ML19269E406

RO on 790607:shutdown Margin of Triga Reactor Was $0.48, Nine Cents Less than Tech Specs Limitation of $0.57.Upon Discovery,Two Fuel Elements Were Moved & Shutdown Margin Went Up to $0.74

ML19269E406
Person / Time
Site:	Oregon State University
Issue date:	06/19/1979
From:	Wang C Oregon State University, CORVALLIS, OR
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
References
NUDOCS 7906280132
Download: ML19269E406 (7)

Text

.

Radiation Center E".

University corvatiis. Oregon 97331 0:37m2m t >

June 19, 1979 U.S. Nuclear Regulatory Commission Region V Office of Inspection and Enforcement 1990 N California Blvd.

Walnut Creek Plaza, Suite 202 Walnut Creek, CA 94596

Reference:

Docket No. 50-243, License No. R-106 Gentlemen:

On June 7,1979, the shutdown margin of our TRIGA reactor was

$1.48, nine cents less than our Technical Specifications (Part 3.2) 1rnitation of $0.57. This was reported to your office by telephone on June 8,1979, as required by our Technical Specifications (Part 6.T.a). This written report, required by Part 6.7.b of our Technical Specifications, provides more details of this occurrence.

Incident.

On June 7,1979, during a core configuration change to accommodate an experimental request, our shutdown margin (with the most reactive rod out) dropped to $0.48, nine cents less than the Technical Specifi-cation limit of $0.57.

Corrective Action As soon as the situation was discovered, two fuel elements were moved and the shutdcwn margin went up to $0.74. These two fuel elements were moved on June 7, 1979. Thus, the situation was corrected physically the same day.

This incident was discussed at a Reactor Operations Committee (ROC) meeting held on June 11, 1979. The ROC, upon review of Oregon State TRIGA Reactor Operating Procedures (OSTROP) No.11 (Fuel Handling Procedures), decided that more guidance should be provided in this OSTROP regarding core excess and shutdown margins during core configura-tion changes. The ROC directed that the reactor staff write such revisions to 0 STROP No.11 and submit them to the ROC for review and approval. Such revisions to OSTROP No.11 hopefully will prevent such a situation from arising again.

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USNRC Page Two June 19, 1979 Background Details The core, prior to these changes, was quite symmetrical (see Fig. 1). An experimenter wanted the core skewed toward beamport #4 (the uoper left quadrant on Fig.1) to enhance the flux for his experiment. This change was discussed and approved by the ROC on March 6, 1979.

The first change (see Fig. 2) was performed with three fuel elements left out of the core (i.e., the core in Fig. 2 has three less fuel elements than the original core in Fig.1). This was done to be ccnservative, as it was hard to estimate how much the rod worths and core excess would change in this new configuration. As expected, the worths of the regulating and safe rods went down and the worths of the shim and transient rods went up. The total rod worth went down ($10.64 vs. $11.45) in going fro:n Fig. I to Fig. 2, and the core excess went down, due to the poorer core geometry and the loss of three fuel elements.

The worth of the fuel element in position G-12 was then measured and found to be worth $0.31. This number was very consistent with previous measurements of fuel element worth. If the three remaining fuel elements were added to the G-ring in positions G-9, G-10, and G-ll, we estimated that this would increase the core excess by about 3(31t) = $0.93. If the rod worths did not change at all, the shut-down margin should be $1.58 - $0.93 = $0.65, still within the Technical Specifications limits. Furthermore, we estimated that the transient rod worth would increase by this fuel addition, and the worths of the other three rods would be basically unchanged.

If this were the case, it would increase our shutdown margin even more.

Thus, we decided to add the remaining three fuel elements to the G-ring (see Fig. 3) . After the rods were calibrated in this configuration, we discovered that the core excess had increased by

$1.11, rather than the 50.93 as predicted, and the shutdown margin was new only 50.48.

Two fuel elements were then moved (from G-9 to F-2S and from G-17 to F-19), and the final core configuration (see Fig. 4) has an acceptable shutdown margin of $0.74.

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USNRC Page Three June 19, 1979 If there is any further information you desire regarding this occurrence, please let us know.

Sincerely, C. H. Wang Reactor Administrator Director, Radiation Center CHW/rk Enclosures cc--OSNRC Office of Inspection & Enforcement, Washington DC Oregon Department of Energy J. C. Ringle, Assistant Reactor Administrator, OSU T. V. Anderson, Reactor Supervisor, OSU A. G. Johnson, Health Physicist, OSU 2170 158

. Fig. 1. Core Befo*e Configuration Change f 5 Core Excess: $6.90 r!n et $ ( rge ro )

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