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| Start date | Reporting criterion | Title | Event description | System | LER | |
|---|---|---|---|---|---|---|
| ENS 55632 | 7 December 2021 17:48:00 | Non 10 CFR 50.72(b)(1), 50.54(x) TS Deviation | Research Reactor Tech Spec Deviation Resulting in a Reactor Scram | On 12/7/2021 at 1248 EST, the Breazeale reactor (50-005) (a TRIGA reactor) was operating for a NUCE 451 lab. The reactor operator was trying to perform a $0.75 (measure of reactivity) square wave with a setpoint of 500 kW. When the operator entered the setpoint, he did not hit ENTER so the 500 kW was not stored in the console, which defaulted to the current power level (100 W) as the setpoint. Once the square wave was executed, the control rods immediately began to move in to counter the $0.75 of reactivity from the pulse rod and maintain the power level at 100 W. The operator noticed that the setpoint was incorrect, and after 9 seconds, changed the power setpoint to 500 kW. At this time, the rod bank began to move out, adding $1.20 over the course of 4 seconds. (The maximum total reactivity beyond critical is estimated to be ~$1.10). The reactor scrammed based on high log range (fission chamber) power and high wide range (GIC) power. The last two points of data from the data historian indicate that the period was +0.25 seconds. Based on the rod insertion speed and differential rod worth at the position from which the scram was initiated, it was estimated that the maximum power following the scram (setpoint = 1.08 MW) was approximately 1.29 MW. The highest data point recorded by the historian was 1.38 MW (log fission chamber data), which is corroborated by the estimate calculated based on rod speed, and 1.38 MW represents the best estimate of the maximum reactor power. The reactor technical specifications (TS) dictate that: "The maximum power level SHALL be no greater than 1.1 MW (thermal)." (TS 3.1.1.b). This condition applies to non-pulse operation. According to the TS definitions, the reactor is neither "secured" nor "shut down" during a scram, and therefore must be considered to be operating while the rods are in motion after the scram is initiated. Therefore, this event resulted in the violation of TS 3.1.1.b by allowing power to reach 1.38 MW, higher than the 1.1 MW scram setpoint. It is worth noting that TRIGA reactors like the Breazeale reactor are designed to be pulsed to several gigawatts of power, and the 1.1 MW limit is based on steady state power analysis, not power transient analysis. The fuel reached a maximum temperature of 42 C, far below the safety limit of 1150 C (TS 2.1). This event is reportable due to: exceeding an LCO in the technical specifications (1.1 MW power limit) and an unanticipated change in reactivity greater than $1 when the rod bank drove out following the change in power setpoint. The root cause of this event was operator error. The operator failed to follow best practices by checking that the setpoint was entered correctly, and then acted outside of procedure to attempt to correct the setpoint. The reactor was immediately secured and tagged out pending corrective actions identified in the event evaluation document, AP4 2021-03. The immediate corrective actions, completed on 12/8/21, were to: 1 - add a pen-and-ink revision to SOP-1 instructing the operator to verify the power setpoint; 2 - hold a reactor staff training on the event, its causes, and the importance of following procedure and checking values entered into the console; 3 - implement an administrative prohibition on square waves until the console software can be changed to add a feature to prevent recurrence of this event. Following these corrective actions reactor operation was approved by the ADO (Level 2). A detailed written report will be sent to the Reactor Safeguards Committee and NRC by December 21st. The licensee will notify the Non-Power Production or Utilization Facility (NPUF) Licensing Branch Project Manager. | Control Rod |