Reactivity worth measurement of the lead target on VENUS-II light water reactor and validation of evaluated nuclear data

Abstract

In this paper, the benchmark experiment of the lead reactivity worth was introduced in detail, which has been carried out under a super-critical state at the light water reactor of the VENUS-II experimental facility. The reactivity worth of the cylindrical lead target was measured and processed as 142.0 ± 11.3 pcm by the period method. In simulations, the reactivity worth of the lead target was calculated by MCNP with the five libraries, i.e., ENDF/B-VII.1, ENDF/B-VII.0, JENDL-4.0, CENDL-3.1 and JEFF-3.2. By comparisons, the MCNP simulated results of the lead reactivity worth with ENDF/B-VII.1, ENDF/B-VII.0, CENDL-3.1 and JEFF-3.2 libraries are underestimated, and that of JENDL-4.0 shows slight better agreement with the experiment data within errors. Through the perturbation analysis, the (n, el) reaction channel is most related to the positive reactivity worth of the lead target. Additionally, the reaction rates of the (n, el), (n, inl) and (n, γ) channels were calculated by FM card in MCNP. It is observed that the (n, γ) reaction rates from different libraries show the maximum difference, which is due to the discrepancy of the (n, γ) cross sections in the thermal neutron region. In conclusion, the lead cross sections from the main libraries in the world have been preliminarily validated based on the measurements, which lays the foundation for the engineering design of CIADS.