ML20137G816

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Ro:On 730125,available Excess Reactivity of Core Exceeded Tech Specs Limit.Caused by Change in Worth of Control Rods. Rearrangement of Core Configuration Initiated to Reduce Available Excess Reactivity
ML20137G816
Person / Time
Site: Dow Chemical Company, 05000000
Issue date: 02/16/1973
From: Hoyle H
DOW CHEMICAL CO.
To:
US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20136D183 List: ... further results
References
FOIA-85-256, FOIA-85-258, FOIA-85-259, FOIA-85-261 1218, NUDOCS 8508270391
Download: ML20137G816 (2)
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  • 50-264

. DOW CHEMICAL U.S.A.

February 16, 1973 MIDLAND, MICMGAN Director Division of Reactor Licensing ,

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%b U.S. Atomic Energy Commission r' 3;f A g ** ? lpp 20545 Washington, D. C.

Gentlemen: N A)g I would like to report an incident concerning the Dow TRIGA Reactor which may have found the facility temporarily in a state beyond the limits stipulated in the Technical Specifications (License R-108, Docket 50-264). At no time was the safety of operating personnel, the public or the facility in jeopardy, but it was a " substantial variance. . . from performance specifications" and therefore reportable under Section 3.D.2.

of our license.

During a scheduled outage of the facility, on January 25, 1973, the annual fuel and control rod inspection was carried out.

Prior to this operation, the available excess reactivity of the core was measured at the 5 watt level as $2.10. (The limit set '

by the Technical Specifications is 1.5% delta k/k. For our facility the beta effective is 0.70%. The limit thus converts to 1.5% (delta k/k) / 0.7% 6k/k =$2.14)

S After the inspection had been completed, the core excess was remeasured at the completion of the checkout. At this time an available excess reactivity of $2.22 was found.

Since such a large increase (from $2.10 to $2.22) had not been experienced by the facility before as the result of a fuel-checking operation, where the "before" and "after" core configuration had been maintained unaltered, it was reasoned that this me'asurement could be due to a change in the worth of the control rods, so that the measurement would have to be verified after a'recalibration of the rods.

After consultation with two other members of the Reactor Operations Committee, the reactor supervisor decided to proceed with the calibration of the control rods as the next operation. During the control rod calibration procedure the reactor was operated at steady state power levels of 0.5 watts and varying power levels up to 1 kw. Using the resulting new control rod calibration curve the available excess reactivity of the core was redetermined as

$2.28.

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PDR FOIA MOHN85-256 PDR -

AN OPERATING UNIT OF THE DOW CHEMICAL COMPANY Awevansany 121e

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USAEC 2 2/16/73 At this time it was realized that the facility was exceeding the limits set by the Technical Specification and a rearrangement of the core configuration was initiated to reduce the available excess reactivity to a measured value of $1.66.

This rearrangement of the core again altered the control rod calibrations and required recalibration of the rods. This was carried out as the next operation. When the available excess reactivity was redetermined using the new control rod calibration it was found to be $1.72, sufficiently below the limit of $2.14 to avoid recurrence of the incident.

From this experience it was learned that an increase in the available excess reactivity is possible during the fuel inspection operation, where fuel elements are merely removed from their core positions, inspected and reinserted, and that remedial action i.e., changes in the core configuration aimed at reducing the available excess reactivity, should be undertaken bumediately, even before a high core excess measurement can be verified af ter recalibration of the control rods.

During the incident and as a result of it, the reactor at no time was out of control of the operator, nor did it pose a safety threat to the operating crew, the facility, or the public.

Operations to calibrate the control rods were performed at levels below the power range. The proper shut-down margins of the control rods were maintained at all times.

The facility was not operated with a high available excess reactivity for purposes other than maintenance and calibrations.

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H. R. )yle Chairman Radiation Safety Committee Midland Location 1701 Building scb l

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P q 'O h DOW CHEMICAL U.S.A.

MIDLAND, MICHIGAN 48640 November 9, 1973 Mr. James G. Keppler Directorate of Regulatory Operations, Region 111 U. S. Atomic Energtj Commission 799 Roosevelt Road Glen Ellyn, Ettinois 60137

Dear Mr. Keppler:

This letter is in reply to your report on the inspection of our Dow TRIGA reactor facility carried out by Messrs Fishbaugher and Brown of tjour office on September 20 and 21, 1973.

The Dow TRIGA reactor has been operated under License Number R-108, Docket Number 50-264, since 1967 at the Midland location of The Dow Chemical Compant).

Item B consisted of "a change to an operating procedure which was inserted into the Operating Log for use on July 23, 1971, without formal rev.iew and approvat by the (Reactor Operations) Committee."

The incident occurred on July 23, 1971, during a major updating project for the saf ettj and control instrumentation of the reactor. The plans for such updating had been discussed by the Reactor Operations committee at meetings cartier in 1971, and detailed information on these plans and the instrumentation involved, as wett as an evaluation of the impact of the proposed modernization upon the technical specifications of our f acilitt) were communicated via our Radiation Safety Committee to the AEC's Division of Licensing. The AEC informed as that the proposed changes were within our technical specifications and re-quired no special action by the Coramission.

Three individuals involved with the instattation were also members of the five member Reactor Operations Committee and were thas intimately f amtliar wi.th the changes that had been ef f ected by the ins tattation of o A "

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Nov 1 g 39,3 AN OPEftATING UNIT OF THE DOW CHEMICAL COMPANY

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. .o Mr. Keppler 2 November 9, 1975 the new equipment. The note placed into the reactor tog book on July 23, 1971, consisted of a description of the changes ef f ected and the concomitant changes of procedure necessitated bij the absence of the old equipment and presence of new equipment having dif f erent control switches.

This note constituted an instruction for the five reactor operators who att were intimately familiar with the instattation of the new equipment. A documented meeting of the three Reactor Operations Committee members present to approve the changes could have prevented the technical violation.

Even after July 23, the instattation had not been completed s atis f actoritsj, as various " bugs" in the new circuitrij had to be identified and cleared up. Only after a representative of the vendor had checked out the equipment with us during the second week of August, 1971, was the instattation completed and the changes of ficially discussed at the meeting of the Reactor Operations committee on August 18, 1971.

The corrective steps taken were:

The instattation of the then new " Flux Contratter" (which necessitated the change to the operating proc ~edures), was discussed bij the Reactor Operations Committee on August 18, 1971, and the steps taken in connection with it were approved by the Committee.

The Reactor Operations Committee took up a review of the startup procedure during its session of October 29, 1971, after the dif ficulties with the flux controtter had been overcome with the help of a representative of the vendor.

The Committee further modified the procedure at that time and approved it.

Corrective steps which will be taken to avoid further violationst An annual requalification program for operators of the facility was instituted in 1973. A review of Operating Procedures and Administrative Requirements has been incorporated to refamiliarize the staf f with the proper procedures to be followed for any change of operatrng procedures to become effective.

e Mr. Keppler 3 November 9, 1973 A review of att existing operating procedures will be carried out by the Reactor Operations Committee on an annual basis and the results recorded in the minutes of the Reactor Operations Committee.

The date when futt compliance will be achieved:

The violation occurred on July 23, 1971. Futt compliance was achieved on August 18, 1971. The proper procedure for an additional change to the operating procedures was followed by the Reactor Operations Committee on October 29, 1971. Since we are not aware of any subsequent violation nor has one been identified by the inspectors, we believe that fatt compliance was achieved at that time.

Very truly yours,

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H. R. oyt , Ia&tm'aii' Radiation Safety Committee DIG Chemical Biology Research 1707 Building sit cc: Members of the Radiation Safety Committee i

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