United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-30: Design Limitations of Gaseous Effluent Monitoring Systems

                                                            SSINS No: 6835 
                                                            IN 86-30       

                                UNITED STATES
                           WASHINGTON, DC 20555

                               April 29, 1986

                                   MONITORING SYSTEMS 


All nuclear power reactor facilities holding an operating license or a 
construction permit 


This notice is provided to alert licensees to two design limitations noted 
in the use of Eberline's SPING-4 (system particulate iodine and noble gas) 
gaseous effluent monitoring systems The first deals with the limitations of
the detection capability of the SPING-4 monitoring system Some licensees 
are incorrectly relying on the SPING-4 to meet all of the post-accident 
requirements of NUREG-0737 The second deals with noble gas adsorption that 
could interfere with routine operational low-level monitoring 

It is expected that recipients will review this information for 
applicability to their facilities and consider actions, if appropriate, to 
preclude problems related to these limitations 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 Eberline SPING-4 is designed to monitor radioactive noble gasses, 
particulates and iodines in plant gaseous effluents By using three 
overlapping channels, the noble gas (NG) monitor has a detection capability 
of 10-7 to 105 Ci/cc (Xe-133 equivalent) The low-range channel employs a 
beta scintillation detector The mid- and high-range channels of the NG 
monitor use energy-compensated GM tube detectors 

Conformance to NUREG-0737 IIF1: 

Item IIF11 of NUREG-0737, "Clarification of TMI Action Plan Requirements,
issued November 1980, require licensees to have the capability to detect and
measure concentrations of NG fission products in plant effluents (up to 105 
Ci/cc for undiluted containment exhaust) during and following an accident 
Recent NRC regional inspections of NUREG-0737 implementation indicate that 


                                                             IN 86-30      
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some licensees have installed SPING-4 monitors and mistakenly consider them 
adequate to meet all of the requirements of Item IIF11 Although the 
SPING-4 does have an upper detection capability of 105 Ci/cc, its associated
microcomputer is vulnerable to radiation damage from a total integrated dose
greater than 1000 rads Therefore, it is unlikely the SPING-4 would survive 
the course of an accident Eberline has indicated that the SPING-4 was 
designed primarily as a normal-range monitor with extended capabilities for 
brief excursions to concentrations greater than 102 Ci/cc Full-range 
monitoring consistent with Item IIF11 can be achieved by using the 
SPING-4 in conjunction with an accident monitor (with a remote 
microprocessor) such as Eberline's model AXM-1 The accident monitor comes 
on line when excessively high activity levels are sensed while the SPING-4 
isolates itself and goes into a purge cycle 

Noble Gas Adsorption: 

Eberline has noted noble gas adsorption with the plastic scintillator while 
performing a SPING-4 calibration This calibration compared the SPING-4 
output with a GeLi detection system output, as the concentration of a 
reference gas (Xe-127) was decreased The concentration of Xe-127 (initially
at 210  Ci/cc) in the closed test loop was decreased by vent and dilution 
operations Calibration was interrupted after 2 days to correct problems 
with the GeLi system The system was allowed to stand idle for 10 days with 
03 Ci/cc Xe-127 concentration When the calibration resumed, the response 
of the beta scintillator did not decrease in the expected proportions An 
investigation indicated that both the inner and outer mylar sheets that 
cover the plastic scintillator had adsorbed Xe-127 gas 

Although the levels of activity used in this calibration were much higher 
than those normally encountered, the noble gas adsorption noted on the low 
range of the detection system could indicate a generic operational concern 
The high background resulting from the adsorbed gas could cause 
overestimations in any effluent release calculations that are based on the 
monitor output This is particularly true if low-level monitoring is resumed
following either a large activity excursion (3 or 4 orders of magnitude 
above normal) or an extended moderate increase (1 order of magnitude for a 
week or more) Following such releases the monitor should be purged and a 
new background taken It should be noted that this gas adsorption phenomenon 
is probably not unique to SPING-4 monitoring systems Other manufacturers of
plastic scintillation detectors use similar construction techniques Any 
effluent monitor that employs a plastic scintillation detector may 
experience the same difficulties 

                                                             IN 86-30      
                                                             April 29, 1986 
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No specific action or written response is required by this information 
notice If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office or this office 

                                   Edward L Jordan Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contact:  Roger L Pedersen, IE
                    (301) 492-9425

                    James E Wigginton, IE
                    (301) 492-4967

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