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940-5 Accident Range Gaseous Effluent Monitor

Accident Range Gaseous Effluent Monitor


The 940-5 Accident Range Gaseous Effluent Monitor is designed to meet regulatory requirements, minimize maintenance, and minimize potential exposure during extreme events.


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Key Features

  • Beta scintillation detector operated in the current mode for noble gas
  • Range 10-3 to 105 µCi/cc
  • Particulate and iodine filters provided
  • Sample flow in direct proportion to process flow
  • May be adapted to existing normal range monitor
  • Automatic purge of sampling system


Regulatory Guide 1.97 of the United States Nuclear Regulatory Commission (USNRC) requires that noble gas must be monitored under accident conditions up to 105 µCi/cc. The Accident Range Gaseous Effluent Monitor may be furnished in conjunction with new or existing normal range monitors. The use of a beta scintillation detector, operated in the current output mode for accident range, assures that the historical problem of 1 decade overlap for normal and accident range detectors is no longer applicable. Through the use of the same species detectors, the radiation measurement assures a minimum of 1 decade overlap between detectors over the entire energy range.

  • Accident range gas monitor suitable as Kaman replacement
  • For use in conjunction with normal range gas monitor
  • Meets requirements of NRC Reg. Guide 1.97
  • 11 cc stainless steel gaseous sample volume
  • Compatible with Model 960 Digital Process Control System, local or remote mounting


The sample is withdrawn from the process flow stream via isokinetic nozzles through the customer’s sample line to the isokinetic splitter. The splitter causes isokinetic flow through the respective motorized selector valve to either the normal or accident range sampling system. (The Normal Range System is described in the Model 940-1 data sheet.) Under accident range conditions, the sample passes through one of the redundant filter paths and the mass flow controller to the accident range gas sample volume and then through the pumping system and back to the process flow stream. Where isokinetic sampling is required, a bypass flow path for the full normal range flow rate is provided, and a flow rate of 1,000 SCCM is routed through the accident range monitor. Filter transfer may be initiated manually, or automatically, based on gas channel activity. Two lead shielded filter carriers are provided to safely remove the loaded filters and transport the filters for laboratory analysis. The normal range system must have the capability of providing a control contact which is set to make contact approximately 1 decade below full scale. This contact initiates the switch-over of the selector valves, closing the sample path to the normal range skid, shutting down the normal range pumping system, starting the accident range pumping system, and sounding the alarm. When the radiation drops below the top of the first decade of the accident range system, the sample flow reverts to the normal range path and resets the alarm. The accident range detector signal is displayed by the accident range Model 960 Local Control Unit in gross noble gas counts or concentration in µCi/cc, and compensated for changes in pressure at the gas volume chamber. A low flow alarm for the accident range sample flow is also provided.


Model Name


940-5 Accident Range Effluent Monitor, includes: Isokinetic sample splitter for sample flow to normal and accident range skids Motorized valves automatically selected by radiation measurement for diversion of sample stream to normal or accident range systems Open-frame sampling skid with the following components mounted, plumbed, and wired:Parallel path particulate/iodine accident range filter assemblies Shielded portable transport for filters Gas sampler, fixed volume, with 4 pi shielding Current mode beta scintillation detector Pressure transmitter upstream of the gas sampler for automatic compensation of count rate for gas density Mass flow controller for isokinetic sample flow rate Positive displacement pumping system Plumbing and valving, as required Model 960 Digital Process Control System, local or remote mounting
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