Information Notice No. 83-25: Standby Gas Treatment System Heater High Temperature Trip Setpoint Adjustment
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 02555
April 28, 1983
INFORMATION NOTICE NO. 83-25: STANDBY GAS TREATMENT SYSTEM HEATER HIGH
TEMPERATURE TRIP SETPOINT ADJUSTMENT
All nuclear power reactor facilities holding an operating license (OL) or
construction permit (CP).
This information notice provides notification of a potentially significant
problem pertaining to the standby gas treatment system. It is expected that
addressees will review the information for applicability to their
No specific action or response is required at this time.
Description of Circumstances:
The Commonwealth Edision Company's (CECO) Quad Cities Unit 1 reported an
inoperable standby gas treatment (SBGT) system due to a high temperature
trip of the heater. The reported causes of the trip, which occurred after
the system had last been turned off, were increased temperatures at the
temperature sensor due to latent heat from the heater and too low of a trip
setpoint (LER 50-254/82-025). Iowa Electric Power reported a similar event
at Duane Arnold (LER 50-331/82-064).
Corrective actions taken by both licensees included testing to determine
peak temperatures in the air stream and establishing a higher trip setpoint.
CECO also planned to investigate the benefits of an automatic reset for high
April 28, 1983
Page 2 of 2
Figure 1 is a schematic diagram of a typical SBGT system for a boiling water
reactor (BWR). The heater is energized automatically with the start of the
SBGT system and remains energized until the system is shut down. A sensor,
located downstream of the heater, measures air temperature. In case of low
air flow, there is a high-temperature trip to prevent heater burnout. The
heater increases the air temperature thus lowering the relative humidity to
increase the effectiveness of the charcoal as a halogen absorber. The
charcoal filter removes greater than 95% of the iodine in the air at 70%
relative humidity and 190F.
After the system is turned off, the heaters will continue to radiate heat.
If temperature sensors are located too near the heater, the high temperature
trip setpoint may be exceeded. If this occurs and there is no automatic
reset, the SBGT system heater will be inoperable, and the system will not
perform its intended function when called upon. This problem may be avoided
by positioning the sensor to minimize the effect of latent heat from the
heater and installing an automatic reset device.
Merely raising the setpoint temperature to avoid a heater trip is not an
acceptable solution. An appropriate setpoint for the high temperature trip
is provided in ANSI N509-1976 "Nuclear Power Plant Air Cleaning Unit and
Components." Paragraph 5.1.1 states, "The sensible heat produced by the
heater stage shall not result in increasing air temperatures to more than
225F. An overtemperature cutoff switch set at this value shall be
provided." An increase in the trip setpoint above 225F causes concern
for the capability of charcoal to adsorb iodines. The data currently
available for charcoal adsorbent characteristics, especially impregnated
charcoal, is not sufficient to support a statement on iodine removal
capability at temperatures above 190F. (See Regulatory Guide 1.52, Rev.
No written response to this notice is required. 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: Mary S. Wegner, IE
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