The Model 940-513 Accident Range Gas Sampler, when used with the Model 943-27 Current Mode Scintillation Detector, Model 940-553 Accident Filter, a vacuum pumping system, and a Model 960 Digital Radiation Processor or Model 942A Digital Ratemeter have been designed to meet the post-accident noble gas effluent monitoring requirements of Regulatory Guide 1.97. The Model 940-513 is an off-line, single channel sampler, suitable for the monitoring of accident range noble gasses. The sampler is a shielded mounting fixture that provides a fixed geometry for the detector. Since the sample volume is fixed, the noble gas concentration measured by the detector is independent of the sample flow rate.
The sampler is manufactured using a 0.25 inch thick steel weldment, filled with three (3) inches of virgin lead. The lead provides shielding of the detector from background radiation. The weldment is designed to retain the lead shielding and provides a stable base for the sample volume and inlet/outlet ports. Because of the high radioactivity of the sample in an accident condition, low sample flow rates, less than 1,000 cc/min, are used in the sampling system. To accommodate the low design flow rate, 0.25 inch OD stainless tube stubs are used for the sample inlet and outlet connections. Internally, the inlet/outlet tube stubs are connected to a welded, 11 cc, stainless steel sample volume.
The detector assembly is removable to permit detector calibration and decontamination of the sample volume. One end of the sample volume is sealed by the detector mounting flange assembly, using Quad-X lobe seals. A removable lead plug is provided to shield the rear of the detector from background radiation. The detector plug assembly is slotted, to provide a path for routing the detector signal and high voltage cables. The opposite end of the sample volume is sealed with a Quad-X lobe seal in the check source plug assembly. A rotary check source solenoid and a 100 µCi 90Sr source are housed in the check source plug. The Quad-X lobe seals provide leak tight operation under vacuum conditions, and up to a pressure of 10 psig.
The Model 940-513 Accident Sampler has been subjected to Seismic Qualification testing. The details of this testing are available upon request.
