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Description
A small modular reactor (SMR) employing calcium hydride (CaH2) as a moderator have attracted attention to the passive safety and economic efficiency. Some integral experiments should be carried out to validate nuclear data of CaH2, however, no integral experiment by reactor for the validation have been reported. As the first integral experiment by reactor, a series of reactivity worth measurements of CaH2 samples was conducted in a university training and research reactor (UTR-KINKI) of Kindai University.
The UTR-KINKI reactor is a light-water-moderated and graphite-reflected two-core (coupled-core) reactor. A graphite region between the two cores has been employed as a standard irradiation field which has a standard neutron spectrum consisting of 1/v and Maxwell distributions. The CaH2 sample was placed in a cavity located at the center of the irradiation field.
The sample reactivity worth was determined from a difference between two excess reactivities of the respective reactors with and without the sample. The respective excess reactivities were measured using positive period method. The reactivity worth measurements were repeated for 21.20 g, 41.00 g, and 72.78 g of CaH2 sample.
From the present experiment, the following reactivity worth could be determined.
1) For 21.29 g of CaH2, -0.00417±0.00028 [%∆k⁄k]
2) For 41.00 g of CaH2, -0.00861±0.00028 [%∆k⁄k]
3) For 78.72 g of CaH2, -0.01587±0.00041 [%∆k⁄k].
Furthermore, the sample reactivity worth was calculated using the continuous energy Monte Carlo codes MVP3.0 with the nuclear library JEFF-3.1, where each cross section of H and Ca constituting a molecule of CaH2 was taken into the thermal neutron scattering law (S(α,β)). The ratios of calculated to experimental values (C/E) were 1.19±0.72, 0.806±0.347 and 0.874±0.189 for 21.29 g, 41.00 g and 78.72 g of the samples, respectively.