*4.4.1 Fuel breeding*

*Nuclear Fusion - One Noble Goal and a Variety of Scientific and Technological Challenges*

design margin of the subcritical blanket.

for THNR in the ThO2 powder cylinder.

above.

shown in [13–15].

*4.3.3 232Th reaction rates in ThO2 powder cylinder*

products, as described below. The stage results could provide reference for the evaluation of neutron-induced thorium fission cross section, and the conceptual

The ThO2 power cylinder assembly for measuring 232Th reaction rates is shown in **Figure 4**. The 232Th reaction rates are measured by the same method as described

The experimental uncertainties are 3.1% for THCR, 5.5% for THFR, and 7.0%

The experiment is simulated by using the MCNP code with different evaluated data [10, 11]. The C/E ratio of 232Th reaction rates with ENDF/B-VII.0 are shown in **Figure 12**. The ranges of C/E ratio are 0.96–0.98 for THCR, 0.96–0.99 for THFR, and 0.74–0.76 for THNR. The results show that calculations and experiments for THCR and THFR are well consistent within the range of experimental uncertainties. The distributions of 232Th reaction rates in the experiments and calculations are

The calculations for THNR underestimate the experiments. Fractions with different energies in ThO2 powder cylinder are calculated by using ENDF/B-VII.0, and neutrons of energy more than 6.5 MeV account for 62–72% in the whole energy range, which is the largest among the assemblies, as shown in **Figure 5**. The suggestion described above is that 232Th(n,2n) reaction cross sections should be studied further.

The ThO2 power cylinder assembly for developing the activation method of measuring THFR is shown in **Figure 4**. THFR in the axial direction of the cylinder is determined by measuring the 1260.409 keV gamma emitted from 232Th fission product 135I, with experimental uncertainties of 6.2% [14]. The experiment is simulated by using the MCNP code with ENDF/B-VII.0, ENDF/B-VII.1, JENDL-4.0, and CENDL-3.1. The calculations and experiments are in good agreement within experimental uncertainties. The activation method to determine THFR is developed

*4.3.4 232Th fission rate based on 135I in ThO2 powder cylinder*

**44**

**Figure 12.**

*C/E ratio of 232Th reaction rates in ThO2 powder cylinder.*

The primary conversion rate is one of the important parameters in the conceptual design of subcritical blanket. The relative reaction rate ratio of 232Th capture to fission as the fissile production rate indicates fuel breeding in the fuel burn-up unit [12]. The ratios of 232Th capture to fission measured in PE shell, DU shell, and ThO2 powder cylinder are obtained.

The ratios are about 10.76–20.17 with the increase in radius of the PE shell. It is demonstrated that the fuel breeding efficiency under the neutron spectra in the PE shell is quite high.

The ratios are about 6.71–12.23 with the increase in radius of the DU shell. It is demonstrated that the fuel breeding efficiency under the neutron spectra in DU shell is high.

The ratios are only about 0.11–0.19 with the increase in radius of the ThO2 powder cylinder. It is demonstrated that the fuel breeding efficiency under the neutron spectra in ThO2 powder cylinder is low.

The results show that the ratios are relevant to neutron spectra in the assemblies. The ratios in the three assemblies are compared and shown in **Figure 13**.
