A comprehensive review of dose limits, triage systems and measurement tools for consequence management of nuclear and radiological emergencies.

During a radiological or nuclear emergency, occupational workers, members of the public, and emergency responders may be exposed to radionuclides, whether external or internal, through inhalation, ingestion, or wounds. In the case of internalized radiation exposure, prompt assessment of contamination is necessary to inform subsequent medical interventions. This review assembles the constituent considerations for managing nuclear and radiological incidents, focused on a parallel analysis of the evolution of radiation dose limits - notably in the emergency preparedness and response realm - alongside a discussion of triage systems and in vivo radionuclide detection tools. The review maps the development of international and national standards and regulations concerning radiation dose limits, illuminating how past incidents and accumulated knowledge have informed present emergency preparedness and response practices, specifically for internalized radiation. Additionally, the objectives and levels of radiation triage systems are explored in-depth, along with a global survey of practices and protocols. Finally, this review also focuses on in vivo detection systems and their capacities for radionuclide identification, prioritizing internalized gamma-emitting isotopes due to their broader relevance. Collectively, this study comprehensively addresses the intricacies of triage management following radiation emergencies, emphasizing the imperative for enhanced standardization and continued research in this critical domain.

Tertiary evaluation of the committed effective dose of emergency workers that responded to the Fukushima Daiichi NPP accident.

In January 2014, Tokyo Electric Power Company (TEPCO) learned that the committed effective dose (CED) for nine emergency workers at the Fukushima Daiichi Nuclear Power Plant accident had been assessed by a method other than the standard assessment methods, established by the Ministry of Health, Labour and Welfare (MHLW) in a secondary evaluation conducted in July 2013. The MHLW requested that the TEPCO and primary contractors review all CED data for 6,245 workers who engaged in emergency work in March and April 2011 except those previously reviewed in the 2013 secondary evaluation. This tertiary evaluation revealed that the recorded CED for 1,536 workers had more than 0.1 mSv discrepancy with the CED evaluated by the standard method. The MHLW requested that TEPCO and primary contractors revise CED data for 142 workers whose CED was 2 mSv or greater that required a CED revision of 1 mSv or greater. The average CED revision was 5.86 mSv. The revised effective dose ranged from 2.17-180.10 mSv. In addition, the number of workers whose CED exceeded 100 mSv increased by one. New issues addressed during the tertiary evaluation included the following: (a) setting of calibration coefficients to convert the CED value from whole body counters equipped with NaI scintillator (WBC(NaI)) to a CED value from WBCs with Ge semiconductor detector; (b) estimation methods for the cases where 131I was not detectable by WBC (NaI) and where 137Cs was not detectable but 134Cs was detected; (c) effects of stable iodine (KI) tablets to block the uptake of 131I by thyroid gland; and (d) complications in determining additional doses during stand-by in the seismically isolated building. To prevent the future use of non-uniform CED assessment methods in the dose assessment for workers, the MHLW issued administrative guidance documents to TEPCO and primary contractors on March 25, 2014.

Internal radiation exposure from TENORM for workers conducting cleaning activities on equipment used at geothermal energy plant.

Geothermal energy is predicted to be one of the most important renewable energy sources in the near future. In geothermal energy plants, the secondary products such as the scale containing naturally occurring radioactive material (NORM) and adhering to the surface of equipment produce radiation fields. The workers who maintain and clean such equipment are at a risk to be exposed by the technically enhanced NORM (TENORM). To estimate the risks of radiation exposure to the workers, we assessed internal doses resulting from the cleaning activities on 150 heat exchanging boards used at a geothermal energy plant, focusing on 222Rn, 226Ra, 210Pb, 228Ra and 228Th. The experiment was performed with the subjects of workers and office workers as control, supplying prepared foods and drinks. Using the analytical results of 210Pb, 226Ra, 228Ra, and 228Th in the excretions of subjects, committed effect doses were determined. The annual internal dose for the workers with protective clothing due to the cleaning activities on removing scale, assuming the cleaning activities requires 170 h (standard monthly working time) a year, was obtained as 26 µSv/y and the total dose including 222Rn inhalation dose was calculated as 323 µSv/y. The additional dose for the cleaning workers was less than the dose limit of 20000 µSv/y for radiation workers, even less than for general population (1000 µSv/y) recommended by International Commission on Radiological Protection (ICRP). However, the elevated inhalation dose for workers conducting cleaning activities may present a health hazard to workers if they deal with excessive materials containing TENORM, work for excessive time or are under inappropriate safety measures.