Dehydrated sludge generated through sewage and water supply processing has been contaminated by radioactive cesium after the severe accident at the Fukushima Nuclear Plant. Incineration and disposal of the dehydrated sludge should be carried out while ensuring the safety of radiation for the workers and the public. In this study, in order to provide the technical information for making the guideline on the incineration and disposal of dehydrated sludge, the dose estimate for scenarios on the incineration and disposal is conducted, based on the method used for driving the clearance levels in Japan. From the result of dose calculation, it is suggested that it is necessary to forbid reusing the disposal site as construction, resident and agriculture in which the calculated effective doses for the public are higher than those in the other exposure pathways. Minimum activity concentration of radioactive cesium in dehydrated sludge and incineration ashes, corresponding to the effective dose criterion indicated by Nuclear Safety Commission of Japan, is estimated to be 8.9 Bq/g under the condition of limited reuse of the site. In the case of the activity concentration below 8.9 Bq/g, the calculated dose of the resident due to direct and sky-shine radiation from the temporary storage place is less than 1 mSv/y, irrespective of the distance from the storage place.
The spectrum-dose conversion operators (hereafter, G(E) function) were calculated for CsI(Tl) scintillation counters based on the response functions obtained by a Monte Carlo simulation code, MCNP5, in the photon energy range from 40 to 10,000 keV. The G(E) functions were determined in the cases of crystal sizes 5.5 × 5.5 × 5.5, 10 × 10 × 10, 13 × 13 × 20 and 38 × 38 × 25 mm3 for ambient dose, H*(10). It was found that the values of H*(10) deduced from the pulse-height spectra and the G(E) function agreed with those of H*(10) evaluated in the calibration field in Japan Atomic Energy Agency (JAEA) within 2% in the case of irradiations by 137Cs, 226Ra and 60Co source, by the measurements using a scintillation counter whose crystal size was 13 × 13 × 20 mm3.
The behavior of 14C from radioactive waste in paddy rice (Oryza sativa L.) at different stages of plant development was studied using the hydroponic and acetic acid as 14C-source. For 14C-application, plant root was soaked for 2 hours in a nutrient solution containing 14C-acetic acid at the vegetative growth stage (Aug. 2, 2007), heading (flowering) stage (Aug. 30, 2007) and milk-ripe stage (Sep. 13, 2007). In final sampling day (Mar. 5, 2008), 0.88-1.96% of the applied radioactivity was recovered from whole plant, however, the ratio of recovered radioactivity was not different at the growth stage. The distribution of 14C absorbed at each stage to each organ was noted to be highest in the submersed root through all the stages. Therefore the mixing of the root residue at the time of plowing would result in enhancement of the soil persistence of 14C.
The Great East Japan Earthquake on March 11, 2011 generated a series of large tsunami waves that resulted serious damage to the Fukushima Daiichi nuclear power plant and radioactive materials were discharged to the environment. Remediation of contaminated environments is of important issue for the Fukushima residents, and Japanese government established legal framework for decontamination. Before the implementation of full scale decontamination, the Cabinet Office commissioned “Decontamination Pilot Project” to Japan Atomic Energy Agency. The purpose of the project is to acquire technical data and knowledge, and provide integrated expertise for full scale decontamination. In the process of the project, radiation protection of workers for remediation activities was demonstrated. External dose was controlled by daily dose check, and internal dose by protective equipment, whole body counting and screening system under the radiation protection plan.
Data are presented on radiation doses to infant, child and adult patients undergoing head, chest and abdominal CT examinations with recent multi-detector row CT scanners (MDCT). Also presented are dose data in CT coronary angiography(CTCA) observed with Toshiba 320MDCT and Siemens 64MDCT. The doses were measured using newborn, 6-year-child and adult anthropomorphic phantoms, in which photodiode dosimeters were implanted at various tissue and organ positions. Measured doses were used to evaluate organ and effective doses. Organ doses in the scan region obtained in head CT were 20-40 mGy for infants and children, and 40-70 mGy for adults. Effective doses in head CT were 2.1-3.3 mSv for infants,and 1.0-2.0 mSv for children and adults. These doses in chest CT were 3-9 mGy and 2-6 mSv for infants, 2-12 mGy and 1-7 mSv for children, and 5-35 mGy and 7-14 mSv for adults. In abdominal CT they were 3-14 mGy and 2-10 mSv for infants, 4-18 mGy and 3-12 mSv for children, and 10-48 mGy and 9-21 mSv for adults. In CTCA radiation doses for helicalscan without using dose modulation were reduced to less than 1/6 and 1/10 by using prospectively gated axial scan of Toshiba320MDCT and “Flash Spiral” scan of Siemens 64MDCT, respectively.
After the Fukushima Daiichi Nuclear Power Plant Accident, many people are concerned about the contamination of radioactive substances in their ordinary surrounding environment. In this study, we determined the levels of radioactive contamination with 137Cs in towels, very common textile products in our life, after exposing those to the soil collected from a farm field near Fukushima city. Three kinds of towels made from the same cotton fiber with different thickness were exposed to the soil under dry or water-suspension conditions. The radioactivities of 137Cs retained/absorbed were 30-50% of the loaded radioactivity per gram weight of the towel. When their weight and absorbency are taken into consideration, the differences in thickness did not so much affect the above values. Under standard washing condition, which mimic those with household washing machine, almost all the radioactive cesium were removed from the towels contaminated under the dry conditions, whereas only 50-70% were removed when the towels were contaminated under the wet conditions. A commercial soil-release treatment (Preshade-SR) didn't reduce the contamination under both dry and wet conditions, although processing the towels with silver nano-particles did.