Dr. Tsubokura's Radiation Lecture Vol.89
Author: Masaharu Tsubokura
Editors: Akihiko Ozaki M.D., Yuki Senoo
177. A different classification method for wastes with radioactive contamination after the Fukushima Disaster
Radioactive wastes produced by nuclear facilities are classified into two categories: “high-level radioactive wastes,” which are the liquid form of radioactive residue produced in the reprocessing of radioactive fuels, and the rest of the radioactive wastes are collectively called “low-level radioactive wastes.” The previous article explained that radioactive wastes are handled differently. For example, the waste is stored in a shallow underground hole and packed in drums after being concentrated and solidified with cement and according to its type. However, the application of this classification method for radioactive wastes is limited to the ones produced by nuclear facilities.
Following the 2011 Fukushima nuclear disaster, a radiation contamination spread to residential areas. Consequently, the policy makers were required to develop new standards to classify the radioactive wastes relating to this disaster. Contaminated wastes generated from the towns located near the Fukushima Daiichi Nuclear Power Plan or a zone within a radius of a few km from the plant was defined as waste in the countermeasure area. Besides, the wastes that are easily contaminated with high levels of radiation, such as sewage sludge and ashes, those with radioactivity exceeding 8,000 becquerels per kilogram were defined as “designated wastes”, even if they are from outside the areas closed to the plants. Furthermore, radioactive wastes classified as “wastes in the countermeasure area” or “designated wastes” must be handled by the government.
A threshold value of 8,000 becquerels per kilogram was determined to make sure the annual radiation exposure dose of landfill workers working on the contaminated waste disposal will be below 1 millisievert.
178. Maintaining an adequate distance from radioactive waste could significantly reduce the risk of radiation exposure
Following the 2011 Fukushima nuclear disaster, a new standard was established to classify the wastes contaminated with radioactive substances that were produced because of the nuclear power plant accident. Before the Fukushima disaster, radioactive wastes were classified into high- or low-level radioactive wastes. Currently, wastes contaminated with a high level of radioactivity, exceeding 8,000 becquerels per kilogram, such as sewage sludge and ashes, are classified as designated wastes even if they are from areas outside of the (former) evacuation areas around the nuclear power plant. Recent fuideline stipulate that the central government must handle designated wastes. Currently, progress is being made to replace the state-owned landfill in Tomioka Town, Fukushima Prefecture”
Some of you may be surprised to learn the designated wastes are contaminated with the radioactivity of 8,000 to tens of thousands of becquerels per kilogram.
However, the level of radiation exposure is reduced by shielding and by maintaining a greater distance from the source. For example, when the radioactive substances are covered with 0.5 m of soil, the level of radiation exposure will be reduced to approximately 1/500. Furthermore, when you are standing 100 m away from the radioactive substances, the level of radiation exposure will be 1/10,000 that of when you are standing 1 m away.
It is estimated that if you live in an area 100 m from the disposal site, you will be exposed to an additional annual radiation dose of 1/500 millisieverts. When the landfill operation is completed in Fukushima, this exposure dose will be reduced further when shielded by the soil. Of course, contentious management of radioactive wastes is necessary from now on to ensure safety. However, it is apparent that you will not receive an extremely high level of radiation exposure even when live close to the designated waste landfill site.
--------------------------------------------------------------------
The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, 3rd and 20th June 2018 was reproduced for MRIC Global under the author's permission.