Demonstration of performance modeling of a low-level waste shallow-land burial site: A comparison of predictive radionuclide transport modeling versus field observations at the nitrate disposal pit site, Chalk River Nuclear Laboratories

Before a license can be obtained to construct a facility for the shallow-land burial of low-level wastes, the US Nuclear Regulatory Commission must be assured that the facility will meet both performance objectives and prescriptive requirements set forth in 10CFR61, Licensing Requirements for Land Disposal of Radioactive Waste. Subpart D of 10CFR61 states that a disposal site shall be capable of being characterized, modeled, analyzed and monitored. To test the concept of site modelability, a 30-year old low-level radioactive waste disposal site at Chalk River Nuclear Laboratories (CRNL), Canada, was used as a field location for evaluating the process of site characterization and the subsequent modeling prediction of radionuclide transport from the site by groundwater. The radionuclide source term was a limestone-lined pit (since covered with soil) which in 1953 to 1954 received approximately 3800 liters of aqueous waste containing 1000 to 1500 curies of aged, mixed fission products, including 700 to 1000 curies of 90Sr and 200 to 300 curies of 137Cs. This evaluation was performed by comparing the actual measured radionuclide migration with predicted migration estimated from hydrologic/radionuclide transport models. This comparison provided valuable insights into the applicability of transport modeling, and to determining what level of effort is needed in site characterization at locations similar to the Nitrate Disposal Pit to provide the desired degree of predictive capabilities. 47 refs., 42 figs., 7 tabs