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.
Page Last Reviewed/Updated Tuesday, March 09, 2021