ENS 45805
ENS Event | |
|---|---|
19:30 Mar 31, 2010 | |
| Title | Failed Active Engineered Control on a Ultrasonic Testing Smart Crane |
| Event Description | On March 29, 2010, Nuclear Criticality Safety (NCS) was notified that a UT Smart Crane had failed its functional test. The Smart Crane is an active engineered control that prevents simultaneous immersion in water of two fuel bearing components of concern in an Ultrasonic Testing (UT) tank. Earlier in the morning the crane tripped into fault mode while being moved to a storage position; there was no fuel bearing component attached to the crane at the time. Plant Maintenance personnel reset the crane's PLC [Programmable Logic Controller] and the required functional tests were performed per procedure prior to returning the crane to service. When the functional test was performed on Tank #3, the crane failed the test. Tank #3 was loaded with a component of concern (> 500 lbs) and the crane failed to prevent movement of a test weight into the tank's exclusion zone. The Smart Crane should have recognized Tank #3 as loaded and should have stopped the test weights at the edge of the tank's exclusion zone.
The crane's PLC was subsequently checked and it was determined that it did not indicate Tank# 3 as loaded with a component of concern. The PLC was manually set to identify Tank #3 as loaded with a component of concern and testing resumed. The crane then failed a test on Tank #1. The UT tank did not contain a component of concern (i.e., it weighed < 500 lbs). As such, the operator using the crane should have been able to transfer the test weights into tank's exclusion zone, but the crane's safety interlock stopped the weights at the zone boundary. Initially, these failures were thought to be caused by errors in conducting earlier tests. If the weights are inadvertently released from the crane within the exclusion zone at the conclusion of a test, the tank status (loaded/unloaded) can be affected. As a result of an earlier corrective action, forklift barriers had been erected to limit the free space around the tanks. It was anticipated that these barriers were possibly interfering with the movement of the weights in/out of the exclusion zone during test. Tank #1 was reset and all tanks successfully passed the required functional test. Since a definite cause could not be determined but the crane passed the functional test and operations continued. The operators were requested to log the status of the Smart Crane indicating lights as the crane moved from tank to tank. On the night of March 30, 2010, the indicating lights did not provide the correct indication of tank loaded/unloaded status. The operation was immediately shutdown and NCS was notified. On March 31, 2010, Plant Maintenance determined the crane's linear encoder was damaged and not accurately tracking the crane's position. This failure mode allowed the crane to move, but gave a false indication of crane position to the PLC. This type of failure did not provide the PLC with accurate data to determine the crane's position. In this state, the Smart Crane would not prevent an operator from loading two items of concern in a single tank. This is a failure of the Smart Crane as an IROFS. This determination was reached at 1530 EDT on March 31, 2010. There was no immediate risk of a criticality or threat to the safety of workers or the public as a result of this event. An operator never attempted to load two components of concern into a UT tank. However, with inaccurate position information, the Smart Crane could not be credited as an IROFS and double contingency could no longer be assured. A criticality was no longer highly unlikely. Babcock & Wilcox Nuclear Operations Group, Inc. is making this 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> report in accordance with 10CFR70, Appendix A(b)(2) - Loss or degradation of items relied on for safety that result in failure to meet the performance requirement of 70.61. An investigation of this event is ongoing. Corrective actions will be determined as a result of the investigation. The licensee has notified the NRC Resident Inspector. |
| Where | |
|---|---|
| B&W Nuclear Operating Group, Inc. Lynchburg, Virginia (NRC Region 2) | |
| License number: | SNM-42 |
| Reporting | |
| Part 70 App A (B)(2) | |
| Time - Person (Reporting Time:+19.7 h0.821 days <br />0.117 weeks <br />0.027 months <br />) | |
| Opened: | Kenny Kirby 15:12 Apr 1, 2010 |
| NRC Officer: | Dong Park |
| Last Updated: | Apr 1, 2010 |
| 45805 - NRC Website | |
B&W Nuclear Operating Group, Inc. with Part 70 App A (B)(2) | |
WEEKMONTHYEARENS 465892011-02-02T19:30:0002 February 2011 19:30:00
[Table view]Part 70 App A (B)(2) Discovery of an Unfavorable Volume Container in the Uranium Recovery Container Controlled Area ENS 458052010-03-31T19:30:00031 March 2010 19:30:00 Part 70 App A (B)(2) Failed Active Engineered Control on a Ultrasonic Testing Smart Crane 2011-02-02T19:30:00 | |