Radiolytic gas generation from calcined nuclear waste

The gas generation rates for both the gamma and alpha radiolysis experiments appear to be about the same, but there was a wider range of products from the ..cap alpha..-radiolysis experiment. Although the major product was oxygen, significant quantities of gas condensable at -78/sup 0/C, probably water, and fairly large fractions of nitrogen oxides are produced. By contrast, the gamma radiolysis experiment yielded nearly 100 percent O/sub 2/. A steady state level should be achieved before all of the NO/sub 3//sup -/ salts are decomposed because of the reverse reaction NO/sub 2//sup -/ + /sup 1///sub 2/O/sub 2/ ..-->.. NO/sub 3//sup -/. The rate of pressure increase is still substantial at a pressure well above 1 atmosphere. Furthermore, in practice the canister will probably be maintained at higher temperature; so the pressure will be further increased by the PV/T relationship. It is concluded that radiolysis of NO/sub 3//sup -/ or H/sub 2/O will pose no insurmountable problems in the shipping and storing of waste calcines even though some additional pressurization will occur from the decomposition of residual nitrate salts. Release of gas by thermal decomposition or thermal desorption will produce gas pressures much more rapidly than radiolysis if the calcine is subjected to high temperatures from accident or fire. Such conditions are expected to lead to pressures of hundreds of atmospheres in closed containers. (DLC