ML19095A291

Submit Supplemental Information Concerning High Density Spent Fuel Storage Racks, as a Result of Discussion with NRC Staff

ML19095A291
Person / Time
Site:	Surry
Issue date:	02/08/1978
From:	Stallings C Virginia Electric & Power Co (VEPCO)
To:	Case E, Reid R Office of Nuclear Reactor Regulation
References
Serial No. 066
Download: ML19095A291 (5)

Text

e* j"'. - : .

• i' I,*,, f', 1.*-~. -

e

't - -: ,

. ~ .. - -- *.. ~-* ... " '

1*

YIRGINIA ELECTRIC A1iD POWER COMPANY Ri:cHMOND, Vi:nGJ:N .IA 23261 Febr.uary 8, 1978 l1r. Edson G. Case, Acting Director Office of Nuclear Reactor Regulation ATTN: Mi. Robert W. Reid, Chief Operating Reactors Branch No. 4 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C. 20355

Dear Mr. Case:

The purpose of this letter is to submit supplemental information concerning the High Density Spent Fuel Storage Racks for Surry Power Station Unit Nos. 1 and 2. This information is being submitted as a result of dis-cussions between Vepco and members of your staff *

..., The applicable codes used in the design of the high density spent fuel storage racks are discussed in section 6.3.1.1 of the report "Summary of Proposed Modifications To The Spent Fuel Pool Associated With Increasing Storage Capacity for Surry Power Station Unit Nos. 1 and 2 11 submitted with our letter of May 27, 1977, Serial No. 186. The codes used in the design, fabrication, inspection, and installation are listed in attachment 1. It should be noted that it was not possible to use the ASME code for the design of the spent fuel racks because the ASME code is a pressure vessel code and does not cover spent fuel racks. However, because the ASME code could be ap-

• plied to other phases of the project besides design, it was used for the fab-rication, inspection, and installation of the spent fuel racks. The design of the spent fuel racks was done using the AISC code.

We believe that both of these codes represent quality standards of the industry and provide reasonable assurance that the racks will perform their intended function in accordance with applicable criteria, rules and re-gulations.

In our letter of September 29, 1977 a response to question 7(c) from your letter of August 25, 1977 was provided. A more detail discussion of this question is provided as attachment 2. .

As*your staff is aware, we plan to refuel Unit No. 1 on or about April 1, 1978. In order to perform this refueling it is necessary that at least a por-tion of the new racks be installed. In order to assure that the racks are. in-stalled by April 1, 1978 it is necessary that we commence installation by March 1, 1978. Your approval is requested so that we can proceed with installation.

780440052

e e VIROINU,. ELECTRIC AND Pow1rn COMPANY TO Mr. Edson G. Case Page No. 2 If you have any questions or comments on this material, we w~u~d be pleased to meet with your staff at their convenience to discuss them.

Very truly yours,

..._y -) 'l

./7 -/ 'I

<'...J.~* . .? t/

/7 .t,,,-r-

~ ...J ,,; l .).. ..

...:..,)/

t'l(;.tl1-.,C,.1/"2./

C*. M. Stallings Vice President - Power Supply and Production.Operations Attachments cc: Mr. James P. O'Reilly, Director Office of Inspection and Enforcement Region II

e

• ATTACHMENT 1 APPLICABLE CODES USED IN THE DESIGN FABRICATION, INSPECTION, AND INSTALLATION OF *THE HIGH DENSITY SPENT FUEL STORAGE RACKS FOR SURRY POWER STATION

1. Design

a. A.I.S.C. Manual -of Steel Construction, Seventh Edition, 1970.

2. Fabrication

a. ASME VIII, ASME Boiler and Pressure Vessel Code,Section VIII.

b. ASME IX, ASME Boiler and Pressure Vessel Code,Section IX Welding and Brazing Qualifications.

3. Inspect~on

a. ASME V, ASME Boiler and Pressure Vessel Code,Section V, Nondestruc-tive Examination.

4. Installation

- a. ASHE VIII", ASHE Boiler-and Pressure Vessel Code,Section VIII, Appendix 9.

b. ASME IX, ASME Boiler and Pressure Vessel Code,Section IX.

i-il l

I

e ATTACHMENT 2 Question 7(c):

Discuss the effects of a straight drop through a storage can and im-pacting on the liner. Indicate the local and overall effects of this postulated impact load.

Response

If a fuel assembly was to drop straight through a storage can it would not impact on the fuel pool liner but would impact on the bottom of the storage can. The storage cell rests on four (4)

1. 5 11 X 1. S" legs *through which the impact loads would be transmitted to the fuel pool floor. A calculation has been performed using empirical equations and energy balance methods to determine the effects of the free fa11 of a fuel assembly through a storage cell from a height of 24.0 inches above the top of the storage cell and its impact on top of th~ storage* cell legs.

By conservatively neglecting the piston effect as the fuel assembly falls through t9e storage cell, but considering buoyancy and drag

- effects, the velocity of impact has been calculated to be 30 feet per second.

It bas been conservatively assumed that the fuel assembly absorbs 30 percent of the kinetic energy of impact. Calculations using the Modi-fied Petri formula for -penetration of a* 11 hard:-1 missile in a concrete target indicate that the storage cell legs may penetrate the concrete floor by approximately 3/4 inch. The ductile stainless steel liner plate will be stretched or "drawn II into the resulting cavity. The maximum calculated plate strain for this condition has been calcula-ed as 72 percent of the stainless steel ultimate strain capacity.

Thus, no tearing or perforation of the liner will occur.

The reaction load resu1ting from the deformation of the fuel assembly has been conservatively calculated using the fuel assembly axial stiff-ness and assuming a uniform compression with buckling. This reaction load (186 Kip) results in concrete bearing stress of 11.6 ksi and a punching shear stress -in the steel liner plate of 31.ksi indicating local crumbling of concrete under ideal "punch and die" support condi-tions which do not exist due to the support provided by the concrete underneath the liner plate.

It can, therefore, be concluded that the straight drop of a fuel assem-bly through a storage cell and its impact on top of the storage cell base legs would result in minor local crumbling of the concrete floor and a small acceptable deformation of the liner plate. However, the structural integrity of the storage rack and the leak tight integrity of the spent fuel storage pool will be maintained.

e ATTACHMENT 2 RESULTS OF FUEL ASSEMBLY DROP ANALYSIS STRAIGHT DROP THROUGH CELL FROM 24 INCHES ABOVE CELL Allowable Value Weight of fuel Assembly, k .. : 1.6 Maximum Drop Height, in.  :._'./,.*\;- **190.5 Free Fall lmpact Velocity, ft/sec 32.0 Impact Velocity Considering Drag and Buoyant Forces, ft/sec 29.8 Kinetic Energy of Drop to be Absorbed by Fuel and Floor, in-k 268.3 Kinetic Energy Absorbed by Fuel Assembly Uniform Compression (assumed),% 30 Kinetic Energy Absorbed by Floor and Liner Plate (assumed),% 70 Maximum *Trans~itted Reaction Force, k 185.6 1

Maximum Concrete Bearing Stress, ksi 11.6 3.57 ,2 Maximum Cell Leg Penetration into Concrete Pool Floor, in o. 76 3 Maximum Liner Plate Tensile Strain, in/in 0.35 0.485

..,Maximum Punching Shear Stress in Stainless 4

Steel Liner Plate, ksi 31.0 41.5

1. Based on Paragraph 10.14 of ACI 318-71

2. There will be local crumbling of the concrete under each leg

3. Strain at ultimate stress (Dynamic)

4. Dynamic Yield Stress for Stainless Steel

'