ML20238E348

Submits Review of Draft NRC Info Notice, Gaps in Neutron- Absorbing Matl in High Density Spent Fuel Storage Racks. Diagnosis of Phenomenon Calls for Careful Consideration of Specifics of Event at Plant

ML20238E348
Person / Time
Site:	Quad Cities
Issue date:	07/27/1987
From:	Singh K HOLTEC INTERNATIONAL
To:	NRC
Shared Package
ML20238E264	List: ML20238E262 ML20238E291 ML20238E322 ML20238E348 ML20238E384 ML20238E387
References
NUDOCS 8709140288
Download: ML20238E348 (7)

Text

m ,,am ne- >- z m =~ -~ = u = = zo = 2 HOLTEC INTBRXATIOXAL l 139 A. Gaither Drivo, Mount Laurel. N.J. 080541713 e (609) 234-8668 f i

July 27, 1987 Mr. Conrad McFadden Chief, Chemical Engineering Branch Office Nuclear Reactor Regulations U.S. N.R.C.

Washington, DC 20555

Dear Mr. McFadden:

I have had an opportunity to review the draft issue of the NRC information notice No. 57-XX, entitled, " Gaps in Neutron-Absorbing Material in High Density Spent Fuel Storage Racks".

Since I have been deeply involved in the Quad cities high density rack during its design and licensing, I believo it> is incur. bent on me to shara some factual information with you, which may help you resvaluate the tone and the substance of notice.

At the time the Quad cities racks were designed and licensed, was Vice-President of Engineering of the contractor, Joseph OatI Corporation of Camden, Now Jersey. I-am also co-inventor of the j design patent of the BWR racks, which manufacturing the Quad Cities racks.

OAT employed in The Quad Cities rack design and licensing was carried out under my leadcrship. As such, I might be expected to have an intimate knowledge of the anatomy of the hardware and its particular attributes. The present issue of the draft notico seems to ignore the special nuances of the Quad Cities' hardware, and draws generalized conclusions on "Boraflex degradation". In my opinion, a correct diagnosis of the event calls for a careful consideration of the " specifics" surrounding the event.

following.

I attempt to provide sono of the " specifics" in the The Quad Cities racks employ the so-called " cruciform" construction wherein angles are welded together along the edges in a fixture (please see attached patent description) to form a cruciferm. The Boraflex is contained between the facos of the angle.

Crucifonns are attached to cach other by welding along their junction. This welding must be done remotoly, and therefore, its quality dependo on the flatness, and straightness of the cruciform surfaces. . Slight dislocation of the weld edge places the welding host input dangerously close to the Boraflex .

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~ Quad: Cities racks were among the first to be built by OAT. CAT's fabrication team learned in time to improve- the. accuracy of' the remote weldingLand minimize the warpage.of the cruciform panels.

Quad Cities . racks,' however, showed 'the . markings 'of a manufacturing team learning its , oats. The early group. of Quad Cities racks.were substantially out-of-tolerance.(as much as 0.75 j inch in. one module!!) ; later modules were much better. Even the forming of the angles was done'using a " process" which was-later found to lead to tolerance. problems.

one consequence of this evolving manufacturing techniques was in the uneven clamping-~ load on Boraflex. Boraflex was not held in a vertical- configuration without scattered- clamping. An inadvertent outcome was -that the in-plane dimensional change, I -

would surmise,.was randomly restricted.

'While'I cannot comment on the actual. tear of.the material during handling with any certainty, . such a possibility should not be precluded from consideration. The stretching of Boraflex during its gluing operation to the angles is another rather unique aspect of the Quad Cities rack fabrication.

' OAT went on to overcome many of the above mentioned fabrication problems; and produced racks of much improved quality in later years.

I trust that your notice should take account of the special configuration of Quad cities-racks, and the special manufacturing problems encountered during their fabrication.

The closing paragraphs of the notice appear to draw heavily from the NETCO report, which in the opinion of many experts in the field, makes speculative proposition sound like unimpeachable '

fact. Perhaps a dig assionate critique.of NETCO's hypotheses is warranted before the NRC embraces it as an established fact.

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HOLTEC INTERNATIONAL l

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.e Finally, I' should inform you from first hand k.nowledge, that the gap in. the Quad cities poison panel was. confirmed by underwater neutron radiography conducted by NUSURTEC, INC. (230 Normandy circle, Palm Earbor, FL 33563, phone 813-787-4625). The draft notice also arrn on this vital piece of information.

. Sincerely, hh b Krishna P. singh, Ph.D.

President KPStmt i

i 1 blSCO REWRITE c.

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IN 87-XX UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, DC 20555 July xx, 1987 l NRC.INFORMATION NOTICE NO. 87-XX: GAPS IN NEUTRON-ABSORBING MATERIAL I IN HIGH DENSITY SPENT FUEL STORAGE RACKS Addressees:

l All nuclear power reactor facilities holding an operating license or a construction permit.

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Purpose:

This notice is to alert recipients to a potentially significant problem pertaining to gaps identified in the neutron absorber component of the high density spent fuel storage racks at Quad Cities Unit 1. The safety concern is that certain gaps might excessively reduce the margin of nuclear subcriticality in the fuel pool. The NRC expects that re-cipients will review this notice for applicability to their facilities ,

and consider actions, if appropriate, to preclude a similar. problem {

occurring at their facilities. However, suggestions in this notice q do not constitute NRC requirements; therefore, no specific action or written response is required.

Related Documents:

" Behavior of High-Density Spent-Fuel Storage Racks," EPRI NP-4274, Electric Power Research Institute, August, 1986. ,

Description of Circumstances:

On May 1, 1987, Commonwealth Edison Company (CECO), the licensee at Quad Cities 1 and 2, presented data to the NRC regarding gaps measured in Boraflex, a neutron absorbing material which was incorporated as a component in high density spent fuel storage racks manufactured by the Joseph Oat Corporation (OAT). Boraflex is a trade name for a boron carbide dispersion in an elastomeric silicone matrix manufactured by Bisco Products, Inc. (BISCO). Data pertaining to the gap size and I distribution had been obtained by National Nuclear Corporation (NNC) and Nusurtec under contract to CECO.

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+- IN-87-XX 4 July 27, 1987 Page 2 of 4 The licensee had retained Northeast Technologies Corporation (NETCO) to interpret the data. NETCO prefaced their assessment as preliminary, noting that there were areas where data was not available, but con-cluded that the gap formation mechanism may be related to large local stresses in the Boraflex by fab

• cation induced restraint within the rack l and tearing and shrinkage of the material.

1 The average gap size is 1-1/2 inches, with the largest about 4 inches. The

-gaps occur in the upper 2/3rds of the cell length.

These gaps are inferred from anomalies in " blackness" testing results by NCC and in one instance was "in-situs" neutron radiographer by Nusurtec.

Commonwealth Edison also discussed the effects these gaps might have on the approved safety analysis for the spent fuel storage racks. They used conservative assumptions for gap size, gap location, and fuel burnup. Considerable margin in k-eff appears to be available before the licensing limit of 0.95 would be approached.

I In July, 1986, Wisconsin Electric Company, the licensee at Point Beach 1 and 2, reported to the NRC that test coupons of Boraflex material had shown considerable degradation under high radiation. However, the licensee argued that this result did not represent the actual condition of Boraflex used in their spent fuel storage racks because of differenes in methods of encapsulation, sample geometry, and handling frequency.

Additionally, the coupons had been subjected to about 5 times more dose than is associated with the average fuel rack position. Subsequent examination of full length panels disclosed no degradation of the Boraflex exposed to negligible gamma radiation and 1-2% of the surface of the panel exposed to significant gamma radiation showed a grey discoloration at the edges, similar to that of the coupon. No change of thickness was noted and no evidence of gaps or b::eakage existed.

Discussion:

The NRC is primarily concerned that seperation of the neutron absorbing material used in high density fuel storage racks might compromise plant i safety and secondarily that such seperation might invalidate currently )

approved safety analyses of such racks. While Quad Cities reports that )

their racks even with gaps in the Boraflex as large as 4 inches can meet  !

the criticality criterion of k-eff less than or equal to 0.95, this may not be the case for larger gaps or for other plants. A list of the 9 sites using high density spent fuel storage racks manufactured by OAT is attached to this notice. A list of the 31 sites using Boraflex is also attached.

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% IN-87-XX July 27, 1987 Page 3 of 4 Efforts to understand the testing anomalies have revealed information needs on several topics. Accordingly, the material supplier BISCO and the Electric Power Research Institute (EPRI) have undertaken research programs to collect this information. Some of the objectives are described below.

The DISCO program aims to establish with increased accuracy the relation-ship between radiation dose and size changes. The program also evaluates the potential effect of handling and restraint, during and subsequent to the fuel rack fabrication on gap formation. BISCO claims that some pre-liminary conclusions in the NETCO report are too conservative and expects the program to generate accurate design and analysis data.

The EPRI program will gather data from the utilities with respect to their neutron absorber coupon surveillance program. EPRI will further examine

' data obtained from CECO, as well as from BISCO and other sources to im-prove the understanding of possible or actual gap formation models, in-cluding the effects of rack fabrication methods and irradiation damage mechanisms. The EPRI Program will also attempt to model the specific Quad Cities experience utilizing absorbed gamma dose as a function of axial axial elevation, change in length / length vs gamma dose measurements, and neutron absorbing sheet restaint parameters.

The effect of rack design and manufacturing methods on the consequences of stress, temperature, and chemical environment to irradiated Boraflex is uncertain. The programs are designed to evaluate each consequence and, in particular, to improve the understanding of stress caused by method of attachment or entrapment of the Boraflex panel to the stain-

- less sheet wall of the cell.

Together, these programs are intended to improve the industry under-standing of the safety implications of the observed gaps in the Boraflex neutron absorber component of the Oat high density spent fuel storage racks, at Quad Cities.

No specific action or written response is required by this information notice. If you have any questions about this matter, please contact the Regional Administrator of the appropriate regional office of this office.

Charles E. Rossi, Director Divisior, of Operational Events Assessment Office or Nuclear Reactor Regulation

g %' .j 4" IN-87-XX 1 July 27, 1987 l

, l Page 4 of 4 i Technical Contacto: Vern Hodge (301 ) 492-8196 Albert D. Morrongiello (309) 654-2227.

Attachments:

1. List of Potentially Affected-Plants

2. List of Recently. Issued Information Notices

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