Risk Perception and Communication, by Petrus, Tokai University

After the Fukushima accident caused by the tsunami on March 11, the public had lost their trust in the safety of nuclear power plants. But, as we have seen in many disasters, people will not protect themselves if they don't believe their lives are at risk. Changing the way people perceive danger is an important way to save lives. To change the way people think, we must have specific plans for communicating the risks of dangers they could probably face.

“Sharing” is one of the ways to know how the public thinks about nuclear power plants before and after the accident. The public is not monolithic. Some people will be directly affected by the risk and some will be indirectly affected. We have to share all of the information transparently, not only information about safety but also about the risk of nuclear power plants that might result when the nuclear power plants operate. It's diffi to make people perceive this risk, because the public has realized that it is not true that “NPP is absolutely safe” or “safety fi is the foundation of nuclear plants. In this condition, engineers can take a role to improve the safety and design to make plants as safe as possible.

Understanding a public risk typically involves the range of benefi and costs associated with nuclear power plants. All aspects of the risk need to be thought through and explained, or the dialogue about the risk may become dominated by one part of the analysis. This risk-benefi analysis can be used as our tool to help us demonstrate the limit of the public risk. However, transparency of the information is better than “hiding” the information from the public. Lack of information may cause one to have exaggerated fears regarding the possible risk of a certain situation. Without factual information, we make uninformed decisions.

If the risk is considered to be the government's or the local government's responsibility, then our role as engineers may be more to coordinate and to support rather than to take responsibility. In this case, public trust in the government also plays a major role. When the government and engineers are not highly trusted, for example after the accident, we can only share accurate information, whether or not the public can take it in. Deliberative processes can provide an inclusive way of involving the public in seeking their views but these also need to be fair.

Radiation Risk Communication, by Kazumasa Shimada, the University of Tokyo

My essay is to respond to questions raised by Prof. Kosako related to the issue of radiation risk communication and estimated number of cancer deaths based on the collective dose.

Calculating the number of cancer deaths based on the collective effective dose caused by very small exposure to a large population has a very huge uncertainty because, statistically and biologically, it is incorrect usage of the amount of protection (ICRP, Pub.103, paragraph 161).

On the other hand, the Chernobyl Forum (performed in several international organizations; IAEA, WHO) reported that targeting about 600,000 people [decontamination personnel (average. dose is 100 mSv), evacuees (10 mSv), most contaminated local residents (50 mSv)], the number of deaths is expected to be 4,000 people and targeting about 6,800,000 people [public and workers (average dose is 7 mSv)], the number of deaths is expected to be 9,000 people (Chernobyl Forum, Chernobyl's Legacy: Health, Environmental and Socio-economic Impacts and Recommendations to the Governments of Belarus, the Russian Federation and Ukraine. IAEA, 2005). In addition, in the report of Cardis in 2006, it is said that the number of deaths is expected to be 16,000 people (CRIEPI, health effects of Chernobyl Research Center for Radiation Safety Accident criepi.denken. or.jp/jp/ldrc/study/topics/20060904.html).

The Fukushima nuclear accident was evaluated to be INES level 7. Therefore, calculation of the number of cancer deaths based on collective dose is unavoidable. If someone calculates the number of deaths based on radiation by this accident as a few hundred people, how is this to be explained to the public, especially the people of Fukushima? At this time, we have no answer to the question: “How do I know if my child will be one of the few hundred victims?”.

Nowadays, we cannot identify whether this cancer is due to radiation. In the future, some cancer patients will likely go to court about the Fukushima nuclear accident. If the court decides to accept a causal connection between low dose and cancer, I am concerned that all cancer will be viewed as radiation. This situation is like the atomic bomb case.

In my opinion, it is against humanism to calculate the number of deaths. We should rethink the meaning of low dose radiation risk.

I propose to develop two things. One is a total health risk evaluation. The other is a minus-dose evaluation. The total health risk evaluation is to be considered with radiation, ultra-violet ray, chemical material, mental stress, etc., to evaluate human health risk. Nowadays, only the radiation risk is evaluated quantitatively and gives some cause for anxiety. Therefore, it is important to know that radiation is not a special cancer risk compared with other risks even if this evaluation has a huge uncertainty. Moreover, minus-dose evaluation is more important. Today, Linear Non-Threshold model (LNT model) can evaluate the cumulative radiation risk forever. Therefore, people have no way to escape radiation to reduce risk. On the other hand, we can find protection functions in our body, for example DNA repair, apoptosis, radioadaptive response, and immunity. This means radiation damage in our body is continually being repaired by these functions. To make quantity evaluations of these functions we can calculate that the dose was canceled by these minusdoses. For example, to increase our immunity function to reduce cancer risks quantitatively, we use methods of ordinary health promotion (for example, spas) so that our radiation risk will be canceled and our health will actually become better.

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