The laboratory conducts research on the technology improvement on safety issues which occurred in the operation, repair, and maintenance of nuclear power plants by means of direct computer calculations and/or the thermo-hydraulic simulation codes, MELCOR. The researchers also simulate virtual severe accidents, so that they can estimate the effects of uncertain physical phenomenon in reactor safety. The researchers are developing the quantitative methods of PRA (Probabilistic Risk Assessment) by establishing mathematical models to assess the risk of the nuclear power plants quantitatively using simulation codes such as AIMS and COFUN. The new methods for risk assessment and management sciences using risk-informed technology include stochastic models, optimization, accident simulation, decision analysis, and decision theory.