In an effort to educate ourselves, we’ll begin a series of posts starting today, to tackle the technical or complicated questions surrounding the Fukushima nuclear crisis and Tohoku quake-tsunami that have been a source of confusion for lay people.
One of the questions that many of our Education in Japan forum members has posed is – how are we to make sense of all the different measurements and readings of radiation in the environment or water that we are being shown daily – bequerels, sieverts, etc.. for example at this site. Below we have some help from our EIJ forum members to sort out some of those answers:
The fallout numbers are measured in megabecquerels per square kilometer (Mbq/km2). I believe this can be converted into microsieverts per hour through a few steps outlined below. There may be an easier way to do this but this is what I believe works:
MBq/km2 –> Bq/cm2 –> nGy/hr –> uGy/hr –> uSv/hr
1 MBq = 1,000,000 Bq
1 km2 = 10,000,000,000 cm2
1 Bq/cm2 = 1319 nGy/h
1 uGy/hr = 1000 nGy/h
1 uGy/hr = 1 uSv/hr
Using a simplified math you can arrive at uSv/hr from MBq/km2 with the
following(n = MBq/km2):
(n / 10,000,000) * 1319
So, for example, todays number for Tokyo is 36,000 Mbq/km2.
(36,000/ 10,000,000) * 1319 = 4.7 uSv/hr or 113 uSv in a day (multiplied by 24)
Assuming constant exposure at that number, for a day that would be half the amount of radiation from a round-trip flight from Tokyo to New York (200 uSv). I would guess the number is likely to fluctuate and perhaps be lower if one is indoors.
My math is attached as a Word file for anyone who wants to check it.
-Sean in Iwate
1 of 1 File(s)
From the NIRS page ‘s Q&As on TV on radiation levels and issues: http://www.nirs.go.jp/ENG/data/pdf/i3_e.pdf where an explanation on the meaning of the numerical values reported by the media is offered:
Dose rates at the Fukushima site continue to trend downwards.
In 28 of the 45 prefectures for which data are available, no deposition of radionuclides was detected in the period 18 to 25 March. In seven of the other 17 prefectures, the estimated daily deposition was less than 500 becquerel per square metre for iodine-131 and less that 100 becquerel per square metre for caesium-137.
On 26 March, the highest values were observed in the prefecture of Yamagata: 7500 becquerel per square metre for iodine-131 and 1200 becquerel per square metre for caesium-137. In the other prefectures where deposition of iodine-131 was reported, the daily range was from 28 to 860 becquerel per square metre. For caesium-137, the range was from 2.5 to 86 becquerel per square metre.
In the Shinjyuku district of Tokyo, the daily deposition of iodine-131 on 27 March was 220 becquerel per square metre, while for caesium-137 it was 12 becquerel per square metre.
No significant changes were reported in the 45 prefectures in gamma dose rates compared to yesterday. In general, gamma–dose rates tend to decrease due to the decay of short-lived radionuclides such as iodine-131.
Two IAEA teams are currently monitoring in Japan. One team made gamma dose-rate measurements in the Tokyo region at 8 locations. Gamma-dose rates measured ranged from 0.08 to 0.15 microsievert per hour, which is within or slightly above the normal background. The second team made additional measurements at distances of 30 to 41 km from the Fukushima nuclear power plant. At these locations, the dose rates ranged from 0.9 to 17 microsievert per hour. At the same locations, results of beta-gamma contamination measurements ranged from 0.03 to 3.1 Megabecquerel per square metre.
The first results of aerial surveys of gamma dose rates by the Japanese authorities have been received by the Incident and Emergency Centre. These are being analysed and will be presented when more detailed data have been received.
New data from monitoring of the marine environment, carried out from 24 March 22:55 UTC to 25 March 03:32 UTC about 30 km offshore, show a decrease in both caesium-137 and iodine 131. The contamination at these locations is influenced by aerial deposition of fallout as well as by the migration of contaminated seawater from the discharge points at the reactor. The measured radiation doses rates above the sea remain consistently low (between 0.04 and 0.1 microsievert per hour). The first results of model predictions received from the SIROCCO Group at the University of Toulouse are being assessed.
Recommendations relating to the restriction of drinking water consumption, based on measured concentrations of iodine-131, remain in place in seven locations (in one location for both adults and infants, and in six locations for infants).
As far as food contamination is concerned, samples taken from 23 to 25 March in five prefectures showed iodine-131 in unprocessed raw milk, but the levels were far below the regulation values set by the Japanese authorities. Caesium-137 was also detected in samples of unprocessed raw milk taken on 23 March in Chiba prefecture, but at levels far below the Japanese regulation values. Caesium-137 was not detected in any of the samples taken from 24-25 March in the other four prefectures.
Based on samples taken on 22 and 24-25 March, three prefectures (Chiba, Ibaraki and Tochigi) reported iodine-131 in celery, parsley, spinach, and other leafy vegetables above the regulation values set by the Japanese authorities. Caesium-137 was also detected above the regulation values in one sample of spinach taken on 24 March in Tochigi prefecture, but in the remaining two prefectures, the results were below regulation values.
The Joint FAO/IAEA Food Safety Assessment Team arrived in Tokyo on Saturday. It will meet regulatory officials in various prefectures where food contamination has been detected. The team left for Fukushima early today. The Mission will assist and provide advice on sampling protocols, analytical procedures, data collected to date, and actions taken by the Japanese authorities for the control of contaminated foods.
Viewpoint: We should stop running away from radiation
By Wade Allison University of Oxford (26 March 2011, BBC)
More than 10,000 people have died in the Japanese tsunami and the survivors are cold and hungry. But the media concentrate on nuclear radiation from which no-one has died – and is unlikely to.
House and power station at Dungeness Modern reactors are better designed than those at Fukushima – tomorrow’s may be better still
Nuclear radiation at very high levels is dangerous, but the scale of concern that it evokes is misplaced. Nuclear technology cures countless cancer patients every day – and a radiation dose given for radiotherapy in hospital is no different in principle to a similar dose received in the environment.
What of Three Mile Island? There were no known deaths there.
And Chernobyl? The latest UN report published on 28 February confirms the known death toll – 28 fatalities among emergency workers, plus 15 fatal cases of child thyroid cancer – which would have been avoided if iodine tablets had been taken (as they have now in Japan). And in each case the numbers are minute compared with the 3,800 at Bhopal in 1984, who died as a result of a leak of chemicals from the Union Carbide pesticide plant.
Continue reading the main story
So what of the radioactivity released at Fukushima? How does it compare with that at Chernobyl? Let’s look at the measured count rates. The highest rate reported, at 1900 on 22 March, for any Japanese prefecture was 12 kBq per sq m (for the radioactive isotope of caesium, caesium-137).
A map of Chernobyl in the UN report shows regions shaded according to rate, up to 3,700 kBq per sq m – areas with less than 37 kBq per sq m are not shaded at all. In round terms, this suggests that the radioactive fallout at Fukushima is less than 1% of that at Chernobyl.
The other important radioisotope in fallout is iodine, which can cause child thyroid cancer.
This is only produced when the reactor is on and quickly decays once the reactor shuts down (it has a half life of eight days). The old fuel rods in storage at Fukushima, though radioactive, contain no iodine.
But at Chernobyl the full inventory of iodine and caesium was released in the initial explosion, so that at Fukushima any release of iodine should be much less than 1% of that at Chernobyl – with an effect reduced still further by iodine tablets.
Unfortunately, public authorities react by providing over-cautious guidance – and this simply escalates public concern.
On the 16th anniversary of Chernobyl, the Swedish radiation authorities, writing in the Stockholm daily Dagens Nyheter, admitted over-reacting by setting the safety level too low and condemning 78% of all reindeer meat unnecessarily, and at great cost.
Bottled water distributed in Tokyo Bottled water was handed out in Tokyo this week to mothers of young babies
Unfortunately, the Japanese seem to be repeating the mistake. On 23 March they advised that children should not drink tap water in Tokyo, where an activity of 200 Bq per litre had been measured the day before. Let’s put this in perspective. The natural radioactivity in every human body is 50 Bq per litre – 200 Bq per litre is really not going to do much harm.
In the Cold War era most people were led to believe that nuclear radiation presents a quite exceptional danger understood only by “eggheads” working in secret military establishments.
To cope with the friendly fire of such nuclear propaganda on the home front, ever tighter radiation regulations were enacted in order to keep all contact with radiation As Low As Reasonably Achievable (ALARA), as the principle became known.
This attempt at reassurance is the basis of international radiation safety regulations today, which suggest an upper limit for the general public of 1 mSv per year above natural levels.
This very low figure is not a danger level, rather it’s a small addition to the levels found in nature – a British person is exposed to 2.7 mSv per year, on average. My book Radiation and Reason argues that a responsible danger level based on current science would be 100 mSv per month, with a lifelong limit of 5,000 mSv, not 1 mSv per year.
People worry about radiation because they cannot feel it. However, nature has a solution – in recent years it has been found that living cells replace and mend themselves in various ways to recover from a dose of radiation.
These clever mechanisms kick in within hours and rarely fail, except when they are overloaded – as at Chernobyl, where most of the emergency workers who received a dose greater than 4,000 mSv over a few hours died within weeks.
However, patients receiving a course of radiotherapy usually get a dose of more than 20,000 mSv to vital healthy tissue close to the treated tumour. This tissue survives only because the treatment is spread over many days giving healthy cells time for repair or replacement.
In this way, many patients get to enjoy further rewarding years of life, even after many vital organs have received the equivalent of more than 20,000 years’ dose at the above internationally recommended annual limit – which makes this limit unreasonable.
A sea-change is needed in our attitude to radiation, starting with education and public information.
Then fresh safety standards should be drawn up, based not on how radiation can be excluded from our lives, but on how much we can receive without harm – mindful of the other dangers that beset us, such as climate change and loss of electric power. Perhaps a new acronym is needed to guide radiation safety – how about As High As Relatively Safe (AHARS)?
Modern reactors are better designed than those at Fukushima – tomorrow’s may be better still, but we should not wait. Radioactive waste is nasty but the quantity is small, especially if re-processed. Anyway, it is not the intractable problem that many suppose.
Some might ask whether I would accept it if it were buried 100 metres under my own house? My answer would be: “Yes, why not?” More generally, we should stop running away from radiation.
Wade Allison is a nuclear and medical physicist at the University of Oxford, the author of Radiation and Reason (2009) and Fundamental Physics for Probing and Imaging (2006).
The radioactive fission products from the affected reactors include noble gases (xenon and krypton), volatile radioactive isotopes (iodine-131 and cesium-137) and non-volatile fission products. As mentioned before, these radioactive products release radiation as they decay. Therefore, over exposure and/or contact with them is dangerous. The noble gases are usually not of a big concern since they are inert, and tend to impose very small doses. Non-volatile fission products usually stay within the fuels so that is not much of a concern to the general public either. The fission products of most concern are the volatile ones such as I-131 and Cs-137 since they can be dispersed in air and get carried far away by wind from the affected reactors. Read the whole article here.
According to Dennis Kucik, M.D., Ph.D., associate professor in the UAB Department of Pathology, very little radioactive materials have been released to the areas surrounding the Fukushima plant in Japan, despite radiation levels reaching high points this past week, in comparison to what was released following the Chernobyl accident. “Moreover, a large component of the radiation released has been types that are unlikely to linger in the environment for prolonged periods,” says Kucik, who studies the effect of radiation on cardiovascular disease. Kucik will travel to Japan in May as a member of the NASA radiation research team and sees no reason to cancel the trip. “I am not at all concerned for my own safety.”
(Note: For the last several years UAB Pathology has had a dominant presence at the annual meeting of the United States and Canadian Academy of Pathology [USCAP], being grouped among the top 20 institutions with accepted abstracts. This year was no exception UAB was ranked in the top 5% of all 400 medical centers having accepted abstracts from around the world.)
Lectures at the Foreign Correspondents Club of Japan given by Japanese experts, including Masashi Goto, formerly a nuclear power plant designer for Toshiba, with simultaneous interpretation. 40 minutes into the recording of the lectures, there is an animation or simulation of how it is predicted by some researchers that the winds will blow the radiation around Japan and the surrounding seas. These experts are with the Citizens’ Nuclear Information Center, an anti-nuclear public interest organization dedicated to securing a safe, nuclear-free world. The Center was formed to provide reliable information and public education on all aspects of nuclear power to ultimately realize this goal. Data gathered, compiled, and analyzed by the Center is condensed into forms useful to the media, citizens’ groups, policy makers, and the general public. The Center is independent from government and industry and is supported by membership fees, donations, and sales of publications.
CNIC was established in 1975 in Tokyo to collect and analyze information related to nuclear energy including safety, economic, and proliferation issues and to conduct studies and research on such issues. During 1995-97, the center spearheaded an independent study on mixed uranium-plutonium oxide (MOX) fuel with a number of prominent researchers from Europe, the U.S.A., and Japan. The Research Director of the International MOX Assessment (IMA) project, Dr. Jinzaburo Takagi, together with the Research Sub-Director, Mycle Schneider, received the Right Livelihood Award for this study and activities relating to plutonium issues. The results of this project have been published in Japanese, English, French, and Russian.
A contrarian position to the above experts’ is taken by anti-nuclear lobbyist, Helen Caldicott, president of the Helen Caldicott Foundation for a Nuclear-Free Planet and the author of Nuclear Power is Not the Answer:
“Internal radiation, on the other hand, emanates from radioactive elements which enter the body by inhalation, ingestion, or skin absorption. Hazardous radionuclides such as iodine-131, caesium 137, and other isotopes currently being released in the sea and air around Fukushima bio-concentrate at each step of various food chains (for example into algae, crustaceans, small fish, bigger fish, then humans; or soil, grass, cow’s meat and milk, then humans). After they enter the body, these elements – called internal emitters – migrate to specific organs such as the thyroid, liver, bone, and brain, where they continuously irradiate small volumes of cells with high doses of alpha, beta and/or gamma radiation, and over many years, can induce uncontrolled cell replication – that is, cancer. Further, many of the nuclides remain radioactive in the environment for generations, and ultimately will cause increased incidences of cancer and genetic diseases over time.
The grave effects of internal emitters are of the most profound concern at Fukushima. It is inaccurate and misleading to use the term “acceptable levels of external radiation” in assessing internal radiation exposures. To do so, as Monbiot has done, is to propagate inaccuracies and to mislead the public worldwide (not to mention other journalists) who are seeking the truth about radiation’s hazards.
Nuclear industry proponents often assert that low doses of radiation (eg below 100mSV) produce no ill effects and are therefore safe. But , as the US National Academy of Sciences BEIR VII report has concluded, no dose of radiation is safe, however small, including background radiation; exposure is cumulative and adds to an individual’s risk of developing cancer.”
She also finds support for her views in the 2009 report, “Chernobyl: Consequences of the Catastrophe for People and the Environment”, published by the New York Academy of Sciences, which she says, “comes to a very different conclusion. The three scientist authors – Alexey V Yablokov, Vassily B. Nesterenko, and Alexey V Nesterenko – provide in its pages a translated synthesis and compilation of hundreds of scientific articles on the effects of the Chernobyl disaster that have appeared in Slavic language publications over the past 20 years. They estimate the number of deaths attributable to the Chernobyl meltdown at about 980,000.” Source: Guardian 11 Apr, 2011, How Nuclear Apologists Mislead the World Over Radiation