ML19340B896

Submits Proposed Change to Tech Specs,Modifying Pages 183, 185 & 185a & Adding Page 185b to Incorporate Definition of Requirements for Spirally Unloading & Reloading Reactor Core

ML19340B896
Person / Time
Site:	Vermont Yankee
Issue date:	11/06/1980
From:	Heider L VERMONT YANKEE NUCLEAR POWER CORP.
To:	Office of Nuclear Reactor Regulation
Shared Package
ML19340B897	List: ML19340B896 ML19340B899
References
WVY-80-156, NUDOCS 8011120532
Download: ML19340B896 (3)

Text

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Proposed Change No. 94 v

V fcavgI3MONT Y AN K MM NUCLEAR POWER CORPOR ATION

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- WESTDORo, M ASS ACHUSETTS 01581 h TELEPHONE 617-366-9011 November 6, 1980 United States Nuclear Regulatory Commission Washington, D.C. 20555 Attention: Office of Nuclear Reactor Regulation Re ference : (a) License No. DPR-28 (Docket No. 50-271)

(b) Letter, T. A. Ippolito to Mr. D. Arnold, Amendment No. 57 to Facility Operating License, dated February 15, 1980

Subject:

Technical Specification Change to Allow Spiral Unloading and Reloading of the Reactor Core

Dear Sir:

Pursuant to Section 50 59 of the Commission's Rules and Regulations, Vermont Yankee Nuclear Power Corporation hereby proposes the fdllowing changes to the technical specifications.

Proposed Change Modify pages 183,185 and 185-a and add page 185-b to incorporate conditions which define requirements for spirally unloading and reloading the reactor core. Modify bases pages 186 and 187 and add page 186a to reflect the changes to page 183 and 185 Reason and Bases for Change The proposed change as described above and on the attached technical specification pages would enable Vermont Yankee to utilize a spiral unloading and loading pattern during core alterations without requiring that a specific count rate be maintained during such activities. This would eliminate the necessity of using special dunking type detectors during core unloading.

Besides being operationally inconvenient, dunking chambers suffer from signal variations due to their lack of fixed geometry. Moreover, the use of dunking chambers increases the risk of loose objects being dropped into the vessel.

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United States Nuclear Regulatory Commission November 6, 1980

- Attention: ' Offico of Nuclear Reactor Regulation Page 2 The proposed Technical Specification would allow spiral unloading and reloading- of the core. LIn such a program, only cells on the edge of the array are unloaded or reloaded._ No major imbedded ' cavities or major peripheral

. concavities would be permitted. In such a case, the neutron multiplication factor of the intermediate arrays must be less than .or equal to that of _ the fully loaded core. Since the shutdown margin of the fully loaded core is well assured by Section 3 3. A. , this proposed change is acceptable from the point of view of shutdown margin. -

~ The purpose of the SRM's is to monitor the neutron flux in the core during reactor shutdowns and core-alterations for the reasons discussed below:

A multiplying medium with no neutrons present foras the basis for an accident scenario in which reactivity is gradually but inadvertently added until.the medium is highly supercritical. No neutron flux will be evident since there are no neutrons present to be multiplied. The introduction of some neutrons at this point would cause the core to undergo a sudden power burst, rather-than a gradual startup, with no warning from the nuclear instrumentation. .This scenario is of great concern' when loading fresh fuel, but is of lesser concern for exposed fuel. Exposed fuel continuously produces neutrons by spontaneous fission of certain plutonium isotopes, photofission and photodisintegration of deuterium in the modertor. This neutron production in exposed fuel is normally gr0at enough to meet the 3 cps minimum for a full core after a refueling outage ~ with tne lumped neutron sources removed.

There is assurance .that a sufficient flux level will be present as long as some exposed fuel is present. The proposed Technical Specification (Section 3 2.B.4) requires.that two diagonally adjacent fuel assemblies, which have previously accumulated exposure in the reactor, be loaded into their previous core positions next to each of the SRM's to provide a minimum.of 3 cps prior to loading any other fuel. Additionally, the proposed Technical Specification (Section 312.E.3) requires that the shutdown margin of the core be verified prior to spiral unloading and that the core ce spirally reloaded only to its original configuration and in . exactly the reverse of the unloading.

spiral with the exception of the eight fbel assemblies described in Section 3 12.B.4. This assures that no unanticipated flux perturbations will' occur during the performance of a' spiral unload / reload. Moreover, at least 50% of the fuel to be reloaded into the. core shall have previously accumulated a minimum exposure of 1000 Mwd /T to ensure the presence of a minimum neutron flux.

.A similar change to the one proposed by this letter was approved by the NRC for the Duane Arnold Energy Center in Reference (b). Due to the similarity between.the Duane Arnold and Veront Yankee reactors, we feel that the same reasons, bases, and safety evaluation apply to this change.

Safety Considerations Based on the above discussions, it is concluded that'this proposed change dcas not present significant hazards not described or implicit in the safety analysis' report, and does ~not involve an unreviewed safety question as describedLin 10 CFR 50 59

United Stat:s Nuclrar R:gulatory Commission November 6, 1980 Att ntion: Offic0 of Nuclear Reactor Regulation Page 3 This submittal has been reviewed by the Vermont Yankee Nuclear Safety Audit and Review Committee.

Fee Determination This proposed change requires an approval that involves e single safety issue and is deemed not to involve a significant hazards consideration. For these reasons, Vermont Yankee Nuclear Power Corporation proposed this change as a Class III Amendment. A payment of $4,000.00 is being forwarded by separate letter.

Schedule of Change This proposed change will be incorporated into Vermont Yankee Technical Specification as soon as possible following NRC approval.

We trust you will find this information satisfactory; however, should you desire any additional information, please contact us.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION L. H. Heider Vice President COMMONWEALTH OF MASSACHUSETTS)

)ss COUNTY OF WORCESTER )

Then personally appeared before me, L. H. Heider, who, being duly sworn, did state that he is a Vice President of Vermont Yankee Nuclear Power Corpora tion , that he is duly authorized to execute and file the foregoing request in the name and on the behalf of Vermont Yankee Nuclear Power Corporation, and that the statements therein are true to the best of his knowledge and belief.

Robert H. Groce Notary Public My Commission Expires September 14, 1984 M,,, ,.. . . * .,,

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