Abstract: The research concerns in nuclear criticality experiments data verifying calculation with MonteCarlo code for uraniumwater system and the simulating calculation of effective multiplication factor, k_eff， in UO₂F₂-CaCl₂ water solution system formed by taking materials from 740 L materials container and leaking CaCl₂ salty water. The calculated results show that the MCNP4B code is effective in uraniumwater system nuclear safety calculation and it is nuclear criticality safe for UO₂F₂-CaCl₂ water solution system. As a result, it can be a theoretical basis in nuclear criticality safety for reality production.