ML20127D016

Application for Amends to Licenses DPR-53 & DPR-69,revising TS 5.6.1 to Decrease Enrichment Limit of Spent Fuel Storage Racks from 5.0 Weight Percent (W/O) U-235 to 4.52 W/O U-235 to Correct Errors in ABB/C-E Calculations

ML20127D016
Person / Time
Site:	Calvert Cliffs
Issue date:	09/01/1992
From:	Creel G BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20127D020	List: ML20127D016 ML20127D027
References
TAC-M68416, TAC-M68417, NUDOCS 9209110104
Download: ML20127D016 (8)

Text

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1

. i f BALTIMORE GAS AND ELECTRIC 1650 CALVERT CtJFFS PARKWAY . LUSBY, MARYLAND 20057-4702 l 0""'M,",',"

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t U. ii. Nuclear Regulatoiy Commission Washington, DC 20555 ATI'ENTION: Document Control Desk ,

SUBJEC'n Calvert Cliffs Nuclear Power Plant Unit Nos.1 & 2; Docket Nos. 50 317 & 50 318 License Amendment Request: Spent Fuel Pool EnrictLrnGl.t.liFil i .

REFERENCES:

(a) Ixtier from htr. S. A. hicNeil (NRC) to htr. G. C. Creel (BG&E),

dated January 10, 1990, Issuance of License Amendment (Unit 1 TAC 68416; Unit 2 TAC 68417)

(b) letter from S. A. Toelle (CE) to htr. R. C. Jones (NRC), dr4ted -

February 28, 1992, Accuracy of Fuel Storage Rack Criticality Calculations (c) Letter from S. A. Toclle (CE) to h1r. L 1. Kopp (NRC), dated h1 arch 27, 1992, Accuracy of Fuel Storage Rael: Criticality Calculations (d) letter from hir G. C. Creel (BG&E) to NRC Document Control ,

Desk, dated June 4,1992, Discovery of Non Conservative Technical SpeciGeations (c) letter from hir. G. C. Creel (BG&E) to NRC Document Control Desk, dated July 28,1992, Update of License Amendment Schedule (f) EPRI NP-6159, December 1988, "An Assessment of Bora0cx Performance in Spent Fuel Storage Racks" Gentlemen:

The Baltimore Gas and Electric Company hereby requests an Amendment to its Operating License Nos. DPR 53 and DPR-69 for Calvert Cliffs Unit Nos.1 and 2, respectively, with the submittal of the proposed changes to the Technical Specifications.

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. Document Control Desk

, September 1.1992 Page 2 DESCHIPTION The proposed amendment would revise the Unit Nos.1 and 2 Spent Fuel Pool enrichment limit. The  ;

Spent Fuel Pool enrichment limit is being decreased from th< .urrent value of 5.0 weight percent  !

(w/o) U.235 to 4.52 w/o U 235 because of errors in the calculations performed by ABB/ Combustion  !

Ungineering which supported 5.0 w/o U 235.

IIACKGROUND The Calvert Cliffs Spent Fuel Pool holds fuel from both units. It is actually two pmts separated by a dividing wall but connected by a weir gate. The north half of the pool connects to the Unit 1 containment and the south half connects to the Unit 2 containment. Fuel from the two units is not sepegated as the two halves of the Spent Fuel Pool are treated as one pool. Figure (1) is a schematic of the Spent Fuel Pool. *

%c Spent Fuel Pool has been reracked several times over the life of the plant. With the existing configuration of high density poisoned racks, the Unit 1 racks are nearly identical to the Unit 2 racks (see Figure 2). De distinction between the two halves is the type of poison material used. %c '

Unit I racks use a boron carbide composite material which is not susceptible to gap formation. The poison material used in Unit 2 racks is Boraflex. Boraficx is susceptible to gap formation for reasons related to irradiation behavior and manufacturing techniques. Therefore a reactivity penalty is typically applied to Boraflex when performing criticality analyses.

In Reference (a) the Nuclear Regulatory Commission (NRC) approved an increase in the maximum allowed enrichment of fuel in the Spent Fuel Pool to 5.0 w/o U 235. This submittal treated the two .

halves of the pool as identical by applying the boraficx penalty to both sets of racks. %is was a conservative step which simplified the analytical treatment of the pools.

E In early 1992, ABB/ Combustion Engineering informed the NRC of errors in the Spent Fuel Pool l criticahty calculations performed for several iower plants l References (b) and (c)]. Baltimore Gas and Electric Company (BG&E) had used t1ese incorrect calculations to support the request to increase the maximum allowed enrichment of fuelin the Spent Fuel Pool to 5.0 w/o U 235.

- Upon notification of the errors, BO&E immediately assessed the situation to confirm that fuel assemblics stored to date in the 1001 had not presented a safety concern and that placement of new fuelinto the pool in support of the reload of Unit 1 Cycle 11 was acceptable. Preliminary analysis showed that the errors reduced the allowable enrichment for the Unit 1 pool to 4.55 w/o U-235 and for the Unit 2 pool to 4.15 w/o U-235. In order to ensure that the preliminary enrichment limits were adhered to, we separated the two pools using administrative controls pending the final analysis.

References (d) and (c) documented BG&E's notification of the problem and the schedule to correct the Technical Specifications. Final analysis resulted in a maximum allowable enrichment of 4.52 w/o U-235 for both pools.

ItEOUESTEI CilANGES l Change Technical Specification 5.6.1 for Unit Nos.1 and 2 to decrease the enrichment limit of the l spent fuel storage racks to 4.52 w/o U 235 as shown in Attachments (1) and (2), respectively.

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. Document Control Desk

.Septensber 1,1992 Page 3 SMislYJNA13 SIN /.1URI11 ICATION The proposed change to the Technical Specifications will allow s*croge of fuel enriched to 4.52 w/o U.235 in the = pent fuel racks of both Units. The Unit I spent fuel storage racks use a poison material made of a toron carbide composite not susceptible to gap formation. The as fabricated areal density of the boron carbide composite is 0.024 grams of U-10 per square centimeter. It has a design end-of life areal density of 0.02 grams of B-10 per square centimeter which was assumed in the analysis. The poison material is 0.09 inches thick and is sandwiched between two stainless steel sheets, each 0.06 inches thick. The poison sheets are 6.5 inches wide.

The Unit 2 storage racks are identical to those of Unit 1 except that a different poison mato ial is used. The Unit 2 racks use Borauex with an areal density of 0.02 grams of B-10 per .quare centimeter. "Ihe poison sheets are nominally 0.08 inches thick (0.07 inches was used in the analysis) and 6.5 inches wide. The effects of Bora0cx gapping were considered. The causes of Horanex gap formation are related to the irradiation behavior of the material and to manufacturing practices.

When the material becomes brittle and shrinks under irradiation, gaps have been shown to form where the material was constrained.

The manufacturer for the Calvert Cliffs racks has indicated that there were no manufacturing directives which would have led to constraint of the Botaflex sheets during rack manufacture.

Therefore, the sheets would be less likely to form gaps. As no measurements have been made to determine the existence of gaps at Calvert Cliffs, a conservative gap penalty was applied to arount for the possibility that they may exist. Four-inch gaps were assumed to exist in eve y shut of Boranex and the gaps in the four walls of any given rack cell were assumed to be axially aligned.

Based on research done by EPRI on Boranex sheets constrained during manufacturing l Reference (f)] relatively few cumulative gaps have been observed to exceed two inches. Therefore, the four. inch gap assumed in the Baranex sheets is conservative.

The four-inch gaps in adjacent tack cells were assumed to be staggered slightly, with a two-inch vertical scparation which leads to a checkerboard pattern when h30 king at the entire pool. This is significantly more conservative than assuming a random gap distribution which industry experience indicates is the more likely case. The gaps were assumed to be distributed preferentially around the axial centerline of the fuel assembly. The worth of the gaps will be the greatest in the highest Dux region of the fuel assembly. The Oux is highest at the fuel centerline, and decreases as the ends of the fuel assembly are approached. Therefore, for conservatism the gap penalty was calculated at the axial location of highest worth, the centerline of the fuel.

The only calculational difference between the two rack designs is the penalty associated with the Boranex gapping for the Unit 2 racks. For operational convenience, the lower calculated enrichment limit for the Unit 2 racks is proposed for the entire pool. The maximum allowable enrichment limit for a k-effective value of 0.95 is 4.52 w/o U-235. Attachment (3)is a description of the analysis used to calculate the new enrichment limit.

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Document Control Desk September 1,1992 Page 4)glitMINglON OF SIGNIFICANT ll A7A1(I)S

             %e proposed changes have been evaluated against the standards in 10 CFR 50.92 and have been determined to not involve a significant harards consideration, in that operation of the facility in accordance with the proposed amendment:

L Would not incohe a sigsificant increase in the pn>bability or consequences of an accident previously evaluated. De only accident previously evahm i in the Updated Final Safety Analysis Report which involves the Spent Fuel Poolis the fte handling accident. Fuel assembly emichment is not a - precursor to this accident. He isotopic inventory co smed in the fuel handling accident is not adversely effected by the decicase in enrichment of U435. Derefore, the proposed change to the Spent Fuel Pool enrichment limit does not imalve a significant increase m the probability or consequences of an accident previously evaluated.

2. Would not increase the possibihty of a new or different type of accident from any accident prcriously evaluated.

The proposed change to the allowed enrichment of fuel in the Spent Fuct Pool does not result in any change to the configuration or operation of the plant. Specifically, no new hardware is being added to the plant as a part of the proposed change nor are there significantly different types of operations being introduced, he only potential for a new type of accident lies in the area of accidental criticality. The Spent Fuel Pool maintains fuel in a suberitical condition with k effective less than 0.95 (no credit is taken for soluble boron being present in the pool). The required degree of suberiticality continues to be met at the new enrichment limit of 4.52 w/o U-235 which ensures an accidental criticality will not occur. Therefore, the proposed change to the Spent - Fuel Pool enrichment limit does not create the possibility of a new or different type of accided from those previously evaluated.

3. Would not invah e a sipsificant reduction in the margin of safety.

The margin of safety maintained in the Spent Fuel Pool is the degree to which the fuel is maintained subcritical. The proposed change to the allowed enrichment of fuelin the Spent Fuel Pool will ensure that the margin of safety is maintained. The maximum multiplication factor for storing fuel assemblies with a 4.52 w/o U-235 is 0.95. The previously approved maximum multiplication factor for 5.0 w/o was 0.946. He new maximum multiplication factor does not represent a significant reduction in the margin of safety. Therefore, the proposed change to the Spent Fuel Pool enrichment limit does not involve a significant reduction in the margin of safety. Based on the above, we have concluded that these changes do not constitute a significant hazard. 1

 ,,       Document Control Desk Sepicmber 1, 692 Page 5 SCilEI)UI.E These changes are requested to be approved and issued by February 28,1993.

S4F1lIlCOMMl'ITEIMINIEW These changes to the Technical Specifications and our determination of significant hazards have been reviewed by our Plant Operations and Safety Review Committee and Off-Site Safety Review Committee. They have concluded that implementation of these changes will not result in an undue risk to the health and safety of the public. Should you have any questions regarding this matter, we will be pleased to discuss them with you. f rVery truly yourt;/ A STATE OF MARYLAND 2 TO WIT COUNTY OF CALVERT I hereby certify that on the f day of Seokmber .1992, before me, the subscriber, a Notary Public of the State of Maryland in' and for ('a loe4 Ocu d d , personally appeared George C. Creel, being duly sworn, and states that he is Vice P/esident of the Baltimore Gas and Electric Company, a corporation of the State of Maryland; that he provides the foregoing response for the purposea therein set forth; that the statements made are true and correct to the best of his knowledge, information, and belief; and that he was authorized to provide the response on behalf of said Corporation. WITNESS my lland and NotarialScal: MNotary / he/ Public My Commission Expires: !u m 8, / N ' Date GCC/LMD/Imd/bjd/dtm Attachments: (1) Unit 1 Technical Specification Page (2) Unit 2 TechnicalSpecification Page (3)' Description of Analysis 1

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       ..                    Document Control Desk
                           . September 1,1992 Page 6 cc:               D. A. Brune, Esquire J. E. Silberg, Esqui:e it A. Capra, NRC D. O. McDonaki, Jr., N RC T. T. Martin, NRC P. R. Wilson, NRC F. L McLean, DNR j.11. Walter, PSC i

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CONCEl'TUAI. IlltAWING OF CitOSS SECilON OF SI'ENT FUEL IRACK POISON SHEET OUTER WALL

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