Mars 2011: Kärnkraftverket i Fukushima - utbruten och sammanfogad tråd

all questions and answers
Category: radiation and health
Q: How many people died in Japan due to the earthquake and tsunami and how many of that were victims to the nuclear powerplants? Could you calculate the percentage? Also, could you estimate how many people from the region surrounding Fukushima will suffer from radiation poisoning or long term radiation-related damage?
A: As of right now(26th March 2011) there has been no death due to the Fukushima accident. The confirmed deaths due to the tsunami is over
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10 102 and there is another 17 053 people missing.

The percentage of deaths due to the Fukushima accident is thus 0 so far. However one can not yet rule out the possibility that some worker might be exposed to lethal levels of radiation during the continuation of the crisis. We will have to revise this question in a months time and see the status then.

There is a lack of data regarding fallout in the most severely effected prefectures. But nothing yet indicates such severe fallout that any local population run the risk of getting acute radiation sickness.

The highest total radiation dose measured so far at the edge of the evacuation zone is 1437 mikrosievert(in the 24 hours since the measuring station was put up). To put this number in perspective a normal person receives around 1000 to 5000 mikrosieverts per year from natural sources. The 5 year limit for nuclear workers is 100 000 mikrosievers. So the dosage measured is to small to expect any visible increase in cancer rates.

Theoretically it can give an increase lifetime risk of lethal cancer by about 0.0072%. If a population of 10 000 is exposed to that level of radiation there might be one extra case of fatal cancer(compared to the about 2500 fatal cases of cancer to be expected naturally in that population).

But caution is in order and it will take weeks before we have the full picture on fallout in the areas around the plant, how many people are present and what effect it will have.

Link to injuries at the Fukushima Daiichi nuclear power plant(march 26th)

Link to the integrated measured dose around Fukushima Daiichi (march 25th)
Category: radiation and health
Q: What radiation dose do i get when I fly over atlantic?
A: You would get about 40 microsievert. That is about ten times more then a daily dose in the vicinity of the Fukushima plant. »
Category: technical
Q: Something that could be clarified is the difference between a melting of the core and a breach of containment. In the media, this is often treated as equivalent. Under what circumstances does one lead to the other?
A: The reactor core essentially consists of a lattice of fuel bundles that are contained in a steel vessel, which is in case of a BWR about 15 »
cm thick. This vessel is enclosed in containment, which is made out of reinforced concrete and it is able to withstand some pressure. The design of the containment varies from a small shell around the reactor, hidden in the structure (Fukushima) to a huge building that dominates the look of a powerplant.
Now, if the core melts sufficiently, the fuel together with the construction materials forms a chunk at the bottom of the reactor vessel. Assuming a good cooling of the vessel, like in Three-Mile Island, the vessel may suffer some damage, but survive, keeping all the melt inside. That is the best meltdown scenario! It may however happen that the cooling fails or is insufficient and the core melt, called “corium”, makes it through the reactor vessel. Upon breaching the vessel a steam and hydrogen explosion may occur, if there is still some water under the vessel. Once the corium reaches the containment, it will start to interact with the concrete. There is about 10 m of the concrete for the corium to “eat trough”. Another mechanism of possible breaching the containment is a hydrogen explosion before the fuel burns through the vessel. If the temperatures are sufficiently high, hydrogen will be formed in the core and it will be released into the containment. There, a hydrogen explosion can take place and it may (but not necessarily) lead to containment damage. In this scenario however, the reactor vessel is still not necessarily damaged, keeping the largest portion of the radiotoxic matter separated from the environment.
To make things more confusing, also the building around the whole reactor hall is called “secondary containment”. This building was severely damaged by hydrogen explosion at units 1and 3.
Category: event scale INES
Q: Nice activity! I would be interested in the INES scale from the formal point of view - who establishes which level it is and based on what criteria? Three Mile Island was INES 5, but Fukushima is classified as INES 6 - is that reasonable, especially compared to the INES 6 incident in the Soviet Union in 1957 that seemed somewhat more severe? At which point did Fukushima stop to be level 5 and become level 6? Thanks. ;o)
A: According to today’s update of the IAEA website (18.3.2011), the Fukushima accident is classified as INES 5, like the Three Mile Island. T »