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Highlight of development at Fukushima after the nuclear accident

  • A Review after the Nuclear Accident Seven Years Ago

by Ir Richard Fung




On 11 March 2011, the Great East Japan Earthquake occurred 130 km offshore to the north east coast of Honshu in Japan.  The earthquake was rated at Magnitude 9.0 on the Richter Scale, that was accompanied with a 8-14 m high tsunami which flooded the region [1], claiming over 15,800 lives with another 2,500 missing [2].


Of the 14 nuclear power generating units all located at 4 coastal sites in the region, 11 were operating and were safely shut down after the earthquake and the remaining 3 were already in planned shutdown.  However, of the 6 Boiling Water Reactor type nuclear units at the Fukushima Daiichi Nuclear Power Plant having 4696 MW of gross total installed capacity and commissioned during 1971-79, Units 1 to 4 sustained serious damage, triggering a significant release of radioactivity and forcing the mass evacuation of 154,000 people [3].  The nuclear accident was classified at Level 7, the highest on the International Nuclear Safety and Radiological Event Scale [1, 4].


The situation has been much stabilized after seven years.  However, recovery at the plant site and the nearby community is still in progress, and is expected to last decades.


Status at the site


The reactor units


Units 1 to 4 of Fukushima Daiichi were seriously damaged in the accident.  They initially sustained the loss of external power connections in the earthquake, and then an hour later the loss of internal power sources due to tsunami flooding because of low site elevation above the sea [5].  Insufficient robustness in plant safety systems together with the complete loss of electrical power led to loss of reactor cooling at the first three units.  Residual reactor heat led to over-temperature producing steam which reacted chemically with fuel clad to produce hydrogen and later fuel melt.  In the next few days, fuel melt and hydrogen explosions, that sometimes accompanied by deliberate if inadequate venting, damaged primary containments and reactor buildings and resulted in the release of radioactivity into the environment.  Unit 4 reactor was not loaded with fuel during the accident, and subsequent investigation showed that its hydrogen explosion was caused by the hydrogen coming to the unit from the adjacent Unit 3 through a common ventilation duct [5].


To remove residual reactor heat after shutdown, initially seawater was injected using mobile equipment brought in from the outside.  External power supply was restored after about 2 weeks so that plant cooling systems could function again to inject fresh water into the reactors [6].  Nitrogen was injected into the reactor pressure vessels to suppress hydrogen explosion risks.  Excess cooling water that had been contaminated was transferred to storage tanks that were continuously added at the site, and after several months the commissioning of a new treatment plant for water used in reactor vessel cooling brought radioactive leakage under control.  With the cooling water brought below boiling at the damaged reactors, “cold shutdown” was declared at the plant in December 2011 following regulatory approval and Fukushima Daiichi completed its accident phase [7].


Temporary covers were installed over the damaged external structures of Units 1 to 4 to provide shelter against the elements, limit potential radioactive release and facilitate remedial work.  Inspections often employing robots have been underway since 2015 to identify the extent of damage at the reactor units so as to formulate a decommissioning plan [8, 9].  Meanwhile, decontamination and debris clearance were completed in 2016 at the general site outside the plant [9].


Units 5 and 6 were under planned maintenance during the accident.  They were kept cooled by an air-cooled diesel generator that was unaffected during the tsunami, and were declared to be at “cold shutdown” one week into the event.


Only minor damages were experienced at the other three sites.  Indeed, the nuclear site in Onagawa to the north was even safe enough to serve as an emergency shelter for the local population in the first few weeks after the earthquake [10].


Spent nuclear fuel


Spent nuclear fuel at Fukushima was stored under water at the reactor buildings of the 6 units and at the common site storage [5].  Its cooling at the reactor buildings was interrupted during the accident and, despite a rise in temperature and a fall in water level at the storage pools, restoration of spent fuel cooling was accomplished after several days, initially by external water injection with mobile equipment and then by plant systems, to be followed by newly commissioned cooling systems.  Despite having fallen debris into some storage pools, no significant damage was sustained by the spent nuclear fuel.


Because of possible structural damage caused by the earthquake, work was conducted soon after the accident to reinforce Unit 4 spent nuclear fuel storage pool which had also received the nuclear fuel unloaded from the reactor during its refueling outage.  Spent fuel at Unit 4 was transferred to the common site storage in 2014 [8] and that at Units 1-3 will be removed in 2018-24 [11].  Older spent fuel will be loaded in temporary dry storage modules.


Contaminated water discharge


With damage at the reactors of Units 1 to 3 and at the plant buildings that contain the reactor cooling system, reactor cooling water containing radioactivity has been escaping through damaged underground site conduits into the site harbour and to the open sea.  The need for continuous nuclear cooling required a continuous supply of water that in turn led to a continuous escape.  The quantity of the flow into the sea was increased by the high water table of adjacent hills which brings groundwater into the damaged plant buildings hence adding to the escaping reactor cooling water leaking to the sea.  After the accident, wells were drilled on the hillside of the site to extract inflowing groundwater to bypass the site or to be treated for discharge into the sea.  A 0.8km long impermeable wall was installed on the harbourside in 2015 and a 1.5km long underground wall using frozen earth technique was installed around the site in 2017 to isolate the environment from radioactive water at the site.  Groundwater flow into the site has since much reduced and radioactivity in the sea water outside the site harbour is within regulatory limits [7].


Current plan


It is planned to decommission the four damaged units in the next 30-40 years, to remove and dispose in particular the highly radioactive nuclear fuel and fuel debris, and to remove both the radioactive and non-radioactive structures of the plant buildings [11].  Before that, Units 5 and 6 will be used to practise decommissioning techniques and demonstrate their feasibility.





Staff radiation dosage


Six workers have each received radiation dose above 250 mSv, the limit set at the height of the accident, with the maximum recorded dose at 678.8 mSv, and the number of workers each received more than 100 mSv (the general limit for an emergency) has been kept at 174 since 2012 [12].  In all cases, no radiation-induced casualties were observed [13] though long term effects will need monitoring.  However, two workers were drowned at Fukushima Daiichi during the tsunami and another one was killed at Fukushima Danni to the south [14].

Over 46,000 workers had been employed in radiation-related work at Fukushima up to January 2016 [15] and the number of workers engaged has gradually reduced from 11,500 in April 2015 [11] to 8,500 in November 2017 [16].  Their individual dosage is being kept at within 100 mSv.


Environmental impact


It has been estimated that 408-770 PBq of Iodine-131 equivalent of radioactivity was released into the air, equivalent to 10-18% of the release in Chernobyl [4, 17].  Prevailing wind initially took the released radioactivity east to the sea but with a change in wind direction, radioactive material was blown inland 4 days into the accident.  An area up to 60km to the north west of the nuclear power station was observed to have radioactivity at about 30 times above local ambient, albeit the effect is within the regulatory public health limit of 1 mSv/year [6, 18, 19].


Radioactivity in the affected land areas reduced by half for every 2 years after the initial release, possibly reflecting the decay of the released radioactive constituents, uptake and runoff [20].  The trend will continue though the quantity reduced will be at a slower rate.


Radioactivity in the sea nearby dropped in the first year after the construction of a temporary sea wall in the site harbour but has been generally maintained at a steady level, possibly due to leaching, soil drainage, and radioactive leaks from the plant that has only recently been controlled.  The levels found at 2km near shore one year after [20] and at the harbour three years later [21], are already within the limits recommended by the World Health Organisation for drinking water [22].





Public protection


Shortly after the release of radioactivity from the nuclear power plant, the Japanese authority took emergency measures to protect the public, by providing shelters and mass evacuation mainly to limit external exposure, administering iodine tablets early in the accident to the public to mitigate the effect of inhaled radioactive iodine, and identifying and isolating contaminated foodstuff to limit internal exposure.


Sheltering and evacuation


In view of the increasing severity of the accident in the first few days, the authority implemented an evacuation zone in steps up to 20 km from the site, displacing some 76,000 people, and recommended voluntary evacuation up to 30km in late March 2011.  The criterion was revised in late April to mark a zone to avoid an annual dose of 20 mSv (and a zone up to 30km from the site was identified for potential evacuation but was later dropped), further displacing 69,000 people beyond 20km and up to 50km to the northwest of the site [23].  In total, 154,000 people were evacuated [3].  The process was accompanied by conflicting messages and inconsistent information disseminated by the authority during such mass evacuation and has incurred considerable loss of public trust and confidence [24, 25].


In the next two years, the evacuation zones were gradually classified into one that evacuation orders could soon be lifted, one that people would not be permitted to dwell, and one that it would be difficult to return for a long time.  Annual radiation dose limits of 20 mSv and 50 mSv were used to demarcate these zones.  Decontamination and reconstruction infrastructure restoration would meanwhile proceed [23].


In early 2014, after confirmation that annual radiation dose had fallen below 20 mSv, sufficient restoration had been made and communication channels had been found between the authorities and the local public, evacuation was progressively if slowly being relaxed that began with certain outlying municipalities [23].  Areas that were still restricted in 2017 extend about 30km to the north west of the site and affected 24,000 people [26].  However, of the regions that people are permitted to return, only about 16% of the people have returned by early 2017 [26] and a 2014 survey of the 80,000 people considered as “evacuees” 22% were willing to return, 42% would not and 36% were undecided [18, 19].  The low return rate is considered partly as an outcome of ineffective public communication compounded with an inadequate public understanding of stipulated criteria, that the dose of 20 mSv per year is the criterion to return while 1 mSv per year is the long term goal, with the latter being mistaken by the population as the objective for complete contamination or else livelihood is not viable [18].

Food control


Radioactivity in foodstuff is monitored to ensure safety for consumption.  Restriction will be imposed on foodstuff at a district found exceeded the limits and will be lifted if continuous monitoring has showed that the limits are met [8].  In 2017, 234,740 samples were examined nationwide with 0.06% exceeding their limits but with 0.2% from the Fukushima Prefecture [27].  Game was found in 2017 to have the highest reject rate at 14% nationwide and 21% at Fukushima [27].  In contrast, the reject rate of marine fish was at 57% immediately after the accident but has reduced to zero since 2015 [28].


The currently acceptable levels of long life radionuclides in Japan, mainly cesium, are 10 Bq/kg for drinking water, 50 Bq/kg for infant foods or milk products, and 100 Bq/kg for general food [29].  The previous levels before April 2012 were 200 Bq/kg for drinking water and milk, and 500 Bq/kg for general food [25].  In comparison, the corresponding EU limits are 1,000 Bq/kg for drinking water, 400 Bq/kg for infant foods, 1,000 Bq/kg for milk products, and 1,250 Bq/kg for general food [30].  Similar limit to the EU for general food is found in the US and in the CODEX STAN of the UN Food and Agricultural Organisation [31].  Bearing in mind that all people are unavoidably exposed to a small dose of natural radiation all the time [32], the very strict food standards on radiation of Japan serves to reduce the radiation dose of the people only by a very small margin but it constitutes a significant economic impact to those people in food production [24].


Public health


Given that the radiation dose expected of the affected population would be no higher than 12-25 mSv in the first year, the World Health Organisation estimated that, even for the most vulnerable groups in the most exposed locations, an additional lifetime risk leading to cancer is within 1% [33].


Since 2011, Japan has been committing to a 30 year surveillance programme for the exposed public.  It was estimated that 15 people received a dose above 15 mSv, with the highest at 25 mSv, among the 460,000 people at Fukushima who were not employed by the plant.  Thyroid cancer screening of children (age under 18) was also conducted.  The first screening in 2011-2014 gave an annual cancer incidence of 11 out of 100,000 for Fukushima compared to 23-130 out of 100,000 in unaffected prefectures.  The second screening in 2014-2016 gave an incidence of 4-14 out of 100,000 [34].  Both showed marginally lower incidences in Fukushima as compared with other unaffected prefectures.


General health observation is being conducted on the evacuees.  Overall improvement in their physical health is found since the accident and is attributed to the gradual improvement in their living conditions.  On assessing psychological consequences, of the 4,400 people given telephone support, the problems for children were mainly excessive emotion, irritability, peer relation problems and rebellious behaviour, while depression was the main problem with adults [34].


Stress and the initial loss of health care of the evacuees have a notable negative effect particularly on the elderly or bedridden [24, 25].  By early 2014, deaths from stress and related illnesses among the evacuees from Fukushima much exceeded that of the adjacent preferences and reached 1656, surpassing its 1,607 direct deaths due to earthquake and tsunami [35].


Investigations and reform


Several national and international investigations were conducted to study the sequence and impact of the accident as well as its underlying cause to develop improvement measures [4, 5, 25, 36, 37].


In particular, the report to the Japan Diet in 2012 investigated the underlying causes and considered that the disaster was caused by the established but defective management culture and ineffective decision process of the plant owner and the government, as well as the submissive national culture [37].  It concluded that Fukushima was a “manmade disaster” that was a coincident result of “collusion between the government, the regulators and Tokyo Electric Power Company” and the “root causes were the organizational and regulatory systems that supported faulty rationales for decisions and actions.”  The regulator was criticized for not sufficiently maintaining independence from the industry in developing and enforcing safety regulations or suffering “regulatory capture”, the government for inadequate emergency preparedness and management, and the plant owner for its poor governance and lack of safety culture.  The fundamental causes of the accident that was “Made in Japan” were reportedly found in “the ingrained conventions of Japanese culture: our reflexive obedience; our reluctance to question authority; our devotion to 'sticking with the program'; our groupism; and our insularity.” The national mindset prevented the country from “absorbing the critical lessons learned from Three Mile Island and Chernobyl.”  "The consequences of negligence at Fukushima stand out as catastrophic, but the mindset that supported it can be found across Japan.  In recognizing that fact, each of us should reflect on our responsibility as individuals in a democratic society." [37]

The report demanded fundamental changes across the Japanese nuclear industry, the government and the regulators, to increase openness, trustworthiness and focus on protecting public health and safety.  A new regulator was formed later in 2012, to be reportable to the Ministry of Environment and no longer to the Ministry of Economic, Trade and Industry [38].  All nuclear power stations are required to be reviewed under new safety regulations before they are allowed again to operate.  In late March 2018, 7 nuclear power units have resumed (or scheduled to resume) operation and another 17 are seeking approval for restart, out of a total of 42 that remain operable today [39].  There were 54 operable units before the accident.


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