Defect Structure Development Mechanisms during Fission and Fusion Neutron Irradiation

A research history at the Oarai Branch for JMTR Utilization of the Institute of Materials Research, Tohoku University, on neutron irradiation of materials for 8 years is reviewed by quoting 35 published papers. It consists of fusion neutron irradiation with RTNS-II (Rotating Target Neutron Source, LLNL) and fission neutron irradiation with JMTR (Japan Materials Testing Reactor, JAERI). Research program of D-T fusion neutron irradiation with RTNS-II is explained. Investigation of defect structures in a variety of materials is the basis for analysis. Major subjects are chracteristics of cascade damage, point defect processes in defect structure evolution, and recoil energy effects. By the improvement of control during JMTR irradiation, the first reliable experimental data are obtained for fission-fusion correlation. Proposals are made for the future prospect of the Oarai Branch

The Effect of Planar Sinks on the Interstitial Loop Growth under High Temperature Neutron Irradiation

The role of planar sinks such as surfaces and grain boundaries for the defect structure developments was studied in fission neutron irradiated Ni and Ni alloys of 2 at% Si, Cu, Ge and Sn to the dose of 4x10^n/m^2 (>1MeV) at 573 K by comparison between thin foil irradiation and bulk irradiation. The number density of interstitial loops increases and then decreases with the increase of distance from planar sinks. Observed defect structure developments were interpreted in terms of the variation of point defect concentration with the change of sink efficiency. The necessity of the introduction of cascade localization induced bias effect is emphasized

Fission-Fusion Correlation in Mechanical Property Changes of Several Pure FCC Metals

Mechanical property changes were observed for pure Ni, Cu and Au irradiated with fission and fusion neutrons. Before comparing the results of fission neutron with fusion neutron irradiation, the importance of irradiation temperature history is discussed. The irradiation below a designed temperature at the start-up of the reactor brings very different results from that obtained from strictly temperature controlled irradiation experiments, and this depends on the relative situation between the irradiation temperature and the temperature range of nucleation stage. Although there was no overlapping for neutron fluence in the fission and fusion neutron irradiation experiments, fluence for equivalent amount of the yield strength change for fusion neutron irradiation could be predicted from the plots of yield strength against 1/4 power of the neutron fluence for fission neutron irradiated specimens , and vice versa

Development of Controlled Temperature-Cycle Irradiation Technique in JMTR

The effects of cyclic temperature changes during neutron irradiation upon radiation induced microstructure evolution and resulting property changes of materials is very important from both fundamental and engineering viewpoints. Therefore, a technique that allows us to do the controlled temperature-cycle irradiation was developed in the Japan Materials Testing Reactor (JMTR). The technique meets the following requirements : (1) the temperature-cycle irradiation is to be performed under three different conditions by changing lower and upper temperatures; 200 --- 400℃, 300 --- 400℃ and 300 --- 450℃. (2) the number and period of the temperature-cycles are to be six for 24-day full irradiation and approximately 44 h/44 h at the lower/upper temperatures. (3) the temperatures of each specimen assembly are to be maintained at the lower temperatures before start-up of the reactor and at the upper temperatures during shut-down until the complete absence of reactor power. In this paper, the details of the irradiation rig, successful results and several problems to be overcome for future improvement are presented

Progress of Research on the Mechanism of Microstructure Evolution during Irradiation with Collision Cascades

Progress of the research on microstructural evolution during radiation damage accompanied with collision cascades, particularly by neutrons, is summarised from the researches reported in 1995 and 1996. The major part of irradiation was performed with JMTR (Japan Material Testing Reactor), and comparisons were made with the result of D-T fusion neutron irradiation with RTNS-II (Rotating Target Neutron Source, LLNL). The subjects concerned are : (1) Microstructure evolution during irradiation, (2) Processes controlling the accumulation of defects during cascade damage, (3) Subcascades from the viewpoint of point defect cluster formation, (4) Mechanism of suppression of microstructure evolution during temperature cycle neutron irradiation of nickel, (5) Identification of the nature of neutron-irradiation-induced point defect clusters in copper by means of electron irradiation, (6) Easy one-dimensional motion of small interstitial clusters, (7) Identification of the nature of small point defect clusters in neutron irradiated Fe-16Ni-15Cr, (8) Spatial distribution of nucleation of point defect clusters by high energy particle irradiation, (9) Crystallographic orientation dependence of dislocation structures in neutron irradiated metals, (10) Examination of defect accumulation mode with multi-section-removable-irradiation-rig in Japan Material Testing Reactor, (11) Estimation of freely migrating point defects during cascade damage by the growth of helical dislocations, (12) Identification of the nature of neutron-irradiation-induced small point defect clusters in Nickel by means of electron irradiation, (13) Thermal stability of point defect clusters in neutron irradiated Fe-16Ni-15Cr