What type of reactor is melting down in japan

Considerable work was done to reduce the amount of radioactive debris onsite and to stabilize dust. The main source of radioactive releases was the apparent hydrogen explosion in the suppression chamber of unit 2 on 15 March.

A cover building for unit 1 reactor was built and the unit is now being dismantled, a more substantial one for unit 4 was built to enable fuel removal during By the end of , Tepco had checked the radiation exposure of 19, people who had worked on the site since 11 March. For many of these both external dose and internal doses measured with whole-body counters were considered. It reported that workers had received doses over mSv.

Of these had received to mSv, twenty-three mSv, three more mSv, and six had received over mSv to mSv apparently due to inhaling iodine fumes early on. There were up to workers onsite each day. Recovery workers wear personal monitors, with breathing apparatus and protective clothing which protect against alpha and beta radiation.

The level of mSv was the allowable maximum short-term dose for Fukushima Daiichi accident clean-up workers through to December , mSv is the international allowable short-term dose "for emergency workers taking life-saving actions". No radiation casualties acute radiation syndrome occurred, and few other injuries, though higher than normal doses, were being accumulated by several hundred workers onsite.

High radiation levels in the three reactor buildings hindered access there. Monitoring of seawater, soil and atmosphere is at 25 locations on the plant site, 12 locations on the boundary, and others further afield.

Government and IAEA monitoring of air and seawater is ongoing. Some high but not health-threatening levels of iodine were found in March, but with an eight-day half-life, most I had gone by the end of April A radiation survey map of the site made in March revealed substantial progress: the highest dose rate anywhere on the site was 0.

The majority of the power plant area was at less than 0. These reduced levels are reflected in worker doses: during January , the workers at the site received an average of 0. Media reports have referred to 'nuclear gypsies' — casual workers employed by subcontractors on a short-term basis, and allegedly prone to receiving higher and unsupervised radiation doses.

This transient workforce has been part of the nuclear scene for at least four decades, and at Fukushima their doses are very rigorously monitored. If they reach certain levels, e. Tepco figures submitted to the NRA for the period to end January showed workers had received more than mSv six more than two years earlier and had received 50 to mSv.

Early in there were about onsite each weekday. Summary : Six workers received radiation doses apparently over the mSv level set by NISA, but at levels below those which would cause radiation sickness. On 4 April , radiation levels of 0. Monitoring beyond the 20 km evacuation radius to 13 April showed one location — around Iitate — with up to 0. At the end of July the highest level measured within 30km radius was 0. The safety limit set by the central government in mid-April for public recreation areas was 3.

In June , analysis from Japan's Nuclear Regulation Authority NRA showed that the most contaminated areas in the Fukushima evacuation zone had reduced in size by three-quarters over the previous two years. In August The Act on Special Measures Concerning the Handling of Radioactive Pollution was enacted and it took full effect from January as the main legal instrument to deal with all remediation activities in the affected areas, as well as the management of materials removed as a result of those activities.

It specified two categories of land: Special Decontamination Areas consisting of the 'restricted areas' located within a 20 km radius from the Fukushima Daiichi plant, and 'deliberate evacuation areas' where the annual cumulative dose for individuals was anticipated to exceed 20 mSv. The national government promotes decontamination in these areas. Intensive Contamination Survey Areas including the so-called Decontamination Implementation Areas, where an additional annual cumulative dose between 1 mSv and 20 mSv was estimated for individuals.

Municipalities implement decontamination activities in these areas. The doses to the general public, both those incurred during the first year and estimated for their lifetimes, are generally low or very low. No discernible increased incidence of radiation-related health effects are expected among exposed members of the public or their descendants.

However, the report noted: "More than additional workers received effective doses currently estimated to be over mSv, predominantly from external exposures. Among this group, an increased risk of cancer would be expected in the future. However, any increased incidence of cancer in this group is expected to be indiscernible because of the difficulty of confirming such a small incidence against the normal statistical fluctuations in cancer incidence.

These workers are individually monitored annually for potential late radiation-related health effects. By contrast, the public was exposed to times less radiation. Most Japanese people were exposed to additional radiation amounting to less than the typical natural background level of 2. The Report states: "No adverse health effects among Fukushima residents have been documented that are directly attributable to radiation exposure from the Fukushima Daiichi nuclear plant accident.

People living in Fukushima prefecture are expected to be exposed to around 10 mSv over their entire lifetimes, while for those living further away the dose would be 0. The UNSCEAR conclusion reinforces the findings of several international reports to date, including one from the World Health Organization WHO that considered the health risk to the most exposed people possible: a postulated girl under one year of age living in Iitate or Namie that did not evacuate and continued life as normal for four months after the accident.

Such a child's theoretical risk of developing any cancer would be increased only marginally, according to the WHO's analysis. The man had been diagnosed with lung cancer in February Eleven municipalities in the former restricted zone or planned evacuation area, within 20 km of the plant or where annual cumulative radiation dose is greater than 20 mSv, are designated 'special decontamination areas', where decontamination work is being implemented by the government.

A further municipalities in eight prefectures, where dose rates are equivalent to over 1 mSv per year are classed as 'intensive decontamination survey areas', where decontamination is being implemented by each municipality with funding and technical support from the national government. Decontamination of all 11 special decontamination areas has been completed. In October a member IAEA mission reported on remediation and decontamination in the special decontamination areas.

Its preliminary report said that decontamination efforts were commendable but driven by unrealistic targets. Also, there is potential to produce more food safely in contaminated areas. The total area under consideration for attention is 13, km 2. Summary : There have been no harmful effects from radiation on local people, nor any doses approaching harmful levels.

However, some , people were evacuated from their homes and only from were allowed limited return. As of July over 41, remained displaced due to government concern about radiological effects from the accident. Permanent return remains a high priority, and the evacuation zone is being decontaminated where required and possible, so that evacuees can return. There are many cases of evacuation stress including transfer trauma among evacuees, and once the situation had stabilized at the plant these outweighed the radiological hazards of returning, with deaths reported see below.

The government said it would consider purchasing land and houses from residents of these areas if the evacuees wish to sell them. In November the NRA decided to change the way radiation exposure was estimated. Instead of airborne surveys being the basis, personal dosimeters would be used, giving very much more accurate figures, often much less than airborne estimates.

Measurement was by personal dosimeters over August-September Disaster-related deaths are in addition to the over 19, that died in the actual earthquake and tsunami. The premature disaster-related deaths were mainly related to i physical and mental illness brought about by having to reside in shelters and the trauma of being forced to move from care settings and homes; and ii delays in obtaining needed medical support because of the enormous destruction caused by the earthquake and tsunami.

However, the radiation levels in most of the evacuated areas were not greater than the natural radiation levels in high background areas elsewhere in the world where no adverse health effect is evident. The figure is greater than for Iwate and Miyagi prefectures, with and respectively, though they had much higher loss of life in the earthquake and tsunami — over 14, Causes of indirect deaths include physical and mental stress stemming from long stays at shelters, a lack of initial care as a result of hospitals being disabled by the disaster, and suicides.

As of July , over 41, people from Fukushima were still living as evacuees. The money was tax-exempt and paid unconditionally. In October , about 84, evacuees received the payments. The Fukushima prefecture had 17, government-financed temporary housing units for some 29, evacuees from the accident. The number compared with very few built in Miyagi, Iwate and Aomori prefectures for the , tsunami survivor refugees there.

In April , the first residents of Okuma, the closest town to the plant, were allowed to return home. According to a survey released by the prefectural government in April , the majority of people who voluntarily evacuated their homes after the accident and who are now living outside of Fukushima prefecture do not intend to return. A Mainichi report said that Of the voluntary evacuees still living in Fukushima prefecture, An August Reconstruction Agency report also considered workers at Fukushima power plant.

The death toll directly due to the nuclear accident or radiation exposure remained zero, but stress and disruption due to the continuing evacuation remains high. Summary : Many evacuated people remain unable to fully return home due to government-mandated restrictions based on conservative radiation exposure criteria.

Decontamination work is proceeding while radiation levels decline naturally. Removing contaminated water from the reactor and turbine buildings had become the main challenge by week 3, along with contaminated water in trenches carrying cabling and pipework. This was both from the tsunami inundation and leakage from reactors. Run-off from the site into the sea was also carrying radionuclides well in excess of allowable levels.

By the end of March all storages around the four units — basically the main condenser units and condensate tanks — were largely full of contaminated water pumped from the buildings. Some storage tanks were set up progressively, including initially steel tanks with rubber seams, each holding m 3.

A few of these developed leaks in Accordingly, with government approval, Tepco over April released to the sea about 10, cubic metres of slightly contaminated water 0. Unit 2 is the main source of contaminated water, though some of it comes from drainage pits.

NISA confirmed that there was no significant change in radioactivity levels in the sea as a result of the 0. By the end of June , Tepco had installed concrete panels to seal the water intakes of units , preventing contaminated water leaking to the harbour.

From October, a steel water shield wall was built on the sea frontage of units It extends about one kilometre, and down to an impermeable layer beneath two permeable strata which potentially leak contaminated groundwater to the sea.

The inner harbour area which has some contamination is about 30 ha in area. In July-August only 0. Tepco built a new wastewater treatment facility to treat contaminated water. A supplementary and simpler SARRY simplified active water retrieve and recovery system plant to remove caesium using Japanese technology and made by Toshiba and The Shaw Group was installed and commissioned in August The NRA approved the extra capacity in August ALPS is a chemical system which will remove radionuclides to below legal limits for release.

However, because tritium is contained in water molecules, ALPS cannot remove it, which gives rise to questions about the discharge of treated water to the sea. Collected water from them, with high radioactivity levels, was being treated for caesium removal and re-used.

Apart from this recirculating loop, the cumulative treated volume was then 1. Almost m 3 of sludge from the water treatment was stored in shielded containers. ALPS-treated water is currently stored in tanks onsite which will reach full capacity by the summer of As of February , more than 1. Some of the ALPS treated water will require secondary processing to further reduce concentrations of radionuclides in line with government requirements.

Disposal will be either into the atmosphere or the sea. In November the trade and industry ministry stated that annual radiation levels from the release of the tritium-tainted water are estimated at between 0. The clean tritiated water was the focus of attention in A September report from the Atomic Energy Society of Japan recommended diluting the ALPS-treated water with seawater and releasing it to the sea at the legal discharge concentration of 0.

The WHO drinking water guideline is 0. The government had an expert task force considering the options. In April the Japanese government confirmed that the water would be released into the sea in This is fed through a catalytic exchange column with a little water which preferentially takes up the tritium. It can be incorporated into concrete and disposed as low-level waste. The tritium is concentrated to 20, times.

The MDS is the first system to be able economically to treat large volumes of water with low tritium concentrations, and builds on existing heavy water tritium removal systems.

Each module treats up to litres per day. Earlier in a new Kurion strontium removal system was commissioned. This is mobile and can be moved around the tank groups to further clean up water which has been treated by ALPS.

Apart from the above-ground water treatment activity, there is now a groundwater bypass to reduce the groundwater level above the reactors by about 1. This prevents some of it flowing into the reactor basements and becoming contaminated. In addition, an impermeable wall was constructed on the sea-side of the reactors, and inside this a frozen soil wall was created to further block water flow into the reactor buildings. In October guidelines for rainwater release from the site allowed Tepco to release water to the sea without specific NRA approval as long as it conformed to activity limits.

Summary: A large amount of contaminated water has accumulated onsite and has been treated to remove radioactive elements, apart from tritium. In April , the Japanese government confirmed that the water would be released into the sea. Some radioactivity has already been released to the sea, but this has mostly been low-level and it has not had any significant impact beyond the immediate plant structures.

Concentrations outside these structures have been below regulatory levels since April In particular, proposals were sought for dealing with: the accumulation of contaminated water in storage tanks, etc ; the treatment of contaminated water including tritium removal; the removal of radioactive materials from the seawater in the plant's 30 ha harbour; the management of contaminated water inside the buildings; measures to block groundwater from flowing into the site; and, understanding the flow of groundwater.

Responses were submitted to the government in November. In December IRID called for innovative proposals for removing fuel debris from units about It works with IRID, whose focus now is on developing mid- and long-term decommissioning technologies. They were in 'cold shutdown' at the time, but still requiring pumped cooling. They were restored to cold shutdown by the normal recirculating system on 20 March, and mains power was restored on March.

In September Tepco commenced work to remove the fuel from unit 6. Prime minister Abe then called for Tepco to decommission both units. Tepco announced in December that it would decommission both units from the end of January They entered commercial operation in and respectively. It is proposed that they will be used for training. Tepco published a six- to nine-month plan in April for dealing with the disabled Fukushima reactors, and updated this several times subsequently.

Remediation over the first couple of years proceeded approximately as planned. In August Tepco announced its general plan for proceeding with removing fuel from the four units, initially from the spent fuel ponds and then from the actual reactors. At the end of Tepco announced the establishment of an internal entity to focus on measures for decommissioning units and dealing with contaminated water.

In June the government revised the decommissioning plan for the second time, though without major change. It clarified milestones to accomplish preventive and multi-layered measures, involving the three principles of removing the source of the contamination, isolating groundwater from the contamination source, and preventing leakage of the contaminated water. It included a new goal of cutting the amount of groundwater flowing into the buildings to less than m 3 per day by April The schedule for fuel removal from the pond at unit 1 was postponed from late FY17 to FY20, while that for unit 2 was delayed from early FY20 to later the same fiscal year, and that at unit 3 from early FY15 to FY Fuel debris removal was to begin in , as before.

In September the government updated the June decommissioning roadmap, with no changes to the framework, and confirming first removal of fuel debris from unit 1 in Treatment of all contaminated water accumulated in the reactor buildings was to be completed by For unit 3, fuel removal was completed in February Fuel debris removal remains scheduled to begin in FY Tepco has a website giving updates on decommissioning work and environmental monitoring.

Storage ponds : Debris has been removed from the upper parts of the reactor buildings using large cranes and heavy machinery. Casks to transfer the removed fuel to the central spent fuel facility have been designed and manufactured using existing cask technology. In July two unused fuel assemblies were removed from unit 4 pond, and were found to be in good shape, with no deformation or corrosion.

Tepco started removal of both fresh and used fuel from the pond in November , 22 assemblies at a time in each cask, with used and new ones to be moved. This was uneventful, and the task continued through By 22 December , all used as well as all new fuel assemblies had been moved in 71 cask shuttles without incident. All of the radioactive used fuel was removed by early November, eliminating a significant radiological hazard on the site. The used fuel went to the central storage pond, from which older assemblies were transferred to dry cask storage.

The fresh fuel assemblies are stored in the pool of the undamaged unit 6. Tepco completed moving fuel from unit 3 in February It will now focus on used fuel assemblies and new ones from unit 1, and then used assemblies and 28 new ones from unit 2 will be transferred. The NRA has expressed concern about the unit 1 used fuel.

Plant chief Akira Ono says the inability to see what's happening inside the reactors means that details about the melted fuel are still largely unknown. Since the disaster, contaminated cooling water has constantly escaped from the damaged primary containment vessels into the reactor building basements, where it mixes with groundwater that seeps in.

The water is pumped up and treated. Part is recycled as cooling water, with the remainder stored in 1, huge tanks crowding the plant. Early in the crisis, highly contaminated water that leaked from damaged basements and maintenance ditches escaped into the ocean, but the main leakage points have been closed, TEPCO says.

Tons of contaminated sandbags filled with a material used to reduce cesium in the highly radioactive water early in the disaster remain in two basements.

Tiny amounts of radiation have continued leaking into the sea and elsewhere through underground passages, though the amount today is small and fish caught off the coast are safe to eat, scientists say.

The 1, tanks filled with treated but still radioactive water tower over workers and visitors at the plant. TEPCO says the tanks' 1. A government panel's recommendation that the water be released into the sea is facing fierce opposition from local residents, especially fishermen concerned about further damage to the area's reputation. A decision on that recommendation is pending.

TEPCO and government officials say tritium, which is not harmful in small amounts, cannot be removed from the water, but all other radionuclides selected for treatment can be reduced to safe levels for release. Even so, they remain in the water, some scientists say, raises a concern about their impact on marine life from a long-term release.

TEPCO has managed to cut the amount of contaminated water to one-third of what it used to be through a series of measures. In another building, plant workers — about 4, per day now — go through automated security checkpoints and radiation measurements.

Because radiation levels have fallen significantly following decontamination, full protection gear is only needed in a few places in the plant, including in and around the melted reactor buildings. Full protection gear, which means hazmat coveralls, a full-face mask, a head cover, triple socks and double rubber gloves, was required at a shared storage pool where fuel relocation from the No. TEPCO says it needs to get rid of the water storage tanks to free up space at the plant so workers can build facilities that will be used to study and store melted fuel and other debris.

There are about , tons of solid radioactive waste, including contaminated debris and soil, sludge from water treatment, scrapped tanks and other waste. Local officials and residents say they expect the complex to one day be open space where they can walk freely.

Tokyo correspondent Mari Yamaguchi has visited the Fukushima nuclear plant nine times, starting in Sections U. Science Technology Business U. Full Coverage: Photography. Connect with the definitive source for global and local news. The Associated Press. All rights reserved.