The Model 940-553 Accident Range Dual Filter Assembly, when used with the Model 940-513 Accident Range Gas Sampler, Model 943-27 Current Mode Beta Scintillation Detector, a vacuum pumping system, and a Model 960 Digital Radiation Processor or Model 942A Universal Digital Ratemeter have been designed to meet the post-accident particulate and halogen collection requirements of Regulatory Guide 1.97. The Model 940-553 is an off-line, dual filter assembly, suitable for continuous collection of particulates and halogens in airborne effluents. The dual filters are shielded to minimize exposure to plant technicians during filter change operations.
The dual filter assembly manufactured using a 0.25 inch thick steel weldment, filled with 2.5 inches of virgin lead. The lead provides shielding to reduce radiation exposure to plant personnel when changing the filter. The weldment is designed to retain the lead shielding and provides a stable base for the internal filter holder components. 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 filter inlet and outlet connections. To permit continuous operation during an accident, dual filters are provided. By using two filters, one filter may be removed for laboratory analysis while the second filter remains in service. Because of the high radioactivity that may be present in the effluent during an accident, it is recommended that the filters be changed every 30 minutes to reduce radiation exposure to plant personnel when changing, transporting and analyzing the filters. Internally, the inlet/outlet tube stubs are connected to the particulate and halogen filter holder assembly.
To prevent radioactive contaminants from escaping, the filters are mounted in a filter cartridge slide designed with o-ring seals and a positive compression spring latch assembly. The o-ring seals are designed to operate from vacuum to 10 psig. An alignment pin is provided to ensure the filter cartridge slides are positioned correctly prior to locking the filters in place. The filter assembly is bolted to a machined stainless steel baseplate to ensure positive alignment with the filter carriers. In addition to the dual filters, two (2) filter carriers are provided. Each filter carrier assembly is manufactured using a 0.25 inch thick steel weldment, filled with two (2) inches of virgin lead. The lead provides shielding to reduce radiation exposure to plant personnel when transporting the filter. The weldment is designed to retain the lead shielding and provides a stable base for the internal filter transport drawer. The filter carriers are normally positioned on the stainless steel baseplate, adjacent to each filter holder. Filter replacement is accomplished by removing the filter cartridge slide, containing the particulate and halogen filters, from the filter assembly and sliding it into the filter carrier.
The filters may then be safely transported for analysis. The filter cartridge slide is removed by aligning the filter carrier with the loaded filter, removing the cartridge alignment pin on the filter holder, removing the filter carrier retaining pin, threading the retractor tool into the filter cartridge, releasing the spring loaded compression latch and pulling the filter cartridge into the filter carrier. Once the filter cartridge is moved into the carrier, the filter carrier retaining pin is inserted to restrain the loaded filter cartridge in the carrier.
By providing a machined baseplate, either filter carrier may be used with either filter assembly. Because of the potential for exposure to high radiation levels, removal and handling of the filters must be performed by personnel trained in the safe handling of radioactive materials, and be under the direction of the plant Health Physics personnel. It is also recommended that prior to filter removal, the filter holder assembly be purged for at least one minute to remove any radioactive gasses that may be present. Protective gloves should also be worn when handling the filters, as the temperature of the effluent may be greater than 100ºF.
The Model 940-553 Accident Range Dual Filter Assembly has been subjected to Seismic Qualification testing. The details of this testing are available upon request.