A sharp increase in mortality among elderly people who were put in temporary housings has been reported, along with increased risk of non-communicable diseases, such as diabetes and mental health problems. The lack of access to health care further contributed to deterioration of health. Similar to what was observed and reported for the Chernobyl population, the displaced Fukushima population is suffering from psycho-social and mental health impact following relocation, ruptured social links of people who lost homes and employment, disconnected family ties and stigmatization.
A higher occurrence of post-traumatic stress disorder PTSD among the evacuees was assessed as compared to the general population of Japan. Psychological problems, such as hyperactivity, emotional symptoms, and conduct disorders have been also reported among evacuated Fukushima children6. While no significant adverse outcomes were observed in the pregnancy and birth survey after the disaster, a higher prevalence of postpartum depression was noted among mothers in the affected region. It included an evaluation of the risks of cancers, non-cancer diseases as well as public health considerations.
There were no acute radiation injuries or deaths among the workers or the public due to exposure to radiation resulting from the FDNPS accident. Considering the level of estimated doses, the lifetime radiation-induced cancer risks other than thyroid are small and much smaller than the lifetime baseline cancer risks. Regarding the risk of thyroid cancer in exposed infants and children, the level of risk is uncertain since it is difficult to verify thyroid dose estimates by direct measurements of radiation exposure.
For the twelve workers who were estimated to have received the highest absorbed radiation doses to the thyroid, an increased risk of developing thyroid cancer and other thyroid disorders was estimated. About additional workers who received whole body effective doses estimated to be over mSv, an increased risk of cancer could be expected in the future although it will not be detectable by epidemiological studies because of the difficulty of confirming a small incidence against the normal statistical fluctuations in cancer incidence.
From a global health perspective, the health risks directly related to radiation exposure are low in Japan and extremely low in neighbouring countries and the rest of the world. Given the exposure to radioactive iodine during the early phase of the emergency, WHO specifically assessed the risk of thyroid cancer. The greatest risk was found among girls exposed as infants i. There have been recent reports about thyroid cancer cases being diagnosed among children exposed to low doses of radioactive iodine as a result of the Fukushima accident.
These reports should be interpreted with caution. A large excess of thyroid cancer due to radiation exposure, such as occurred after the Chernobyl accident, can be discounted because the estimated thyroid doses due to the Fukushima accident were substantially lower than in Chernobyl. Nevertheless, the highly-sensitive thyroid screening of those under 18 years old at the time of the accident is expected to detect a large number of thyroid cysts and solid nodules, including a number of thyroid cancers that would not have been detected without such intensive screening.
Similar or even slightly higher rates of cysts and nodules were found in prefectures not affected by the nuclear accident. The substantial number of cases that have already been observed in the Fukushima Health Management Survey have been considered likely due to the sensitivity of the screening rather than to radiation exposure. Further analysis of epidemiological data being currently collected in Japan will be necessary to evaluate a potential attribution of thyroid cancer to radiation exposure. Radioactive iodine and caesium in concentrations above the Japanese regulatory limits were detected in some food commodities as a result of food monitoring in the early period after the accident.
Since the early phase of the emergency, the Japanese authorities have monitored food contamination closely and implemented protective measures to prevent sale and distribution of contaminated food in Japan and outside of Japan. The Fukushima nuclear accident as a part of a triple disaster was unprecedented in its scale and nature. Eleven reactors at four nuclear power plants in the region were operating at the time and all shut down automatically when the quake hit. Subsequent inspection showed no significant damage to any from the earthquake.
The main problem initially centred on Fukushima Daiichi units Unit 4 became a problem on day five. The reactors proved robust seismically, but vulnerable to the tsunami. Power, from grid or backup generators, was available to run the residual heat removal RHR system cooling pumps at eight of the eleven units, and despite some problems they achieved 'cold shutdown' within about four days.
The other three, at Fukushima Daiichi, lost power at 3.
This disabled 12 of 13 back-up generators on site and also the heat exchangers for dumping reactor waste heat and decay heat to the sea. The three units lost the ability to maintain proper reactor cooling and water circulation functions. Electrical switchgear was also disabled. Thereafter, many weeks of focused work centred on restoring heat removal from the reactors and coping with overheated spent fuel ponds. This was undertaken by hundreds of Tepco employees as well as some contractors, supported by firefighting and military personnel.
Some of the Tepco staff had lost homes, and even families, in the tsunami, and were initially living in temporary accommodation under great difficulties and privation, with some personal risk. A hardened emergency response centre on site was unable to be used in grappling with the situation, due to radioactive contamination.
Three Tepco employees at the Daiichi and Daini plants were killed directly by the earthquake and tsunami, but there have been no fatalities from the nuclear accident. Among hundreds of aftershocks, an earthquake with magnitude 7. On 11 April a magnitude 7. The Daiichi first and Daini second Fukushima plants are sited about 11 km apart on the coast, Daini to the south.
The recorded seismic data for both plants — some km from the epicentre — shows that Gal 0. The recording was over seconds. All nuclear plants in Japan are built on rock — ground acceleration was around Gal a few kilometres north, on sediments. The original design basis tsunami height was 3. The Daini plant was built 13 metres above sea level. In the design basis was revised to 5. In the event, tsunami heights coming ashore were about 15 metres, and the Daiichi turbine halls were under some 5 metres of seawater until levels subsided.
Daini was less affected. The maximum amplitude of this tsunami was 23 metres at point of origin, about km from Fukushima. In the last century there have been eight tsunamis in the region with maximum amplitudes at origin above 10 metres some much more , these having arisen from earthquakes of magnitude 7. Those in and in were the most recent affecting Japan, with maximum heights at origin of The June earthquake of estimated magnitude 8.
The tsunami countermeasures taken when Fukushima Daiichi was designed and sited in the s were considered acceptable in relation to the scientific knowledge then, with low recorded run-up heights for that particular coastline. But some 18 years before the disaster, new scientific knowledge had emerged about the likelihood of a large earthquake and resulting major tsunami of some Discussion was ongoing, but action minimal.
The tsunami countermeasures could also have been reviewed in accordance with IAEA guidelines which required taking into account high tsunami levels, but NISA continued to allow the Fukushima plant to operate without sufficient countermeasures such as moving the backup generators up the hill, sealing the lower part of the buildings, and having some back-up for seawater pumps, despite clear warnings. A report from the Japanese government's Earthquake Research Committee on earthquakes and tsunamis off the Pacific coastline of northeastern Japan in February was due for release in April, and might finally have brought about changes.
The document includes analysis of a magnitude 8. The report concludes that the region should be alerted of the risk of a similar disaster striking again. The 11 March earthquake measured magnitude 9. Tsunami waves devastated wide areas of Miyagi, Iwate and Fukushima prefectures.
It appears that no serious damage was done to the reactors by the earthquake, and the operating units were automatically shut down in response to it, as designed. At the same time all six external power supply sources were lost due to earthquake damage, so the emergency diesel generators located in the basements of the turbine buildings started up.
Initially cooling would have been maintained through the main steam circuit bypassing the turbine and going through the condensers. Then 41 minutes later, at pm, the first tsunami wave hit, followed by a second 8 minutes later. These submerged and damaged the seawater pumps for both the main condenser circuits and the auxiliary cooling circuits, notably the Residual Heat Removal RHR cooling system. So there was a station blackout, and the reactors were isolated from their ultimate heat sink.
The tsunamis also damaged and obstructed roads, making outside access difficult. All this put those reactors in a dire situation and led the authorities to order, and subsequently extend, an evacuation while engineers worked to restore power and cooling. Unit 3 had battery power for about 30 hours. He visited the plant soon after. On Saturday 12th he extended the evacuation zone to 20 km. Reactors came into commercial operation When the power failed at 3.
Without heat removal by circulation to an outside heat exchanger, this produced a lot of steam in the reactor pressure vessels housing the cores, and this was released into the dry primary containment PCV through safety valves. Later this was accompanied by hydrogen, produced by the interaction of the fuel's very hot zirconium cladding with steam after the water level dropped.
Seawater injection into unit 1 began at 7pm on Saturday 12th, into unit 3 on 13th and unit 2 on 14th.
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Tepco management ignored an instruction from the prime minister to cease the seawater injection into unit 1, and this instruction was withdrawn shortly afterwards. Inside unit 1 , it is understood that the water level dropped to the top of the fuel about three hours after the scram about 6 pm and the bottom of the fuel 1. After that, RPV temperatures decreased steadily. As pressure rose, attempts were made to vent the containment, and when external power and compressed air sources were harnessed this was successful, by about 2.
The venting was designed to be through an external stack, but in the absence of power much of it apparently backflowed to the service floor at the top of the reactor building, representing a serious failure of this system though another possibility is leakage from the drywell. The vented steam, noble gases and aerosols were accompanied by hydrogen. Oxidation of the zirconium cladding at high temperatures in the presence of steam produces hydrogen exothermically, with this exacerbating the fuel decay heat problem. In unit 1 most of the core — as corium comprised of melted fuel and control rods — was assumed to be in the bottom of the RPV, but later it appeared that it had mostly gone through the bottom of the RPV and eroded about 65 cm into the drywell concrete below which is 2.
This reduced the intensity of the heat and enabled the mass to solidify. In mid-May the unit 1 core would still be producing 1. In unit 2 , water injection using the steam-driven back-up water injection system failed on Monday 14th, and it was about six hours before a fire pump started injecting seawater into the RPV. Before the fire pump could be used RPV pressure had to be relieved via the wetwell, which required power and nitrogen, hence the delay. Meanwhile the reactor water level dropped rapidly after back-up cooling was lost, so that core damage started about 8 pm, and it is now provisionally understood that much of the fuel then melted and probably fell into the water at the bottom of the RPV about hours after the scram.
Pressure was vented on 13th and again on 15th, and meanwhile the blowout panel near the top of the building was opened to avoid a repetition of unit 1 hydrogen explosion. Early on Tuesday 15th, the pressure suppression chamber under the actual reactor seemed to rupture, possibly due to a hydrogen explosion there, and the drywell containment pressure inside dropped.
However, subsequent inspection of the suppression chamber did not support the rupture interpretation. Later analysis suggested that a leak of the primary containment developed on Tuesday 15th. Most of the radioactive releases from the site appeared to come from unit 2. In Unit 3 , the main back-up water injection system failed at about 11 am on Saturday 12 th and early on Sunday 13 th , water injection using the high pressure system failed also and water levels dropped dramatically.
RPV pressure was reduced by venting steam into the wetwell, allowing injection of seawater using a fire pump from just before noon. Early on Sunday venting the suppression chamber and containment was successfully undertaken. It is now understood that core damage started about am and much or all of the fuel melted on the morning of Sunday 13 th and fell into the bottom of the RPV, with some probably going through the bottom of the reactor pressure vessel and onto the concrete below. Early on Monday 14 th PCV venting was repeated, and this evidently backflowed to the service floor of the building, so that at 11 am a very large hydrogen explosion here above unit 3 reactor containment blew off much of the roof and walls and demolished the top part of the building.
This explosion created a lot of debris, and some of that on the ground near unit 3 was very radioactive. In defuelled unit 4 , at about 6 am on Tuesday 15 March, there was an explosion which destroyed the top of the building and damaged unit 3's superstructure further. This was apparently from hydrogen arising in unit 3 and reaching unit 4 by backflow in shared ducts when vented from unit 3.
Units Water has been injected into each of the three reactor units more or less continuously, and in the absence of normal heat removal via external heat exchanger this water was boiling off for some months. In June this was adding to the contaminated water on site by about m 3 per day. In January 4. There was a peak of radioactive release on 15th, apparently mostly from unit 2, but the precise source remains uncertain. Due to volatile and easily-airborne fission products being carried with the hydrogen and steam, the venting and hydrogen explosions discharged a lot of radioactive material into the atmosphere, notably iodine and caesium.
NISA said in June that it estimated that kg of hydrogen had been produced in each of the units. Nitrogen is being injected into the containment vessels PCVs of all three reactors to remove concerns about further hydrogen explosions, and in December this was started also for the pressure vessels. Gas control systems which extract and clean the gas from the PCV to avoid leakage of caesium have been commissioned for all three units.
RPV pressures ranged from atmospheric to slightly above kPa in January, due to water and nitrogen injection. However, since they are leaking, the normal definition of "cold shutdown" does not apply, and Tepco waited to bring radioactive releases under control before declaring "cold shutdown condition" in mid-December, with NISA's approval.
This, with the prime minister's announcement of it, formally brought to a close the 'accident' phase of events. The AC electricity supply from external source was connected to all units by 22 March. Power was restored to instrumentation in all units except unit 3 by 25 March. However, radiation levels inside the plant were so high that normal access was impossible until June. Results of muon measurements in unit 2 in indicate that most of the fuel debris in unit 2 is in the bottom of the reactor vessel.
Summary : Major fuel melting occurred early on in all three units, though the fuel remains essentially contained except for some volatile fission products vented early on, or released from unit 2 in mid-March, and some soluble ones which were leaking with the water, especially from unit 2, where the containment is evidently breached. Cooling is provided from external sources, using treated recycled water, with a stable heat removal path from the actual reactors to external heat sinks. Temperatures at the bottom of the reactor pressure vessels have decreased to well below boiling point and are stable.
Access has been gained to all three reactor buildings, but dose rates remain high inside. Nitrogen is being injected into all three containment vessels and pressure vessels. Tepco declared "cold shutdown condition" in mid-December when radioactive releases had reduced to minimal levels. See also background on nuclear reactors at Fukushima Daiichi. Used fuel needs to be cooled and shielded. This is initially by water, in ponds.
After about three years under water, used fuel can be transferred to dry storage, with air ventilation simply by convection. Used fuel generates heat, so the water is circulated by electric pumps through external heat exchangers, so that the heat is dumped and a low temperature maintained. There are fuel ponds near the top of all six reactor buildings at the Daiichi plant, adjacent to the top of each reactor so that the fuel can be unloaded under water when the top is off the reactor pressure vessel and it is flooded.
There is some dry storage on site to extend the plant's capacity. At the time of the accident, in addition to a large number of used fuel assemblies, unit 4's pond also held a full core load of fuel assemblies while the reactor was undergoing maintenance, these having been removed at the end of November, and were to be repplaced in the core.
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A separate set of problems arose as the fuel ponds, holding fresh and used fuel in the upper part of the reactor structures, were found to be depleted in water. The primary cause of the low water levels was loss of cooling circulation to external heat exchangers, leading to elevated temperatures and probably boiling, especially in heavily-loaded unit 4.
Here the fuel would have been uncovered in about 7 days due to water boiling off. However, the fact that unit 4 was unloaded meant that there was a large inventory of water at the top of the structure, and enough of this replenished the fuel pond to prevent the fuel becoming uncovered — the minimum level reached was about 1.
After the hydrogen explosion in unit 4 early on Tuesday 15 March, Tepco was told to implement injection of water to unit 4 pond which had a particularly high heat load 3 MW from used fuel assemblies in it, so it was the main focus of concern. From Tuesday 15 March attention was given to replenishing the water in the ponds of units 1, 2, 3 as well. Initially this was attempted with fire pumps but from 22 March a concrete pump with metre boom enabled more precise targeting of water through the damaged walls of the service floors. There was some use of built-in plumbing for unit 2.
Analysis of radionuclides in water from the used fuel ponds suggested that some of the fuel assemblies might be damaged, but the majority were intact. There was concern about structural strength of unit 4 building, so support for the pond was reinforced by the end of July. Each has a primary circuit within the reactor and waste treatment buildings and a secondary circuit dumping heat through a small dry cooling tower outside the building.
The next task was to remove the salt from those ponds which had seawater added, to reduce the potential for corrosion.
In July two of the fresh fuel assemblies were removed from the unit 4 pool and transferred to the central spent fuel pool for detailed inspection to check damage, particularly corrosion. They were found to have no deformation or corrosion. Unloading the spent fuel assemblies in pond 4 and transferring them to the central spent fuel storage commenced in mid-November and was completed 13 months later.
These comprised spent fuel plus the full fuel load of The next focus of attention was the unit 3 pool. In the damaged fuel handling equipment and other wreckage was removed from the destroyed upper level of the reactor building. Toshiba has built a tonne fuel handling machine for transferring the fuel assemblies into casks and to remove debris in the pool, and a crane for lifting the fuel transfer casks. Installation of a cover over the fuel handling machine was completed in February The dry storage area held fuel assemblies at the time of the accident, and have been transferred there since to mid In June , Tepco announced it would transfer some of the fuel assemblies stored in the communal fuel storage pool to an onsite temporary dry storage facility.
The company aims to clear sufficient space for the fuel assemblies held in unit 3's pool. Summary: The spent fuel storage pools survived the earthquake, tsunami and hydrogen explosions without significant damage to the fuel or significant radiological release, or threat to public safety. The new cooling circuits with external heat exchangers for the four ponds are working well. Temperatures are normal.
Analysis of water has confirmed that most fuel rods are intact. All fuel assemblies have been removed from unit 4 pool. Those at unit 3 will be removed next. Regarding releases to air and also water leakage from Fukushima Daiichi, the main radionuclide from among the many kinds of fission products in the fuel was volatile iodine, which has a half-life of 8 days. The other main radionuclide is caesium, which has a year half-life, is easily carried in a plume, and when it lands it may contaminate land for some time.
It is a strong gamma-emitter in its decay. Cs is also produced and dispersed, it has a two-year half-life. Caesium is soluble and can be taken into the body, but does not concentrate in any particular organs, and has a biological half-life of about 70 days. In assessing the significance of atmospheric releases, the Cs figure is multiplied by 40 and added to the I number to give an "iodine equivalent" figure.
As cooling failed on the first day, evacuations were progressively ordered, due to uncertainty about what was happening inside the reactors and the possible effects. By the evening of Saturday 12 March the evacuation zone had been extended to 20 km from the plant. See later section on Public health and return of evacuees. A significant problem in tracking radioactive release was that 23 out of the 24 radiation monitoring stations on the plant site were disabled by the tsunami.
There is some uncertainty about the amount and exact sources of radioactive releases to air. See also background on Radiation Exposure. Most of the release was by the end of March Tepco sprayed a dust-suppressing polymer resin around the plant to ensure that fallout from mid-March was not mobilized by wind or rain. In addition it removed a lot of rubble with remote control front-end loaders, and this further reduced ambient radiation levels, halving them near unit 1.
In mid-May work started towards constructing a cover over unit 1 to reduce airborne radioactive releases from the site, to keep out the rain, and to enable measurement of radioactive releases within the structure through its ventilation system. The frame was assembled over the reactor, enclosing an area 42 x 47 m, and 54 m high. The sections of the steel frame fitted together remotely without the use of screws and bolts. All the wall panels had a flameproof coating, and the structure had a filtered ventilation system capable of handling 40, cubic metres of air per hour through six lines, including two backup lines.
The cover structure was fitted with internal monitoring cameras, radiation and hydrogen detectors, thermometers and a pipe for water injection. The cover was completed with ventilation systems working by the end of October It was expected to be needed for two years. In May Tepco announced its more permanent replacement, to be built over four years.
It started demolishing the cover in and finished in A crane and other equipment for fuel removal would then be installed in a new cover over the building, similar to that over unit 4. A cantilevered structure was built over unit 4 from April to July to enable recovery of the contents of the spent fuel pond.
Each tank takes seven to 10 days to fill and holds between 1, to 1, tons of liquid, Tepco officials told reporters during a tour in February organized by the Japan National Press Club. The water issue is eating up both space and resources, but a solution is unlikely to emerge anytime soon. Nearly 1, water tanks are scattered across the grounds of the Fukushima No. Some are over 10 meters tall, hold 1, to 1, tons and take seven to 10 days to fill.
Beyond , Tepco has not allocated any additional space for holding treated water on the site and has no plans to do so at this time. The utility said the tanks will likely become a headache if they remain at the plant. Eight years ago when the monstrous tsunami hit, the entire plant lost power and reactors 1, 2 and 3 lost coolant, causing their cores to overheat. The fuel rods consequently melted, dripping molten fuel that burned through their pressure vessels and pooled in their primary containment vessels.
Reactors 1, 3 and 4 then suffered hydrogen explosions. Reporters look up at the pressure vessel from inside the primary containment vessel of a reactor at the Fukushima No. At the sister plant of Fukushima No. Tepco must inject water into the reactors indefinitely to keep the melted cores cool, but water tainted by contact with the fuel and associated debris has been leaking from the damaged containment vessels and into the basements of the reactor buildings, where tons of fresh groundwater flows in daily through holes in their damaged walls. The contaminated water is pumped out and passed through a filtration device called the Advanced Liquid Processing System — which is supposed to remove every radionuclide except for tritium — and stored in the tanks.
Tepco has taken steps to limit the amount of groundwater seeping into the reactor buildings, including wells to intercept and divert it and an underground ice wall around the buildings to block any inflow. According to Tepco, however, about 83 tons of water are seeping into the reactor buildings each day. Although this is an improvement from some tons in previous years, Tepco must keep making more tanks.
The panel is considering five disposal methods: ground injection, sea discharge after diluting the tritium concentration, discharging it as steam, discharging it as hydrogen, and solidification followed by underground burial.