B13080, Responds to 881116 Request for Addl Info Re Spent Fuel Pool Capacity Expansion.Evaluation of Resultant Gaps & Refinement of Seismic Displacement Analysis Performed to Reconcile as-fabricated Condition.W/Revised Module Layout & Addl Info

Responds to 881116 Request for Addl Info Re Spent Fuel Pool Capacity Expansion.Evaluation of Resultant Gaps & Refinement of Seismic Displacement Analysis Performed to Reconcile as-fabricated Condition.W/Revised Module Layout & Addl Info

ML20196B890
Person / Time
Site:	Millstone
Issue date:	12/02/1988
From:	Mroczka E NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
B13080, NUDOCS 8812070078
Download: ML20196B890 (8)

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(203) 665 5000 December 2, 1988 Docket No. 50-245 B13080 Re: 10CFR50.90 U.S. Nuclear Regulatory Comission Attention: Document Control Desk Washingten, DC 20555 Gentlemen:

Millstone Nuclear Power Station, Unit No. 1 Spent Fuel Pool Capacity Expansion Additional Information In a letter dated June 24, 1988,(1) Northeast Nuclear Energy Company (NNECO) requested a change to the Hillstone Nuclear Power Station, Unit No.1 Tech-nical Specifications to allow expansion of the spent fuel pool storage capa-bility. Additional information supporting NRC Staff in letters dated July 29,1988gis and requestAugust was 12,submitgd 1988. 1 toThese the submittals delineated the proposed module layout and module spacings and also provided the bounding seismic displacement results. The purpose of this letter is to provide a revised module layout with revised spacings as shown on Figure 2.1, Revision 1, included as Attachment 1. NRC Staff approval for the installation of the new modules in accordance with the revised layout is respectfully requested by December 9, 1988 to meet our construction schedule.

In addition, Attachment 2 provides the NRC Staff with the additional inform-ation requested during a telephone conversation between the NRC Staff and NNECO on November 16, 1988.

The inter-rack gaps between the new spent fuel racks have been reduced to accomodate an increase in module envelope size. The increase resulted during fabrication for proper fuel cell sizing. As a result, the increases are larger for the modules with the most cells.

(1) E. J. Mroczka letter to U.S. Nuclear Regulatory Comission, "Millstone Nuclear Powcr Station, Unit No. 1, Proposed Change to Technical Specifications, Spent Fuel Pool Capacity Expansion," dated June 24, 1988.

(2) E. J. Hroczka letter to U.S. Nuclear Regulatory Comission, "Millstone Nuclear Power Station, Unit No. 1, Response to Request for Additional Information, Spent Fuel Capacity Expansion, dated July 29, 1988.

(3) E. J. Hroczka letter to U.S. Nuclear Regulatory Comission. "Millstone Nuclear Power Station, Unit No. 1, Response to Request for Additional Information, Spent Fuel Pool Capacity Expansion", dated August 12, 1988.

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U.S. Nuclear Regulatory Commission B13080/Page 2 December 2, 1988 To reconcile the as-fabricated condition, an evaluation of the resultant gaps and a refinement of the seismic displacement analysis was performed. Figure 2.1, Revision 1, illustrates the resultant inter-rack gaps.

The bounding seismic displacements, es provided in earlier submittals, are 0.438" in the north-south direction and 0.225" in the east-west direction.

The bounding north-south displacement (0.438") was for the "A" rack which was analyzed with consolidated fuel loadings only. Based on the results of the "D" rack, which was analyzed for both consolidated and regular fuel loadings, the displacements of the "A" rack with regular fuel would be significantly less. The "D" rack regular fuel loading displacements are only 60% of the consolidated fuel displacements. In addition, the proposed north-south gaps for the "A" module are at least 2". Generally, because of the arrangement of the new modules in the proposed layout, the north-south gaps are not significantly affected except with the "0" racks.

The "D" racks are unique in that (1) the most significant reduction occurs in the north-south gaps and (2) the bounding east-west seismic displacement of 0.225" occurs here. Figure 2.1, Revision 1, identifies the resultant gaps in both the north-south and east-west directions to be equivalent (1-1/4 1/4").

Since the resultant gaps are equivalent and since the east-west displacements are sionificantly larger than the north-south, the east-west resultant gap and seis u. displacements of the "D" rack will have most limiting and least conservative safety factor to impact. Conservatively assuming that the "D-1" and "D-2" rack move 1800 out of phase and that they reach their maximum displacements at precisely the same instant, the maximum gap closure would be 0.45". Again conservatively assuming the most disadvantageous installation tolerances existed, a gap of 1" and a safety factor to impact of 2.22 would exist. It should also be noted that if the gaps in the revised layout were used to reanalyze the modules, the seismic displacements would be less due to the added hydrodynamic effects caused by the gap reductions.

It is concluded that the revised module layout and spacings will preclude any rack to rack / wall impacts and is therefore acceptable since a minimum safety factor to impact of 2.22 would result from the revised layout, the displace-ment is reduced by the gap reduction, and a final as-built layout evaluation will be performed.

We trust the Staff will find this information utisfactory and we remain available to assist you in the review of this matter. We appreciate the timely efforts the Staff has, and continues to, put forth on this matter.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY "C W E. W pfoczka #

Senior Vice President

U.S. Nuclear Regulatory Comission B13080/Page 3 December 2, 1988 cc: W. T. Russell, Region I Administrator M. L. Boyle, NRC Project Manager, Millstone Unit No. 1 W. J. Raymond, Senior Resident Inspector, Millstone Unit Nos. 1, 2, and 3 i

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Docket No. 50-245 B13080 Attachment 2 Millstone Nuclear Power Station, Unit No. 1 Resoonse to Reauest for fdditional Information 1

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" ' Attachment 2 B13080/Page 1 Attachment 2 Millstone Nuclear Power Station, Unit No.1 Resoonse to Reauest for Additional Information Question #1: Provide justification for the use of single-rack analyses instead of multi-rack analyses.

Response #1:

Multi-rack analyses have been performed by other utilities in a number of other rack licensing efforts. Usually, these multi-rack analyses were done to confirm that rack-to-rack or rack-to wall impact loads as )redicted by the single rack 3-D analysis r.re of the correct order of magnituce. It was found in these previous studie', that if rack-to-wall impact does not occur, then all racks in a line move ir phase and will not impact, even though the individual rack displacements ma', be greater than that in a single rack analysis. For Hillstone Unit No. s single rack analyses, the displacement results are compared against the expected rack-to-rack gaps assuming that the racks move out of phase. This will conservatively predict any potential impact. With one exception, Georgia Power Company's Vogtle )lant, all previous multi-rack analyses have been carried out for racks whic1 were designed to impact one another during a seismic event. For the Vogtle plant, a multi-rack study is currently being performed to examine the effect of higher rattling mass fraction, and to provide added insu,ance that rack impact will not occur. The Vogtle plant racks are designed to preclude rack-to-rack and rack-to-wall impacts and preliminary results indicate that the multi-rack analyses will show no ' ack-to-rack or rack-to-wall impacts. In addition, the Vogtle rack analyses assumes a more severe seismic event than postulated for Millstone Unit No.1, and because the Vogtle racks are of the same size and have the same order of rack gap conditions, it is expected that the Vogtle results would be more severe for the same fuel assembly mass. Additionally, the Vogtle multi-rack analyses account for a fuel assembly with an approximate weight of 1600 lbs/ cell, while the Hillstone Unit No I's fuel assembly weight is 680 lbs/ cell.

Based on the similarity of Vogtle and M111 stone's rack configurations, '

Millstone being subjected to a less severe seismic event, and the Millstone analysis assuming that any rack movement occurs out of phase, we believe that the single rack analyses provides a correct analysis of displacements and stresses. Therefore, a multi-rack analyses is not necessary and would not Indicate any rack-to-rack or rack-to-wall impacts.

Question #2: Provide detailed new module displacement results and gap information for each rack type.

Response #2:

The following data of maximum new module displacements are based on actual calculational results for the most limiting gaps and estimates for the remain-ing modules.

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