*4.4.2 Neutron breeding*

The bred neutrons from 232Th(n,2n) and 232Th(n,f) react with thorium or relevant nuclides to maintain the Th/U fuel cycle. THNRs in three assemblies, that is, under different neutron spectra, are compared and shown in **Figure 14**. The results show that the 232Th(n,2n) reaction rates are relevant to the fraction of high-energy neutrons in the assemblies as described above, and the decreasing trend of THNR with the increase in distance to the neutron source are similar for three assemblies.

**Figure 13.** *Ratios of 232Th capture to fission in the three assemblies.*

**Figure 14.** *THNRs in the three assemblies.*

**Figure 15.** *THFRs in the three assemblies.*

Since 230Th half-life (7.54 × 104 years) is very long, measurement of 232Th(n,3n) 230Th (with threshold of 11.6 MeV) reaction rate by the activation method is very difficult. The 232Th(n,4n) reaction has high threshold 19 MeV and is not involved in this work.

The prompt neutron and delayed neutron yields from 232Th(n,f) reaction are about 3.7 and 0.0265 per fission at 14.1 MeV [28], respectively. THFRs in three assemblies, that is, under different neutron spectra, are compared and shown in **Figure 15**. From **Figures 14** and **15**, THNRs are higher than THFRs in the three assemblies.

#### **4.5 Leakage neutron spectra**

Three assemblies consist of the ThO2 cylinders with thicknesses of 50, 100, and 150 mm (without DU cylinder), respectively, as shown in **Figure 3**. The front

**47**

*Fusion Neutronics Experiments for Thorium Assemblies DOI: http://dx.doi.org/10.5772/intechopen.81582*

is at a 0° to the incident D+

**Figure 16.**

background neutrons is negligible.

*Leakage neutron spectra from ThO2 cylinders.*

further, as shown in **Figure 16**.

**5. Conclusions**

surface of the assembly is 0.22 m from the center of a T-Ti target. The leakage neutron spectra are measured by using a 50.8 mm diameter and 50.8 mm length BC501A liquid scintillator coupled to a 50.8 mm diameter 9807B photomultiplier [16]. The distance from the detector to the neutron source is 10.75 m. The detector

The leakage neutron spectra from the three assemblies are measured. The spectra are normalized to one source neutron and unit area. The experimental uncertainties are 9.7% for 0.5–1 MeV, 6.7% for 1–3 MeV, and 6.3% for 3–16 MeV. The experiments are calculated by using MCNP code with ENDF/B-VII.0. The results show that the experiments and calculations are generally consistent within the range of experimental uncertainties, and the spectra (<5 MeV) should be analyzed

To validate 232Th nuclear data, the fusion neutronics experiments for the three kinds of thorium assemblies with a D-T neutron source have been carried out. The two spherical assemblies based on the DU and PE shells, and the cylindrical assemblies based on ThO2 have been designed and established. The assembly materials are referable to the conceptual design of subcritical blanket of a hybrid reactor. The 232Th(n,γ), 232Th(n,f), and 232Th(n,2n) reaction rates in the assemblies are measured by the foil activation technique. The results show that the developed activation approach can work well for the experiments, and the 232Th reaction rates are relevant to neutron spectra in assemblies. The reaction rate ratios of 232Th capture to fission are obtained. The fuel and neutron breeding properties under different neutron spectra are compared and analyzed. The leakage neutron spectra from ThO2 cylinders are measured. The experimental results are compared to the numerical results calculated by using the MCNP code with different evaluated data. The results show that the experiments are benefit to validate Th nuclear data and support the conceptual design of subcritical blanket with thorium in a hybrid reactor. Furthermore, it should be beneficial to measure relevant 232Th excitation curve at white neutron source of China Spallation Neutron Source (CSNS) [29] for verifying 232Th nuclear data.

beam and arranged in shielding room. The influence of

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

**46**

this work.

**Figure 15.**

**Figure 14.**

*THNRs in the three assemblies.*

*THFRs in the three assemblies.*

Since 230Th half-life (7.54 × 104

**4.5 Leakage neutron spectra**

years) is very long, measurement of 232Th(n,3n)

230Th (with threshold of 11.6 MeV) reaction rate by the activation method is very difficult. The 232Th(n,4n) reaction has high threshold 19 MeV and is not involved in

The prompt neutron and delayed neutron yields from 232Th(n,f) reaction are about 3.7 and 0.0265 per fission at 14.1 MeV [28], respectively. THFRs in three assemblies, that is, under different neutron spectra, are compared and shown in **Figure 15**. From **Figures 14** and **15**, THNRs are higher than THFRs in the three assemblies.

Three assemblies consist of the ThO2 cylinders with thicknesses of 50, 100, and 150 mm (without DU cylinder), respectively, as shown in **Figure 3**. The front

**Figure 16.** *Leakage neutron spectra from ThO2 cylinders.*

surface of the assembly is 0.22 m from the center of a T-Ti target. The leakage neutron spectra are measured by using a 50.8 mm diameter and 50.8 mm length BC501A liquid scintillator coupled to a 50.8 mm diameter 9807B photomultiplier [16]. The distance from the detector to the neutron source is 10.75 m. The detector is at a 0° to the incident D<sup>+</sup> beam and arranged in shielding room. The influence of background neutrons is negligible.

The leakage neutron spectra from the three assemblies are measured. The spectra are normalized to one source neutron and unit area. The experimental uncertainties are 9.7% for 0.5–1 MeV, 6.7% for 1–3 MeV, and 6.3% for 3–16 MeV. The experiments are calculated by using MCNP code with ENDF/B-VII.0. The results show that the experiments and calculations are generally consistent within the range of experimental uncertainties, and the spectra (<5 MeV) should be analyzed further, as shown in **Figure 16**.
