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Information Notice No. 84-38: Problems with Design, Maintenance, and Operation of Offsite Power Systems
INS No. 6835 IN 84-38 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, DC 20555 May 17, 1984 Information Notice No. 84-38: PROBLEMS WITH DESIGN, MAINTENANCE, AND OPERATION OF OFFSITE POWER SYSTEMS Addressees: All power reactor facilities holding an operating license (OL) or construction permit (CP). Purpose: This information notice is provided as a notification of potentially significant problems pertaining to the design, maintenance, and operation of offsite power systems. It is expected that recipients will review their facilities and consider actions, if appropriate, to preclude similar problems occurring at their facilities. However, suggestions contained in this information notice do not constitute NRC requirements and, therefore, no specific action or written response is required. Description of Circumstances: Turkey Point Nuclear Units 3 and 4 recently experienced a series of events that included reactor trips, unscheduled shutdowns, and loss of offsite power to Unit 3. These events occurred as a direct result of problems with the design, maintenance, and operation of the offsite power systems. The first event occurred on February 12, 1984, when an improperly calibrated relay for the startup transformer of oil fired Units 1 and 2 sensed a current differential and isolated the portion of the switchyard bus feeding the single Unit 3 startup transformer and a new 3C auxiliary transformer for that unit. The Unit 3 reactor tripped on loss of an electrically driven main feedwater pump powered from the 3C auxiliary transformer and bus. With the start-up transformer also lost, emergency diesel generators were required to provide power to the vital buses and the unit was stabilized on natural circulation. Later that day, while attempting to restore offsite power to Unit 3 from the Unit 4 new 4C auxiliary transformer, a switching error resulted in reactor trip of Unit 4. There were no written procedures for realignment of offsite power systems following the loss of offsite power to one of the units (Unit 3 in this case). Another event occurred on February 16, 1984, when the Unit 4 reactor tripped and Unit 3 experienced loss of offsite power. This event was initiated by a relay in the recently installed offsite power cross-tie feeder switchgear that included buses 3C and 4C. This relay was mounted on a metal-clad switch-gear door that was improperly installed, which caused it to bind. The vibrations 8405160193 . IN 84-38 May 17, 1984 Page 2 of 2 from forcing the door open or closed actuated the relay. This resulted in a Unit 4 trip from loss of power to the 4C bus which supplied one electrically driven main feedwater pump. Seconds later, jarring of a similarly mounted relay caused isolation of the switchyard quadrant feeding Unit 3 and result- ant loss of power to the 3C bus, loss of one electrically driven main feed- water pump, reactor trip, and loss of power to the Unit 3 startup transform- er. Following these events, the licensee informed the NRC that the new 3C and 4C auxiliary transformers and associated equipment were added with the objective of enhancing the availability of offsite power,systems. The design changes for these additions were classified as non-safety-related but were covered in the quality assurance program. However, they were not reviewed with respect to the requirements of 10 CFR 50.59 by the plant nuclear safety committee. As a followup to these events, the licensee instituted short- and long-term corrective action programs to review the overall design of offsite power systems and to strengthen the procedures and administrative controls. As a part of the short-term program, functional testing of 4-kV breakers for non- safety-related buses was performed; this test revealed loose bolts, misaligned and dirty contacts, worn parts, and the mechanical failure of one breaker to trip. The short-term corrective actions program was completed before unit startup. A partial listing of other similar loss-of-offsite-power events is provided in Attachment 1 to this notice. The general concern is that design, maintenance, and operational problems in electrical equipment considered to be non-safety related can greatly degrade access to offsite power sources. This is not consistent with the General De- sign Criteria objectives. The concern is particularly valid where station service loads are arranged, as at Turkey Point Units 3 and 4, such that a single electrical fault can cause a transient resulting in a plant trip and also defeat immediate access to offsite power sources. The concern is also particularly valid for facilities with multiunit plants or a common switch- yard for nuclear and non-nuclear units. If you have any questions regarding this matter, please contact the Regional Administrator of the appropriate NRC regional office or this office. Edward L. Jordan, Director Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement Attachments: 1. Partial List of Recent Loss of Offsite Power Events 2. List of Recently Issued IE Information Notices Technical Contact: R. Singh, IE (301) 492-8068 . Attachment 1 IN 84-38 May 17, 1984 PARTIAL LIST OF RECENT LOSS-OF-OFFSITE-POWER EVENTS Plant/Date Event Summary 1. LaSalle 1, Partial loss of offsite power caused by a 10/26/83 procedural error and personnel oversight when securing a Unit 2 transformer. 2. Summer 1, Internal fault at Parr Steam Plant (a 9/11/83 non-nuclear unit) caused loss of offsite power. 3. Brunswick 1, Personnel error caused loss of offsite power 4/26/83 when a 230 kV bus was inadvertently tripped. 4. Quad Cities 2, Preferred power was being taken out of service 6/22/82 for maintenance, and a personnel error caused a reactor trip resulting in complete loss of offsite power. Twenty-two minutes into the event, one of the emergency diesel generators tripped as a result of underexcitation. 5. Prairie Island 1, During an attempted start of a cooling tower 7/8/81 pump, an improperly set undervoltage protection relay caused a partial loss of offsite power. 6. Salem 1 and 2, Partial loss of offsite power to both units 5/21/81 resulting from a design deficiency in the, gas turbine Unit 3. 7. Monticello, A bus fault was caused by operator error. A 4/27/81 design error caused the undervoltage relays to trip all offsite power sources instead of isolating only the faulted bus. 8. LaCrosse, Loss of offsite power caused by an operator 2/1/81 opening a wrong breaker. 9. Beaver Valley 1, Loss of 138 kV bus resulted in partial loss of 2/1/81 offsite power. During the event, the auto load sequencer of one of the emergency diesel generators failed as a result of improper wiring (design error) and a disconnected timer relay.
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