Japan Fukushima Daiichi incident Q&As (Gyakran ismételt kérdések – angol nyelven)

25. 03. 2011.

1. How dangerous it is? What type radiation exposure could occur in a nuclear power plant accident?

In the event of the reactor's  core damage both an accidental and a planned (precautionary) release of the radioactivity off site may occur and include a mixture of nuclear fission products.

Main radionuclides representing health risk will be radioactive caesium and radioactive iodine. The population exposure to these radionuclides may occur in lower doses due to external exposure from radioactive plume or internally through inhalation  and/or ingestion of contaminated food/drink.

In addition, the rescue workers, first responders or NPP workers may be exposed to higher doses as a result of external or internal contamination due to their professional activities (see below for health effects of high and low doses)

The half-life of the radioactive iodine (I-131) is 8.04 days. This means that in about three months, nearly all radioactive iodine that would fall out will disappear.

The half life of Cs-137 is 30 year. Depending on the amount of the radioactivity in the fallout, some mitigation and clean up procedures may be necessary (agricultural, forestry, etc.).

 

2. What are the public health measures to be implemented to reduce these exposures?

- To prevent or minimize the external exposure main protective actions are evacuation of population from immediate vicinity and sheltering for population of more remote areas.

 - To prevent internal exposure to radioactive iodine, the uptake which would affect thyroid gland, especially for those at the 0-18 age group, potassium iodide (KI) pills should be administered according to the national emergency planning criteria. If radioactive fallout occurs, consumption of leafy vegetables should be banned. Locally produced milk and dairy products should also be banned and replaced by imported products and baby formula.

 - Internationally agreed criteria for KI  administration recommend  thyroid blocking when predicted thyroid doses are above 50 mSv. "Arrangements for Preparedness for a Nuclear or Radiological Emergency, IAEA Safety Standards Series No. GS-G-2.1,  co-sponsored by WHO. IAEA, Vienna (2007), p.15)

 

3. Will KI pills protect from radiation and how? How much potassium iodide should be given?

Physiologically, in human body iodine gets primarily up-taken by thyroid gland which uses iodine for production of thyroid hormones. KI is stable iodine which will saturate thyroid gland and block it from the uptake of radioactive iodine.

The experience of Chernobyl shows that radioactive iodine was the main cause of the largest impact of the Chernobyl accident that lead to some 5000+ cases of childhood thyroid cancer among those who were exposed at the age of 0-18. Therefore, first priority for KI distribution are young children and pregnant women.

Iodine tablets do not protect against radiation which comes from outside the body, or against radioactive substances other than iodine which are absorbed by the body. That is why iodine thyroid blocking will in most occasions will be combined with other protective measures, such as sheltering (staying indoors, doors and windows shut).

Exposure to radioactive iodine can result in a significant increase in thyroid cancer, especially in young children.  Inhaled and ingested radioactive iodine is taken up by the thyroid gland.  Potassium iodine given before exposure prevents the absorption of radioactive thyroid and reduces the risk of cancer in the longer term.

To obtain full effectiveness of stable iodine for iodine thyroid blocking requires that it be administered shortly before exposure or as soon after as possible. However, iodine thyroid uptake is blocked by 50% even after a delay of several hours. To protect against inhaled radioactive isotopes of iodine, a single high  dose of stable iodine would generally be sufficient, as it gives adequate protection for 24 hours. This may well be enough to protect from inhaled radioactive isotopes of iodine  present in a passing cloud. In the event of a prolonged release, however, repeated daily doses might be indicated (2 or 3, but maximum 7 days).

Again the protective benefit is only achieved if the potassium iodide is given before exposure to the radioactive iodine.

 

4. Where is potassium iodide available?  Does WHO have stockpiles?

National governments are in charge of national stocks of potassium iodide. Prepositioning of KI pills is a requirement and an essential component of emergency response planning for any operational nuclear power plant. WHO does not have a stockpile.

 

5. Will it affect anyone outside of Japan?

This will depend on the amount of released radioactivity and meteorological conditions (wind direction and velocity, rain, etc.)

In any case, based on the limited information we have, it is unlikely that even neighbouring countries will be significantly affected.

 

6. How far away do you need to be to be safe?

In general the first priority is to limit the  exposure to radiation which occurs, primarily, through radioactive plume and fallout, either  by evacuation or by sheltering the affected population. Depending on the amount of the radioactivity amount released in the atmosphere and the prevailing meteorological conditions (e.g. wind and precipitation), a radius around the explosion epicenter defined in the national  response plans should be covered by urgent protective actions.

 

7. What is WHO's role in nuclear emergencies?

Within the United Nations System, the IAEA  is the lead agency for coordination of international response to nuclear emergencies.  This is described in the “Joint Plan of International Organizations for Response to Nuclear Emergencies” (IAEA, Vienna, 2010).  Under the existing arrangements, WHO is responsible for assessing health risk and providing technical consultation,  advice and assistance (upon request or acceptance of an offer) with public health interventions in nuclear emergency.

 

8. What is the Radiation Emergency Medical Preparedness and Assistance Network?

REMPAN is a global network of WHO comprising more than 40 institutions specialized in radiation emergency medicine, dosimetry, public health interventions, long-term care and follow-up. It is a technical assistance arm of WHO for radiation emergency preparedness and response (at regional level).

 

9. Will it blow up completely?

Japanese authorities say the explosion was outside the container housing of the reactor and explosion of the the reactor vessel can be prevented due to planned release of radioactively contaminated steam under high pressure.

 

10. How can I protect myself?

First of all avoid panic, listen to the radio and TV to follow up your government's instructions. Stay inside if radioactive fallout justifies it.

As only the authorities, after evaluating the accident situation, can decide whether or not the taking of iodine tablets is necessary, tablets should not be taken through personal initiative or in pure response to fear.

 

11. What are the risks related to pregnancy and what should be done to reduce these risks?

Special attention should be given to pregnant women with regard to iodine thyroid blocking, because of two reasons. Firstly, the thyroid of a pregnant woman uptakes radioactive iodine at a higher rate as compared to other adults. Secondly, the thyroid of fetus has to be protected as well, especially in the 2nd and 3rd trimester. Hence iodine thyroid blocking of pregnant women is necessary and justified but only after the responsible authority announces it.

Despite this, however, there is no particular medical reason under the current circumstances for conception to be avoided or interrupted!

 

12. Do I need to take iodine tablets? See Q3.

 

13. How far can these clouds spread?

This is very difficult to predict. It depends on wind-speed and other climatic conditions. It might be some radioactivity originated from the injured Japanese Nuclear Power Plant will be detected in Europe, but due to the nature of the reactor damage and the huge distance to Japan, health consequences from this contamination of the air are unlikely and certainly not expected in Europe.

 

14. How much would be radiation doses from the released radioactivity and what would be the health effects?

Depending on the amount of radioactivity released, doses that may be received by population would be from low to very low. Natural background radiation doses are about 2.4 mSv per year with variations throughout the world (e.g. 20-50 mSv/yr are usual, and even 200 mSv/yr in some areas of Iran and India are being calculated for a long time).

At whole-body doses approaching 1 Gy and above, acute health effects such as acute radiation syndrome may develop. However, in the event of radioactive fallout from a nuclear power plant accident, when radioactive plume would  travel very substantial distances, such high doses of radiation are unlikely.

 

15. What long-term effects could we see and from what doses?

Exposure to ionizing radiation may increase the risk of cancer.  Epidemiological studies on populations exposed to external radiation, e.g. atomic bomb survivors, radiotherapy patients, occupationally exposed cohorts, and Chernobyl affected Soviet citizens do not show a clear increase of radiation-induced cancer risk at doses below 100 mSv whole-body dose.

In the Japanese atomic bomb survivors studies, risk of leukemia increased for a few years after the exposure, whereas risk of solid cancers started to increase 10 years after the exposure.

In nuclear emergencies, if radioactive iodine is accumulated in the thyroid, it can result in local dose to thyroid gland (not the whole  body dose). The experience of Chernobyl shows that radioactive iodine was the main cause of the largest impact - some 5000+ cases of thyroid cancer among those who were exposed at the age of 0-18. All of these cases were surgically treated.

One of the largest impacts of the Chernobyl accident was psychological impact. This was a result of poor risk communication strategy. Therefore, a good public communication is a key in such emergency.

 

16. Below what dose is there not expected to be any effects?

Epidemiological data do not demonstrate statistically significant cancer risk increase below 100 mSv dose. However, a linear non-threshold model of risk for ionizing radiation is used as a basis for radiation protection. This means, that theoretically any dose of radiation may cause an effect as shown in biological studies, but this cannot be demonstrated in humans, especially at the level of individual risk. Therefore, we cannot tell below which dose there is absolute zero risk. However, at very low doses below the natural background radiation exposure, neither increase of cancer risk can  be detected nor it is  expected. Exposure to ionizing radiation should be kept as low as reasonably achievable (ALARA principle).

Original source: WHO

Reviewed and updated by Istvan Turai, MD, PhD, MPHM, Med.Habil. 
Acting Director General of  „Frédéric Joliot-Curie”
National Research Institute for Radiobiology and Radiohygiene  –
the national radiation health institute
of the National Public Health and Medical Officer Service
Budapest, Hungary