Verification and validation of neutronic codes using the start-up fuel load and criticality tests performed in the China Experimental Fast Reactor

Under the framework of coordinated research activities of the International Atomic Energy Agency (IAEA), the China Institute of Atomic Energy (CIAE) proposed a coordinated research project (CRP) to develop a benchmark based on the start-up tests of the China Experimental Fast Reactor (CEFR). 29 international organizations from 17 countries are participating in this CRP. Among the different physical start-up tests conducted in 2010 in the CEFR, the fuel loading and criticality experimental data is included. Before the start-up of the reactor, the core was preliminarily loaded with mock-up fuel sub-assemblies (SAs) in the active fuel positions. The reactor reached first criticality by replacing these mock-up SAs with real fuel SAs step by step. In a sub-critical extrapolation process, the number of fuel SAs to be loaded is determined by extrapolation of reciprocal of count rate and following safety requirements. As the reactor core approaches to criticality, the subcritical extrapolation ended and the next process is called super-critical extrapolation, which uses the control rods to reach criticality by period method. For the CEFR, the final clean-core criticality state was reached with 72 fuel SAs and the regulating control rod at the position of 70mm with a measured sodium temperature of 245°C. In the paper, the main results of the contributing international organizations for the fuel loading process in the blind and refined phase are summarized and compared with the experimental data. Additionally, code to code comparisons for normalized radial power are also presented. In general, results from all institutions show very good agreement while comparing with the experimental data. The results are divided in deterministic and stochastic codes and in each case, discussion and deep analysis is presented.