Japanese Journal of Health Physics

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The effect of electromagnetic field on electronic personal dosimeters in a nuclear fusion facility was examined in a Magnetic Resonance Imaging (MRI) examination room instead of a nuclear fusion facility. Three types of electronic personal dosimeters, the PDM-111, the 112, and the 117, were used as typical ones. We surveyed the electromagnetic field distribution and dosimeters were placed at locations with various strengths of the electromagnetic field. The natural radiation dose was measured for about one week. We found that while dosimeters were not affected by the electric field, they were affected by the magnetic one. Dosimeters detected radiation levels less sensitively as the magnetic field strength was increased up to 150 mT. The dosimeters underestimated the environmental radiation dose rates by about 10-30% when the magnetic field strength was larger than 150 mT. We assumed that hall-effect caused the reduction in radiation sensitivity. We concluded that the strength of the magnetic field needs to be carefully considered when an electronic personal dosimeter is used for monitoring both personal and area dose in a nuclear fusion facility.

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The Japan Atomic Energy Agency (JAEA) and Okayama University have carried out the experimental animal study and its related studies since 2007 in order to examine the physiological effects of radon in detail. Thus, a radon test facility for small animals was developed in order to increase the statistical certainty of our animal tests. This paper illustrates the performances of that facility, the first large-scale facility of its types in Japan. The facility has a potential of approximately 150 mousescale tests at the same time. The apparatus for exposing small animals to radon has six animal chamber groups each of which consists of five independent cages. Different radon concentrations in each animal chamber group are available. The major functions of the facility controlling radon and avoiding thoron were shown theoretically and experimentally. The relative standard deviation of radon concentration at the highest concentration group was about 5%, although the lower concentration groups seemed to be affected by variations in background radon.

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The zinc injection technique has been applied to many PWRs (Pressurized Water Reactors) around the world as one of the most effective countermeasures against a radiation source reduction. More than 10 years have passed since the first application of the zinc injection technique mainly in Europe and the US, and its dose reduction effect has been confirmed in each nuclear power plant. The Japan Atomic Power Company has applied the zinc injection technique to Tsuruga nuclear power plant unit 2 (PWR, 1,160 MWe, Commercial operation started in 1987) since 2005. Zinc concentration in primary coolant had been controlled around 5ppb by not more than 10 ppb. Dose equivalent rates on primary equipment and pipes were reduced about 20-30% after zinc injection. Although the dose reduction effect of 20-30% is included the various factors, it was estimated that the effect of about 10% is due to the zinc injection technique. There were no negative effects caused by the zinc injection for the plant operation, water chemistry and fuel integrity in the case of Tsuruga unit 2.

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In the past, due to the limited application of radiation and radioisotope in the national economic branches, radiation safety was not paid much attention to in Vietnam. However, according to the Strategy for Peaceful Utilization of Atomic Energy up to 2020 approved by the Prime Minister on January 3, 2006 the application of radiation and radioisotopes as well as nuclear power in Vietnam is expected increasing strongly and widely, then radiation safety should be developed correspondingly. This paper presents the history of radiation protection, the current status and prospect of utilization of atomic energy and the anticipated development of the national radiation safety system to meet the demand of utilization of nuclear technology in Vietnam.

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