[en] Purpose: To rapidly and reliably detect failures in a fuel cladding tube thereby prevent accidents. Method: Off-gases discharged from an air extractor are mixed at a certain ratio with cleaning water and gamma spectra for short-life radioactive rare gases and for long-life radioactive rare gases in the off-gases are measured by gamma ray detectors. The spectra are analyzed by a Pulse-height analyzer so as to quantitatively determine the nuclides of radioactive rare gases thereby calculate the release rate on each of the nuclides. Further, a central data-processing unit calculates the composition ratio of each release models about recoil, diffusion and equilibrium in the whole radioactive rare gases based on the release rate. As the total value of the release rate is rapidly increased, recoil part will be decreased suddenly and the diffusion and equilibrium parts will be increased by so much, upon failure of a fuel can; thus the failure can rapidly be detected. (Sekiya, K.)

[en] In a through hole sealing structure for a reactor container, when an inner pressure and an atmospheric temperature are elevated, there is a possibility that the sealing material is melted if the temperature exceeds a heat-resistance limit value and the through hole structure is deteriorated, to leak and release radioactive gases. The radioactive gases are diffused while incorporating iodines generated due to nuclear fission of radioactive elements such as uranium. Then, in the present invention, iodine eliminating materials are incorporated to the sealing materials in electrical pipelines perforated and secured to the wall of the container. Since the iodine eliminating materials adsorb the radioactive iodine, the iodines out of the reactor container is suppressed and, accordingly, leak and release of radioactive gases are reduced to improve decontamination coefficient even if the sealing materials are deteriorated due to the elevation of the inner pressure and the atmospheric temperature. (N.H.)

[en] Purpose: To effectively trap tritium in an exhaust gas processing device upon cutting control rods. Constitution: In a case of cutting a used control rod, since tritium formed in the control rod is released into the working circumstance to cause exposure at the inside and the outside of operator's bodies, it is necessary to collect tritium at high accuracy. Upon cutting, there are formed scattering particulate radioactive materials and tritium formed from boron carbide as absorbents. The radioactive particulate materials can be collected by way of dust filters, etc., but collection of tritium is difficult since its chemical nature is similar to that of hydrogen. In view of above, a tritium collector incorporating a filter made of hydrogen absorbing alloy is disposed at an appropriate portion of dust filter, blower, compressor, cooler, exhaust processing device, etc. to trap tritium thereby reduce the operator's exposure dose. (Kamimura, M.)

[en] Object: To effectively attenuate low density radioactive rare gases and radioactive iodine contained in waste gases in a large airflow ventilation system to purify the waste gases before discharging into atmosphere. Structure: In discharging large airflow waste gases in a ventilation system in an atomic power plant through a chimney, the aforesaid waste gases are introduced into a liquefaction and distilling apparatus to separate into nitrogen and oxygen, which occupy a greater part thereof, and small quantities of oxygen or the like containing enriched rare gases and iodine, the former being discharged through the chimney directly, while the latter is sent to a delay device to attenuate the radioactivity before the discharge thereof through the chimney. (Kamimura, M.)

[en] Object: To reduce the producing amount of ozone within a liquefaction and distillation apparatus for processing radioactive dilute gas. Structure: The radioactive dilute gas containing gases are supplied to a rectification tower through a heat exchanger. Oxygen and nitrogen are cooled by a condenser cooled with liquid nitrogen, and they are partly condensed into a circulating liquid, the remainder being released into atmosphere through a purifying gas line. The radioactive dilute gas is taken out of the tower bottom through a liquid taking-out line and heated by a heater, after which ozone is removed by an ozone remover unit, finally meeting the raw gases. The tower bottom is filled with filler such as Raschig ring to absorb radioactive energy and thus prevent generation of ozone within the tower. (Kamimura, M.)

[en] Object: To eliminate a danger of explosion in case where oxygen is safely removed from waste gases containing radioactive rare gases for recovery thereof into a gas cylinder. Structure: In an atomic power plant, carbon dioxide gas and water are removed in a pretreatment system. Next, it is cooled by liquefied nitrogen in a heat exchanger and transported to a first condensing system composed of a low temperature adsorption bed to condense radioactive rare gases in the adsorption bed. The thus condensed rare gases are fed under pressure by a pump to a second condensing system composed of Cu and Cu group alloy bed. Next, oxygen in the condensed gases is reacted and removed in the Cu alloy bed maintained at 600⁰C and the rare gases are fed to the gas cylinder for recovery. (Yoshihara, H.)

[en] Object: To prevent discharge of waste gases having a high radioactivity density into atmosphere at the time of failure or damages of machineries, piping and seals in valves or the like. Structure: Hydrogen and stream contained in waste gases from a turbine condenser are removed by a re-coupler unit, cooler and water-gas separator, and radioactive substances are attenuated and removed by a delay pipe and filter, after which water and carbon dioxide gas are removed by a water-carbon dioxide gas remover unit and cooled by a heat exchanger, and thereafter introduced into a rectification tower. A vacuum pump is installed on the purifying gas line at the outlet of the heat exchanger, whereby process for adsorbing and removing water and carbon dioxide gas and process for rectifying and separating the radioactive rare gas are accomplished under negative pressures. A heater is installed on the liquid taking-out line from the bottom of the rectification tower to heat and vaporize the taken out liquid by means of a heater, after which the liquid is returned to inlet of an air extractor and the impurities are removed by the re-coupler. (Kamimura, M.)

[en] Object: To securely perform separation and enrichment of radioactive rare gases to store safely them for a long period of time. Structure: The wastes extracted by an air extractor are processed by a heater and a recombiner and hydrogen and oxygen are changed into water thereby and it is passed through a gas and water separator to be dewatered, after which water and carbon dioxide gas are removed by passing through a delay pipe, filter, and water- and carbon dioxide gas removing device and then fed to a lower temperature adsorbing device to adsorb and remove the radioactive rare gases. This low temperature adsorbing device is composed of two towers, one of which is designed to saturate the radioactive rare gases, which are processed by a heater and passed through a recycle line to meet raw gases. Then, it is fed to the other lower temperature adsorbing device and this cycle is repeated to enrich the radioactive rare gases. Oxygen and impurities in the enriched gases are removed by the impurity removing device and thereafter are stored in a gas holder and finally sealed in a cylinder. (Kamimura, M.)

[en] Low level radioactive wastes are successively charged into a container while sliding a partition plate such that the wastes are kept substantially in a fully charged state in the direction of the height. Radiation rays from the low level radioactive wastes contained in the container are measured by a radiation dose measuring means constituted so as to be slidable together with the partition plate. Further, the weight of the low level radioactive wastes in the container is measured by the weight measuring means, and the radioactivity concentration per unit container is calculated by a calculation means based on the result of the measurement. Accordingly, the optimum storage period and the radioactivity level can be estimated on every containers. Further, since the measuring vessel is used also as a storage vessel, long time measurement can be conducted by measuring the radioactivity for the wastes successively to enable exact evaluation. Accordingly, it is possible to save the labors for processing operation and save the storage facility. (T.M.)

[en] Purpose: To detect fuel failures at high sensitivity. Constitution: A sampler attached with an ionizing box detector, a NaI detector and a CdTe detector is disposed to the outlet of an off-gas attenuation pipe, while a sampler attached with a NaI detector and a CdTe detector is disposed to the outlet of a charcoal tower respectively. Signals from a plurality of detectors and information such as off-gas flow rate are inputted into a computer to determine the quantitative value for Xe-133 thereby judging the absence or presence of the fuel failure. If fuel failure should be present, the quantitative value for Kr-85 is determined to calculate the burn-up degree of the failed fuel rod. According to this device, it is possible to detect the fuel failure neither with the interference by N-13, etc. nor with the effect of fluctuations in the off-gas flow rate, as well as the position of the failed fuel rod can be estimated from the burn-up degree. (Horiuchi, T.)