Long-term performance assessment of grouted phosphate/sulfate waste from N Reactor operations

Phosphate sulfate waste (PSW) is a low-level liquid generated by activities associated with N Reactor operations. The waste will be mixed with dry solids and permanently disposed of as a cementitious grout in sub-surface concrete vaults at Hanford's 200-East Area. Categories of scenarios were analyzed that could cause humans to be exposed to radionuclides and chemicals from the grouted waste include contaminated groundwater and direct intrusion. In the groundwater scenario, contaminants are released from the buried grout monoliths, then eventually transported via the groundwater to the Columbia River. As modeled, the contaminants are assumed to leach out of the monoliths at a constant rate over a 10,000-year period. The other category of exposure involves intruders who inadvertently contact the waste directly, either by drilling, excavating, or gardening. Long-term impacts that could result from disposal of PSW grout were expressed in terms of incremental increases of chemical concentrations in the groundwater and surface waters, and radiation doses. None of the calculated impacts exceeded the corresponding regulatory limits set by Washington State, the Department of Energy, or the Nuclear Regulatory Commission. 38 refs., 17 figs., 27 tabs