|NEWS AND INFORMATION
|Year : 2013 | Volume
| Issue : 2 | Page : 95-96
News and Information
Ex-BARC, Mumbai, India
|Date of Web Publication||14-Mar-2014|
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Pushparaja. News and Information. Radiat Prot Environ 2013;36:95-6
Main Findings of the Recent IAEA International Mission on Remediation of Large Contaminated Areas: Fukushima Daiichi Nuclear Power Point
For the purpose of remediation of large contaminated areas, based on the above criteria, secondary level of dose rate in the air and radionuclide concentration in different pathways were established. Long-term annual dose criterion being followed is 1 mSv/y for the public (ICRP).
The government of Japan has established the "Guideline on Prevention of Radiation Hazards for Workers Engaged in Decontamination Works", in December 2011. As per the guidelines, contractors, performing decontamination works, make serious efforts to minimize exposure of their employees to ionizing radiation. The new scheme of radiation protection for workers regulates the disposal of radioactive wastes generated during the accident. The contractors are required to train the workers in protection from external exposures and prevent themselves from internal contamination. The contractor also shall perform monitoring of contamination levels and air dose rates during the decontamination activities to assess the effectiveness of the procedure.
The IAEA first conducted the international mission in October 2011 to support remediation of large contaminated areas. Subsequently, a follow-up mission was undertaken in October 2013, to take stock of the status of remediation measures.
| Radiation Protection Aspects|| |
The affected areas were categorized as:
- Special decontamination area (located within a 20 km radius, where anticipated annual effective doses exceeded 20 mSv. The government organized decontamination of areas in this category.
This special decontamination area was further divided into three categories based on estimated annual dose levels -green (1 to 20 mSv), yellow (20 to 50 mSv) and red (above 50 mSv)
- Extensive contamination survey was conducted in the areas where the estimated additional individual annual cumulative dose was in the range of 1 to 20 mSv. The average air dose rate in the area exceeded 0.23 microSv/h. Municipalities were responsible for the decontamination of such areas.
The status during the follow-up mission of the team
The Mission Team has observed that many good radiation protection practices are implemented by the authorities in line with the IAEA standards for planned exposure situations for radiation workers. This is expected to increase public confidence in the decontamination program undertaken by the Japanese government. This also facilitated return of the evacuees who are undergoing some adjustments in life styles and daily routines to reduce individual doses and optimized protection.
- Gamma doses in air: Air dose rates were measured and for an assumed 8 hours - outdoor and 16 hours -indoor activities, dose rate assessments were performed for a typical individual in the affected area. These assessments are found to be conservative as compared to the external exposure measurements made by the personal dosimeters
- Activity levels in food: Radionuclides considered are Cs-137/Cs-134. WHO limit for drinking water of 10 Bq/L (leading to an annual dose of 0.1 mSv) was assumed. The limit followed for Cs-137 and Cs-134, together, is 10 Bq/L for drinking water, 50 Bq/kg for milk, 50 Bq/kg for infant food and 100 Bq/kg for other food items. However, the actual measured radionuclide concentrations in vast majority of food items found to be significantly lower than the limits
- External exposure: Measurement of individual external radiation doses -data collected from about 70,400 participants covering 22 municipalities was done. The average dose was in the range of 0.1 to 0.2 mSv, which is 3 to 7 times lower than the estimated values. The air dose rates have been decreasing since 2011 and the resulting annual doses fall in the range of existing exposure situations. It is recommended to continue monitoring of the air dose rates in the future for reassurance in response to the population's concerns about health risks.
- Internal exposure: A whole body counting survey was carried out for 149,578 residents of Fukushima Prefecture during June 2011 to August 2013. Except for twelve cases, the committed effective dose due to radio-Caesium intake was below 1 mSv. For 10 cases, the estimated internal dose was about 2 mSv and for 2 cases, the dose was 3 mSv. The whole body counting program was discontinued except for those who are returning back to their homes.
As part of the food control measure, there was a large-scale program of radiation survey of packaged rice in Date city. The activity detected in majority of the packages was below 100 Bq/kg. Negligible percentage of the packages was showing activity above this level.
Radiation protection of Remediation Worker
Soil and forest decontamination workers and waste management workers are provided with personal monitors. In the case of temporary waste storage facilities, workers are provided with radiation detectors to regularly measure exposure levels. The workers in incineration facility, which is part of waste management process, make use of many kinds of personal protective equipment needed for radiation protection. The air pressure inside the incinerator building is kept lower than the outside air pressure to prevent potentially contaminated air going outside the facility. Air contamination levels are measured in-situ regularly. The incineration facility also performs worker's internal and external contamination monitoring regularly. Stand-alone air dose monitors are placed in some strategic points such as in the entry and exit of building's offices area. The reading can be easily checked by people. Records of the exposures received by the workers are kept by the contractors.
Main findings of the Mission team
- With the aim of enhancing living conditions, the government of Japan has allotted enormous resources for remediation of large contaminated areas which will enable evacuated people to return and to reduce exposures in the affected areas
- The government encouraged involvement of all the stakeholders, including local communities and local authorities
- Decision-taking process derived great support from the technical experts and doctors with reference to the dose rates and the associated risk perceptions in the affected areas
- The air dose rate measurements (showing the decreasing trend) supported by the adjustment in life-style changes and daily routines of the people in the affected areas, raised the confidence levels of returning evacuees considerably
- There is an on-going aquatic monitoring program which includes radioactivity measurements in environmental samples such as water samples, suspended sediment, sediment samples, crops and marine food
- Temporary storage facilities for interim storage of large quantity of radioactive waste generated by the remediation measures are established by the local and national government authorities. Incineration was one of the measures used for volume reduction. Off-gas was treated to meet emission standards and to reduce public exposure
- National regulation Authority has been actively participating in the review of the remediation process. The authorities tend to accept the international standards of annual estimated dose range: 1 to 20 mSv for the purpose of remediation of the affected areas. However, the long-term goal is expected to be 1 mSv/y for the public.
- The Mission team recommended continued optimization of the remediation measures through continued monitoring of the freshwater and marine environments, optimized protection of the remediation workers, and remediation of forest areas, farmland and public spaces (Source: Final Report of the Follow-up IAEA International Mission on Remediation, Fukushima, Japan, 23-01-2014).