**2.1 232Th reaction rates**

The experimental method of activation of γ-ray off-line measurement of 232Th reaction rates is used. The activation γ-rays are measured by using an HPGe γ spectrometer.

The 232Th capture reaction rate (THCR) indicates the fuel breeding, that is, the production rate of fissile 233U (233Pa decay). THCR can be deduced by measuring 311.98 keV γ rays emitted from 233Pa [6, 7]. The reaction process is as follows: <sup>232</sup>*Th*⎯

$$\text{ys emitted from } ^{233}\text{Pa [6, 7]}\text{. The reaction process is as follows:}$$

$$\text{P}^{232}\text{Th} \xrightarrow{\text{(7.7)}} ^{233}\text{Th} \xrightarrow{\text{232.3min}} ^{233}\text{Pa} \xrightarrow{\text{233}} ^{\text{f}}\text{P} \text{.} 26.967d \xrightarrow{\text{233}} ^{233}\text{U} \tag{1}$$

$$\text{where (with the bandwidth of 0.7 MeV) reaction rate (TIED) indicates}$$

**35**

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

<sup>232</sup>*Th* (*n*,*f*),*Yf* ⎯⎯→<sup>85</sup>*mKr <sup>β</sup>*

from 231Th [9]. The reaction process is as follows:

ized to one source neutron and one 232Th atom.

**2.2 Breeding properties**

measured 232Th reaction rates.

**2.3 Neutron spectra**

**3. Assemblies**

**3.1 Polyethylene shell**

channel at 0° to the incident D+

foils are about 4.2 g and ϕ30 × 1 mm, respectively.

samples.

(n,2n)

232Th⎯

− ⎯ ,4.48⟶*<sup>h</sup>* <sup>⟶</sup>

−

The 232Th(n,2n) 231Th (with threshold of 6.5 MeV) reaction rate (THNR) indicates neutron breeding. THNR is obtained from measuring 84.2 keV γ rays emitted

<sup>→</sup>231Th *<sup>β</sup>*

The 232Th reaction rates are deduced from the measured activity and corrections, which include detection efficiency of the HPGe γ spectrometer, cited value of branching ratio, D-T neutron yield during irradiation, self-absorption of gamma rays in the foils, 85mKr yield only for THFR, etc. The 232Th reaction rates are normal-

The breeding ratio in the conceptual design of subcritical blanket is more than one [1]. The experiment on breeding properties of thorium is used to support the design [17]. The breeding properties are relevant to the reaction type, cross section, and neutron spectrum. The breeding properties contain the fuel breeding and neutron breeding. The fuel breeding is derived from the reaction rate ratio of 232Th capture to fission, and neutron breeding from the 232Th(n,2n) and fission reaction rates. The different neutron spectra are constructed by using the macroscopic assemblies in which the material is relevant to that of the conceptual design. The breeding properties under different assemblies are obtained and analyzed from the

The neutron spectra leaking from the ThO2 cylinders of different thickness are measured by the proton recoil method and the liquid scintillator [16]. The n-γ pulse shape discrimination is based on the cross-zero method. The spectra are resolved by

The experimental assemblies are composed of polyethylene shell, depleted uranium shell, and ThO2 cylinder with a D-T fusion neutron source and thorium

One can assume the elastic scattering cross sections of H and C, which are widely used as standard cross sections [18] to be reliable. The polyethylene (PE) shell is adopted for checking the method of measuring the 232Th reaction rates. The inner radius (IR) and the outer radius (OR) of the PE shell are 80 and 230 mm [11], respectively. Five slices of ThO2 (concentration > 99.95%) foils are put in the radial

beam, as shown in **Figure 1**. The mass and size of

using iterative method, and their range is from 0.5 to 16 MeV.

<sup>85</sup>*Rb* (2)

,25.52h ⎯⎯⟶231Pa (3)

The 232Th fission (with threshold of 0.7 MeV) reaction rate (THFR) indicates energy amplification and neutron breeding. The fission fragment yield correction method is used [8]. THCR can be deduced by measuring 151.16 keV γ rays emitted from the decay of 85mKr from 232Th (n, f) reaction. The reaction process is as follows:

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

from Networks: Experimentents for Theorem Asemblies

It: http://h.w.l.ol.org/to.gy/to.gy/2/int.teh.open.s1582

$$^{232}Th \xrightarrow{\begin{pmatrix} n\_f \end{pmatrix}, Y\_f \underset{85m}{\longrightarrow} Kr \xrightleftharpoons}{\begin{pmatrix} n\_i \end{pmatrix}} \begin{array}{l} \text{vs} \\ \text{23} \end{array} \tag{2}$$

The  $^{233}Th(n,2n)$ ^{233}Th (with threshold of 6.5 MeV) reaction rate (THNR) individual is in a non-trivial way.

The 232Th(n,2n) 231Th (with threshold of 6.5 MeV) reaction rate (THNR) indicates neutron breeding. THNR is obtained from measuring 84.2 keV γ rays emitted from 231Th [9]. The reaction process is as follows: 232Th⎯

$$\text{H}^{232}\text{Th} \xrightarrow{\text{(n,2n)}} \text{Th} \xrightarrow{\text{\tiny{}^{231}\text{Th}}} \text{\textasciic{\textquotedbl{}}^{231}\text{Pa}} \text{\textquotedbl{}}^{231}\text{Pa} \tag{3}$$

The 232Th reaction rates are deduced from the measured activity and corrections, which include detection efficiency of the HPGe γ spectrometer, cited value of branching ratio, D-T neutron yield during irradiation, self-absorption of gamma rays in the foils, 85mKr yield only for THFR, etc. The 232Th reaction rates are normalized to one source neutron and one 232Th atom.

#### **2.2 Breeding properties**

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

breeding properties.

are analyzed.

**2. Methods**

spectrometer.

**2.1 232Th reaction rates**

<sup>232</sup>*Th*⎯

ment ratio was 1.17 employing ENDF/B-IV [5].

assemblies with a D-T fusion neutron source.

(*n*,γ)

<sup>→</sup><sup>233</sup>*Th <sup>β</sup>*

design for the subcritical blanket based on thorium depend on the accuracy of 232Th nuclear data and calculational tool. It is essential to carry out the fusion neutronics experiments for validating the evaluated 232Th nuclear data and studying the

A small number of fusion neutronics experiments on thorium were carried out, and there exist essential differences between the calculations and experiments [3–5]. The 232Th fission rate with fast neutrons was determined by detecting the gamma rays emitted from 140Ba and 140La, and the calculated-to-experimental ratio was 0.9 based on ENDF/B-IV [4]. The thorium fission reaction rate in a metallic sphere setup was determined by absolute measurement of the gamma-emission from 143Ce, the experimental uncertainty was 5.2%, and the calculation to experi-

The integral fusion neutronics benchmark experiments for macroscopic thorium assemblies with a D-T fusion neutron source were carried out at Institute of Nuclear Physics and Chemistry (INPC) [6–17]. The method for measuring integral 232Th reaction rate and its application in an experimental assembly were developed and investigated [6–8]. In this chapter, the progress in the fusion neutronics experiments for thorium assemblies is described. The overview of main results is presented. The thorium assemblies with a D-T fusion neutron source consist of a polyethylene shell, depleted uranium shell, and thorium oxide cylinder. The 232Th reaction rates in the assemblies and leakage neutron spectra are measured separately. The benchmark experiments on fuel and neutron breeding properties derived from the 232Th reaction rates in representative thorium assemblies are carried out and analyzed. The breeding properties are valuable to the breeding ratio in the conceptual design of subcritical blanket based on the Th/U fuel cycle. The experimental results are simulated by using the MC code with different evaluated data. The ratios of calculation to experimental values

The fusion neutronics experiments contain the measurements of the 232Th(n,γ), 232Th(n, f), and 232Th(n,2n) reaction rates, and the neutron spectra for thorium

The experimental method of activation of γ-ray off-line measurement of 232Th

The 232Th capture reaction rate (THCR) indicates the fuel breeding, that is, the production rate of fissile 233U (233Pa decay). THCR can be deduced by measuring 311.98 keV γ rays emitted from 233Pa [6, 7]. The reaction process is as follows:

,22.3min ⎯⎯⟶<sup>233</sup>*Pa <sup>β</sup>*

The 232Th fission (with threshold of 0.7 MeV) reaction rate (THFR) indicates energy amplification and neutron breeding. The fission fragment yield correction method is used [8]. THCR can be deduced by measuring 151.16 keV γ rays emitted from the decay of 85mKr from 232Th (n, f) reaction. The reaction process is as

−

,26.967*<sup>d</sup>* ⎯⎯⟶<sup>233</sup>*<sup>U</sup>* (1)

reaction rates is used. The activation γ-rays are measured by using an HPGe γ

−

**34**

follows:

The breeding ratio in the conceptual design of subcritical blanket is more than one [1]. The experiment on breeding properties of thorium is used to support the design [17]. The breeding properties are relevant to the reaction type, cross section, and neutron spectrum. The breeding properties contain the fuel breeding and neutron breeding. The fuel breeding is derived from the reaction rate ratio of 232Th capture to fission, and neutron breeding from the 232Th(n,2n) and fission reaction rates. The different neutron spectra are constructed by using the macroscopic assemblies in which the material is relevant to that of the conceptual design. The breeding properties under different assemblies are obtained and analyzed from the measured 232Th reaction rates.

#### **2.3 Neutron spectra**

The neutron spectra leaking from the ThO2 cylinders of different thickness are measured by the proton recoil method and the liquid scintillator [16]. The n-γ pulse shape discrimination is based on the cross-zero method. The spectra are resolved by using iterative method, and their range is from 0.5 to 16 MeV.
