ML20147G025

Requests Exemption from Certain Requirements of 10CFR72 IAW Provisions of Section 72.7, Specific Exemptions

ML20147G025
Person / Time
Site:	Trojan  File:Portland General Electric icon.png
Issue date:	03/20/1997
From:	Quennoz S PORTLAND GENERAL ELECTRIC CO.
To:	Cool D, Kane W NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS)
References
VPN-023-97, VPN-23-97, NUDOCS 9703270319
Download: ML20147G025 (8)

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M M M WW Stephen M. Quennoz Trojan Site Executive March 20,1997 VPN-023-97 Trojan ISFSI Docket 72-017 Mr. Donald A. Cool Director, Division ofIndustrial and Medical Nuclear Safety Office ofNuclear Material Safety and Safeguards U. S. Nuclear Regulatory Commission Washington, DC 20555 Mr. William F. Kane Director, Spent Fuel Projects Office Office of Nuclear Material Safety and Safeguards U. S. Nuclear Regulatory Commission Washington, DC 20555

Dear Sir:

Reauest for Exemption from the Reauirements of 10 CFR 72.124(b)

This letter requests an exemption from certain requirements of 10 CFR 72 in accordance with the provisions of Section 72.7, " Specific exemptions." Section 72.7 authorizes the NRC to grant exemptions from the requirements of 10 CFR 72 if such exemptions are authorized by law, will not endanger life or property or the common defense and security and is otherwise in the public interest.

PGE is requesting an exemption from a provision of paragraph 72.124(b), " Methods of criticality control," requiring that the design of an ISFSI include a positive means of vedfying the continued efficacy of solid neutron absorbing materials used for criticality control. As described in the attached request for exemption (Attachment I), the Trojan ISFSI does include the use of solid neutron absorbing material. However, this neutron absorbing material is not credited or relied upon to preclude criticality during the storage of spent fuel at the Trojan ISFSI. Since the neutron absorbing material is not relied upon for criticality control during storage of the spent fuel and the sealed nature of the storage system design precludes direct monitoring or inspection of the material, PGE is requesting an exemption from this requirement. More detail concerning the basis for this request is contained in Attachment I. This request is being submitted as an l f!?Olr ii 9703270319 970320 4 DR ADOCK 0500 gg 71760 Columbia River Highway, Rainier, OR 97048 503/556-3713

VPN-023-97 March 20,1997 Page 2 of 2 i

amendment to PGE's previously submitted application for an ISFSI license (PGE letter VPN-012-96 dated March 26,1996).

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, If you have any questions regarding this information, please contact Ray Pate, Licensing, at (503) 556-7480.

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Sincerely, i

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! Stephen M. Quennoz Trojan Site Executive Attachment c: NRC Document Control Desk

! M. T. Masnik, NRC, NRR D. G. Reid, NRC, NMSS R. A. Scarano, NRC Region IV David Stewart-Smith, ODOE 1

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STATE OF OREGON )

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COUNTY OF COLUMBIA ) f

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I, Stephen M. Quennoz, being duly sworn, subscribe to and say that I am the Trojan Site I Executive for Portland General Electric Company, the applicant herein; that I have full authority to execute this oath; that I have reviewed the foregoing; and that to the best of my knowledge, i information, and belief the statements made in it are true.  !

l Date # ## _,1997 i

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, @ % > % c:ih n = = Q j Stephen M. Quennoz U Trojan Site Executive Portland General Electric Company On this day personally appeared before me Stephen M. Quennoz, to me known to be the I individual who executed the foregoing instrument, and acknowledged that he signed the same as his free act.

GIVEN under my hand and seal this 20 day of NOfdl ,1997.

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,, Notary Public in ankor the State of Oregon 9 angERLEYA.LINMg NOTARY PUBUCN ur coMMESDN EH E 997 Residing at blthtI1UL00tu314 My commission expires lo - / - 4'7 "

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i Attachment I Request for Exemption from the Requirements of l 10 CFR 72.124(b)," Methods of criticality control" I

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Attachment I to VPN-023-97 i March 20,1997 Eane1of4 Request for Exemption Background Information By letter dated March 26,1996 (PGE letter VPN-012-96) PGE submitted an application for a specific license for an independent spent fuel storage installation (ISFSI) to be constructed at the existing site of the Trojan Nuclear Plant. The license application included a safety analysis report for the Trojan ISFSI which describes the proposed ISFSI design. As described in the SAR, the Trojan ISFSI will use the Sierra Nuclear Corporation (SNC) TranStor design for spent fuel 1 storage. This is a vertical cask, dry storage system. Spent fuel assemblies are contained in sealed metal baskets (PWR baskets) which are in turn housed in cylindrical concrete casks. Up to

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twenty-four spent fuel assemblies may be stored in each basket. The system is designed to allow  !

the transfer of the sealed PWR baskets from the storage casks to approved shipping containers for subsequent transport of the spent fuel to a final repository or interim storage facility without the need to reopen the PWR baskets or directly manipulate spent fuel assemblies.

Specific Exemption Requested The specific regulatory requirement from which PGE seeks exemption is contained in 10 CFR 72.124(b), " Methods of criticality control." This paragraph is repeated below.

(c) Methods ofcriticality control. When practicable the design of an ISFSI or MRS must be based on favorable geometry, permanently fixed neutron absorbing materials (poisons), or both.

Where solid neutron absorbing materials are used, the design shall provide for positive means to verify their continued efficacy.

PGE seeks an exemption from the second sentence of this paragraph which requires the design of an ISFSI to provide for a positive means of verifying the continued efficacy of neutron absorbing materials.

Bases for Exemption Request In accordance with regulations, the storage system is designed to ensure that the spent fuel assemblies remain in a subcritical configuration throughout the storage period. As noted in Section 3.3.4.1, " Control Methods for Prevention of Criticality," of the Trojan ISFSI SAR, the TranStor storage system relies solely on the geometiy of the spent fuel assemblies i . the PWR basket to maintain the required subcritical conditions during storage. PGE submitted the

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Attachment I to VPN-023-97

! - March 20,1997 Pane 2 of 4 supporting criticality calculation (PGE01-10.02-01, Revision 0) in response to NRC's request for 1 additional information dated November 25,1996 (PGE letter VPN-085-96 dated December 23, 1 1996). As shown in this calculation, the geometry of the dry storage configuration alone  !

maintains a large margin to criticality (a k,, ofless than 0.41, even accounting for uncertainty and

computer code bias).

l The TranStor* PWR basket does incorporate solid neutron absorbing material in its design.

However, the neutron absorbing material is not necessary to maintain subcritical conditions during ,

storage and is not credited in the calculations supporting subcriticality during spent fuel storage at I the Trojan ISFSI.

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, The solid neutron absorbing material, along with the spent fuel, will be sealed inside the PWR' baskets. The PWR baskets are welded closed following initial loading of spent fuel. The design i j of the TranStor system provides for the ultimate transfer of these sealed baskets from the f

concrete storage casks to approved transportation containers. Once the spent fuel is loaded into

the PWR basket and the basket lid is welded in place, the basket remains sealed throughout the ,

storage period at the Trojan ISFSI, the transfer to the shipping container, and shipment to the final repository location. This design helps to minimize the radiation exposure to workers that

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t would result from repeated direct handling of spent fuel assemblies. The sealed basket design, i however, a'so precludes any direct monitoring or inspection of the solid neutron absorbing materialinside the PWR basket. I I

Following completion of the storage period at the Trojan ISFSI, the loaded PWR baskets will eventually be transferred to a shipping container and moved to a permanent repository or interim storage facility. The shipping container will be licensed under the provisions of 10 CFR 71,

" Packaging and Transportation of Radioactive Material." 10 CFR 71 requires the evaluation of potential transportation accident conditions including the immersion of the shipping cask in water and the intrusion of water into the PWR basket. Criticality calculations performed to support such potential transportation accident conditions consider the effects of the neutron poison materials in the PWR basket. PGE submitted this calculation, PGE01-10.02.02-03, Revision 0, to the NRC by letter dated March 10,1997 (VPN-017-97 dated March 10,1997). PGE referenced this calculation on the Trojan ISFSI docket in order to demonstrate appropriate margins to criticality during the initial loading of spent fuel into the PWR baskets in the Trojan fuel building. The initial PWR basket loading is performed under water. After the spent fuel is loaded into the PWR

basket, the PWR basket is sealed and the water is evacuated prior to placing the PWR basket into a concrete cask.

The criticality calculation for a potential transportation accident is considered to conservatively bound the conditions that exist during loading of the PWR baskets based on the following factors: l

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c Attachment I to VPN-023-97

March 20,1997 Pane 3 of 4 r

e The calculation usumes a fuel uranium enrichment of up to 4.2% wt.% U s The 23 i maximum enrichment of spent fuel to be stored in the Trojan ISFSI is 3.56%.

e The calculation assumes fresh fuel. All of the spent fuel assemblies to be stored in the Trojan ISFSI have been exposed to varying degrees of burnup during operation of the

Trojan Nuclear Plant.

e The calculation assumes pure water fills and surrounds the PWR basket. The spent fuel l

! loading operation at Trojan will be conducted with borated water of at least 2000 ppm ,

boron.

Credit is taken for the neutron poison material incorporated in the PWR basket design only during i

this initial loading of spent fuel into the PWR baskets. These conditions will exist only for a short time prior to the closure, evacuation, and vacuum' drying of PWR baskets and their subsequent

placement into concrete casks for storage at the Trojan ISFSI. During the entire storage period, l the TranStor* storage system maintains subcritical conditions by relying solely on the favorable l geometry maintained by the PWR basket design. Since the neutron absorbing material is not l i'

relied upon to maintain subcritical conditions, the monitoring of the effects of this material for 1 potential degradation during the storage period would not serve to provide any additional

assurance of subcritical conditions in the storage casks.

l As noted above, the neutron absorbing material will be relied upon in the licensing of the shipping

! container under the provisions of 10 CFR 71. Although 10 CFR 71 does not contain a requirement for positive means of verifying the efficacy of the solid neutron absorbing materials l similar to that contained in 10 CFR 72.124(b), there is adequate basis to conclude that the solid

neutron absorbing material used in the TranStor system will perform adequately following the storage period at the Trojan ISFSI.

i As noted in reponse to Question 3-10 ofNRC's request for additional information dated l November 25,1996 (PGE letter VPN-085-96 dated December 23,1996), Boral was selected as

the neutron absorbing plates in the TranStor basket internals because it maintains its material

characteristics for the duration of storage and shipment. Boral plates are able to maintain their neutron absorption properties over a long period of time because of the large number of boron-10 27 i atoms present in the plates. The Boral plates in a PWR basket contain about 10 boron-10 atoms,

- which is several orders of magnitude larger than the 2 x 10" neutrons that would be emitted by a basket over a 40-year storage period. Therefore, the neutron absorption characteristics of the Boral would not be appreciably affected by a 40-year storage period. The maximum temperatures specified by the Boral vendor for the dry storage condition are 1000*F short term and 850*F long 1 term. The temperatures listed for normal operation and off-normal events in Trojan ISFSI SAR

(Table 4.2-12) for fuel cladding are less than these temperatures (the fuel cladding would be at a

higher temperature that the Boral plates). Therefore, the Boral will not experience significant

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Attachment I to VPN-023-97

] March 20,1997 j Pane 4 of 4 1

i e thermal degradation during the 40-year storage period. The Boral will also experience minimal -

corrosion while in the PWR basket's inert helium atmosphere. The low oxygen content and lack

of an electrolyte (water) minimize potential corrosion. Based on these properties there is .

adequate evidence to ensure the efficacy of the Boral plates following 40 years of storage within j the ISFSI environment.

Conclusions l

i The solid neutron absorbing material incorporated into the design of the Trojan ISFSI is contained inside sealed PWR baskets and is not accessible for direct monitoring or inspection during the storage period. The desip" of the storage system does not rely on this material to maintain  ;

subcritical conditions duru s mrage of spent fuel at the Trojan ISFSI. During the storage period J j at the Trojan ISFSI, favorabic geometry alone will maintain the spent fuel in a subcritical

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condition by a large margin. Therefore, monitoring of the efficacy of the neutron absorbing l

} material during the storage period would not add to the assurance that the subcritical configuration described in the ISFSI SAR will be maintained during the storage period. The requested exemption would in no way endanger the health and safety of the public or be inimicable to the common defense and security.

Therefore, in accordance with 10 CFR 72.7, " Specific exemptions," PGE requests that an exemption from the requirement for monitoring of the continued efficacy of neutron absorbing

! material, contained in 10 CFR 72.124(b), be included in the Trojan ISFSI license, an application l for which is currently pending before the NRC.

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