**4.2 232Th reaction rates in DU shell**

The DU shell assembly for measuring 232Th reaction rates is shown in **Figure 2**. The 232Th reaction rates are measured by the same method as described above.

The experimental uncertainties are 3.1% for THCR, 5.3–5.5% for THFR [6, 8], and 6.8% for THNR in DU shell.

The experiment is simulated using the MCNP code with different evaluated data, including ENDF/B-VII.0, ENDF/B-VII.1, JENDL-4.0, and CENDL-3.1 [27]. The distributions of 232Th reaction rates from the experiments and calculations with ENDF/B-VII.0 are shown in **Figure 8**. The ranges of C/E ratios with ENDF/B-VII.0

**Figure 6.** *232Th reaction rates in PE shell.*

**Figure 7.** *C/E ratio of 232Th reaction rates in PE shell.*

are 0.97–1.04 for THCR and 0.95–1.02 for THFR [8, 12], respectively. The results show that calculations and experiments are well consistent within the range of experimental uncertainties. The ratio of 232Th capture to fission is about 6.71–12.23 with the increase of radius in DU shell.

**41**

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

The C/E ratios of 232Th reaction rates with different evaluated data are shown in **Figure 9**. The calculations for THNR overestimate the experiments. Meanwhile, large differences still exist in C/E of THNR. The range of C/E with ENDF/B-VII.0 is 1.07–1.12. Fractions with different energies in DU shell are calculated by using ENDF/B-VII.0, and neutrons of energy more than 6.5 MeV account for 4–9% in the whole energy range, as shown in **Figure 5**. Since U(n,f) cross sections are standard in the wide energy range, it is suggested that U inelastic cross sections and

The ThO2 assembly for measuring 232Th reaction rates in three ThO2 cylinders with the thickness of 150 mm (without DU cylinder) is shown in **Figure 3**. The 232Th fission and (n,2n) reaction rates are measured by the same method as

The ranges of C/E are 0.77–0.91 for THFR, and 0.92–1.0 [12] for THNR, respectively. The results show that the calculations generally underestimate the experiments for THFR. The PEO influence on THFR is described below. The distributions of 232Th reaction rates by the experiments and calculations are shown in **Figure 10**.

Experimental and simulative studies of THFR are carried out on three sets of ThO2/DU cylinder assemblies to validate the evaluated thorium fission cross section and code [9, 10]. The size of each ThO2 cylinder and DU cylinder is ϕ300 × 50 mm. The ThO2 cylinders with PEO contents of 7.28, 1.1, and 0.55% are named as number 1, number 2, and number 3, respectively. The DU cylinder is named as number 4. Three sets of cylinder assemblies are combined with different cylinders, and named as "3 + 2 + 1," "4 + 2 + 1" (as shown in **Figure 3**) and "3 + 4 + 2 + 1" assembly, respectively.

The experimental uncertainties are 5.3–5.5% for THFR and 7.1% for THNR [9, 10]. The 232Th reaction rates are calculated by using MCNP code with ENDF/B-VII.0.

232Th(n,2n) reaction cross sections should be studied further.

*4.3.1 232Th fission and (n,2n) reaction rates in ThO2 cylinder*

**4.3 232Th reaction rates in ThO2 cylinders**

*4.3.2 232Th fission rates in ThO2/DU cylinders*

described above.

**Figure 8.**

*232Th reaction rates in DU shell.*

#### **Figure 8.** *232Th reaction rates in DU shell.*

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are 0.97–1.04 for THCR and 0.95–1.02 for THFR [8, 12], respectively. The results show that calculations and experiments are well consistent within the range of experimental uncertainties. The ratio of 232Th capture to fission is about 6.71–12.23

**40**

**Figure 7.**

with the increase of radius in DU shell.

*C/E ratio of 232Th reaction rates in PE shell.*

The C/E ratios of 232Th reaction rates with different evaluated data are shown in **Figure 9**. The calculations for THNR overestimate the experiments. Meanwhile, large differences still exist in C/E of THNR. The range of C/E with ENDF/B-VII.0 is 1.07–1.12. Fractions with different energies in DU shell are calculated by using ENDF/B-VII.0, and neutrons of energy more than 6.5 MeV account for 4–9% in the whole energy range, as shown in **Figure 5**. Since U(n,f) cross sections are standard in the wide energy range, it is suggested that U inelastic cross sections and 232Th(n,2n) reaction cross sections should be studied further.
