Study of Radiation Induced Electrical Degradation of Alumina in a Dynamic Pumping Condition in a Fission Reactor

The electrical conductivity of two ceramic insulators, alumina, and silicon nitride was measured in a fission reactor, JMTR under a dynamic vacuum condition. The instrumented irradiation rig was dynamically evacuated during fission reactor operation. The uppermost vacuum level attained was better than 10^ Torr. In this experiment, we attempted to reveal effects of the gaseous environment on the measurement of electrical conductivity under ionizing irradiation. The results showed that the gaseous environment has a most hazardous effect in a certain gas pressure range. In the second experiment, an electrical resistivity of polycrystal α-alumina was measured at about 680K in a dynamic pumping condition. In a good vacuum, we observed smaller RIC(radiation induced conductivity) than our previous results. We observed RIED(radiation induced electrical degradation)-like behavior. The results suggested that RIED would take off faster at a higher ionizing dose rate. In the meantime, the take-off occurred at about the same displacement damage of about 0.03-0.05dpa in the range of fast neutron flux of 3.4-15.1x10^n/cm^2s

Irradiation Behavior of developed radiaiton resistance optical-fibers and observed optical radiation from their SiO_2 cores under reactor irradiation

Two kinds of optical fibers were irradiated in a fission reactor, JMTR(Japan Materials Testing Reactor), up to a 1.55x10^n/cm^2 fast neutron fluence and a 3.3x10^9Gy ionizing dose at 370K. Optical transmission spectra were measured in the wavelength range of 450-1750nm, in-situ. Growth of strong optical absorption bands were observed in the range of wavelength shorter than 750nm. In the meantime, the fibers showed good radiation-resistance in the range of wavelength longer than 750nm. Optical radiations were observed from SiO_2 optical fibers under irradiation. A major part of the observed optical radiations is thought to be composed of broad optical radiation in the whole wavelength range studied in the present experiment. This broad optical radiation will be generated by the process of so-called Cerenkov radiation. Also, a sharp optical radiation peak was found at 1270nm on a F-doped fiber. This peak is thought to relate with doped Fluorine ions and ionizing gamma-ray irradiation

Development of Irradiation Techniques for Material Study in JMTR

The Oarai Branch has been carrying out the irradiation of materials using the JMTR, for these twenty years. We have made efforts to improve the irradiation conditions and to satisfy. the various demands evoked by our users. Here, we describe our efforts to improve the irradiation rigs and the irradiation techniques

Development Of High Time-Resolution Laser Flash Equipment For Thermal Diffusivity Measurements Using Miniature-Size Specimens Irradiated Heavily In A Reactor

For measurements of thermal diffusivity of miniature-size specimens heavily irradiated by neutrons, a new Q-switched laser-flash instrument was developed. In the present instrument the time resolution was improved to 0.1 ms by using a laser-pulse width of 25 ns. The realization of high time-resolution made it possible to measure the thermal diffusivity of thin specimens. It is expected that copper of 0.7mm thick, and SUS 304 of 0.1mm could be used for the measurements. In case of ATJ graphite, 0.5mm thick specimen could be used for the reliable measurement in the temperature range of 300-1300K

Radiation effects in Ceramics I. Study of Dynamic Irradiation Effects on Electrical Conductivity in JMTR : in comparison with results obtained with other irradiation sources

In the Oarai Branch, Institute for Materials Research, Tohoku University, we have been studying radiation effects in materials, using mainly a water-cooled fission reactor, JMTR. Comparing a fission reactor irradiation with other irradiation sources such as ion-beams, we can point out many attracting features of a fission reactor irradiation. Especially in the course of development of fusion reactor materials, importance of the fission reactor irradiation has bee stressed repeatedly. Ceramic materials are expected to play very important roles in heavy irradiation environments in fusion reactors. Extensive studies have been accumulated and now we will move from the materials science phase to the engineering phase. Here, we will summarized the accumulated date on radiation effects on ceramic materials, focusing on their irradiation effects of dependence on irradiation sources. In the first paper, we will summarize results on dynamic radiation effects on electrical properties on which we are actively devoting our efforts currently using JMTR. In the second paper, we will summarize the fundamental aspects, dimensional stability and dielectric properties

Neutron Irradiation Effects on Optical Fibers

Irradiation effects on optical fibers were observed with 14 MeV fusion neutron and fission neutron. As a result, the following characteristics have become clear. Permanent absorption loss after fission and fusion neutron irradiation, were greater than that of gamma ray irradiation. In case of fission neutron, large absorption loss appeared at wavelength of shorter than 700 nm and loss peak of 600 nm, and absorption loss increased exponentialy to the fluence of 10^ n/cm^2. During irradiation, the light emission was observed in the wavelength of 400 to 1700 nm and peak of light at about 1200 nm was appeared. Two kinds of the SiO_2 fibers were survived irradiated up to 3 x 10^ n/cm^2