Performance of electromagnetic shielding cases for preventing malfunction of semiconductor-type electronic personal dosimeters (SEPDs) caused by high frequency electromagnetic fields emitted from a digital cellular telephone (cell phone) and a card reader of access control system were analyzed. The cases were handcrafted by using cloth of activated carbon fiber, polyester film laminated metal, and two kinds of metal netting. Five kinds of SEPDs put in the cases were exposed to the high frequency electromagnetic fields for 50 sec or 1 min. The cases prevented perfectly the malfunction due to the cell phone. The cases shortened distances required to prevent the malfunction due to the card reader, but did not prevent the malfunction. The electromagnetic immunity level of SEPD inserted in the cases increased from greater than 11.2 to greater than 18.7 times for the cell phone and from 1.1 to greater than 4.3 times for the card reader. The maximum of electromagnetic shielding effectiveness of each case was greater than 18.7 timesfor the cell phone and greater than 4.3 times for the card reader.
Six kinds of radioactive organic liquid wastes were incinerated by using city gas. The test liquid wastes were methanol simulated as a low heat of combustion waste, xylene simulated as a high heat of combustion waste, and 4 kinds of wastes of unknown composition. Combustion temperature was monitored by using a thermocouple sensor. Temperature variations were classified into five types: stable pattern, increasing pattern, decreasing pattern, vibrating pattern and the mixed pattern. Stable pattern wastes were burned most efficiently. The other four patterns can be changed to a stable pattern by controlling the gas flow rate.
Since December 2003, the Expert Group on Decommissioning of Radiation Facilities has been working under the Planning Committee of JRSM. In order to study the past cases, the first questionnaire was sent out to 92 facilities, which were closed between 2001 and 2003. We received 51 answers, according to which RI tracers were used in biological research in 86% facilities, and only two major isotopes of H-3 and C-14 in 33 facilities. Other conditions such as the opening year and the area of controlled region depend on each case. It is necessary to confirm radiological safety after decommissioning by measuring the dose rate and the residual activity both in the control area and on the building. So, the second questionnaire was carried out to obtain more detail information about technical procedures. We recognized from the answers that most radiation protection supervisors desired a manual or instruction for decommissioning to be published. In the next step, our group will propose a typical procedure of decommissioning referring to the results of this survey.
The tritium facility at the National Institute for Fusion Science has been closed in 2002 after decommissioning procedure. A number of works have been completed including technical measures and administrative documentations to be reported to the Ministry of Education, Culture, Sport, Science and Technology. All the operations were carried out in three successive terms; 1) survey and preparations, 2) actual decommissioning works, and 3) report of all procedures to the Minister.A valuable experience we had during this project has been summarized, and some problems have also been pointed out from a viewpoint of radiation safety management.