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v t e ENS Event
07:00 Apr 6, 2011
Title	Violation Of Limiting Condition Of Operation 3.8.1, Reactivity Limits
Event Description	{{#Wiki_filter:Summary of Events: The Oregon State University TRIGA� Reactor (OSTR) staff is designing a new experiment which will utilize reactivity oscillation to measure reactor parameters. During attempts to measure the maximum worth of the oscillating absorber on Wednesday, April 6, it was determined that the worth of the preliminary test absorber is $0.60 at the mid-plane of the core. Technical Specification 3.8.1, Reactivity Limits states in part that 'The absolute value of the reactivity worth of any single unsecured experiment shall be less than $0.50.' Measurements were taken in a manner such that the apparatus qualifies as a movable experiment, and moveable experiments are taken to be a subcategory of unsecured experiments. A neutron absorber was fabricated by crushing an existing � inch segment of B4C absorber and placing 29.8 grams of the material in a sealed aluminum TRIGA� tube. The reactivity of the absorber was not formally calculated, but it was believed that the worth of the absorber would be less than $0.20. This was based on the fact that a full length control rod absorber (15 inch) is worth about $2.00, depending on position in the core. Past experience has also shown that several grams of Cadmium, a very strong thermal neutron absorber, have a reactivity worth of ~$0.20 in the B-1 position where the absorber was being tested. To characterize the worth of the absorber, the reactor was first taken critical with the In-Core-Irradiation-Tube (ICIT) installed in the B-1 position. Critical rod heights were measured and core excess was calculated. The reactor remained critical at 15 watts in automatic mode. The absorber was then manually lowered to the bottom of the ICIT by an operator using a length of nylon line. The regulating rod was observed to behave as anticipated, automatically withdrawing until some maximum worth position near core center was reached by the absorber, and then automatically inserting as the absorber was lowered to the bottom of the core. The worth of the absorber when resting at the bottom of the core was estimated to be less than $0.07. When power and reg rod position were stable, the absorber was slowly withdrawn 7.5 inches to the geometric center of the core. The reg rod automatically withdrew to compensate. The difference between reg rod position with no absorber present and reg rod position with the absorber at core center indicated that the worth of the absorber at core center was $0.60. As soon as absorber worth was determined, the reactor was shut down and the absorber was withdrawn from the ICIT. Although oscillatory operation was not planned, the fact that the absorber was moved while the reactor was critical qualified the experiment as a moveable experiment. Since $0.60 is in excess of L.C.O. 3.8.1, reactor operation was secured in accordance with Technical Specification 6.6.2.a. }}

ENS 46738 +/-
Where
Oregon State University Corvallis, Oregon (NRC Region 4)
License number:	R-106
Reporting

Non
Time - Person (Reporting Time:+32.42 h1.351 days <br />0.193 weeks <br />0.0444 months <br />)
Opened:	Steve Reese 15:25 Apr 7, 2011
NRC Officer:	Steve Sandin
Last Updated:	Apr 7, 2011
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