**4.1 232Th reaction rates in PE shell**

The PE shell assembly for measuring 232Th reaction rates is shown in **Figure 1**. THCR is deduced from measuring 311.98 keV γ rays emitted from 233Pa (its half-life is 26.967 days, it is obtained from 233Th decay). THFR is deduced from measuring 151.16 keV γ rays emitted from 85mKr decay (its half-life is 4.48 hour), which is one of the fragments of 232Th(n,f) reaction, and using the fragment yield correction method. THNR is deduced from measuring 84.2 keV γ rays emitted from 231Th (its half-life is 25.52 hour).

The experimental uncertainty of THCR is 3.1%, including neutron yield 2.5%, γ-ray detection efficiency 1.0% (HPGe-GEM 60P), self-absorption 1.0%, characteristic gamma branch ratio 1.0%, 232Th nucleus number 0.5%, and counting statistics 0.3–0.6%.

The experimental uncertainty of THFR is 5.3%, including neutron yield 2.5%, γ-ray detection efficiency 1.0%, self-absorption 1.0%, average fission yield of 85mKr 4.3%, characteristic gamma branch ratio 0.7%, 232Th nucleus number 0.5%, and counting statistics 0.8–1.0%.

The experimental uncertainty of THNR is 6.8%, including neutron yield 2.5%, γ-ray detection efficiency 1.0%, self-absorption 1.0%, characteristic gamma branch ratio 6.1%, 232Th nucleus number 0.5%, and counting statistics 0.5–0.6%.

**39**

**Figure 6.**

*232Th reaction rates in PE shell.*

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

tion cross sections should be studied further.

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

and 6.8% for THNR in DU shell.

assembly; it takes into account the target chamber and experimental hall. The calculated statistical uncertainty is less than 1%. The ranges of C/E with ENDF/B-VII.0 are 0.96–1.02 for THCR, 0.95–0.97 for THFR, and 0.89–0.91 for THNR. The results show that the experiment and calculation for THCR and THFR are well consistent within the range of experimental uncertainties, respectively. It is shown that the

The distributions of 232Th reaction rates obtained from the experiments and calculations with ENDF/B-VII.0 are shown in **Figure 6**. The reaction rate ratio of 232Th capture to fission gives fissile production rate in unit of fuel burn-up [12]. The relative ratios measured are about 10.76–20.17 with the increase of radius in PE shell. The ratios of calculation to experimental values (C/E) are analyzed. The C/E ratios of 232Th reaction rates are shown in **Figure 7**, and the 232Th(n,f) reaction results for different evaluated nuclear data are shown in Ref. [11]. The calculations with ENDF/B-VII.0 and ENDF/B-VII.1 for THNR underestimate the experimental values. Meanwhile, large differences still exist in the 232Th(n,2n)231Th cross sections among different evaluated data [26]. Fractions with different energies in the PE shell are calculated by using ENDF/B-VII.0, and neutrons of energy more than 6.5 MeV account for 33–48% in the whole energy range, as shown in **Figure 5**. Since the neutron spectra in the PE shell are reliable, it is suggested that 232Th(n,2n) reac-

The DU shell assembly for measuring 232Th reaction rates is shown in **Figure 2**.

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

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],

γ-ray off-line method is feasible for determining the 232Th reaction rates.

The experiment is simulated by using the MCNP code with evaluated nuclear data from different libraries, including ENDF/B-VII.0, ENDF/B-VII.1 [24] and JENDL-4.0 [25]. The model is completely consistent with the structure of the

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

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

energy and intensity are calculated by "DROSG-2000" code [23]. The neutron spectra at foils with different distances *d* to the neutron source in three assemblies are relatively compared, as shown in **Figure 5**. The ordinate is a normalized neutron fraction, that is, the proportion of the neutron number in each energy segment to the one in the whole energy range [11, 13]. The results show that the differences of

The PE shell assembly for measuring 232Th reaction rates is shown in **Figure 1**. THCR is deduced from measuring 311.98 keV γ rays emitted from 233Pa (its half-life is 26.967 days, it is obtained from 233Th decay). THFR is deduced from measuring 151.16 keV γ rays emitted from 85mKr decay (its half-life is 4.48 hour), which is one of the fragments of 232Th(n,f) reaction, and using the fragment yield correction method. THNR is deduced from measuring 84.2 keV γ rays emitted from 231Th (its

The experimental uncertainty of THCR is 3.1%, including neutron yield 2.5%, γ-ray detection efficiency 1.0% (HPGe-GEM 60P), self-absorption 1.0%, characteristic gamma branch ratio 1.0%, 232Th nucleus number 0.5%, and counting

The experimental uncertainty of THFR is 5.3%, including neutron yield 2.5%, γ-ray detection efficiency 1.0%, self-absorption 1.0%, average fission yield of 85mKr 4.3%, characteristic gamma branch ratio 0.7%, 232Th nucleus number 0.5%, and

The experimental uncertainty of THNR is 6.8%, including neutron yield 2.5%, γ-ray detection efficiency 1.0%, self-absorption 1.0%, characteristic gamma branch

The experiment is simulated by using the MCNP code with evaluated nuclear data from different libraries, including ENDF/B-VII.0, ENDF/B-VII.1 [24] and JENDL-4.0 [25]. The model is completely consistent with the structure of the

ratio 6.1%, 232Th nucleus number 0.5%, and counting statistics 0.5–0.6%.

the fractions are very obvious, especially in the low-energy region.

**38**

**4. Results**

**Figure 5.**

**4.1 232Th reaction rates in PE shell**

*Neutron spectra at foils in three assemblies.*

half-life is 25.52 hour).

statistics 0.3–0.6%.

counting statistics 0.8–1.0%.

assembly; it takes into account the target chamber and experimental hall. The calculated statistical uncertainty is less than 1%. The ranges of C/E with ENDF/B-VII.0 are 0.96–1.02 for THCR, 0.95–0.97 for THFR, and 0.89–0.91 for THNR. The results show that the experiment and calculation for THCR and THFR are well consistent within the range of experimental uncertainties, respectively. It is shown that the γ-ray off-line method is feasible for determining the 232Th reaction rates.

The distributions of 232Th reaction rates obtained from the experiments and calculations with ENDF/B-VII.0 are shown in **Figure 6**. The reaction rate ratio of 232Th capture to fission gives fissile production rate in unit of fuel burn-up [12]. The relative ratios measured are about 10.76–20.17 with the increase of radius in PE shell.

The ratios of calculation to experimental values (C/E) are analyzed. The C/E ratios of 232Th reaction rates are shown in **Figure 7**, and the 232Th(n,f) reaction results for different evaluated nuclear data are shown in Ref. [11]. The calculations with ENDF/B-VII.0 and ENDF/B-VII.1 for THNR underestimate the experimental values. Meanwhile, large differences still exist in the 232Th(n,2n)231Th cross sections among different evaluated data [26]. Fractions with different energies in the PE shell are calculated by using ENDF/B-VII.0, and neutrons of energy more than 6.5 MeV account for 33–48% in the whole energy range, as shown in **Figure 5**. Since the neutron spectra in the PE shell are reliable, it is suggested that 232Th(n,2n) reaction cross sections should be studied further.
