Abstract: Uranyl fluoride solution criticality accident is one of potential criticality accidents for nuclear fuel cycle facility. It is necessary to make corresponding accident emergency assessment, which can provide auxiliary support for emergency decision. Fission number of the criticality is an important part and one of the technical difficulties in nuclear critical accidents emergency assessment. It reflects the size and scale of nuclear criticality accident, and directly affects the decision of emergency protection action. There are many ways to estimate the fission number, and have themselves applicable conditions. With the time passed, the more abundant information obtained, and the selected evaluation method may change to follow it. Therefore, a method for estimating fission number of uranyl fluoride solution criticality based on accident process was proposed, which solved the practical application of critical accident emergency assessment and the difficult problem of which method users should choose.

Key words: uranyl nitrate solution, criticality accident, emergency assessment, fission number