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Fukushima: Lessons learned from soil decontamination after nuclear accident

Following the accident at the Fukushima nuclear power plant in March 2011, the Japanese authorities carried out major decontamination works in the affected area, which covered more than 9,000 square kilometres ( 3,470 square miles). On Dec. 12, 2019, with most of this work having been completed, researchers provided an overview of the decontamination strategies used and their effectiveness in the Scientific Journal Soil.

Of primary concern after the Fukushima nuclear incident was the release of radioactive cesium in the environment because this radioisotope was emitted in large quantities during the accident,  it has a half-life of 30 years, and it constitutes the highest risk to the local population in the medium and long term.

This analysis in the journal provides new scientific lessons on decontamination strategies and techniques implemented in the municipalities affected by the radioactive fallout from the Fukushima accident. This synthesis indicates that removing the surface layer of the soil to a thickness of 5 cm, the main method used by the Japanese authorities to clean up cultivated land, has reduced cesium concentrations by about 80% in treated areas.

The removal of the uppermost part of the topsoil, which has proved effective in treating cultivated land, has cost the Japanese state about $35 billion (Cdn.).  This technique generates a significant amount of waste, which is difficult to treat, to transport and to store for several decades in the vicinity of the power plant, a step that is necessary before it is shipped to final disposal sites located outside Fukushima district by 2050. By early 2019, Fukushima’s decontamination efforts had generated about 20 million cubic metres of waste.

Decontamination activities have mainly targeted agricultural landscapes and residential areas. The review points out that the forests have not been cleaned up -because of the difficulty and very high costs that these operations would represent – as they cover 75% of the surface area located within the radioactive fallout zone.

 

What is the difference between external & internal radiation exposure?

Written by Steven Pike, Argon Electronics

Radiological incidents where there is the potential for the release of ionising radiation can occur in a wide variety of scenarios – be it a fire in an industrial facility, a transportation accident that involves radioactive materials or the deliberate use of a radiological dispersal device (RDD).

Any accident or incident that involves a radiological hazard can place significant operational demands on first response teams as well as placing those personnel at risk of exposure to potentially dangerous levels of ionising radiation.

Radiation exposure refers to any situation in which the body is in the presence of radiation.

In order to keep radiation doses at a level that is low as reasonably achievable (ALARA) it is vital that first responders both minimise the time that they spend in affected areas and that they maximise the distance between themselves and the radiation source.

When we consider the concept of radiation exposure it is important to bear in mind not just the type of radiation that is being emitted, but also the route by which that radiation enters the body.

A commonly held image of radiation is that it emanates from a source device and strikes the outside of the body – in what’s known as external exposure.

However the radioactive material from radiation also has the ability to deposit its energy in our internal organs through the process of ingestion, injection, absorption or inhalation – what is termed internal exposure.

What is external radiation exposure?

External radiation exposure occurs when part or all the body is exposed to a penetrating radiation field from an external source. In some cases this radiation will be absorbed by the body, while in others it may pass straight through.

Any source outside of the body that emits ionising radiation can pose an external radiation exposure hazard – be it in the form of a beta source, neutron source or gamma source.

How extensive this hazard is depends on the amount of exposure received, the duration of the exposure, the energy of the emitted radiation and the total amount of radioactive material that is present.

All ionising radiation sources produce an external radiation field, however some radiation fields are so so small that they pose no radiation risk at all – for example in the case of low and moderate energy beta radiation emitters such as Tritium (H-3), Nickel-63 (Ni-63) or Phosphorus 33 (P-33).

Other sources of ionising radiation – such as the gamma sources Caesium-137 (Cs-137) and Cobalt-60 (Co-60) – are able to produce much more powerful external radiation fields, so care must be taken to shield the source and monitor exposure.

What is internal radiation exposure?

Internal radiation exposure occurs when a radioactive material is released into the environment in the form of a solid, liquid or gas.

It is then able to enter the body through the route of ingestion through the digestive tract, inhalation into the respiratory airways, percutaneous absorption through the skin or penetration via contamination from a wound.

Radioactive materials that are incorporated into the body will emit radiation as they decay. In addition, that individual will continue to be exposed to radiation until such time as those radioactive materials have been excreted in the form of either urine or faeces.

Specific radioactive materials have a tendency to target specific organs depending on their unique chemical properties.

The radioactive isotope strontium, for example, shares similar properties with calcium, which means it tends to accumulate in calcium-rich areas of the body such as bones.

Radioactive caesium shares properties that are similar to potassium, which means it tends to distribute throughout the body.

Radio-iodine, meanwhile, tends to concentrate in the thyroid gland in the same manner as non-radioactive iodine (and the effects of which were evidenced after the Chernobyl nuclear accident where there was a marked increase in the number of thyroid cancer cases among children.)

Any exposure to ionising radiation in the context of a radiological emergency – and even if it is only for short periods of time – can increase the chance of both short-term and long-term health impacts for first responders.

In any situation where there is deemed to be a radiation hazard it will be crucial to ensure that emergency personnel are sufficiently trained in managing the risks, that they are adequately equipped and that they are appropriately protected.


About the Author

Steven Pike is the Founder and Managing Director of Argon Electronics, a leader in the development and manufacture of Chemical, Biological, Radiological and Nuclear (CBRN) and hazardous material (HazMat) detector simulators. He is interested in liaising with CBRN professionals and detector manufacturers to develop training simulators as well as CBRN trainers and exercise planners to enhance their capability and improve the quality of CBRN and Hazmat training.