ML20235U932

Responds to NRC 871008 Request for Addl Info Re Spent Fuel Consolidation Demonstration Project.Probability of Fuel Handling Accident Not Significant.Addendum to SER Encl

ML20235U932
Person / Time
Site:	Prairie Island
Issue date:	10/08/1987
From:	Musolf D NORTHERN STATES POWER CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM), Office of Nuclear Reactor Regulation
References
NUDOCS 8710140318
Download: ML20235U932 (7)

Text

Northern States Power Company 414 Nicollet Mall Minneapolis, Minnesota 55401 Telephone (612) 330 5500 October 8, 1987 Director of Nuclear Reactor Regulation US Nuclear Regulatory Conunission Attn:

Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PIANT DOCKET NOS. 50-282 LICENSE NOS. DPR-42 50-306 DPR-60 Additional Information Related to Fuel Rod Consolidation

Reference:

(a) Letter dated September 22, 1987 from D Musolf, NSP, to Director of NRR, NRC, " Fuel Rod Consolidation" (b) NRC Request for Additional Information da%d October 8, 1987 Reference (a) provided, for the information of the NRC Staff, a copy of our project description and safety evaluation report for the Spent Fuel Consolidation Demonstration Project at the Prairie Island Nuclear Gen-erating Plant.

In response to a request for additional information from the NRC Staff, we have prepared and are forwarding a copy of an addendum to the pro-ject safety evaluation report.

This addendum provides further justi-i fication of our finding that this project does not increase the proba-bility of occurrence of a fuel handling accident as required by 10 CFR Part 50, Section 50.59(a)(2)(i).

Northern States Power Company believes that the probability of a fuel handling accident associated with the Spent Fuel Consolidation Demon-stration Project is insignificant when viewed in the context of all past and future fuel handling operations which are part of the routine operation of the Prairie Island Nuclear Generating Plant and other power reactor facilities. The total number of fuel moves that will be made during the Consolidation Demonstration Project represent only 0.4%

of 30,000 fuel moves, which is the estimated minimum number of fuel moves that will be made over the 40-year design life of the plant.

This increase is offset by the improved expertise in fuel handling operations gained over 13 years of operation at Prairie Island. We have therefore concluded that the probability of occurence of a fuel handling accident has not. increased, l

8710140310 871000 PDR ADOCK 05000282

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Northem States Power Company Director of NRR October 8, 1987 Page 2 In addition, the worst case radiological consequences of a fuel drop

- accident during the Consolidation Demonstration Project are estimated to be less than 1/10 of the consequences of the design basis fuel hand-ling accident evaluated in the Prairie Island Updated Safety Analysis Report (USAR). This is because the fission products in the fuel used during the demonstration project will have decayed for several years and the design basis accident assumes a freshly discharged assembly is dropped.

The fuel handling activities that will take place during the demonstra-tion project fall within the scope of those activities previously re-viewed and found to be acceptable by the Commission.

They are a neces-sary part of. normal plant operation authorized by the operating li-cense.

For example, approximately 900 fuel moves have been made in the past for fuel sipping and reconstitution to provide assurance of con-tinuing fuel integrity.

As a result of fuel sipping activities, reac-tor coolant piping radiation levels and annual occupation radiation exposure are among the lowest in the industry. An additional 1200 fuel moves resulted from spent fuel pool expansion activities.

Four full core off-loads and reloads have been performed to accomplish routine ASME Code vessel inspection. Two two full core off-loads and reloads have been necessary for replacement of the vessel upper internal as-semblies in each unit with assemblies of an improved design.

As you can see, spent fuel moves and spent fuel handling routinely occur for a number of reasons other than periodic refueling operations.

These activities have become an integral part of normal plant operation.

Please contact us if you have any questions related to the additional information we have provided. We request that review of this matter be given priority to minimize additional delays in beginning the demon-stration project.

Thank you for your consideration in this matter.

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David usolf Manager Nuclear Support Services c: NRR Sr Project Manager, NRC Sr Resident Inspector, NRC Regional Administrator, Region III, NRC G Charnoff Stato cf Minnesota William Clausen Brad Moore Dr John Ferman Attachment I

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Modification'86L944' Addendum'l SAFETY EVALUATION.~

. SPENT. FUEL CONSOLIDATION DEMONSTRATION This: addendum:to the1 safety evaluation'of modification 86L944

'is intended to' address the issue.of whether or not this 1modificationiincreases :the probability of. occurance of a. fuel:

handling accident.'While the original safety. evaluation

-concluded thatithis. modification would not' increase the

probability,1this addendum is-intended to'further expand on

the subject-and: provide additional justification for this conclusion ~

e.

This modificationiinvolves movement of fuel by three.(and' possibly four) different tools. These tools are the spent fuel. handling tool, the7 fuel transition canister handling-

.too1~,;the consolidatedirod storage ca;ister handling tool, Y

and1possibly.the thimble grip spent. fuel handling tool.

The spent fuel. handling tool is_the current handling tool tused at Prairie Island. This tool will be used to move the 1 sfuel assemblies from the spent fuel storage racks _to the rod

-consolidation ~ elevator / rotator. This tool has-been'used.

successfully'at. Prairie Island for thousands of fuel moves in the:past:13 years. No changes.to this tool or it's operation are: required for. rod consolidation.

The fuel transition ~ canister handling tool is part of the Westinghouse rod consolidation equipment. This tool is used to--move the fuel transition ~ canister, loaded with the fuel rods from one assembly-(179 rods), from the transition

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-canister loading frame to the consolidated storage can loading station.-This is a move of approximately 10 feet that takes. place-entirely within the fuel transfer canal area of

the spent fuel pit. This tool never carries the-transition

-canister over the spent fuel racks,-but will be used to position the transition canister over a storage canister previously loaded with the rods from one assembly. This tool has been designed in accordance with ANSI N14.6-1978, "American National Standard for Special Lifting Devices for

-Shipping Containers 10,000 pounds (4500 Kg) or More for

~ Nuclear Materials".

The consolidated rod storage canister handling tool is used to lift and carry the rod storage canisters. This toll will

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Modification 86L944 L

. Addendum 1

.beLused to move'emptyLeanisters to the loading frame, and to l

/ move'loadedtcanisters to the spent. fuel" racks. These canisters will be:loadediwith'the.rodsLfrom twoLfuel 1

L assemblies.L.This tooliwas also designediin accordance with-c

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LANSI N14.~6-1978._The. safety. factor for this tool is 8 based on' the = ultimate: strength,'.and 4.when based on the yield ~

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. strength. This' exceeds the safety factors of-5Eand 3 required.

Jby-ANSI N14.6-1978J An additional consideration when moving canisterspis the design of the storage canisters'used to hold the1 fuel ~ rods.;These canisters were. designed in accordance with NUREG-0612,_" Control'of heavy loads.at. Nuclear Power 7

Plants"..These canisters are designed'with a. safety.. factor oof111, as: opposed;to-a NUREG-0612 required safety factor of 10.

M The Thimble Grip. Spent Fuel Handling Tool is a new tool

designed?especially for the! movement of assemblies from region 1D,. E,Jand F at Prairie Island. These assemblies have

suspected weak joints at the point where the' nozzles attach to

the' guide _ tubes. An assembly 1from these regions has

' experienced a! failure at'this joint that resulted irt the

assembly' falling from the tool duringla fuel move (Reference 1). This' tool was designed in accordance with the'ASME Boiler and Pressure. Vessel Code,Section III,. Appendix XVII.. The

-design 11oad was-based on two times ~the fuel assembly weight.

The' faulted condition was' set at six and one half times the fuel assembly weight.

?As-the' previous information-shows, the lifting equipment has all'been designed in accordance with applicable standards, and~therefore nothing' associated'with thie modification reduces'the margin of safety of the. fuel handling equipment.

i This-means that this modification does not increase the i

. probability that the. fuel; handling equipment will fail,

'resulting in'the dropping of a fuel assembly.

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1 An' argument ~could be made that this modification results in

.an' increase-in the number of fuel moves at Prairie Island, increasing the chance that an assembly will be dropped. This argument is based on the reasoning that while it may be true that nothing has been done to increase the probability that a handling tool will' fail on any particular move, an increased

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number of uses of the tool'will increase the probability of a failure. However,xthis approach assumes the probability of a L

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E:fueluhandling' accident is based on.the number of fuel moves required solely to. refuel the reactor and ship fuel to a lpermanentLdisposal site, with'any. moves in-addition to these resulting;inlan increase in the probability'of a fuel handling;accidentLand therefore not satisfying the-I

. requirements: of ;10CFR50.59. -

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InLfact,Lmovement of fuel in support of projects, unrelated to refueling:or'off-site; shipment has been done many times under-

.the. authority granted in 10CFR50.59 at Prairie Island and many other~ plants. Some examples'of.this are:

Fuel' Sipping / Reconstitution: Prairie. Island has a_-policy

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that:no leaking fuel will be returned-to the core duringua

' refueling < outage.;When leaking fuel is indicatedLduring a cycle, all' fuel returning to the core during.the next outage is sipped tofdetermine if'it contains leakingLfuel.

Assemblies identified as having a. failed fuel rod (s);have eachirod individually' inspected for failure. Failed rods are removed from ;the. assembly and replaced by either: dummy rods-or. intact rods from unused-assemblies. Prairie Island L

Thas performed approximately 900 fuel moves in support of l

fuel sipping.and reconstitution.

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Bulge Joint-Inspections: After the failure of a fuel assembly top nozzle bulge joint attach. point to the fuel assembly.that. resulted in a ' dropped assembly, a bulge joint inspection program was' instituted at Prairie Island. This program involved removing fuel assemblies from the spent

-fuel racks in order to perform visual inspections of the

. suspect joints. This program was' reviewed and endorsed by

-the NRC (Reference 2).

Inservice' Inspection Program: As part of the 10 year inservice inspection program at Prairie Island, the cores of each unit are off-loaded into the spent fuel pit in order ~to inspect the reactor vessel welds. off-loading the core involves approximately 484 fuel moves, half in the J

. spent fuel' pit and half in containment. It should be noted i

that approximately 400 of these moves involve freshly discharged assemblies, with much higher potential radioactive releases from a postulated accident than the fuel used in consolidation, which has all been out of the reactor for at least 2 years. This inspection program is

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Page 4 of 5 Modification 86L944 Addendum 1 required as part of Section 11 of the ASME boiler and j

Pressure Vessel code.

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Incore Thimble / Upper Internals Replacement: During two recent outages, the upper internals and incore thimbles i

were replaced in each reactor. The upper internals were l

replaced to prevent potential problems associated with guide tube split pin cracking. Incore thimbles were replaced due to internal blockages in some of the thimbles.

As a part of the installation of these modifications, the cores were off-loaded to the spent fuel pit. These modifications were performed under 10CFR50.59.

Monticello Recirculation Piping Replacement: In 1984, Northern States Power's other nuclear unit, Monticello, replaced the the reactor recirculation piping. This modification involved off-loading all 484 fuel assemblies from the Monticello core. This modification was performed under 10CFR50.59.

These examples are designed to demonstrate that the probability of a fuel handling accident should not be based 4

solely on the narrow scope of fuel handling associated with i

reactor refueling and shipment to a permanent disposal site, but rather should be based on the realization that fuel is safely moved in support of many plant operations and modifications, all performed under 10CFR50.59. In comparison to several other projects already performed under 10CFR50.59, the 125 fuel moves associated with the consolidation is not even a large number of fuel moves.

This additional information reaffirms that this modification does not increase the probability of occurrence of an 4

accident or malfunction of equipment important to safety previously analyzed in the USAR or subsequent commitments.

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. Modification'86L944 Addendum.1-I l

References-l I

1.. Licensee Event" Report 81-031/OlT ]

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2. Safety' Evaluation by the Office of Nuclear Reactor.

Regulation, Northern States Power Company Prairie Island Units'11.and 2, Docket nos. 50-282 and.50-306', Spent Fuel Assembly: Degradation, December 1981

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-Reviewed By: N,MM,

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