An algorithm for pressure equation in a computational code PCCSAP-3 D,which is dedicated to analyze transient process of PCCS(Passive Containment Cooling System),is introduced.GMRES is introduced to accelerate calculation speed.Pre-conditioning of GMRES is applied.Convergence rates of GMRES and ML-ADI are compared.It shows that pre-conditioned GMRES can be used to solve pressure equations more efficiently.Since pressure equation coefficient matrix is structural and sparse,pre-conditioned GMRES is more efficient than ML-ADI as pressure equation coefficient matrix is larger.

3D-cylinder reactor core neutron space-time kinetics is simulated with an improved quasi-static method. The program is developed. In a supposable 250 MW modular HTGR model, the core neutron space-time kinetics is simulated. Calculated results obtained from this program and CITATION code agree well with each other at initiatory state. Variance of the core reactivity, average neutron flux of each group, and relative power with time is computed.