Models for the release of airborne radioactivity in fires have been developed. These radioactive source term models are used as subroutines in a compartment fire code called FIRIN. Each model is based on release factors developed using information from experiments. Models are developed for the following release mechanisms:

  1. burning of contaminated combustible solids
  2. burning of contaminated combustible liquids
  3. heating of noncombustible contaminated surfaces
  4. heating of unpressurized radioactive liquids
  5. pressurized releases of radioactive powders
  6. pressurized releases of radioactive liquids.
The potential for release from these mechanisms was examined in an analysis of three types of fuel cycle facility fires. The types of fires considered were mixed oxide (MOX) general facility fires, MOX stored combustible waste fires, and solvent extraction fires in fuel reprocessing plants. Input parameters were varied to determine relative importance of release mechanisms and sensitivity of predicted releases to changes in initial conditions. Total radioactive material released ranged from 8 × 10−4 g of plutonium (0.002% of material at risk) given off in a combustible waste fire to 75 g of mixed isotopes (0.3% of material at risk) given off in a solvent extraction fire. Fuel loading and burn area were the parameters that caused the greatest change in total release of radioactive material. Changes in ventilation rate also made a significant difference in release for overventilated fires, but not for underventilated fires. Work is under way at Battelle Pacific Northwest Laboratory to improve the models for burning of contaminated combustible solids and liquids.