Measurement of tungsten granular target worth on VENUS-II light water reactor and validation of the granular target model

In this paper, a benchmark experiment of tungsten granular target worth has been performed on the VENUS-II light water zero-power facility of CIAE in Beijing. The reactivity worth of the tungsten granular target was measured and processed as ( - 1.007 ± 0.096 ) mk by a period method. In MCNP simulations, three modeling methods of tungsten grains, i.e., the homogeneous, body center and face center models, were used to calculate the tungsten granular target reactivity worth. Through the comparison, the simulated tungsten granular target reactivity worth values with three modeling methods are in good agreement with the experimental result within errors and the maximum C/E and (C-E) deviations are respectively 3.7% and 0.037 mk. By the perturbation analysis in MCNP and the comparison on the cross sections of tungsten, iron and nickel, the negative reactivity worth of tungsten granular target is mainly caused by the tungsten radiation capture reaction channel. It is recommended to adopt the efficient homogeneous modeling method to simulate the tungsten granular target, which establishes a foundation for the systematic integration design of CIADS.