Fukushima: As bad as Chernobyl?

The Chernobyl (l) and Fukushima (r) plants The Fukushima (r) incident is now rated on a par with Chernobyl (l)... but will it prove to be that bad?

Chernobyl is regularly labelled "the world's worst nuclear accident" - and with good reason.

A working reactor caught fire, explosively. Radioactive debris was sent 30,000 feet into the air - the height at which airliners conventionally fly.

Some of that debris came down thousands of kilometres away, in concentrations strong enough to prohibit the eating of meat and the drinking of milk produced locally.

The upgrading of Japan's Fukushima incident to a level seven - the maximum - on the International Nuclear and Radiological Event Scale (INES) puts it on a par with Chernobyl.

And a spokesman for Tokyo Electric Power Company (Tepco), which runs the plant, suggested it could even end up being worse than Chernobyl.

This, though, appears to be a minority view among engineers - both those who generally support nuclear power, and those who have in the past voiced criticisms.

World's worst nuclear incidents

  • Level 7: Chernobyl, Ukraine, 1986 - explosion and fire in operational reactor, fallout over thousands of square kilometres, possible 4,000 cancer cases
  • Level 7: Fukushima, 2011 - tsunami and possibly earthquake damage from seismic activity beyond plant design. Long-term effects unknown
  • Level 6: Kyshtym, Russia, 1957 - explosion in waste tank leading to hundreds of cancer cases, contamination over hundreds of square kilometres
  • Level 5: Windscale, UK, 1957 - fire in operating reactor, release of contamination in local area, possible 240 cancer cases
  • Level 5: Three Mile Island, US, 1979 - instrument fault leading to large-scale meltdown, severe damage to reactor core

"The classification of seven means there's a leak of radiation into the wider environment; and although it'll be interpreted as being 'the same as Chernobyl', it's not the same," said Paddy Regan, professor of physics at the UK's University of Surrey.

"The amount of radiation release is a lot less, and the way it's released is very different.

"The Chernobyl fire was putting lots of radioactive material into the atmosphere and taking it over large distances; here, there have been a couple of releases where they've vented [gas from] the reactor, and then released some cooling water."

Don Higson, a retired Australian nuclear safety specialist, was more pithy.

"To my mind, [rating Fukushima equivalent to Chernobyl] would be nonsense," he said.

In the month following the Chernobyl explosion, he said, 134 workers were hospitalised with acute radiation sickness and 31 died.

The equivalent figures for Fukushima are none and none. (Although workers have been taken to hospital with radiation burns, this is not the same as acute radiation sickness.)

Two units

So why the uprating?

Start Quote

The potential for atmospheric release is very large, with 250 tonnes of material sitting in that pond”

End Quote John Large Nuclear consultant

What it does not mean is that things have got worse at the plant; in fact, conditions appear to be markedly more stable than in the days following the Tohoku earthquake and tsunami, although not completely under control.

Rather, Japan's Nuclear and Industrial Safety Agency (NISA) has re-analysed data from the incident and decided that collectively the releases of radioactivity mean it slots into a level seven categorisation.

The manual for agencies using the INES scale, published by the International Atomic Energy Agency (IAEA), runs to 218 pages.

One of the criteria for evaluating the severity of an incident is the total release of radioactive material.

This is derived by first adding up the amounts of each different radioactive isotope released, then multiplying each by a conversion factor related to the characteristics of that particular isotope, then adding up all of the resulting numbers.

Radioactivity is measured in becquerels (Bq); a million million of these is a terabecquerel (TBq).

A level seven rating is defined as "An event resulting in an environmental release corresponding to a quantity of radioactivity radiologically equivalent to a release to the atmosphere of more than several tens of thousands of TBq of Iodine-131."

NISA puts the Fukushima figure at 370,000 TBq of Iodine-131 equivalent; the Nuclear Safety Commission, which has a more over-arching role in the Japanese system, says 630,000 TBq.

Testing for radiation Japanese authorities have acted very differently from their Soviet counterparts in 1986

Either way, it's clearly beyond the threshold for classification as an INES level seven event, although an order of magnitude lower than the 5.2 million TBq released from Chernobyl.

But that tells you nothing about the danger to people.

Becquerels are a measure of the rate of radioactive decay; if one atomic nucleus decays per second, that is defined as one becquerel.

By contrast, sieverts - another unit commonly used during the last month's reporting - measure the likely medical impact of the radiation to which an individual is exposed.

And a huge number of becquerels does not automatically translate into a huge amount of sieverts.

"It's hard to make a comparison between Three Mile Island, Chernobyl and Fukushima because the radioactive release is different and so is the population," said John Large, a UK-based independent nuclear engineer.

"In Ukraine and Belorussia (now Belarus) it was primarily a rural population, whereas in Japan you've got a highly sophisticated public living in fairly dense population groups.

"And the way the state intervenes is different. With Chernobyl, loads of workers were brought in with no concern for their health - but Japan's a democracy."

In some quarters, Japan's swift decision to establish an exclusion zone, initiate monitoring of people and food, and dispense iodine tablets has received praise - and the volume of advice and warnings issued to the public has been very different from the silence that pertained after Chernobyl, despite criticisms from other quarters over the quality and timing of some of the Japanese advice.

Not spent

Nuclear experts are cautioning, however, that the situation at Fukushima is still very much in play.

Where most attention has centred on reactors 1, 2 and 3, there is also concern about the spent fuel pond in reactor building 4.

In the week following the tsunami, it became clear that the pond was running dry, meaning that fuel rods would have heated up.

This meant likely degradation of their zirconium alloy cladding, the possible release of hydrogen, and - by Tepco's admission - the risk that a nuclear chain reaction could begin.

"The potential for atmospheric release is very large, with 250 tonnes of material sitting in that pond," said Dr Large.

"If you were to have an energetic event you could have a very large release indeed."

The priority is, as it has been all along, to restore adequate coolant to the fuel ponds and the reactors themselves - while hoping that earthquake aftershocks and bad weather do not hamper operations any more.

Radiation levels

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  • rate this

    Comment number 40.

    It's just not true that the area by the plant is now uninhabitable for hundreds of thousands of years.

    Radioactive iodine, which causes thyroid cancer, has a half life of 8 days. This means that in six months time the radiation levels will be 0.00005% of the current level; a dose equivalent now to standing next to the chernobyl reactor core becomes the same as what you get on a flight to chicago.

  • rate this

    Comment number 39.

    @ChuckBlues : "I appreciate balanced reporting by BBC"

    I generally agree with your comments but take issue with the above quote. From what I've read, the BBC are only reporting the feelings of those Japan residents who are living in fear of radiation. The majority of folk here are just getting on with things, trying to remain calm and sensible. The overall coverage has been quite imbalanced, imo.

  • rate this

    Comment number 38.

    I think what this shows is that a new Event Scale needs to be drawn up, as it's rather vague. Chernobyl could've been much a more serious accident, but it would've still been a category seven.

    Maybe it's vague deliberately so that governments can play down just how bad an accident is?

  • rate this

    Comment number 37.

    As an engineer, I appreciate balanced reporting by BBC. To "dumb-down" 218 pages of calculations to 7 levels is indeed "nonsense" ; Afterall 6.7x10e5 TBq is a small fraction of 5.3x10e6 & sievert levels which are more relevant to human danger were almost 1000x higher @ Chernobyl so that a worker exposed died within 48 seconds but @ Fukushima outside the plant, exposure is less than a chest x-ray.

  • rate this

    Comment number 36.

    I'm also confused by those who keep complaining about the lack of transparency, or the lack of information. There are daily press conferences given by TEPCO, NISA, IAEA and the government. Several agencies are providing rdaily reports on the situation at the plant, as well as the monitoring of radiation in the atmosphere, tap water and food. It's all available online! What more do people want?

  • rate this

    Comment number 35.

    Bob in The US , there is radiation all around you, despite nuclear power. Powerful radiation from cosmic rays strike you every day. You receive a daily dosage of radiation from your immediate environment too. Not to mention the billions of neutrinos streaming right through you every second, 24/7! Ever had an MRI? X-ray? Airplane flight? You receive bigger doses from those than from Fukushima.

  • rate this

    Comment number 34.

    It dismays me to see people disparaging nuclear power. The fact that the reactors survived a magnitude 9 quake and a pretty epic tsunami seems to elude these people. It was the tsunami which ruined the backup generators for the cooling system, creating the chain of events afterwards.

    I'm still in full support of nuclear power. Future stations should be better designed of course.

  • rate this

    Comment number 33.

    Nuclear power, in terms of deaths per TWh of power generated, is still the safest form of electricity generation :


  • rate this

    Comment number 32.

    There's radiation in the rain water here. Not much, but now I need to know that 125 pico curies per liter isn't harmful, if certain exposure times are limited. I also need to know that radio active Iodine 131 has a 1/2 life of 8 days, roughly. Nothing pollutes like radioactivity, and its not over. This is also 1 set of reactors, with 500+ in operation. The risk is not worth the reward.

  • rate this

    Comment number 31.

    I'm confused: if most, if not all, experts in the field agree that the Fukushima situation is not comparable with what happened in Chernobyl, why are they the same on the scale? It seems the authorities responsible for devising the scale are as guilty of lacking foresight as the authorities in Japan who are being accused of incompetence.

  • rate this

    Comment number 30.

    Living in Saitama, about 200 kms away from Fukushima, things are pretty normal but the lack of information and transparency about what is actually happening there is annoying. Maps detailing the spread of radiation should be shown on news programs but aren't. My Japanese friend said he wants to know what the worst case scenario is because people really aren't sure how this will pan out.

  • rate this

    Comment number 29.

    I live 54km due west of the Fukushima nuclear power stations, on the eastern outskirts of Koriyama. I decided to stay at my house during the the last month since the disaster began.

    Here, I think we've been rather fortunate in that we appear to have dodged any nasty deposits of radioactive material. Latest measurements from my geiger counter are 0.22 uSv/hr inside, 0.57uSv/hr out, so not bad.

  • rate this

    Comment number 28.

    I guess it depends on the wind direction strongly, so far was steady towards empty ocean, excellent luck. There where nobody lives (and nobody measures either).
    Russian meteo says winds will turn soon for the summer patten to the landmass. :o(
    That's with what vapours into the air.
    With water no changes of old currents are envisaged:o), main routes - travels to the USA/Canada.

  • rate this

    Comment number 27.

    The more confusing the terms and tallies, the less likely mere citizens are to comprehend the colossal danger of nuclear power. I read this article twice and still don't know if Fukushima poses a danger to people in Asia and the rest of the world. It's the highest danger level, but 'engineers' says that's no big deal. What? What? Huh? If you don't know, just say so. This article is useless.

  • rate this

    Comment number 26.

    It's worse than Chernobyl. The U.S. lied about 3 Mile Island and just plain covered up a meltdown in California in the 1950s. The Russians lied using the same "pollen" excuse for the yellow rain. The track record of govts and media is clear. The fact that mainstream media is still trying to spin it as something less than is sad, pathetic and irresponsible.

  • rate this

    Comment number 25.

    Dipnorhynchus, the Int'l Health Organisation these days has formal agreement with Int'l Agency of Nuclear Energetics, an article, that stipulates they issue nuclear health risks warnings after these are approved by them.
    The table in the link you've provided is very beautiful.
    Surely communistic radiation is bad and democratic is healthy.

  • rate this

    Comment number 24.

    Long term storage solutions for nuclear waste require the security of the waste to be assured over geological time periods. In this uncertain and unstable world, how can we confidently make that assurance?

  • rate this

    Comment number 23.

    Upgrading the Fukushima nuclear power disaster to a level 7 event says more about the INES scale and the IAEA than it does about the comparison between Fukushima and Chernobyl. Although a catastrophic release of more dangerous radioactive contamination is still possible at Fukushima, the events are very different in other ways. See http://docsgreen.blogspot.com/2011/03/fukushima-vs-chernobyl.html

  • rate this

    Comment number 22.

    I would say the incident at Fukushima actually shows how well designed and safe Japanese nuclear power plants are. The place is 30+ years old. It was hit by 1 of the largest earthquakes in recorded history, followed by a 15 meter Tsunami (3+ times larger than designed ) & It was still standing after.
    It is not a surprise things went wrong, it's a miracle the did not go worse.

  • rate this

    Comment number 21.

    "Chernobyl was behind a closed state and beyond our prevention."

    Same feeling now in Russia as our offer of help was turned down.


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