Information Notice No. 90-77: Supplement 1:Inadvertent Removal of Fuel Assemblies from the Reactor Core
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 February 4, 1991 Information Notice No. 90-77, SUPPLEMENT 1: INADVERTENT REMOVAL OF FUEL ASSEMBLIES FROM THE REACTOR CORE Addressees: All holders of operating licenses or construction permits for pressurized-water reactors (PWRs). Purpose: This information notice supplement is intended to provide additional information to that previously provided in Information Notice No. 90-77, "Inadvertent Removal of Fuel Assemblies from the Reactor Core." It is expected that recipients will review this information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice do not constitute NRC requirements; therefore, no specific action or written response is required. Description of Circumstances: On October 4, 1990, at Indian Point Station Unit 3, while the upper core internals package (UIP) was being lifted during preparations for defueling, two fuel assemblies (FAs) were inadvertently lifted from the reactor core. In response to this event, the NRC sent a Special Inspection Team to the site to monitor the licensee's recovery of these FAs. The NRC issued Information Notice No. 90-77 on December 12, 1990, to report this event. The licensee's recovery activity was detailed in NRC Inspection Report 50-286/90-19, dated December 13, 1990. The NRC also sent an Augmented Inspection Team (AIT) to the site after recovery of the FAs to determine the probable cause and relevant facts of this event and to evaluate the licensee's proposed corrective actions. The AIT concluded that the two FAs were stuck to the UIP because of bent guide pins on the upper core plate. The guide pins were bent during movement of the UIP for reinstallation into the reactor vessel in May 1989. The refueling crew had moved the UIP laterally before raising it to a height above its storage stand adequate to avoid bumping the guide pins against the stand. Refueling personnel did not recognize that the UIP had inadvertently bumped against the storage stand and bent the guide pins. The UIP was thus reinstalled with bent guide pins into the reactor vessel. As a result, the bent guide pins severely damaged the top 9101290331 . IN 90-77, Supplement 1 February 4, 1991 Page 2 of 3 nozzles of two FAs. In addition, the bent guide pins caused mechanical deformation of a portion of the fuel rods in one of the two FAs. The outwardly bent fuel rods in this FA caused mechanical deformation of the fuel rods in an adjacent FA. None of these component-related damages were identified by the licensee until the next refueling. The detailed inspection findings are described in NRC Inspection Report 50-286/90-80, dated January 8, 1991. Discussion: Since 1985, the NRC and the Institute of Nuclear Power Operations (INPO) have provided the nuclear industry with three documents regarding the inadvertent lifting of FAs from the reactor core. NRC Information Notice 86-58, "Dropped Fuel Assembly," and two INPO Significant Event Reports (proprietary information) addressed events involving stuck FAs. As a result of reviewing these generic communications, the licensee revised its refueling procedure before this refueling outage to require the placement of an underwater camera and extra lights on the reactor cavity floor to inspect the UIP for stuck FAs. The procedure revision also included a step for performing a video inspection after the upper internals were raised approximately 1 foot above the reactor vessel flange. However, the licensee's implementation of these procedural steps was not effective because, as noted in the AIT findings, (1) the operators did not place extra lights on the upper reactor cavity floor as directed by the note in the procedure and (2) the operators did not move the camera around the reactor vessel flange in order to view the underside of the upper internals from different angles. At the time this step was performed, the lighting was particularly inadequate at this location because about half of the lamps in the reactor cavity were burned out, and the angle and distance of the lights to the UIP created a dark shadow underneath the UIP. The problem of ineffectiveness was compounded by the fact that the camera was in place only on the eastern side of the vessel. Under these circumstances, the camera apparently was not able to scan the distance across the vessel to detect the stuck FAs, which were located peripherally on the western side of the vessel. As a result, the stuck FAs were lifted upward and transported horizontally for a short distance before being noticed by refueling personnel. The licensee utilized a refueling contractor (Westinghouse) to perform major steps of the refueling operations. The licensee limited its overall supervisory control of these operations because of the contractor's extensive experience with the design of the plant and with refueling at similar plants. This lack of oversight resulted in the licensee's failure to provide adequate control, either supervisory or technical, over key steps of the refueling operations. For example, the AIT found that the licensee's refueling Senior Reactor Operator job tasks and responsibilities related to maintaining overall supervision and coordination of the safety related aspects of refueling operations were not identified or included in training. The AIT also found the procedure that controlled movement of the UIP during the previous refueling outage (May 1989) to be deficient in that (1) it did not contain the detailed information necessary to inform refueling person-nel on how to move the UIP without bumping it, (2) it contained action steps in the form of notes, and (3) information important to the proper completion of some procedural steps was included in notes located several pages away from the steps. . IN 90-77, Supplement 1 February 4, 1991 Page 3 of 3 The AIT also identified an apparent shortcoming in the design of the storage stand. The storage stand has three guide studs, which extend 3 feet 10 inches above the support stand flange seating surface (see Figure 1). These guide studs provide guidance and protection for critical features of the UIP during the lifting and setting-down evolutions involving the storage stand. One of the most critical features of the UIP is the FA guide pins. The guide pins are appended to the UIP upper core plate, which is located about 13 feet below the UIP upper support plate and lifting rig guide bushing. Because of the short guide stud design (3 feet 10 inches), when the UIP is being lowered onto the storage stand, the guide pins are approximately 8 feet below the stand flange by the time the lifting rig guide bushings engage the stand guide studs. Similarly, when the UIP is being lifted from the storage stand, at the point the lifting rig guide bushings clear the stand guide studs, the guide pins, upper core plate, and some portion of the upper internal guide tubes are still beneath the stand flange. Consequently, the alignment of the stand guide studs and the UIP lifting rig guide bushings is not a factor in preventing interference between the storage stand flange and the guide pins. This information notice requires no specific action or written response. If you have any questions about the information in this notice, please contact one of the technical contacts listed below or the appropriate NRR project manager. Charles E. Rossi, Director Division of Operational Events Assessment Office of Nuclear Reactor Regulation Technical Contacts: Peter C. Wen, NRR (301) 492-0832 James A. Prell, RI (215) 337-5108 Attachments: 1. Figure 1, Simplified Elevated View of West Side of Containment 2. List of Recently Issued NRC Information Notices .ENDEND
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Page Last Reviewed/Updated Tuesday, March 09, 2021