On Tuesday Japan upgraded the incident level for the Fukushima nuclear power plant from 5 to 7 on the International Nuclear and Radiological Event Scale (INES), a classification reserved for the most severe nuclear crises. The level 7 classification has only been used once previously – for the 1986 Chernobyl disaster.
What does the the new rating mean? 
Our colleagues at the UK SMC and Australian SMC gathered the comments below on the latest situation from scientists. Feel free to use their comments in your articles.
To talk to a local expert on radiation and incident classification, contact the NZ SMC.
Expert reaction to the raised severity rating at Fukushima – SMC UK.
Prof Richard Wakeford, Visiting Professor in Epidemiology at the University of Manchester, said:
“The Japanese authorities have temporarily assessed the Fukushima events as Level 7 on the International Nuclear Event Scale (INES) on the basis of the estimated quantities of radioactive iodine and caesium released since the earthquake on 11 March – around 10% of the releases from the Chernobyl accident, the only other INES Level 7 event. However, the Chernobyl accident had a much greater radiological impact, and the Japanese authorities have acted to limit the radiation doses received by both emergency workers and members of the public. Indeed, the only INES Level 6 event – the “Kyshtym” accident in the USSR in 1957*, when a radioactive waste tank exploded – had a much greater radiological impact than is predicted from the events at Fukushima.
“The Japanese authorities have extended the 20 km evacuation zone around the Fukushima site to include some additional communities that have been particularly contaminated by releases of radioactive material. It has been known since mid-March that a sector to the north-west of the site had been affected by a plume of radioactivity released a few days after the earthquake on 11 March, and the Japanese authorities had banned the consumption of contaminated foods from the area as a consequence. Radiation levels from deposited radioactive material have fallen since the deposition, but have remained sufficiently elevated to warrant the evacuation of people. Most other areas, including those within the 20 km evacuation zone, are less contaminated, but it is unlikely that people will be able to return to the evacuation zone until the Fukushima site is under control.
* “The only INES 6 is the “Kyshtym” accident (at Mayak) in 1957 when an explosion in a waste tank led to 740 PBq (740 000 TBq) of fission products being released (10% beyond the Mayak perimeter), >10 000 residents being evacuated with an average effective dose of 120 mSv, >5000 workers receiving doses up to 1 Sv within a few hours, and ~30 000 clean-up workers receiving doses >250 mSv during 1957-59.”
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Dr. J.T. Smith, Reader in Environmental Physics at the University of Portsmouth, said:
“The preliminary grading of the Fukushima accident as Level 7 on the International Nuclear Events Scale reflects the severity of radionuclide releases to land and sea. But there are key differences between Fukushima and Chernobyl, the only previous Level 7 accident. From the data so far, it seems that about ten times more radioactivity was released at Chernobyl. Crucially, key health protection countermeasures have been put in place at Fukushima. At Chernobyl, local people were not evacuated until about 48 hours after the accident: children were still playing outside as the reactor burned, and potassium iodide tablets were not distributed. In the weeks after Chernobyl, people continued to eat milk and leafy vegetables highly contaminated with radioactive iodine.
“By evacuating and sheltering the population, implementing food bans, and distributing potassium iodide tablets, the Japanese authorities will have prevented the most serious health effects of Fukushima. Levels of radioactive iodine are declining rapidly by radioactive decay – current levels are about a tenth of what they were when the accidents happened. But, it is clear that there has been a major contamination of land and sea. The effects of this are being seen now, with evacuation and food bans in place over a wide area. It appears from the data available so far, that there has been significant radiocaesium contamination, particularly of an area of land to the northwest of Fukushima. Radiocaesium remains in the environment for the long term and initial data suggests that this could mean that countermeasures (for example, food bans) will need to be in place in some areas for decades.”
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Prof Laurence Williams FREng, Professor of Nuclear Safety at the John Tyndall Institute, University of Central Lancashire, said:
“I am a little surprised by the uprating to level 7. On the basis of the publically available information there has been no significant change in the state of the 3 affected reactors or the 4 spent fuel ponds and there has been no sudden increase in radioactivity released into the atmosphere.
“I can only assume that the Japanese authorities are taking a very conservative line given that the 3 reactors are not yet under control and the conditions in the fuel storage ponds in reactors 1 to 4 where there are significant quantities of spent nuclear fuel is also not fully under control.”
From the SMCAus
Dr Pradip Deb is a Senior Lecturer in Medical Radiations at the School of Medicals Sciences, RMIT University
“The increase of the level of Fukushima incident to level 7 is combined re-classification of the earlier individual assessments of the different level of incidents of different reactors. This does not mean that it will do any extra harm to the public life. Although this level 7 is the same level as Chernobyl incident, the Japanese Nuclear and Industrial Safety Agency estimated that the amount of radioactive material released in Fukushima is ninety percent less than Chernobyl.
The International Nuclear and Radiological Event Scale (INES) is a scale of nuclear incident and accidents to report to the public like earthquake scales.
Level 1: Anomaly. This level is when minor problems with safety components, breach of operating limits at a nuclear facility, loss or theft of low activity radioactive sources.
Level 2: Incident. 10 times higher than Level-1. Exposure rate more than 50 mSv/hour with significant contamination within the facility.
Level 3: Serious Incident. 10 times higher than Level-2. Exposure rate is more than 1 Sv/hour in an operating area with severe contamination. Low probability of significant public exposure.
Level 4: Accident with local consequences. 10 times higher than level-3. Fuel melt or damaged and release of significant quantities of radioactive material within an installation with high probability of public exposure. Level-4 is called for if at least one death from radiation and minor release of radioactive material so only local food controls are necessary.
Level 5: Accident with Wider Consequences. This level is 10 times higher than level-4 and is called for when the reactor core is severely damaged and large amount of radioactive materials are released with a high probability of significant radiation exposure to the public. And also when several deaths from radiation exposure and planned radiation control is needed.
Level 6: Serious Accident. 10 times higher than level-5. This level is declared when significant amount of radioactive material is released in the environment and planned controlling procedures need to be taken.
Level 7: Major Accident. This is 10 times higher than level-6 and the highest level of accident. This is declared when significant amount of radioactive material is released into the environment which can affect public health. Implementation of planned and extended radiation safety programs are needed at this level.
“Level- 5 is the highest contamination level as was declared earlier. Now after accumulating the total release of radioactive materials in this accident the level is re-classified as the highest level as a one whole accident. Due to yesterdays 7 scale earthquake, there was no extra radioactivity. The radiation level near the reactors are decreasing as it should be. So this new classification (level-7) should not add extra impact.”
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Dr Don Higson is a retired nuclear safety specialist and Fellow of the Institution of Engineers Australia, Fellow of the Australasian Radiation Protection Society
“This refers to the IAEA event scale. I do not have it in front of me but, as I recall, it relates to nuclear incidents/accidents on a scale of 1 to 7 with 7 being the worst. This would imply that someone is rating the Fukushima incident as being as bad as the Chernobyl reactor accident. To my mind, this would be nonsense. Consider the following consequences:
Number of workers hospitalised with acute radiation sickness
Chernobyl 134
Fukushima none
Number of deaths of workers within a month
Chernobyl 31
Fukushima none
I could go on.”
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Dr John Price is a former member of the Safety Policy Unit of the National Nuclear Corporation UK, an Adjunct Associate Professor at Monash University, Australia, and now a private consultant
“Although the level has been raised to 7 today, it doesn’t mean the situation today is worse than it was yesterday. It means the event as a whole is worse than previously thought.
The INES levels are used to define a nuclear event as a whole, they aren’t a moment-by-moment measure. To a certain extent you can say that they are non-objective as it’s just a case of when the boxes are ticked rather than someone saying this is now a really big event.
The reason Fukushima Dai ichi can be placed in Level 7 is because of the INES definition:
‘Major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures.’
The releases of radiation got worse due to several events during the first week (explosions at the plant etc), and it is measuring the extent of these first-week events that has increased the level now.
The 10000 TBq has now reduced to 1000 TBq presumably through decay. The total Bq being stated is presumably the total radioactivity that a Japanese organisation has calculated to have been released from the reactors for the incident up to this date. 1 Bq is one decay per second. It is impossible to determine what is happening to humans near the plant since the radio-active particles will settle. The human effect depends on where the human is in relation to the particles.
One problem is that the radioactive material is able to be spread by the wind. It appears that they are now scattering an “anti-scattering agent” (NISA update 9 April 0800) which is presumably to stop particles from leaving the plant site.”
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