Effects of engineering controls on radioactive air emissions from the Los Alamos Neutron Science Center

Abstract

Under federal regulations set forth in 40 CFR 61, releases of radioactive airborne effluents from a Department of Energy facility must be limited so that no member of the public receives more than 0. IO miflisievert (IO milhrem) effective dose equivalent annually. At Los Alamos National Laboratory (LANL), the Los Alamos Neutron Science Center (LANSCE) has implemented engineering controls to ensure that emissions remain below this limit. At the accelerator beam stop, a delay line was constructed to delay exhaust air releases, and thereby allow for decay of any radioactivity prior to release. Also, an air scrubber was built at the beam stop to remove excess water, acids, triti@ and carbon dioxide from the air stream. This thesis describes the effectiveness of these emissions control efforts. Using a flow-through ionization chamber and high-purity germanium (HPGE) detector, the delay line was shown to reduce overall facility emissions by 29%. The scrubber effectiveness at removing tritium was found by collecting grab samples of the air stream on silica gel, both upstream and downstream of the scrubber. Results of liquid scintillation analysis show the tritium removal effectiveness to be greater than 95%. Removal of carbon-I I was determined by two methods. First, air samples upstream and downstream of the scrubber were collected on a carbon dioxide absorber and analyzed with a sodium iodide detector. The second method used a bench-top model scrubbing system to analyze scrubber performance with an BPGE detector. Different scenarios were examined with this model system, including varying the pH of the scrubber water and using catalytic conversion to convert all carbon in the air to carbon dioxide. The highest removal effectiveness of the model system was greater than 95%, under high pH and complete conversion of all carbon forms to C02-