United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 84-88: Standby Gas Treatment System Problems

                                                         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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