On this day in science history: Chernobyl nuclear plant explosion

In 1986, in Pripet, Russia, one of the four reactors at the Chernobyl nuclear plant exploded in the world's worst civil nuclear catastrophe. It sent a cloud of radioactive dust over Europe. 

The disaster began during a systems test on 26 April 1986 at reactor number four of the Chernobyl plant.  There was a sudden and unexpected power surge, and when an emergency shutdown was attempted, an exponentially larger spike in power output occurred, which led to a reactor vessel rupture and a series of steam explosions. These events exposed the graphite moderator of the reactor to air, causing it to ignite. The resulting fire sent a plume of highly radioactive fallout into the atmosphere and over an extensive geographical area, including Pripyat. The plume drifted over large parts of the western Soviet Union and Europe. From 1986 to 2000, 350,400 people were evacuated and resettled from the most severely contaminated areas of Belarus, Russia, and Ukraine. According to official post-Soviet data, about 60% of the fallout landed in Belarus.

The abandoned city of Pripyat with Chernobyl plant in the distance, by Jason Minshull [Public domain], via Wikimedia Commons

Russia, Ukraine, and Belarus have been burdened with the continuing and substantial decontamination and health care costs of the Chernobyl accident. A report by the International Atomic Energy Agency examines the environmental consequences of the accident. Another UN agency, UNSCEAR, has estimated a global collective dose of radiation exposure from the accident "equivalent on average to 21 additional days of world exposure to natural background radiation"; individual doses were far higher than the global mean among those most exposed, including 530,000 local recovery workers who averaged an effective dose equivalent to an extra 50 years of typical natural background radiation exposure each. Estimates of the number of deaths that will eventually result from the accident vary enormously; disparities reflect both the lack of solid scientific data and the different methodologies used to quantify mortality—whether the discussion is confined to specific geographical areas or extends worldwide, and whether the deaths are immediate, short term, or long term.

Thirty-one deaths are directly attributed to the accident, all among the reactor staff and emergency workers. An UNSCEAR report places the total confirmed deaths from radiation at 64 as of 2008. The Chernobyl Forum predicts the eventual death toll could reach 4,000 among those exposed to the highest levels of radiation (200,000 emergency workers, 116,000 evacuees and 270,000 residents of the most contaminated areas); this figure is a total causal death toll prediction, combining the deaths of approximately 50 emergency workers who died soon after the accident from acute radiation syndrome, nine children who have died of thyroid cancer and a future predicted total of 3940 deaths from radiation-induced cancer and leukemia.

In a peer-reviewed publication in the International Journal of Cancer in 2006, the authors (following a different conclusion methodology to the Chernobyl Forum study, which arrived at the total predicted death toll of 4,000 after cancer survival rates were factored in) stated, without entering into a discussion on deaths, that in terms of total excess cancers attributed to the accident:

The risk projections suggest that by now Chernobyl may have caused about 1000 cases of thyroid cancer and 4000 cases of other cancers in Europe, representing about 0.01% of all incident cancers since the accident. Models predict that by 2065 about 16,000 cases of thyroid cancer and 25,000 cases of other cancers may be expected due to radiation from the accident, whereas several hundred million cancer cases are expected from other causes.

Also based upon extrapolations from the linear no-threshold model of radiation induced damage, down to zero, the Union of Concerned Scientists estimates that, among the hundreds of millions of people living in broader geographical areas, there will be 50,000 excess cancer cases resulting in 25,000 excess cancer deaths.

For this broader group, the 2006 TORCH report, commissioned by the European Greens political party, predicts 30,000 to 60,000 excess cancer deaths. The environmental advocacy group Greenpeace reports the figure at 200,000 or more.

The Russian founder of that region's chapter of Greenpeace also authored a book titled Chernobyl: Consequences of the Catastrophe for People and the Environment, which concludes that among the billions of people worldwide who were exposed to radioactive contamination from the disaster, nearly a million premature cancer deaths occurred between 1986 and 2004. The book, however, has failed the peer review process. Of the five reviews published in the academic press, four considered the book severely flawed and contradictory, and one praised it while noting some shortcomings. The review by M. I. Balonov published by the New York Academy of Sciences concludes that the report is of negative value because it has very little scientific merit while being highly misleading to the lay reader. It characterized the estimate of nearly a million deaths as more in the realm of science fiction than science.

The accident raised concerns about nuclear power worldwide and slowed or reversed the expansion of nuclear power stations. The accident also raised concerns about the safety of the Soviet nuclear power industry, slowing its expansion for a number of years and forcing the Soviet government to become less secretive about its procedures. The government coverup of the Chernobyl disaster was a "catalyst" for glasnost, which "paved the way for reforms leading to the Soviet collapse".

The final shutdown of the undamaged last reactor on the site took place ceremoniously on 15 Dec 2000.

For more information visit:-

https://en.wikipedia.org/wiki/Chernobyl_disaster

http://www.todayinsci.com/4/4_26.htm

http://www.prlabs.co.uk/lab-supplies.php?N=piston-assay-812-200-graphite&Id=66063

On this day in history - the Bikini H-Bomb test took place

In 1954, at Bikini, in the Pacific Ocean, the blast of the U.S. hydrogen bomb code-named Bravo was the most powerful of all U.S. thermonuclear bomb tests in the area.

The 15 megaton nuclear explosion far exceeded the expected yield of 4 to 8 megatons (6Mt predicted), and was about 1,000 times more powerful than each of the atomic bombs dropped on Hiroshima and Nagasaki during World War II. The scientists and military authorities were shocked by the size of the explosion and many of the instruments they had put in place to evaluate the effectiveness of the device were destroyed.

Bikini is a Pacific archipelago that is part of the Marshall Islands. In this test, one of the atolls was totally vaporized and disappeared in the over 100-mile wide mushroom cloud.

Fallout exceeded predictions. Earlier tests began in 1946 after the indigenous people were evacuated to an island believed to be a safe distance away. (They were moved again in 1949.)

Castle Bravo blast. By United States Department of Energy [Public domain], via Wikimedia Commons

The military authorities and scientists had promised the Bikini Atoll's native residents that they would be able to return home after the nuclear tests. A majority of the island's family heads agreed to leave the island, and most of the residents were moved to the Rongerik Atoll and later to Kili Island. Both locations proved unsuitable to sustaining life, resulting in starvation and requiring the residents to receive ongoing aid.

Despite the promises made by authorities, nuclear tests rendered Bikini unfit for habitation, contaminating the soil and water, making subsistence farming and fishing too dangerous. The United States later paid the islanders and their descendants $2 billion in compensation for damage caused by the nuclear testing program and their displacement from their home island.  

As of 2014, it may be technically possible for the former residents and their descendants to live on the atoll's islands, but virtually none of those alive today have ever lived on the atoll and very few want to move there.

For more information visit:

https://en.wikipedia.org/wiki/Nuclear_testing_at_Bikini_Atoll

http://www.todayinsci.com/3/3_01.htm

http://www.prlabs.co.uk/lab-supplies.php?N=urea-hydrogen-peroxide&Id=1606

Thorium

Thorium has been in the news recently as it was suggested as a safer and more readily available element than Uranium for generating power.

Thorium is a naturally occurring radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 by the Norwegian mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius and named after Thor, the Norse god of thunder.

Thorium produces a radioactive gas, radon-220, as one of its decay products. Secondary decay products of thorium include radium and actinium. In nature, virtually all thorium is found as thorium-232, which undergoes alpha decay with a half-life of about 14.05 billion years. Other isotopes of thorium are short-lived intermediates in the decay chains of higher elements, and only found in trace amounts. Thorium is estimated to be about three to four times more abundant than uranium in the Earth's crust, and is chiefly refined from monazite sands as a by-product of extracting rare earth metals.

Pure thorium is a soft, lustrous silvery-white metal. If it doesn't burst into flames first, thorium will slowly tarnish when exposed to air, becoming grey, as you see above, and then finally black in colour. Thorium is very ductile and, like all actinoids, thorium is radioactive.

Monazite, a rare earth and thorium phosphate mineral, is the primary source of the world's thorium

When compared to uranium, there is a growing interest in developing a thorium fuel cycle due to its greater safety benefits, absence of non-fertile isotopes and its higher occurrence and availability.

India's Kakrapar-1 reactor is the world's first reactor which uses thorium rather than depleted uranium to achieve power flattening across the reactor core. India, which has about 25% of the world's thorium reserves, is developing a 300 MW prototype of a thorium-based Advanced Heavy Water Reactor (AHWR). The prototype is expected to be fully operational by 2016, after which five more reactors will be constructed. The reactor is a fast breeder reactor and uses a plutonium core rather than an accelerator to produce neutrons. As accelerator-based systems can operate at sub-criticality they could be developed too, but that would require more research. India currently envisages meeting 30% of its electricity demand through thorium-based reactors by 2050.



For more information visit:-
http://en.wikipedia.org/wiki/Thorium
http://www.theguardian.com/science/grrlscientist/2013/jun/07/1?guni=Article:in%20body%20link
http://en.wikipedia.org/wiki/Thorium-based_nuclear_power
http://www.bbc.co.uk/news/science-environment-24638816

What are Nuclear Weapons?

Given this is in the news of late, we ask what are Nuclear Weapons?

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.

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 tonnes) of TNT. 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 have been a major focus of international relations policy since their debut.

The basics of the Teller–Ulam design for a hydrogen bomb: a fission bomb uses radiation to compress and heat a separate section of fusion fuel.

Fusion Weapons

This type of nuclear weapon produces a large proportion of its energy in nuclear fusion reactions. Such fusion weapons are generally referred to as thermonuclear weapons or more colloquially as hydrogen bombs (abbreviated as H-bombs), as they rely on fusion reactions between isotopes of hydrogen (deuterium and tritium). All such weapons derive a significant portion, and sometimes a majority, of their energy from fission. This is because a fission weapon is required as a "trigger" for the fusion reactions, and the fusion reactions can themselves trigger additional fission reactions.

Fusion reactions do not create fission products, and thus contribute far less to the creation of nuclear fallout than fission reactions, but because all thermonuclear weapons contain at least one fission stage, and many high-yield thermonuclear devices have a final fission stage, thermonuclear weapons can generate at least as much nuclear fallout as fission-only weapons

The International Atomic Energy Agency was created in 1957 to encourage peaceful development of nuclear technology while providing international safeguards against nuclear proliferation.

Apart from their use as weapons, nuclear explosives have been tested and used for various non-military uses, and proposed, but not used for large-scale earth moving. When long term health and clean-up costs were included, there was no economic advantage over conventional explosives.

Synthetic elements, such as einsteinium and fermium, created by neutron bombardment of uranium and plutonium during thermonuclear explosions, were discovered in the aftermath of the first thermonuclear bomb test. In 2008 the worldwide presence of new isotopes from atmospheric testing beginning in the 1950s was developed into a reliable way of detecting art forgeries, as all paintings created after that period may contain traces of cesium-137 and strontium-90, isotopes that did not exist in nature before 1945.

25 Aug 2010 - "Storax Sedan" underground nuclear test - July 1962

Storax Sedan (yield 104 kt) - shallow underground nuclear test conducted by the United States on 6 July 1962 at Nevada Test Site. The main purpose of the detonation was to asses the non military dimension of a nuclear explosion.

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions in all environments, for military or civilian purposes. It was adopted by the United Nations General Assembly on 10 September 1996 but it has not entered into force as of December 2012

See http://www.ctbto.org/ for more details on the Comprehensive Nuclear Test Ban Treaty Organisation

Also visit http://en.wikipedia.org/wiki/Nuclear_bomb