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* Please be aware that the comments below are in response to the information that was available at the time they were given.
Our colleagues from the UK Science Media Centre gathered these comments from nuclear engineering and safety experts. As of March 18 22:01 JST.
NB. Sv = sieverts, mSv = millisieverts (1 Sv = 1000 mSv)
Prof Paddy Regan, Professor of Nuclear Physics at the University of Surrey, said:
"There have been a lot of questions about the amount of radioactivity that those working at the nuclear plant are being exposed to and the effects of this exposure on those individuals. We know they are not being exposed to over 20 Sv of whole body gamma-ray dose because they would collapse due a breakdown of the central nervous system; if they were exposed to more than 1-2 Sv whole body gamma-ray dose they would be too sick to work.
"Reports say that on site workers are being exposed to up to 250 mSv (=0.25 Sv) of total additional radiation. Assuming this refers to 'whole body gamma-ray dose', the most recent International Commission on Radiological Protection (ICRP) report, ICRP 103, suggests that this dose of radiation would constitute an increase in cancer risk over a lifetime of approximately 1% (one per cent). In the average population, risk of a terminal cancer over a lifetime is about 25%, so the additional risk of getting a cancer induced from this level of radiation exposure would be expected to increase by around 1%."
SOURCES:
Prof Richard Wakeford, Dalton Nuclear Institute and Visiting Professor of Epidemiology, University of Manchester, said:
"There seem to be some erroneous perceptions about the Fukushima emergency workers. This brief note may help.
"Comparisons have been made between the emergency workers at Fukushima and those at Chernobyl, 28 of whom died of the immediate effects of high levels of exposure to radiation (doses of several thousand millisieverts). The radiation doses received by the heroic emergency workers at Fukushima are being carefully monitored by specialist radiation protection staff – usually to a cumulative dose limit of 100 millisieverts, but under these conditions probably to a limit of 250 millisieverts. These limits, although higher than would normally be permitted in the workplace (20 millisieverts per year) will prevent any serious early health effects (e.g. radiation sickness) in the workers. Late effects, primarily cancer, will also be controlled by these emergency dose limits – a worker receiving a dose of 100 millisieverts from these emergency operations will have a future risk of a serious cancer from this dose of less than 1%, which compares to a background risk of cancer mortality in the absence of this radiation exposure of around 20-25%."
This ‘Q&A’ from Dr Jim Smith, Reader in Environmental Physics at Portsmouth University, was provided for a Chinese organisation; please feel free to quote it in the normal way.
Q1: According to your observation, how do you comment on Japan's rescue solutions so far?
Japan is facing an extremely difficult situation in the Fukushima nuclear plant. The workers are having to cope with extremely high radiation doses which limit their ability to introduce cooling water to the reactors and, apparently, one of the spent fuel storage ponds. If power and cooling water can be restored, the situation should stabilise, but at present it is possible that it could get much worse.
Q2: What's the worst situation of stricken nuclear plant? Will the case in japan make tremendous influences on environment as the accident of Chernobyl?
A fire or explosion in one of the reactor cores or the spent fuel store could release significant radioactivity into the environment, but it is difficult to tell what is the worst case scenario. Some reactor engineers say that "another Chernobyl" couldn't happen in a reactor of this type. The Chernobyl accident was an explosion which breached the primary containment followed by a fire which burned for 10 days. About 6.7 Tonnes of radioactive material were released from the core, including about 60% of the radioactive iodine and 30% of the radioactive caesium.
Q3: There are increasing concerns in other countries about the effects on them from the radioactivity of japan's nuclear plant and people even began to buy a great amount of salt with iodine, worrying the seawater has been contaminated. How do you see the impact on other countries from environmental perspective?
I think it highly unlikely that there will be a significant risk. Certainly at present there have been no reports of a radioactive release big enough to have an impact at large distances. In the extremely serious case of the Chernobyl accident, radioactivity travelled a long distance, even causing problems of high levels of radiocaesium in UK sheep. But even with this massive release of radioactivity, the risk to populations living in countries of Western Europe such as the UK was very low and not a real health concern. This is because radioactive plumes disperse at long distances from an accident, resulting in much lower levels of radioactivity. Although radioactivity can be transported in seas, there is enormous dilution and dispersal of activity in the marine system, so this is unlikely to be a risk except in areas local to the Japanese coast.
I would not recommend taking potassium iodide tablets unless advised to do so.
Q4: You did many research on environmental impacts of nuclear energy. How do you view the future of this kind of energy after the accident in Japan?
I think it is too early to address this question fully: it would be wrong to make quick decisions about nuclear power in the middle of an accident situation. These questions should be addressed after the crisis is over and an evaluation can be made. However, it should be borne in mind that this accident was caused by an extreme event – a 9.0 Richter scale earthquake. It therefore differs from the two previous major accidents: Three Mile Island and Chernobyl, which occurred in normal circumstances. I personally believe that in the long term mankind will still need nuclear power: our energy demands are growing. Unless nuclear fusion can be made to work, we will need nuclear fission power, which has a relatively secure supply and does not emit greenhouse gases.
Rick Hallard, a radiation protection consultant with more than 30 years’ experience working in a UK nuclear facility, said:
Emergency systems in the Nuclear Industry are based on a tiered response, with multiple levels of control to provide protection. These are derived as follows;
- Firstly, prevent the accident occurring
- Secondly, mitigate the consequences if the controls were to fail
“The protection arrangements are based on a hierarchy, using passive engineered controls first (eg shielding), supported by highly reliable active engineered controls (for example a valve which closes automatically to cut off the cause of the fault or preventing activity escaping) supported with manual procedures (for example a person manually closing a valve).
“The engineered controls provide defence in depth, providing multiple layers of response against a serious failure so that if one control fails there will be backups to take over.
“The controls are also designed where possible to avoid common cause failures, ie a failure mechanism which could affect several control arrangements with a single fault. The controls incorporate ‘diversity’ and ‘redundancy’, ie multiple systems operating in different ways.
“Older plant will clearly be designed to different engineering standards to modern plant. To take account of this, all nuclear facilities, such as reactors, have a 10 year review to compare the design with the current standards and to upgrade the design where practicable to meet these standards.”
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