fuel in the other half of the checkerboard array. As expected, the multiplication factor was less than with burned fuel in these locations (0.931).
The staff' prefers to have physical restraints to prevent fuel loading errors
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which could: lead to undesirable configurations rather than relying entirely on administrative procedures. However, the licensee, in a letter dated December 16, 1988, was opposed to a staff suggestian that the low enrichment, high burnup fuel assemblies: presently in the spent fuel pool be positioned prior to the introduction of_any fuel assemblies external to the spent fuel pool into the
_1 high enriched low burnup fuel assemblies would be appropriately surrounded by j
storage racks. This would provide a more positive means of ensurir.g that any
. four low enriched assemblies. The licensee's objection to this " pre-checker-1 boarding" was' based primarfly on the increased fuel movements required and the increased worker exposure due to these additional movements.
The introduction of the checkerboard loading pattern without physical blockage means that misloading 3.8 weight percent fuel in any location must be considered. The limiting case is the loading of such fuel throughout the racks.
In such misloading events credit may be taken for the borated water in 1
the pool and the multiplication factor is well below the value for normal d
storage.. The~11cen:ee calculated the multiplication factor with only 1000 ppm of soluble boron present in the pool water to be less than 0.80. Additional-calculations also showed that even if loss of boron in the water were postulated along with the full misloading of 3.8 weight percent fuel, the fuel in the racks > would re: main subcritical. The DD1 Technical Specifications require a minimum bornn concentration of 1800 ppm during refueling.
In addition, plant. operating procedures require daily verification of this minimum boron concentration until video inspections verifying proper fuel assembly storage are completed. Based on the staff's request, the licensee has
-committed, by letter dated January 26 1989, to providing plant procedures 3
which require verification of the midfmum bcron concentration every 7 days during'non-refueling operations. Bued on these requirements,1the staff accepts the use of administrative procedures (without physical blockage) to govern proper fuel placement and concurs that credit may be taken for the presence of 1800 ppm of soluble boron in the spent fuel pool for abnormal' events and accidents.
The licensee has provided an analysis of the effective multiplication factor of the' fresh fuel storage racks as a function of moderator density. The calculations were performed with the KENO-IV code which has been previously
-approved by the staff for the analysis of fresh fuel racks. The results of l
the analyses showed thet a completely filled (80 assemblies) new fuel storage rack of 3.8 weight percent fuel in a fully flooded condition yielded a 1
multiplication factor of 0.9332. This is below the staff's acceptance i
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4 criterion of 0.95 and is, therefore, acceptable. However, the analyses showed that these 80 fresh fuel assemblies under optimum moderation conditions of approximately 0.07 grams per-cubic centimeter would not be subcritical.
Therefore, the licensee has made a commitment to physically block rows 4 and 7 to ensure that fresh fuel assemblies will not be placed in any locations in rows 4 and 7 of the new fuel storage racks. This limits to 64 the number of fresh fuel assemblies that can be stored in the new fuel storage racks.
Calculations have shown that 64 fresh assemblies enriched to 3.6 3eight percent U-235 results in a multiplication fc;.tur of 0.9663 under optimum moderation conditions. This is below the staff's acceptance criterion of 0.98 for fresh fuel storage under optimum moderation conditions and, therefore, acceptable.
The licensee has proposed changes to Sections 3.9, 5.3 and 5.6 of the DBI j
Technical Specifications. Section 3.9.13 has been added and includes the curve of required burnup as a function of initial enrichment illustrating the restrictions on the storage of fuel with enrichment between 3.3 and 3.8 weight percent U-235.
The proposed changes are consistent with the analysis submitted and are acceptable. The change to Section 5.3.1 is merely to change the maximum permitted enrichment from 3.3 to 3.8 weight percent U-235 and is accestable. The change to Section 5.6.1.2 changes the reference from the FSAR less than or equal to 0.98 to tie USAR and adds a requirement to maintain k,hdrogenous mist of such a in the new fuel storage racks when immersed in a density that provides optimum moderation (highest reactivity). This change is diso Consistent with the safety analysis and is Acceptable.
l 8ased on the review, which is described above, the staff finds that the proposed Technical Specification modifications are acceptable and that fuel assemblies having initial enrichments up to 3.8 weight percent U-235 may be safely stored in the fresh and spent fuel racks if the requirements of the Technical Specifications are met. The administrative procedures described above as well as the commitments to verify the minimum pool water boron concentration every seven days during non-refueling operations and to piiysically block rows 4 and 7 of the new fuel stcrage racks must also remain in place, when' storing fuel with an initial enrichment greater than 3.3 weight percent.U-235.
4.0 ENVIRONMEN1AL CONSIDERATION
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Pursuant to 10 CFR 51.21, 51.32, and 51.35 an environmental assessment and finding of no signifigagI gacg9gs been prepgrg4and published in the i
(54 FR
).
Accordingly, based Federal Register on p
e upon the environmental assessment, the Connission has determined that the issuance of this amendment will not have a significant effect on the quality r
of the human environment.
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5.0 CONCLUSION
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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 anendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: L. Kopp Dated: April 13, 1989
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