ML20195G550
| ML20195G550 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie, 05000000 |
| Issue date: | 10/28/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20151V292 | List:
|
| References | |
| FOIA-88-497 NUDOCS 8811280052 | |
| Download: ML20195G550 (7) | |
Text
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ENCLOSURE __1 SAFETY EVALUATION BY THE OFFICE OF NUCLE /.R RE ACTOR REGULATION RLATING TO SPENT FUEL P00_L HODIFICATIONS FLORIDA F0Kg AN9 LIGHT COMPANY ST. LUCIE UNIT I DOCKET NO. 50-335 1.0 ETRODUCTION Ry letter dated June 12, 1987, Florida Power and Light Company (FPL) applied for an amendment to operating license CPR-67 of St. Lucie Unit 1 to increase the storage capacity of the spent fuel pool for the plant.
This expansion is to be accorrplished by installing new storage racks in the existing fuel pool which can store spent (irradiated 1 fuel assemblies in a high density array.
l The proposed rnodifications will increase the spent fuel storage capacity of St. Lucie Unit t orn 728 to 1705 fuel assemblies, thus extending the full core reserve storage capacity until the year 2009.
Tre spent fuel storage pool will be divided into two regiors. Region 1 contains 342 storage cells with a nominal center-to-center spacing of 10.12 inches and is designed to accocitodate non-Irradiated fuel assemblies with U-235 enrichments up to 4.5 weight percent.
Region 2 will contain 1364 sbrage cells with i nominal : enter-to-center spacing of 8.P6 inches.
pl.a ceme n t t 6n. H Segion ? is restricted by burnup and enrichment limits.
The high density spent fuel storage rack cells are fabricated from 0.080 inch thick type 304L stainle?.s steel plates.
In Region 1, strips of Boraflex neutron absorber traterial are sandwiched between the cell walls and a stainless steel coverplate, and the cells re separated by a 1.120 inch water In Region 2, the Boraflex strips are sandwiched between the adjacent t
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cell w ll', wi thout a wa ter gap.
The criticality aspects of both regions are evaluated below.
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2 2.0 EVALUATION Calculation Methods The calculation of the effective multiplication factor, k,ff, makes use of the In rASM0-2E two dimensional rnultigroup transport theory computer code.
addition, for independent verification, criticality calculations were also l
perforced with the KENO-!V Monte Carlo code as well as the EPRI-CELL and NULIF These independent verification calculations substantiate the CASMO-2E codes.
calculations and resulted in a calculational bias of 0.0013 and a 95/95 probability / confidence uncertainty of 0.0018.
In order to calculate the criterion for acceptabhc burnup for storage in Region 2, calculations were made for fuel of several different initial enricheents and, at each enricheent, a limiting reactivity value, which included an additional factor for uncertainty in the burnup analysis, was l
established.
Burnup values which yielded the limiting reactivity values were then determined for each enrichment from which the acceptable burnup domain The staff
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for storage in Region 2, as st.cwn in Figure 5.6-1, was obtained.
finds this procedura acceptable.
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Treatnent of Uncertainties i
l for the Region 1 analysis, the total uncertainty is the statistical I
coebination of the calculational bias unctrtainty and manufacturing and
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uncertalnfies due tc variatir,ns in boron loading in the Roraflex l
met.ha n i c a l absorcer :ineets, 8nraflex width tolerance, Boraflex thickness, inner stainless i
steel storage box dimension, ' lux trap water gap thickness, stainless steel Other l
l thickness, fuel enricreent and density, and fuel pin pitch.
uncertainties due to temperature variations and eccentric positioning of the j
l fuel essenbly in the storage rar> ore Accounted for by assuming worst case
- enditior.s, i.e., conditions which result in the highest calculated i
re ctivity.
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3 in the Region 2 analysis, the same uncertainties are considered except there is no water gap and, hence, no gap thickness uncertainty.
In additien, an l
uncertainty due to the burnup analysis is estimated and treated as an additive tem in determining the burnup versus enrichment limiting reactivity values in Figure 5.6 1 rather than being combined statistically with the other uncertainties.
The staff cencludes that the appropriate uncertainties have been considered and have been calculated in an acceptable manner.
In addition, these uncertainties were detemined at least at a 95% probability 951 confidence level, thereby metting the NRC requirements, and are acceptable, r
Results of Analysis For Region 1. the rack multiplication factor is calculated to be 0.9409, including uncertaintics at the 95/95 probability / confidence level, when fuel having an enrichment of 4.5 weight percent U-235 is stored therein.
Fuel of either the Combustion Engineering (CE) or Advanced Nuclear Fuels ( ANFl type from St. l.ucie Unit 1 or Unit 2 may be stored.
For Region 2, the rack multiplication f actor is calculated to be 0.9435 for the most reactive irradiated fuel pemitted to be stored in the racks, i.e.,
fuel with the minimum burnup pemitted for each initial enrichment as shown in Figure 5.6-1.
The design will accept fuel of 4.5 weight percent U-235 initial enrichment. burned to 36.5 MWD /kgu of either the C" nr ANF type from Units 1 l
and.:.
Tht:refore, the results of the criticality analyses meet the staf f's acceptance criterion of k,f f no greater than 0.95 including all uncertainties at the 95/95 probability / confidence level.
4 i
Accident Analyses Most abnonnal storage conditions will not result in an increase in the k,ff of the racks.
For example, loss of a cooling system wtil re.tult in an increase in pool temperature but this causes a decrease in the k,ff value.
1 It is possible to postulate events, such as an inadvertent misplacement of a fresh fuel assembly either into a Region 2 storage cell or cutside and adjacent to a rack module, which could lead to an increase in pool reactivity. However, for such events credit tray be taken for the Technical Specificatico riainimum requirdment of 1720 ppm of boron in the pool water. The reduction in the k,ff value caused by the boron (approximately 0.24) more than offsets the reactivity addition caused by credible accidents.
I i
Technical Specification Changes The following Technical Specification (TS) changes have been proposed as a result of the replacement of the existing spent fuel pool racks at l' nit 1.
l The staff finds these changes acceptable, l.
T5 5.6.1.a.1 is revised to correspond to the Standard Technical Specifications for Combustion Engineering PWRs (NUREG-0212 Rev. 2).
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TS 5.6.1.a.2 is revised to show the nominal center-to-center spacing for
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the new storage racks.
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T', d.6.1.a.3 15 edited to discuss the boron concentration in the pool water only.
4 1.
TS 5.6.1.a.4 is added to indicate the presence of Boraflex in the storage cells.
TS 5.0.1.0 ano accompanying Figure 5.6-1 are added to show the increased 3,
spent fuel enrichment perinitted in the pool.
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b i
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6.
TS 5.6.1.c is editorially changed from "b" to "c".
7 TS 5.6.3 is char.ged to show the capacity of the high-capacity spent fuel storage racks.
3.0 CONCLUSION
Based on the review described above the staff finds the criticality aspects 3
of the design of the St. Lucie Unit 1 spent fuel racks to be acceptable.
The staf f ccncludes that CE or ANF fuel from Unit 1 or Unit 2 may be safely stored in Region 1 provided that the enrichxent does not exceed 4.5 weight percent U-235. Any of these fuel types rnay also be s'.ored in Region 2 provided it rneets the burnup and enrichment limits specified in Figure 5.6-1 of the St.
Lucie Unit ] Technical Specifications.
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BURNUP DOMAIN 15 g
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2 3.0 3.5 4.0 4.5 1.5 2.0 INITIAL ENRICHMENT, WT % U 235 F isuRE 5.6'l INITI AL ENRICHMENT VS BURNUP REQUIREMENTS FOR STORAGE OF FUEL ASSIMALIES IN REGION 2.
ET. LUCK PLAMT UNTT 1 S-G q.
INCLOSURE 2 ST. LUCIE UNIT 1 SYSTEMATIC ASSESSMENT OF LICENSEE PERFORMANCE Functior.al Areas 1.
Management Involvement in Assuring Quality.
Technical review of the sutoittal indicates that the management reviews are timely and tech 6teally appropriate.
Pating: Category 1 Approach to Resolution of Technical Issues from a Safety Standpoint.
2.
The licensee showed a general understanding of the technical issue and used acceptable approaches.
Rating: Category 1 3.
Responsiveness to NRC Initiatives The licensee responded favorably to NRC initiatives.
Rating: Category 1 4
Enforcernent History N/A j
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5.
Operational and Construction Events Np 6.
Staf fing (including Managerrent)
N/A 7.
Training and Qualification Effectiveness
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N/A i
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