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  On March 11 last year a magnitude 9.0 (Mw) earthquake hit off the coast of Japan triggering a powerful tsunami and resulting in the most serious nuclear accident since Chernobyl. Over 15,000 people were confirmed dead as the tsunami inundated a total area of approximately 561 km2 (217 sq mi) in Japan. A series of fires and explosions within the Fukushima Daiichi nuclear power station triggered a full meltdown in three reactors whilst a fourth was significantly damaged by fire. The Fukushima Daiichi nuclear disaster was rated as a level 7 (major accident) on the international nuclear and radiological event scale. Now, one year after the disastrous events unfolded, nuclear and disaster experts examine the current situation and what lessons can be learnt.

  Below are comments from Australian experts provided by the Australian Science Media Centre. The collaboration between the Australian Science Media and the Science Media Centre of Japan is supported by the Commonwealth through the Australia-Japan Foundation which is part of the Department of Foreign Affairs and Trade.


Tony Irwin

Chartered Engineer and is a visiting lecturer for the Masters course in Nuclear Science at the ANU. Tony is the Chairman of the Engineers Australia Nuclear Engineering Panel
Tony worked for British Energy in the UK for more than thirty years commissioning and operating eight nuclear power reactors. Following the Chernobyl accident he was a member of a World Association of Nuclear Operators (WANO) mission that reviewed operating practices at Russian RMBK reactors. In 1999 he moved to Australia and joined the Australian Nuclear Science and Technology Organisation (ANSTO) and was Reactor Manager during the construction and operation of the OPAL research reactor; he retired from ANSTO in late 2009.
 On the sequence of events:
We now have a better understanding of what happened:
 Event Sequence – Key Events


Reactor 1

Reactor 2

Reactor 3

Loss of all AC supplies

+ 51 mins

+ 54 mins

+ 52 mins

Loss of cooling

+ 1 hr

+ 70 hrs

+ 36 hrs

Water level drops to Top of Active Fuel (TAF)*

+3 hrs

+ 74 hrs

+ 40 hrs

Core damage*

+ 4 hrs

+ 77 hrs

+ 42 hrs

Fire pumps inject freshwater

+15 hrs


+ 43 hrs

Hydrogen explosion

+ 25 hrs

Service floor

+ 87 hrs

Suppression chamber

+ 68 hrs

Service floor

Fire pumps inject seawater

+ 28 hrs

+ 77 hrs

+ 46 hrs

Off-site electrical supplies restored

+ 11-15 days

Freshwater cooling

+ 14-15 days


*Estimated                                            source: Tony Irwin

- First core damage estimated to have occurred within 4 hours of the earthquake and reactors 1,2 and 3 cores largely melted within the first 3 days

- Hydrogen explosions caused the main damage and release of radioactivity

- Reactors stable within 2 weeks
On the Fukushima site today:
  The four damaged reactors are in a stable cold shutdown state, cooled by water circulated through a treatment plant. Site clean-up, including removal of radioactive rubble, continues. A mid and long-term roadmap for the decommissioning of units 1-4 was issued in December 2011. Phase 1 prepares for the removal of spent fuel from the cooling ponds to commence by 2013. Phase 2 prepares for the removal of fuel debris from the reactor core to commence within 10 years. The final phase completes the decommissioning of the reactors in 30-40 years.
  There are still over 100,000 people evacuated from Fukushima Prefecture. In the areas within the 20km evacuation zone with an annual radiation dose of <20mSv/year, it is expected that people will be allowed to return in March 2012. For higher radiation areas, remediation is required before restrictions are lifted by perhaps 2014.


On nuclear power in Japan today:

  Before the accident, there were 54 reactors operating in Japan supplying 29% of the electricity demand. Since the accident, as reactors have been shut down for routine inspection (every 13 months) they have not been allowed to restart pending a comprehensive assessment of the response of individual reactors to extreme accidents (‘stress tests”). To date, the Japanese safety authorities have not approved the restart of any reactor.

  As of March 2012, there are only 2 reactors operating. Japan trade deficit is at record levels as fuel imports have soared.


On the world situation:
  The severity of the accident and the need to ensure reactor safety in extreme events was recognised worldwide. Germany took the political decision to immediately shutdown 8 old reactors, and all reactors by 2022. Most countries announced plans to continue with nuclear power and assess the safety of their reactors. For example, the UK has confirmed the safety of their existing nuclear power plants and has recently approved design certification for two types of new reactor to be built in the UK.
On lessons learnt:
  Reactor cooling is essential and must be maintained irrespective of external conditions. Modern reactors, for example the Westinghouse AP-1000 have passive cooling systems that require no external supplies and would have survived even this severe accident. The safety of existing reactors is being assessed to ensure they have diverse and physically separated cooling systems and electrical supplies.

Dr Pradip Deb

Senior Lecturer in Medical Radiations at RMIT University
  The Fukushima Daiichi accident has been one of the two major accidents in the international nuclear and radiological event scale (INES) in the last twenty five years (the other one was Chernobyl). The latest IAEA (international atomic energy agency) status report shows that the estimated external doses to the public from the cities within 20 kilometres from Fukushima Daiichi reactors are within the acceptance level for the public (1 mSv). Food monitoring data shows that in more than 99% samples (based on 14344 samples) the radioactive caesium and iodine isotopes (Cs-137 & Cs-134 and I-131) are within the acceptance level.
  It is not practical to say that the world should be free of nuclear power. The next generation power reactors will be safer. The lesson we have learnt again is that it is radiophobia that harms us psychologically more than actual radiation doses do. Not only in the developing countries, but also in the technologically advanced countries, people are likely to believe unscientific reasoning about the effects of radiations. Topics of Radiation physics are currently not included in the school curriculum in most of the countries in the world, not even in Japan. To reduce radiophobia, the radioactivity and their effects should be understood by the general public. One way to make the public more trusting of radiation issues is teaching radiation physics starting from the school level science education.

Professor James Goff

Director of the Australia-Pacific Tsunami Research Centre and Natural Hazards Research Laboratory, University of New South Wales
 Tsunami comment
  A year on from the 2011 Tohoku tsunami and we are still asking questions, more than we have answers to. I have been invited by Tohoku University in Sendai to attend a special ‘One-year Memorial of the 2011 Tohoku Earthquake and Tsunami Disaster’. This will happen on the same day as a ‘Forum for International Research Collaboration’. This will be the fourth visit by people from our centre. First in May to carry out some of the earliest international research on the tsunami – how big it was, what it left behind and so on. We visited again in August to revisit this work and to see how things had changed. Currently a member of our team, Dr Catherine Chague-Goff, is also on a Visiting Professorship to the University of Hokkaido. Why so much commitment? Essentially because we want to help the Japanese to understand the 2011 event, its precursors and other events in the region. However, we are also committed to helping our Japanese colleagues. Our centre has skills that the Japanese are interested in exploring and we are keen to work in collaboration with them to make this happen.
  What have we learnt so far? Well, one of the more interesting finds in that for nearly 50% of its inundation distance inland the tsunami left almost no sand deposit, just mud and debris. Who cares? Well, if you are looking at how big and how often these events have happened in the past – you need to look for more than just the sand or else you might under-estimate things. Hence the interest in our work and what we have done elsewhere. We have also learnt a lot about the longer term after effects of these events. What one might call the ‘what are things like on the ground one year on’. Yes, much of the debris has been being cleared up, yes much of the evidence of destruction has been erased by diggers and work crews, but what seems a minor point is starting to become an issue – there is still a vast amount of salt in the soil and rice doesn’t like salt – and so in these places crops are hard to grow. There are implications here for long term recovery. Add to this things such as the loss of communities, poor roads, contaminated land and the sheer enormity of the devastated area and you can see that there is no simple fix.
  We are returning to Sendai again to start putting the 2011 events in context. We really do need to know how big and how often these events occur because we don’t want to under-estimate the next one, not just in Sendai but for the whole of Japan. We also want to take these lessons with us to the rest of the Pacific so that we can do a better job there as well. Whether we can achieve this quickly or not remains to be seen. We all still have lots to learn.


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