Yesterday afternoon, while performing retests on replacement control
shim arm switches, reactor operators placed the reactor in a condition that would allow more than one
shim control rod to be withdrawn. This violated
Technical Specification 3.4.1, "Operations that require confinement." The reactor facility did not have full confinement in place at that time. The specific language of
Technical Specification 3.4.1 is "Confinement shall be maintained when changes of components or equipment within the confines of the thermal shield, other than rod drop tests or movement of experiments, are being made which could cause a significant change in reactivity." Although the
shim control rods were not withdrawn and the rod bottom lights never cleared, the circumstances, in the licensee's opinion, were that they could have caused a significant change in reactivity, allowing more than one
control rod to be withdrawn when the reactor was not in full confinement.
The licensee notified the NRC Reactor Inspector.