Home > NRC Library > Document Collections > Generic Communications > Information Notices > 1993 > IN 93-47
Information Notice No. 93-47: Unrecognized Loss of Control Room Annunciators
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 June 18, 1993 NRC INFORMATION NOTICE 93-47: UNRECOGNIZED LOSS OF CONTROL ROOM ANNUNCIATORS Addressees All holders of operating licenses or construction permits for nuclear power reactors. Purpose The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice to alert addressees to the potential problem of unrecognized loss of control room annunciators. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems. However, suggestions contained in this information notice are not NRC requirements; therefore, no specific action or written response is required. Description of Circumstances Callaway On October 16, 1992, while the Callaway Plant was operating at 100 percent power, approximately 75 annunciators on the main control board illuminated. After verifying that the annunciators were not valid, the shift supervisor (SS) notified the plant manager and the engineering duty officer of the condition and requested instrumentation and control (I&C) technicians to begin repairs. The I&C technicians found that one of four field power supplies for the annunciators had failed. The failed power supply was replaced and the annunciators appeared to return to normal. Two minutes later, while removing jumper cables installed during the replacement, an electrical short occurred. In the control room, 371 of the 463 main control board annunciators illuminated and remained lit. The I&C technicians inspected the power supplies and determined that the output fuses for all four field power supplies had blown. The blown fuses resulted in the loss of all main control board annunciators. This was not recognized by the plant staff. Callaway procedure EIP-ZZ-00101, "Classification of Emergencies," describes those conditions which constitute entry into established emergency action levels (EALs). The procedure states that, for an initiating condition of "Most or All Alarms (Annunciators) Lost," the proper emergency classification is an Alert. 9306150062. IN 93-47 June 18, 1993 Page 2 of 3 Approximately one hour after the loss of all annunciators, the blown output fuses were replaced and power was restored to the annunciator system. Plant personnel verified that power was available to the annunciators by depressing test switches in the control room. However, this did not test the annunciator logic circuitry and, as a result, the operating crew was unaware that 164 annunciators with re-flash capability were completely inoperable. Apparently, the short that blew the output fuses in the field power supplies also blew fuses in eight annunciator logic power supplies. Later, while investigating problems with the annunciators, the I&C engineer found and replaced the blown fuses in the eight logic power supplies and an appropriate test was performed. However, there was not an approved procedure for this test nor was it properly documented. By 7:37 p.m. on October 17 the main control board annunciators had been restored to fully operable status. Because the SS failed to recognize that all of the main control board annunciators were inoperable after the four field power supply output fuses had blown, an Alert was not declared on October 17, 1992. On October 19, the licensee determined that an Alert should have been declared and notified State and local authorities and the NRC of the event. Inspection of this event by an NRC Augmented Inspection Team (AIT) found the following weaknesses: (1) insufficient knowledge of the annunciator system by the plant staff, (2) poor communications and inadequate teamwork, (3) lack of a questioning attitude, and (4) inadequate work performance. Contributing to the insufficient knowledge of the annunciator system was the failure to have an off-normal operating procedure or other procedure that addressed loss of annunciators. Salem Unit 2 On December 13, 1992, control room operators at Salem Unit 2 Nuclear Station discovered that the overhead annunciators had been inoperable for about 90 minutes. The inoperable condition was detected when an alarm printer printed a change in alarm status which was not reflected by the overhead annunciators. The operators reset the annunciator system and restored it to operable status within two minutes. Subsequent inspection of the event by an NRC AIT identified several weaknesses that contributed to the problem. The operators were not adequately trained to verify proper operation of a recently installed micro-processor based annunciator system. The new system was not designed with annunciation as a priority task and therefore it did not indicate a critical mispositioned switch. Attempts by the operators to enter files, despite a procedure caution, contributed to locking up the system. The plant staff delayed in notifying plant management and the NRC. The licensee did not have a procedure to deal with the loss of annunciators. The AIT concluded that the overall knowledge of the system was inappropriate for a system that, if lost, required the declaration of an Alert. . IN 93-47 June 18, 1993 Page 3 of 3 Discussion Although plant annunciators are not considered safety related, they are important for the safe operation of a nuclear power plant. Further, an unrecognized loss of annunciators may increase the difficulty of diagnosing problems in plant operations and equipment. In order for plant operators to recognize and respond properly to a loss of annunciators, it is important to have clear procedures, appropriate training, and effective communications between operators and plant support personnel. For the events described above, an off-normal operating procedure that clearly stated required actions would have significantly aided the operators to diagnose the extent of the problem, take necessary response actions, and make required notifications. Loss of annunciator events were covered by the emergency classification procedures of both licensees, premised upon guidance of Appendix 1 of NUREG-0654/FEMA-REP-1, "Criteria for Preparation and Evaluation of Radiological Emergency Response Plans and Preparedness in Support of Nuclear Power Plants," (November 1980). The NRC recently issued Revision 3 to Regulatory Guide 1.101, "Emergency Planning and Preparedness for Nuclear Power Reactors" (August 1992). That revision endorsed NUMARC/NESP-007, Revision 2, "Methodology for Development of Emergency Action Levels," (January 1992), as an acceptable alternative. With respect to loss of annunciators, the NUMARC/NESP-007 guidance provides an alternative delineation of thresholds for declaring an Unusual Event, Alert or Site Area Emergency. 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 Office of Nuclear Reactor Regulation (NRR) project manager. ORIGINAL SIGNED BY Brian K. Grimes, Director Division of Operating Reactor Support Office of Nuclear Reactor Regulation Technical contacts: Bruce L. Bartlett, RIII (314) 676-3181 Rolf A. Westberg, RIII (708) 790-5776 Scott A. Boynton, NRR (301) 504-2926 Attachment: List of Recently Issued NRC Information Notices .
Page Last Reviewed/Updated Tuesday, November 12, 2013