[en] The CELVA-3D computer code was developed to evaluate thermofluid phenomena and transport behavior of radioactive materials in a cell during hypothetical explosion in the fuel reprocessing plant. The code calculates temperature, pressure, flow velocity in the cell by three-dimensional thermofluid analysis and calculated an ability to confine the radioactive materials by transport analysis taking into consideration the thermofluid in the cell. And the CELVA-3D is separated into CELVA-3D(M) for a deflagration analysis and CELVA-3D(R) for a detonation analysis; the numerical solution of CELVA-3D(M) for the deflagration was applied to SIMPLE and SIMPLEST for a semi-implicit method, and the solution of CELVA-3D(R) for the detonation by ICE for an explicit method. The mathematical models in CELVA-3D were verified by comparison of code calculations with the results of JAERI's demonstration tests simulating hypothetical explosion in the reprocessing plant. (author)