AECM-88-0233, Applicant Exhibit A-3,consisting of Util Forwarding Response to NRC Request for Addl Info Re Boraflex Matl Contained in Racks & Associated Boraflex Monitoring Program

Applicant Exhibit A-3,consisting of Util Forwarding Response to NRC Request for Addl Info Re Boraflex Matl Contained in Racks & Associated Boraflex Monitoring Program

ML20246N046
Person / Time
Site:	Saint Lucie
Issue date:	01/24/1989
From:	Cesare J SYSTEM ENERGY RESOURCES, INC.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
AECM-88-0233, AECM-88-233, OLA-A-003, OLA-A-3, NUDOCS 8903270291
Download: ML20246N046 (6)

Text

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/g g[9j,Ey' m o ctsa .n November 21, 1988 U$ tenng '89 11AR 22 P6 :55 "

S. Nuclear R gulatory Comission ,;;

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Mail Station P1-137 20555 Washington, D. C.

Attention: Document Control Desk Gentlemen:

SUBJECT:

Grand Gulf Nuclear 5tation ) )

Unit 1 i  !

Docket No. 50-416 License No. NPF-29 Request for Additional Information 1 Criticality Analysis for Cycle 4 '

AECM-88/0233 l

15,1988(AECM-88/0206and 27, 1988 and November By letters dated October,SystemEnergyResources,Inc.(SERI)requestedtheNRC 0228 respectively)lity analysis for Cycle 4 fuel to be stored in the Grand Gulf j.

review Nuclear the Station, critica Unit 1 spent fuel pool storage racks prior to loading in t\

reactor. .

j Based on its review, the NRC Staff requested additional infomation l; dated November 8, 1988) regarding the Boraflex material SERI's (MAEC-88/0336, )

contained in the racks and the associated Boraflex monitoring program.

response to the NRC request for additional information is attached.

If you have additional questions please advise.

Yours truly,

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b k- ,I JGC:swb Attachment ,

cc: (Seenextpage) 5 0 00$ $ ,

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1 AECM-88/0233

. Page 2 r.

1m c'c : Mr. W. T. Cottle (w/a)

Mr.T.H.Cloninger(w/a) .

Mr.

Mr, N.R.

S. B. McGehee Reynolds (w/a (w/a))

Mr. H. L. Thomas (w/o)(w/a)

Mr. H. O'. Christensen Mr. Malcolm L. Ernst (w/a)

Acting Regional Administrator U. S. Nuclear Regulatory Comission k

Region II101 Marietta St., N. W., Suite 2900 Atlanta, Georgia 30323  ;

.l Mr. L. L. Kintner, Project Manager (w/a) j l

Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Mail Stop 14B20 Washington, D.C. 20555 I i

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Attachment to

'.- AECM-88/0233

• Response to NRC Question Regarding GGNS Boraflex Gap Surveillance Program i

Introduction; *'

l As described in NRC Infomation Notice No. 87-43, Commonwealth Edison Company ,

(CECO) has observed gaps in the neutron-absorbing material used in the QuadT Cities high-density spent fuel storage racks.The neutron-absorbing material is a i by the Joseph Oat Corporation (OAT).

boron carbide dispersion in an elastomeric silicone matrix which is manufactured by Bisco Products, Inc. (BISCO) under the trade name Boraflex.

l On May 5, 1987, CECO presented to the NRC under Dockets No. 50-254 and 50 the results of measurements and criticality analysis relating to the observed j presence racks.

of gaps in Boraflex panels used in the Quad. Citie i the degradation of Boraflex as reported in the November 1988 presentation of the draft report RP-2813-4 to EPRI Boraflex working group member utilities. l Gap Formation As described in these reports, the formation of gaps is postulated to be caused by radiation inducedWhen shrinkage in the Boraflex panels due to crosslinking .in this shrinkage occurs in the presence of some.

the Boraflex polymer.

structural element (s) which restrict the shrinkage, local stress accum until the panel tears. l density spent fuel racks manufactured by OAT such as those installed at Quad Cities and GGNS.

Gap Measurements l

In response to NRC Information Notice 87-43, tests for the presence of gaps in the GGNS spent fuel racks were conducted during August, 1988.

l The test apparatus consisted of a Californium-252 neutron source and 4 sets of Boron tri-Flouride thermal neutron detectors enclosed in a specially designed logging tool. The detectors are shielded from the fast neutron.s produced by the Ca-252 source but detect any thermal neutrons which will be reflected A set cf from

~ four adjacent storage rack cells if gaps in the Boraflex areto present. de Boraflex panels at once. This This design minimizes uncertainties with respt the elevation of gaps. device is lowered into the storage' rack cea to be .

This tested and slowly moved up the channel at approximately 1 foot / minute. i process allows detection of gaps greater than 1/2 inch, '

The results of this test were provided to SERI in October,1988. -The testsThese were performed on 101 storage rack cells (total of 404 Boraflex panels).

cell locations have typical radiation histories for the GGNS spent fuel storage No ,

racks. Of these, 48 had not previously been used to store irradiated fuel. i In the irradiated cells 87 gaps gaps were found in the unirradiated cells. The were observed in 85 ' panels with 127 panels showing no evidence of gaps.

average gap size was approximately 0.8 inch, with a maximum gap size of 1.4 J14 MISC 88111802 - 1

i V' Attachment to AECM-88/0233 i

Gap Impact Assessment 3-D KEN 0 models were developed to assess the impact of the. observed gaps on the spent fuel rack criticality analysis. These models included gaps in the mid-plane of all Boraflex panels. equal to the maximum observed gap size plus the associated measurement uncertainty. An infinite number of cells, in this ..

configuration, was assumed to be present in the radial direction. This is a very conservative treatment since the GGNS and Quad Cities measurements indicate that the gaps are essentially randomly distributed except for a slight bias towards the mid-plane. No storage cells in the GGNS racks were observed to have 4 gaps in the same plane.

I Results of analyses using the .3-D KENO models demonstrated that if the presence of the maximum observed gap size had been explicitly accounted for in'the Cycle l

4 spent fuel criticality analyses [SERI letters to NRC serial AECM-88/0206 and ,

l AECM-88/0228], the reported reactivity would not have increased. An analysis

' of a 3 inch gap in the mid-plane of all Boraflex panels demonstrated significant margin to the 0.95 k-effective acceptance criteria. Additionally, if a more realistic treatment of the distribution of gap sizes and locations had been included, gaps substantially larger than those observed would not result in an increase in the reported rack reactivity. . Since the fomation and' growth of gaps is slow, no imediate concern for the integrity of the GGNS racks exists.

However, the potential for continued growth and gap fomation exists. In order to assess the long term impact of.the degradation of the Boraflex panels upon spent fuel rack criticality, a detailed evaluation of the available industry data is currently in progress. The objective of this evaluation is to establish a maximum credible gap size and distribution for the GGNS racks. In conjunction with this assessment, a more detailed criticality analysis is underway in order to determine the long tem impact of the femation of gaps on the criticality of the spent fuel racks at GGNS. These analyses are currently scheduled for completion on or about February 15, 1988.

Surface Degradation In July of 1986, Wisconsin Electric Company, the licensee of Point Beach 1 and 2 reported significant degradation in test coupons of Boraflex material.

As reported in NRC Information Notice 87-43, subsequent examination of full length panels disclosed 1-2 percent of the surface showed a gray discoloration at the edges. No evidence of this degradation has been observed in the GGNS test coupons. ,

Ponitorinr: program Since little industry data is available concerning the fomation of gaps in the Boraflex for 0AT racks, SERI intends to continue monitoring the GGNS spent fuel racks until gap sizes and the distribution of gaps are no longer  ;

significantly changing. The monitoring will use methods equivalent to those .

previously described. Due to the observed slow formation and growth of these gaps, one set of measurements each cycle is considered adequate.

i J14 MISC 88111802 - 2 i

v Attachment to

! AECM-88/0233 1

The Approximately 50 storage rack cells are planned for monitoring each cycle.

cells will be loaded with discharged fuel during each refueling outage. After significant additional irradiation, the fuel in the specified cells will be moved and ajditional measurements will be performed. This process will maximize th'e formation of gaps. This process will provide an early indication ..

of any sign'ificant changes in the behavior of the Boraflex and a confirmation of any assumptions used in the criticality analyses.

The Boraflex coupon surveillance program described in the original licensing basis for the racks (SERI letter to NRC serial AECM-85/0143) will continue and provide ,

a basis-to monitor for the possible surface degradation of the panels. 1 Summary While the presence of small gaps in the GGNS spent fuel rack Boraflex has been- '

detected, they have no impact upon the criticality safety analysis currently under review by the NRC Staff. Since larger gaps have been observed at other ,

l sites, a detailed assessment of the long term impact is on schedule for-completion in February, 1989. In order to assure that the. basis for this . l assessment remains valid, periodic measurements of the specified storage rack cells will be performed until gap sizes and the gap locations are no longer significantly changing.

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