Information Notice No. 86-30: Design Limitations of Gaseous Effluent Monitoring Systems
SSINS No: 6835
IN 86-30
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
April 29, 1986
Information Notice No. NO 86-30: DESIGN LIMITATIONS OF GASEOUS EFFLUENT
MONITORING SYSTEMS
Addressees:
All nuclear power reactor facilities holding an operating license or a
construction permit
Purpose:
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
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IN 86-30
April 29, 1986
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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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