The performance of the computer code system, SIERRA-II, for calculating the environmental radiation dose due to an accident
was assessed over a coastal area, using the environmental monitoring data around the coastally located Tokai Reprocessing
Plant (TRP) when 85Kr was discharged during its operation. The agreement within a factor of 5 between the calculated and observed air concentrations
of 85Kr in areas of a few km from the TRP was achieved in 57% of the comparison data, disregarding the internal boundary layer.
The mean fraction bias was −0.6, which meant a slight overestimation. According to the vertical profile of the atmospheric
temperatures, the internal boundary layer was modeled with the SIERRA-II and the agreement became better than when the internal
boundary layer was not considered.