Nuclear critical safety analysis is the key technology to ensure the safety of spent fuel reprocessing plant. However, the present critical safety analysis codes for solution system are either limited in the geometric scope of application, or have poor engineering practicability due to low computational efficiency.

This study aims to develop a method suitable for wide application range and high accuracy for nuclear critical safety analysis, so as to provide technical support for spent fuel reprocessing plant.

According to the characteristics of spent fuel solution system, a set of methods, such as the zero-dimension cross-section calculation and whole system group condensation model, the three-dimensional space-time neutron dynamics model based on PCQS, and the R-Z two dimensional thermal and radiolysis gas simulation model, were combined to establish a paralleled 3D critical safety analysis code hydra-TD. In addition, some experiments of SILENE facility at France were modeled and calculated by using hydra-TD code to verify its effectiveness.

The verification results indicate that there are very small errors of key parameters such as the first fission power peak, multiplication time and total fission times.

The code hydra-TD developed in this study can be applied to simulation of the multi-physics processes in the critical transients of the fuel solution, hence has the ability of critical safety analysis.