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SSINS No.: 6835 IN 84-88 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C. 20555 December 3, 1984 Information Notice No. 84-88: STANDBY GAS TREATMENT SYSTEM PROBLEMS Addressees: All boiling water reactor facilities holding an operating license (OL) or construction permit (CP). Purpose: This information notice is provided to inform licensees of operational problems in standby gas treatment systems identified in Engineering Evaluation Report E410, May 1984, issued by the Office for Analysis and Evaluation of Operational Data (AEOD), NRC. This information notice expands on a previous notice, 83-25, which discussed heater trip set points, one of the potential failure mechanisms involved. The NRC expects that recipients will review this notice for applicability to their facilities and consider actions, if appropriate, to preclude similar problems from occurring at their facilities. However, suggestions contained in this notice do not constitute NRC requirements; therefore, no specific action or written response is required. Description of Circumstances: The standby gas treatment (SBGT) system is a subsystem of the secondary containment system. When called upon to operate, the SBGT system filters and pumps air from secondary containment to the environment and maintains a negative pressure within the secondary containment in order to limit the release of radioactive material. Each SBGT train generally consists of a mist eliminator/roughing filter; an electric heater; a prefilter; two absolute (HEPA) filters; an activated charcoal filter; an exhaust fan; and associated valves, ductwork, dampers, instrumentation, and controls. The signals that trip the SBGT system are plant-specific; however, automatic trips are generally associated with the electric heaters and a high temperature condition in the charcoal filters. The AEOD report described 14 licensee-reported events at seven sites over a three year period. These events involved potentially common-mode failure mechanisms which can be attributed to design, maintenance, and testing. These events and their failure mechanisms are summarized in Attachment 1. 8412030028 . IN 84-88 December 3, 1984 Page 2 of 2 Discussion: An evaluation of the referenced events identified three problems in the design of the SBGT system: (1) functional operation of monitoring devices, such as radiation monitors or temperature sensors, such that loss of power to the sensing device results in a trip of the SBGT system; (2) nonconformance to single failure criteria for the electric power supply; and (3) improper application of overtemperature trip devices. The evaluation also identified seven events in which maintenance and testing procedures and actual practices resulted in failure or degradation of the SBGT system. The events indicate that potentially common-mode failures are not usually associated with starting logic but with the trip devices and controls. Some factors which have been used to mitigate problems are (1) an automatic reset feature for the overtemperature trip of the electric heaters; (2) a one-time, train-oriented loss-of-power test to verify that the system functions as designed and to verify that the power supplies meet single failure criteria; and (3) alternating maintenance and testing activities on redundant trains. No specific action or written response is required by this notice. 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 Technical Contact: M. S. Wegner, IE (301) 492-4511 Attachments: 1. Table of Referenced Events 2. References 3. List of Recently Issued IE Information Notices . Attachment 1 IN 84-88 December 3, 1984 Page 1 of 2 Table of Referenced Operating Experiences1 FAILURE PLANT/DATE MECHANISM2 DESCRIPTION Hatch 2 M&T The relative humidity controller of the B 06/11- train was out of calibration and cycled off 06/17/82 and on due to set point drift, keeping the heater on until it tripped from overtemperature. Then the B train of SBGT could not be started manually. Quad Cities DESIGN Repeated trips of electric heaters occurred. 08/24/- Testing was performed to determine appropriate 09/07/82 trip set point (see Information , Notice 83-25). Susquehanna DESIGN During startup testing, a simulated loss- 10/25/82 of-offsite-power test caused a radiation monitor to fail high which prevented start- . ing the A SBGT train. B train started but tripped on a high
T across the heater element. Oyster Creek DESIGN Operations personnel discovered that racking 03/07/83 out the circuit breaker for one train of the SBGT system caused solenoid operated diaphragm valves to fail open. This prevented dampers from closing, allowing a portion of the discharge from the operating train to recirculate through the inoperable train. Oyster Creek DESIGN It was found that power to the heating 04/06/83 coil circuitry for both of the trains of the SBGT came from the same motor control center powered from diesel generator 1. Susquehanna DESIGN During a simulated loss-of-off-site-power 05/08/83 test, both trains of the SBGT system tripped when they failed to develop a 10 T across their heaters in 200 seconds because the temperature controllers failed to minimum demand upon loss of power. Quad Cities DESIGN During testing of A train, the heater high 06/23/83 temperature trip switch was found tripped. The set point was altered. 1 See Attachment 2 for individual references 2 DESIGN refers to the one or more of the three problems in design of the SBGT discussed in the text. M&T refers to maintenance or testing problems. . Attachment 1 IN 84-88 December 3, 1984 Page 2 of 2 Table (continued)1 FAILURE PLANT/DATE MECHANISM2 DESCRIPTION Susquehanna M&T Racking out two 120 volts-ac breakers to 03/01/83 work on one train, in accordance with procedures, caused both trains of the SBGT system to be inoperable. The alarm response procedures for loss of power did not clearly indicate to the operator that both trains of the SBGT system were inoperable. FitzPatrick M&T The SBGT system could not be started. A 08/14/80 plugged drain line had caused the line from the SBGT system to the stack to be filled with water. Browns Ferry M&T B train heater failed to operate due to 06/13/83 insufficient flow. Damper was adjusted using faulty indicating instrumentation, to improve flow switch operation so the heater would operate. Excessive flow indication was received. The train was declared inoperable. Browns Ferry M&T A and C SBGT trains were adjusted using 06/14/83 faulty flow indicators so that their flow rates were below Tech. Spec. requirements. Susquehanna M&T During system calibration, a false flow 08/08/83 signal energized the heater with no flow across it. The heater tripped. The train was then inoperable until manually reset. Quad Cities M&T Proper operation of the internal flow 08/16/83 switch, which starts the alternate train if the primary train fails to start, was not verified by testing. Brunswick M&T Shared position indicator lights for inlet 09/13/83 and outlet dampers could have resulted in (Report Date) misleading test results. Lights gave indications for the first valve to open rather than for each valve to open. 1 See Attachment 2 for individual references 2 DESIGN refers to the one or more of the three problems in design of the SBGT discussed in the text. M&T refers to maintenance or testing problems. . Attachment 2 IN 84-88 December 3, 1984 Page 1 of 1 References (Available in NRC Public Document Rooms): 1. Power Authority, State of New York, LER 80-065/03T-0, Docket No. 50-333, August 27, 1980. 2. Georgia Power Company, LER 82-064/03L-0, Docket No. 50-366, July 6, 1982. 3. Commonwealth Edison Company, LER 82-025/03L-0, Docket No. 50-254, September 29, 1982. 4. Pennsylvania Power and Light Company, LER 82-032/01T-0, Docket No. 50-387, November 8, 1982. 5. Pennsylvania Power and Light Company, LER 83-026/01T-0, Docket No. 50-387, March 15, 1983. 6. General Public Utilities, LER 83-010/0IT-0, Docket No. 50-219, March 23, 1983. 7. General Public Utilities, LER 83-014/01T-0 Docket No. 50-219, April 20, 1983. 8. Pennsylvania Power and Light Company, LER 83-061/01T-0, Docket No. 50-387, May 20, 1983. 9. Tennessee Valley Authority, LER 83-035/01T-0, Docket No. 50-259, July 11, 1983. 10. Tennessee Valley Authority, LER 83-034/03L-0, Docket No. 50-259, July 12, 1983. 11. Commonwealth Edison Company, LER 83-010/03L-0, Docket No. 50-265, July 19, 1983. 12. USNRC, IE Inspection Report Nos. 50-254/83-20 and 50-265/83-18, August 16, 1983. 13. Pennsylvania Power and Light Company, LER 83-114/03L-0, Docket No. 50-387, September 8, 1983. 14. USNRC, IE Inspection Report Nos. 50-324/83-30 and 50-325/83-30, September 13, 1983.
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