Information Notice No. 83-25: Standby Gas Treatment System Heater High Temperature Trip Setpoint Adjustment

                                                           SSINS No.:  6835 
                                                           IN 83-25        

                                UNITED STATES
                       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 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP). 

Purpose: 

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 
facilities. 

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
temperature trips. 
.

                                                           IN 83-25        
                                                           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.
2.) 

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 
                    301-492-4511 

Attachment: 
List of Recently Issued Information Notices