Nuclear weapon

A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission ("atomic") bomb test released the same amount of energy as approximately 20,000 tons of TNT. The first thermonuclear ("hydrogen") bomb test released the same amount of energy as approximately 10,000,000 tons of TNT.^[1]

A modern thermonuclear weapon weighing little more than 2,400 pounds (1,100 kg) can produce an explosive force comparable to the detonation of more than 1.2 million tons (1.1 million metric tons) of TNT.^[2] Thus, even a small nuclear device no larger than traditional bombs can devastate an entire city by blast, fire and radiation. Nuclear weapons are considered weapons of mass destruction, and their use and control has been a major focus of international relations policy since their debut.

Only two nuclear weapons have been used in the course of warfare, both by the United States near the end of World War II. On 6 August 1945, a uranium gun-type device code-named "Little Boy" was detonated over the Japanese city of Hiroshima. Three days later, on 9 August, a plutonium implosion-type device code-named "Fat Man" was exploded over Nagasaki, Japan. These two bombings resulted in the deaths of approximately 200,000 Japanese people—mostly civilians—from acute injuries sustained from the explosions.^[3] The role of the bombings in Japan's surrender, and their ethical status, remain the subject of scholarly and popular debate.

Since the bombings of Hiroshima and Nagasaki, nuclear weapons have been detonated on over two thousand occasions for testing purposes and demonstrations. Only a few nations possess such weapons or are suspected of seeking them. The only countries known to have detonated nuclear weapons—and that acknowledge possessing such weapons—are (chronologically by date of first test) the United States, the Soviet Union (succeeded as a nuclear power by Russia), the United Kingdom, France, the People's Republic of China, India, Pakistan, and North Korea. In addition, Israel is also widely believed to possess nuclear weapons, though it does not acknowledge having them.^[4][5][6] One state, South Africa, has admitted to having previous fabricated nuclear weapons in the past, but has since disassembled their arsenal and submitted to international safeguards

Nuclear accident shakes Japan

Japan is facing an unprecedented nuclear emergency after a major uranium leak.

Radiation levels at the Tokaimura nuclear fuel-processing plant in north-east Japan are 15,000 times higher than normal.

The authorities have warned thousands of residents near the site of the accident to stay indoors and to wash off any rain that falls on them.
"There is a strong possibility that abnormal reactions are continuing within the facility," Chief Cabinet Secretary Hiromu Nonaka told an emergency news conference. "There are concerns about radiation in the surrounding areas."

He said that it was very likely that there had been a "criticality incident" at the plant.

Criticality is the point at which a nuclear chain reaction becomes self-sustaining.

"The situation is one our country has never experienced," Mr Nonaka said.

Three workers from the plant have been taken to hospital and hundreds have been forced to leave their homes.

One of the three workers in hospital is reported to be in a serious condition, suffering from continuous vomiting.

Prime Minister Keizo Obuchi has set up an emergency task force to tackle the accident.

A government request for help from US military forces in Japan for help was turned down. The US said its forces were not equipped to handle such accidents.

Blue smoke

The cause of the leak - detected at 1035 local time (0135GMT) - was not immediately known.

The head of the company's Tokyo office, Makoto Ujihara, said the workers told other staff at the plant that "they saw a blue flame rising from the fuel" and complained of nausea.

"We are still trying to find what exactly happened but we believe the uranium reached the critical point", the spokesman for JCO was quoted as saying.

Local schools were ordered to close their windows and keep pupils indoors.

The Prime Minister postponed a cabinet reshuffle planned for Friday because of the accident.

"Forbidden zone"

At a distance of two kilometers (1.24 miles) from the accident, radiation was still 10 times the normal level said Tatsuo Shimada, an official of Ibaraki Prefecture.

Police cordoned off a 6km "forbidden zone" around the uranium processing plant.

The International Atomic Energy Agency (IAEA) said that initial reports suggested a radiation leak in Japan was not a "major incident," although it was waiting for more data.

Early estimates suggested the incident was serious but would not rank above three on a seven-level scale of nuclear incidents, said an IAEA spokesman in Vienna.

The environmental organisation Greenpeace criticised the accident as a symptom of a safety "crisis" in Japan's nuclear industry.
"Today's accident at Tokaimura confirms our fears - the entire safety culture in Japan is in crisis and the use of dangerous plutonium in reactors here will only increase the probablity of a nuclear catastrophe," Greenpeace International activist Shaun Burnie said.

The organisation pointed out that the accident came just one day before a UK-flagged ship was expected to deliver 225 kilograms (495 pounds) of mixed plutonium-uranium oxide (MOX) fuel to a plant in Takahama, central Japan.

History of accidents

Tokaimura was the site of Japan's worst nuclear plant incident in 1997, when 35 workers were contaminated by radiation after a fire at a processing plant was not extinguished properly and caused an explosion.

A series of incidents at Japanese nuclear power stations in recent years has undermined confidence in the safety of this form of energy production, says BBC Tokyo correspondent Juliet Hindell.

In July, cooling water leaked from a pipe in the building that houses the reactor at the Tsuruga nuclear power plant in northern Japan.

It took Japan Atomic Power, the company that operates the plant, 14 hours to shut down operations after the leak was discovered.

Executives in charge of the reactor said radiation from the leak was 11,500 times the safety limit.

The earlier figure given was 250 times the limit, and the change has sparked accusations of a cover-up.

Nuclear programme

Japan has 51 commercial nuclear power reactors that provide one-third of the country's electricity.

With few natural resources of its own, Japan imports nearly all its fuel oil.

Since the oil crisis of 1973, successive governments have made concerted efforts to become self-sufficient.

By the year 2010, Japan wants to produce 42% of its energy in nuclear plants.

City after Nuclear Disaster - Pripyat

Pripyat (city)

Pripyat

is a ghost town in the zone of alienation in northern Ukraine, in the Kiev Oblast (province), near the border with Belarus.^[2]

The city has a special status within the Kiev Oblast being the city of oblast-level subordination (see Administrative divisions of Ukraine) although it is located within the limits of Ivankiv Raion. The city also is being supervised by the Ministry of Emergencies of Ukraine as part of the Zone of alienation jurisdiction.

Pripyat was founded in 1970 to house workers for the nearby Chernobyl Nuclear Power Plant. It was officially proclaimed a city in 1979, but was abandoned in 1986 following the Chernobyl disaster. It was the ninth nuclear-city ("атомоград" (atomograd) in Russian, literally "atom city") in the Soviet Union at its time. Its population had been around 50,000 before the accident. Annual Rate of natural increase was estimated at around 800 persons, plus over 500 newcomers from all corners of the Soviet Union each year. It had been planned that the Prypiat's population should have risen up to 78,000 in the nearest future. Prypiat had a railroad link to Yazov station(Kiev railroad line) as well as a navigable river nearby.

Background
Access to Pripyat, unlike cities of military importance, was not restricted before the disaster. Before the Chernobyl accident, nuclear power stations were seen by the Soviet Union as safer than other types of power plants. Nuclear power stations were presented as being an achievement of Soviet engineering, where nuclear power was harnessed for peaceful projects. The slogan "peaceful atom" (Russian: мирный атом, mirnyj atom) was popular during those times. The original plan had been to build the plant only 25 km (16 mi) from Kiev, but the Ukrainian Academy of Sciences, among other bodies, expressed concern about the station being too close to the city. Thus the station and Pripyat^[3] were built in their current location, about 100 km (62 mi) from Kiev. After the disaster, the city of Pripyat was evacuated in two days

Development

Along with its prime goal as being home to nuclear power plant's employees, Pripyat had been viewed as a major railroad and river cargo port in Northern Ukraine. The urban nomenclature was quite typical for the time. There were traditional ideological names on the city map like Lenin Av., International Friendship St., Heroes of Stalingrad St. etc. There also were some street names that had local bearings, e.g. Embankment St., Builders Ave., and Enthusiasts Ave. Lesya Ukrainka St. has some cultural implications since it bears the name of one of the greatest poets of Ukraine. The "atom for peace" theme was also included in the naming scheme, owing to Igor Kurchatov street, which was named after a nuclear physicist who worked for a peaceful use of the nuclear technology.

Pripyat had a defined city centre where city hall (or city council), the largest shopping centres, major recreational and public catering facilities and the Polissya hotel were located.

The chief idea of the urban layout was the so-called triangular principle developed by Moscow architects, the project which then famous Nicolay Ostozhenko had been running. After some adjustments by Kiev architects, the plan of the city's development was finally approved. At the time this triangular one-of-a-kind layout was unique, though by the time the building-up of Pripyat started it had been implemented in dozens of Soviet cities and the novelty soon wore off.

The triangular method featured alternations of five-storey buildings with high-rises which made the city lined with broad vistas, open spaces, and the horizon visible from almost every corner. Unlike the old cities with their tiny yards and narrow streets, Pripyat had been initially planned to look free and vivid, all for the comfort of its inhabitants. Besides the calculated boost of street space, the goal had been achieved by making the streets and blocks symmetrical. Taken together, these solutions were intended to immunize Pripyat from such scourge of modern times as traffic-jams.

Evacuation note, April 27, 1986

"For the attention of the residents of Pripyat! The City Council informs you that due to the accident at Chernobyl Power Station in the city of Pripyat the radioactive conditions in the vicinity are deteriorating. The Communist Party, its officials and the armed forces are taking necessary steps to combat this. Nevertheless, with the view to keep people as safe and healthy as possible, the children being top priority, we need to temporarily evacuate the citizens in the nearest towns of Kiev Oblast. For these reasons, starting from April 27, 1986 2 p.m. each apartment block will be able to have a bus at its disposal, supervised by the police and the city officials. It is highly advisable to take your documents, some vital personal belongings and a certain amount of food, just in case, with you. The senior executives of public and industrial facilities of the city has decided on the list of employees needed to stay in Pripyat to maintain these facilities in a good working order. All the houses will be guarded by the police during the evacuation period. Tovarishchs, ("Comrades") leaving your residences temporarily please make sure you have turned the lights, electrical equipment and water off and shut the windows. Please keep calm and orderly in the process of this short-term evacuation."

Fukushima Disaster

Fukushima I nuclear accidents

The Fukushima I nuclear accidents (福島第一原子力発 電所事故, Fukushima Dai-ichi  are series of ongoing equipment failures and releases of radioactive materials at the Fukushima I Nuclear Power Plant, following the 2011 Tōhoku earthquake and tsunami at 14:46 JST on 11 March 2011. The plant comprises six separate boiling water reactors maintained by the Tokyo Electric Power Company (TEPCO). Reactors 4, 5 and 6 had been shut down prior to the earthquake for planned maintenance.^[3] The remaining reactors were shut down automatically after the earthquake, but the subsequent 14 metres (46 ft) tsunami^[4] flooded the plant, knocking out emergency generators needed to run pumps which cool and control the reactors. The flooding and earthquake damage prevented assistance being brought from elsewhere.

Evidence arose of partial core meltdown in reactors 1, 2, and 3; hydrogen explosions destroyed the upper cladding of the buildings housing reactors 1, 3, and 4; an explosion damaged the containment inside reactor 2; and multiple fires broke out at reactor 4. In addition, spent fuel rods stored in spent fuel pools of units 1–4 began to overheat as water levels in the pools dropped. Fears of radiation leaks led to a 20 kilometres (12 mi) radius evacuation around the plant. Workers at the plant suffered radiation exposure and were temporarily evacuated at various times. On 18 March, Japanese officials designated the magnitude of the danger at reactors 1, 2 and 3 at level 5 on the 7 point International Nuclear Event Scale (INES).^[5] Power was restored to parts of the plant from 20 March, but machinery damaged by floods, fires and explosions remained inoperable.^[6]

Measurements taken by the Japanese science ministry and education ministry in areas of northern Japan 30-50 km from the plant showed radioactive caesium levels high enough to cause concern.^[7] Food grown in the area was banned from sale. World wide measurements of iodine-131 and caesium-137 suggested release levels had reached 2/3 of those from the Chernobyl accident, although at Chernobyl this was accompanied by releases of many other radioactive materials from the reactor fire.^[8] Tokyo officials temporarily recommended that tap water should not be used to prepare food for infants.^[9][10] Plutonium contamination has been detected in the soil at two sites in the plant.^[11]

The IAEA announced on 27 March that workers hospitalized as a precaution on 25 March had been exposed to between 2 and 6 Sv of radiation at their ankles when standing in water in unit 3.^[12][13][14] The international reaction to the accidents was also concerned. The Japanese government and TEPCO have been criticized for poor communication with the public.^[15][16] On 20 March, the Chief Cabinet Secretary Yukio Edano announced that the plant would be closed once the crisis was over.^[17] On 30 March 2011, the president of Tepco, Masataka Shimizu, was hospitalised with symptoms of dizziness and high blood pressure.^[18]

Fukushima I Nuclear Power Plant

The Fukushima I Nuclear Power Plant is located in the town of Okuma in the Futaba District of Fukushima Prefecture, Japan, about 210 kilometers (130 miles) north of Tokyo.^[102] It consists of six light water, boiling water reactors (BWR) designed by General Electric driving electrical generators with a combined power of 4.7 gigawatts, making Fukushima I one of the 25 largest nuclear power stations in the world. Fukushima I was the first nuclear plant to be constructed and run entirely by the Tokyo Electric Power Company (TEPCO).

Unit 1 is a 439 MWe type (BWR3) reactor constructed in July 1967. It commenced commercial electrical production on 26 March 1971.^[103] It was designed for a peak ground acceleration of 0.18 g (1.74 m/s²) and a response spectrum based on the 1952 Kern County earthquake.^[104] Units 2 and 3 are both 784 MWe type BWR-4 reactors, Unit 2 commenced operating in July 1974 and Unit 3 in March 1976. The design basis for Units 3 and 6 were 0.45 g (4.41 m/s²) and 0.46 g (4.48 m/s²) respectively.^[105] All units were inspected after the 1978 Miyagi earthquake when the ground acceleration was 0.125 g (1.22 m/s²) for 30 seconds, but no damage to the critical parts of the reactor was discovered.^[104]

Units 1–5 have a Mark 1 type (light bulb torus) containment structure, unit 6 has Mark 2 type (over/under) containment structure.^[104] From September 2010, unit 3 has been fueled by mixed-oxide (MOX) fuel.^[106]

At the time of the accident, the units and central storage facility contained the following numbers of fuel assemblies:^[107]

Radiation levels and radioactive contamination

Radioactive material was released from containment on several occasions after the tsunami struck, the result of deliberate venting to reduce gaseous pressure, deliberate discharge of coolant water into the sea, and accidental or uncontrolled events. Using Japanese Nuclear Safety Commission numbers, Asahi Shimbun reported that by 24 March the accident might have emitted 30,000 to 110,000 TBq of iodine-131.^[292] On the INES scale, the accident would rate 6 rather than the official level 5, according to the newspaper. The radiation dose rate at one location between reactor units 3 and 4 was measured at 400 mSv/h at 10:22 JST, 13 March, causing experts to urge rapid rotation of emergency crews as a method of limiting exposure to radiation.^[293] 1 Sv/h were reported (but not confirmed by the IAEA)^[2] close to the leaking reactor units on 16 March, prompting a temporary evacuation of plant workers, with radiation levels subsequently dropping back to 800–600 millisieverts.^[43] On 29 March, at times near unit 2, radiation monitoring was hampered by a belief that some radiation levels may be higher than 1000 mSv/hr, but that "1,000 millisieverts is the upper limit of their measuring devices."^[211] The maximum permissible dose for Japanese nuclear workers was increased to 250 mSv/year, for emergency situations after the accidents.^[294][295]

The Japanese Ministry of Health, Labour and Welfare announced that levels of radioactivity exceeding legal limits had been detected in milk produced in the Fukushima area and in certain vegetables in Ibaraki. Measurements made by Japan in a number of locations have shown the presence of radionuclides on the ground.^[296] On 23 March, Tokyo drinking water exceeded the safe level for infants, prompting the government to distribute bottled water to families with infants.^[297] World wide measurements of wind-born radioactive iodine and caesium vented from reactors suggest that levels have reached around 2/3 those during the Chernobyl disaster, though in that case other radioactive material was also released.^[8]