Keitaro Kondo

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.

Neutron Source for Material and Component Tests by Using IFMIF/EVEDA Prototype Accelerator

A neutron source for material and component tests is an essential tool for the DEMO reactor development. An accelerator-based neutron source such as IFMIF is regarded as the most promising one in Japan and the EU. The construction plan of IFMIF is still open due to the influence of the large cost overrun of ITER procurements. Japan Atomic Energy Agency (JAEA) has a plan of a neutron source for material and component tests using an IFMIF/EVEDA prototype accelerator and a lithium test loop for the IFMIF target facility. Expected performances of three options; 9 MeV and upgrading to 26 or 40 MeV of deuteron beam, are discussed. At the back plate position of the target, 1.5, 14, and 25 dpa/fpy are expected for 9, 26, and 40 MeV case, respectively. The option of 40 MeV is desirable, however, the option of 26 MeV is acceptable for blanket functional tests and material tests.

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.

Application of a 6LiF Small Neutron Detector with an Optical Fiber to Tritium Production Rate Measurement in D-T Neutron Fields

6LiF small neutron detectors with an optical fiber have been used to measure 6Li(n,α)T reaction rate distributions at thermal research reactors and accelerator facilities. In the present study, we developed an experimental method for the measurement of tritium production rate (TPR) of 6Li using this small detector in deuterium-tritium (D-T) neutron fields. Reaction rate measurements with the detector were conducted in the D-T neutron fields at the Fusion Neutronics Source (FNS) facility. From the results, we determined that this detector can be used to measure the TPR distribution in soft neutron spectrum fields such as in a Be assembly. It is difficult to obtain 6Li(n,α)T reaction rate separately in hard neutron spectrum fields such as in a Li2O assembly, because many kinds of charged particle production reactions need to be taken into consideration. However, a time-dependent reaction rate measurement method combined with the 6LiF detector and the ZnS detector is effective to separate the 6Li(n,α)T reaction from other reactions even in a hard spectrum field, and it can be applied to the measurement of the TPR distribution accurately.

Neutronic Analysis of the IFMIF Tritium Release Test Module Based on the EVEDA Design

Abstract The International Fusion Materials Irradiation Facility (IFMIF) is an accelerator-based intense neutron source to test fusion reactor materials under irradiation conditions expected to be experienced by a future fusion power plant (DEMO). The Tritium Release Test Module (TRTM) is intended for the irradiation of solid breeder ceramics as well as beryllium involving in-situ tritium release measurements in IFMIF. During the EVEDA (Engineering Validation Engineering Design Activities) phase, a detailed engineering design for the TRTM has been elaborated. A new 3-dimesional Monte Carlo geometry model of TRTM was prepared for a neutronic analysis directly from engineering CAD data using the McCad conversion software developed at KIT. The analysis was performed with the latest version of the Monte Carlo code McDeLicious, an enhancement to MCNP5 for IFMIF neutronics calculations, using a state-of-the-art nuclear data library FENDL-3. The result emphasizes the importance of the neutron reflector which should be placed behind TRTM in order to make the irradiation properties close to the European HCPB DEMO. Although the achievable dpa is lower than that expected in DEMO, the T/dpa and He/dpa values can be simulated very well when the neutron reflector is appropriately designed, in particularly by utilizing beryllium.

DOSE RATE ANALYSES FOR THE HIGH ENERGY BEAM TRANSPORT SECTION OF IFMIF

Abstract This work presents neutronic analyses to support the layout of the high energy beam transport (HEBT) section of the IFMIF neutron source in the framework of the Broader Approach (BA) EVEDA activities. In the HEBT section, neutron back streaming from the lithium target can cause significant damage to accelerator components and result in their activation. In order to estimate the resulting radiation doses, detailed neutron and photon flux distributions inside the Target Interface Room (TIR) and the Radiation Isolation Room (RIR) during operation are evaluated by using the Monte Carlo code McDeLicious, which is an enhancement to MCNP5. The obtained results show that the major contribution to the TIR dose during operation will come from neutrons streaming from the target through the beam ducts and from secondary photons produced in these parts. It seems to be impossible to use any semiconductor devices inside TIR, while for mechanical devices there should be no problem. The dose after shutdown due to decay gammas was preliminarily estimated for the beam duct at the most activated place in TIR. In order to reduce the shutdown dose rate, the use of a low-Mn-content aluminium alloy is proposed.

Interrelationship between True Stress–True Strain Behavior and Deformation Microstructure in the Plastic Deformation of Neutron-Irradiated or Work-Hardened Austenitic Stainless Steel

True stress–true strain relation and deformation microstructure have been examined for high purity Fe-18Cr-12Ni alloy and its alloys doped with 0.7 wt % Si or 0.09 wt % C. In high purity alloy and C-doped alloy irradiated at 240°C up to 3 dpa, the work hardening rate is equivalent to that in unirradiated alloys. These alloys show dislocation channel structure after irradiation and deformation. In irradiated Si-doped alloy, however, the work hardening rate is different from that in unirradiated alloys. This alloy shows fully developed dislocation cell structure after deformation, as seen in unirradiated deformed stainless steels. The cell structure in irradiated Si-doped alloy was much smaller than that in unirradiated Si-doped alloy and in type 316L stainless steel. One of the factors affecting the change in the work hardening rate of irradiated austenitic stainless steel at 240°C is strong obstacles such as γ precipitate that acts as dislocation pining and dislocation loops such as Frank loops that do not act as obstacles.

Measurement of Reaction Rate Distribution in Partial Mockups for the ITER TBM with DT Neutrons

In the previous studies, the calculated TPRs were overestimated by more than 10 % compared with the measured values in the experiment with a neutron source reflector. In order to confirm that these overestimation are found on other reactions, reaction rate distributions are measured on 197Au(n,γ)198Au and 93Nb(n,2n)92mNb in the ITER TBM mockups with and without a reflector by the activation foil method with DT neutron irradiation experiments. Analyses are performed with MCNP-4C and FENDL-2.1. The ratios of the calculation results to the experimental ones with a reflector are slightly larger than those without a reflector on the reaction rate of 197Au(n,γ)198Au.

Overview of Material Challenges in IFMIF Test Cell Design

Abstract As the core region of IFMIF, the test cell (TC) suffers intense neutron and gamma irradiations. Major material challenges of the TC faced during engineering design phase are outlined and the current key material allocations are described. Actively cooled magnetite concrete is selected as the major biological shielding material for the TC, and actively cooled closed liner made of 316L stainless steel is selected to cover the complete TC internal surfaces. Material selections for sealing gaskets and electric insulations inside the TC are preliminarily defined based on dose rate maps at different locations. Metal based sealing gaskets and glass/ceramic electric insulations are applied in the areas with high dose rate, while organic based gaskets and conventional insulation materials can only be arranged behind sufficient biological shielding. Leak tight welding seams between removable interface shielding plugs and the TC liner are located in the region with very low helium generation rate (<0.01 appm/fpy) in steel so that cutting and re-welding during the complete IFMIF life span is guaranteed.

Measurement of Reaction Rates in Li/V-Alloy Assembly with 14 MeV Neutron Irradiation

Abstract To examine the accuracy in the neutronics calculations for the Li/V-alloy blanket system without Be neutron multiplier, a fusion neutronics experiment on a Li/V-alloy assembly has been performed with a 14 MeV neutron source. Reaction rates and tritium production rates (TPRs) in the assembly were measured with activation foils and Li2CO3 pellets. The measured reaction rates sensitive to fast neutrons agreed almost within ~10 % with ones calculated by using the MCNP5 code, JENDL-3.3 library and JENDL dosimetry file 99. Though there appeared a possibility of a significant underestimation in the transport calculations for the energy range of <~4 keV due to nuclear data of vanadium, the measured TPR was consistent with the calculated one within ~8 %.