Measurement and calculation of U and Th reaction rates in uranium mock assemblies

• For validating nuclear data by integral experiments, U mock assemblies are established.
• In spherical assemblies with DU and PE, 238U capture rates, U fission rates and ratio are measured.
• In cubic assembly with natural U, 238U capture rates are reanalyzed.
• In DU spherical shell, 232Th capture rates, fission rates and ratio are measured.
• The measured results are compared to the calculated ones with MCNP and ENDF/B-VII.0.

The conceptual blanket based on a subcritical reactor for a fusion–fission hybrid energy reactor with magnetic confinement fusion is being studied. To validate nuclear data and code of neutronics calculation for the blanket design, measurement of reaction rates for U and Th is performed by integral experiments. Based on the fission blanket, the uranium mock assemblies are established, and include the depleted uranium shell, the depleted-uranium/polyethylene/graphite shell and the natural uranium cube. A depleted-uranium/polyethylene/graphite assembly of 131 mm in inner radius and 365 mm in outer radius consists of three layers of depleted uranium shells, two layers of polyethylene shells and a graphite shell, and these shells are arranged alternatively. A D–T fusion neutron source is centered of the spherical assemblies. The U reaction rates for capture, fission and ratio of capture to fission in the assemblies are measured by depleted uranium foils and an HPGe gamma spectrometer. The 232Th reaction rates for capture, fission and ratio of capture to fission are measured by ThO2 foils put into the depleted uranium shell. The measured results are compared to the calculated ones by using MCNP code with ENDF/B-VII.0 library data.