ジドウ ソウサホウ ニヨル ガン チリョウヨウ 125 Ｉ シード ホウシャセン キョウド ケンテイ システム ノ カイハツ

A new scanning system using a NaI(Tl) scintillation survey meter, copper slit and drive-unit has been developed for quality control of radioactive seeds. Radioactive seed implants, also called brachytherapy, are widely used modality in the treatment of early stage prostate cancers. Seeds containing the iodine-125 are most commonly used for permanent implant prostate brachytherapy. These seeds are commercially available and delivered in a sterile environment in the form of packaged cartridge. It is impractical to re-sterilize and re-load seeds after calibration. This paper describes a new method to calibrate all seeds in the seed cartridge in a sterile package

First measurements of thermal neutron distribution in the LHD torus hall generated by deuterium experiments

For the estimation of the neutron field generated by deuterium plasma operation in the Large Helical Device (LHD), the first measurement of the thermal neutron distribution on the floor level of the LHD torus hall was carried out. For the thermal neutron detection, indium was used as activation foils. The radioactivity of these foils were evaluated by a high-purity germanium detector (HPGe) and an imaging plate (IP). The major components of radioactive isotope of indium was 116mIn. The mapping of thermal neutron distribution in the torus hall was performed. The interactions between neutron and components around LHD were observed in the thermal neutron distribution. Also, the borated polyethylene blocks effectively absorbed the thermal neutron. The thermal neutron distribution evaluated in this work can be helpful to predict the amount of radioactive waste in the torus hall proceeding with deuterium experiment in LHD

Radiation control in LHD and radiation shielding capability of the torus hall during first campaign of deuterium experiment

The activities carried out to obtain public consent for deuterium experiments in LHD, which began in 2017, are reviewed in this paper. In addition, the upgrades and the safety management of LHD for deuterium experiments, including neutron yield measurement system, exhaust detritiation system, institutional regulation for radiation control, and other issues, are briefly presented.During the first campaign of the deuterium experiments in LHD, the shielding of gamma-ray and neutron by the concrete wall of the LHD torus hall was evaluated. Also, the confinement of radioactive isotopes in air inside the torus hall was investigated. No increase of radiation dose was measured outside the torus hall, although the high radiation dose field inside the torus hall was found during deuterium experiments. Therefore, almost all gamma-rays and neutrons were shielded by the concrete wall of the torus hall due to its sufficient thickness of 2 m. The radioactive isotopes in air as well as in other components were well confined in the torus hall. In particular, the pressure control inside the torus hall being lower than outside the torus hall effectively prevented the radioactive isotopes in air from diffusing to the unprescribed area

Integrated radiation monitoring and interlock system for the LHD deuterium experiments

The Large Helical Device (LHD) successfully started the deuterium experiment in March 2017, in which further plasma performance improvement is envisaged to provide a firm basis for the helical reactor design. Some major upgrades of facilities have been made for safe and productive deuterium experiments. For radiation safety, the tritium removal system, the integrated radiation monitoring system, and the access control system have been newly installed. Each system has new interlock signals that will prevent any unsafe plasma operation or plant condition. Major interlock extensions have been implemented as a part of the integrated radiation monitoring system, which also has an inter-connection to the LHD central operation and control system. The radiation monitoring system RMSAFE (Radiation Monitoring System Applicable to Fusion Experiments) is already operating for monitoring γ(X)-rays in LHD. Some neutron measurements have been additionally applied for the deuterium experiments. The LHD data acquisition system LABCOM can acquire and process 24 h every day continuous data streams. Since γ(X)-ray and neutron measurements require higher availability, the sensors, controllers, data acquisition computers, network connections, and visualization servers have been designed to be duplicated or multiplexed for redundancy. The radiation monitoring displays in the LHD control room have been carefully designed to have excellent visual recognition, and to make users immediately aware of several alerts regarding the dose limits. The radiation safety web pages have been also upgraded to always show both dose rates of γ(X)-rays and neutrons in real time

Verification of the Thermal Neutron Shielding Effect of the Shielding Door of the LHD Experimental Hall

Evaluating the performance of the shielding walls and shielding doors at radiation facilities is important to ensure proper radiation safety management. In the first period of the deuterium experiment, the neutron-shielding ability of the shielding door of the experimental hall containing the large helical device (LHD) was evaluated using the gold-foil activation method. The gold foil was inserted into a small gap between the shielding door and the shielding wall. Meanwhile, the shielding effect of the wall against the neutrons and gamma rays was verified using the badge-type dosimeters that were placed both inside and outside the experimental hall near the wall. The radiation derived from Au-198, which was visualized using by imaging plate, reached approximately 35 cm inside the shielding door. The results provided visual evidence that the shielding door safely excluded the thermal neutrons that were generated in an LHD. Furthermore, the measurement results of the badge-type dosimeters confirmed that the neutrons and gamma rays were completely trapped by the concrete wall of the experimental hall

Measurement of Absorbed Dose Rate in Air at NIFS Site after the First Deuterium Plasma Experiment in LHD

The latest measurement of the absorbed dose rate in air was performed at the National Institute for Fusion Science (NIFS) site during the period for the first deuterium plasma experiment conducted in Large Helical Device (LHD). The arithmetic mean of the absorbed dose rates in air for 222 measurement points at the NIFS site was 43 nGy h^. Very little change was observed in the distribution maps of the absorbed dose rates in air before and after the deuterium experiment in the LHD. In addition, the absorbed dose rates in air around the buildings were distributed at similar high levels before and after the deuterium experiment. A radionuclide analysis of soil and broken stone was conducted using a high-purity Ge semiconductor detector. The absorbed dose rates in air at the NIFS site were mainly defined by the radiation from the ground and the building material around the measurement points. The effect of the deuterium experiment was so small that it was undetectable in this study