ML20127P409

Safety Evaluation Re Amend to License DPR-22,proposing Shipment of Sf from Monticello Nuclear Generating Plant Using GE IF-300 Shipping Cask

ML20127P409
Person / Time
Site:	Monticello
Issue date:	07/25/1976
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20127P387	List: ML20127P384 ML20127P409
References
NUDOCS 9212020212
Download: ML20127P409 (2)

Text

. NORTHERN STATES POWER CO.

i MONTICELLO NUCLEAR GENERATING PLANT

SPENT FUEL SHIPPING CASK HANDLING Northern States Power Company previously proposed shfpping of spent fuel from their Monticello Nuclear Generating Plant using a General Electric Company IF-300 shipping cask. Analysis showed that the reactor building structures could not, for all cases considered, withstand the impact of a dropped IF-300, seventy ton cask. Due to the length of time established to implement proposed plant modi-fications to provide redundant cask handling equipment at Monticello, an interim program for spent fuel shipping, using a lighter shipping cask, has been established by Northern States Power Company. The proposed shipping cask. is a model NFS-4 cask manufactured by Nuclear Fuel Services, Incorporated, of West Valley, New York. This is a two element cask weighing 25 tons and it has been licensed for use under Title 10, Code of Federal Regulations,. Part 71.

Eight critical cask drop sites were postulated. The reactor building structural capability, the spent fuel pool integrity, and the protection of spent fuel and vital systems were assessed for these postulated drops . Four of these sites were located on the operating floor, two on the spent fuel storage pool slab, and two in the area of the base of the equipment hatch. These eight locations were chosen as the most critical drop sites-along the path traveled by the spent fuel cask.

Impact loads at both the center and the edge of the concrete slabs, the dead weight of the structure, live loads on the floor, and the weight of water above the fuel pool floor were all included in the analysis.

For each drop location the-principles of conservation of energy and conservation of linear momentum were used to evaluate the effects of impact on slabs and beams for flexure, bending shear, punching shear, perforation, and spalling in accordance with Topical Report BC-TOP-9A, gg20gogg D g gj63 p PDR- ,

. .. ' 2-

" Design of Structures for Missile impact," approved by the NRC staff on November 25, 1974. The analyses allowed plastic deformation of the beams and slabs and took credit for energy absorbtion' by the deformation of the cask impact devices and the increase in allowable stresses in concrete and steel due to the dynamic nature of the loads. The effects of bouyancy and drag forces were included for postulated drops into the spent fuel storage pool. Results of these analyses were compared with code allowables in accordance with the Standard Review Plan, Section 3.8.4 in order to determine structural reliability. We have reviewed the above analyses and find them to be acceptable.

The possibility of overturning of the spent fuel shipping cask due to seismic loading was assessed. For SSE floor response values of 0.129 horizontal acceleration and 0.089 vertical acceleration taken from the Monticello FSAR the spent fuel cask will not overturn.

The material properties of concrete and steel used in the analyses were reviewed and verified.

With the exception of costulated drop site number 7, at the base of the equipment hatch, adcquate factors of safety exist along the path of the spent fuel cask, and movement of the cask should not threaten structural integrity. Postulated drop site number 7 is on the 24" thick equipment hatch slab. Analysis has shown that the slab could not sustain a 93' 2" free drop of the cask onto this location. The appli-cant has suggested that administrative control can be implemented to essentially preclude the likelihood of a cask drop in this location.

The possibility of spent fuel damage due to a postulated cask drop into the spent fuel pool has been reviewed for the NFS-4 twenty-five ton cask with all the spent fuel stored in the north end of the fuel

,. pool. Under these circumstances there should be no undue risks.

However, for a change in fuel cask, movement of stored fuel from the north end of the pool, or a fuel pool expansion the cask drop accident will have to be re-evaluated.

Except as noted above, we find that the applicants proposal is acceptable.

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