N. Kubota

Measurement of tritium production rate in water cooled pebble bed multi-layered blanket mockup by DT neutron irradiation experiment

For the first time, tritium production rates in the water cooled pebble bed blanket are experimentally examined by using DT neutrons with two partial mockups; multi-layered mockup with water and pebble bed mockup. Tritium production rates (TPRs) are calculated by numerical analyses using Monte Carlo code MCNP-4C with nuclear data libraries FENDL-2.1 and JENDL-3.3. For experimental analysis on the pebble bed mockup, precise modelling method is proposed using the hexagonal close-packed heterogeneous geometry. Prediction uncertainties of TPRs are clarified through the experimental analyses. Ratios of the calculation results to the experimental results on local TPRs are 0.89–1.10 in the multi-layered mockup, and 0.95–1.13 in the pebble bed mockup. The calculation results on integrated tritium productions agree well with the experimental ones in both mockups. It is clarified that integrated tritium productions can be accurately evaluated.

Measurement and Analysis of Neutron-Induced Alpha Particle Emission Double-Differential Cross Section of Carbon at 14.2 MeV

We carried out a detailed measurement of the neutron-induced α-particle emission double-differential cross section of carbon at 14.2MeV, for which there are few measured data in spite of its importance in many applications. In our measurement, a superior S/N ratio, high angular/energy resolutions and a wide detection energy range were realized with a pencil DT neutron beam and a countertelescope system. The obtained cross section for the 12C(n,α0)9Be(ground state) reaction agreed well with the results of previous experiments and evaluated nuclear data. The obtained angular-differential cross section of the 12C(n,n′+3α) reaction for α-particles showed a strong forward-peaked distribution that suggested a significant contribution of the direct reaction process to the 3α breakup. We attempted to calculate the emitted particle spectra by a Monte Carlo method and estimate the branching ratio of the channels that contribute to the 12C(n,n′+3α) reaction. As a result, it was found that the 12C(n,α)9Be* channels play an important role in generating the experimental double-differential cross section both of emitted α-particles and neutrons. The estimated ratio of the 12C(n,α)9Be* channels was approximately 40%, somewhat larger than those evaluated in previous studies.

Measurement of Charged-Particle Emission Double-Differential Cross Section of Fluorine for 14.2MeV Neutrons

We carried out detailed measurement of the double-differential cross sections of fluorine for the emissions of protons, deuterons, tritons, and α-particles with 14.2MeV incident neutrons. An improved charged-particle spectrometer with a pencil DT-neutron beam furnished at the FNS facility of the Japan Atomic Energy Agency enabled us to obtain precise data with a fine energy resolution over a wide energy range and an angular range from 15 to 150°. The present experiment is the first simultaneous measurement of the four different kinds of charged particles and provides useful data to establish a nuclear reaction model of fluorine as well as to confirm previous experimental data. Angular-differential cross sections for several discrete peaks corresponding to excited states of residual nuclei were extracted to discuss the reaction mechanism of charged-particle emission. The obtained data suggest that the charged-particle emission reaction of fluorine has a complicated mechanism in which there are contributions from the direct reaction, pre-equilibrium, and equilibrium processes. The obtained data were compared with the nuclear data evaluated in JENDL-3.3 and ENDF/B-VII.0. The results show large differences in the energy and angular distributions of emitted particles and the charged-particle production cross sections between the measured and evaluated data.

Confined alpha particle diagnostics for ITER based on measurements of gamma rays emitted from D(α,γ)6Li reaction

For the diagnosis of confined alpha particles in D-T plasma, we propose the observation of 2.186MeV gamma ray produced by D(α,γ)6Li reaction. However, there are few nuclear data of the D(α,γ)6Li reaction rate. Therefore, we carried out the experimental verification of the gamma ray diagnostics technique by using an accelerator. Helium ions in the energy range of 2–4MeV were bombarded into a thick deuterated polyethylene, where the gamma ray spectrum was measured with a Ge detector. Photopeak of the 2.186MeV gamma ray was clearly observed. From our experiment, the emission rate of the 2.186MeV gamma ray from the D(α,γ)6Li reaction is estimated to be 1012–1013s−1 in the ITER typical plasma condition. So we obtained a good prospect of the gamma ray measurement as the confined alpha particle diagnostics by using a high efficiency detector.