Nuclear Fuel Cycle Science and Engineering

Ian Crossland, Ian Crossland

• Publisher: Woodhead Publishing
• Year: 2012
• ISBN:
  9780857096388
• Topic: Business
• Subtopic: Energy Industry
• Index: Business

The nuclear fuel cycle is characterised by the wide range of scientific disciplines and technologies it employs. The development of ever more integrated processes across the many stages of the nuclear fuel cycle therefore confronts plant manufacturers and operators with formidable challenges. Nuclear fuel cycle science and engineering describes both the key features of the complete nuclear fuel cycle and the wealth of recent research in this important field.Part one provides an introduction to the nuclear fuel cycle. Radiological protection, security and public acceptance of nuclear technology are considered, along with the economics of nuclear power. Part two goes on to explore materials mining, enrichment, fuel element design and fabrication for the uranium and thorium nuclear fuel cycle. The impact of nuclear reactor design and operation on fuel element irradiation is the focus of part three, including water and gas-cooled reactors, along with CANDU and Generation IV designs. Finally, part four reviews spent nuclear fuel and radioactive waste management.With its distinguished editor and international team of expert contributors, Nuclear fuel cycle science and engineering provides an important review for all those involved in the design, fabrication, use and disposal of nuclear fuels as well as regulatory bodies and researchers in this field.

• Provides a comprehensive and holistic review of the complete nuclear fuel cycle
• Reviews the issues presented by the nuclear fuel cycle, including radiological protection and security, public acceptance and economic analysis
• Discusses issues at the front-end of the fuel cycle, including uranium and thorium mining, enrichment and fuel design and fabrication

Part I

Introduction to the nuclear fuel cycle

1

Nuclear power: origins and outlook

I. Crossland, Crossland Consulting, UK

Abstract:

This chapter traces the rise, fall and possible resurgence of nuclear power through the years from the discovery of atomic fission to the present day. It describes how the technology was discovered and developed – first for the purpose of waging war and then for commercial electricity generation. It explains how concerns over nuclear proliferation and safety produced a period of diminishing public confidence in which, paradoxically, there was increased reliance on the technology for electricity production. Finally, it describes how fears over man-made climate change caused many states to turn towards nuclear power only for some to execute a U-turn after the Fukushima accident. This is described by reference to the examples of France, Sweden, California and Germany, all of whom aim to meet the challenge of large scale reductions in greenhouse gas emissions, albeit through different strategies.

Key words

separation and purification of uranium isotopes

nuclear weapons

nuclear power

public opinion on nuclear energy

nuclear fuel reprocessing

1.1 The rise of nuclear power: 1938 to 1970

1.1.1 Early science and the making of the bomb

Nuclear fission was first recognised by Otto Hahn and Fritz Strassmann in Berlin in 1938. They bombarded uranium with neutrons and found that atoms of barium – roughly half the atomic weight of uranium – were produced. They showed the results to their colleague, Lise Meitner, exiled in Stockholm with her nephew Otto Frisch. Together they used Bohr’s liquid drop model to explain how the addition of a neutron had caused resonant vibrations in the uranium nucleus, splitting it in two. The following year, 1939, Frederic Joliot and his co-workers, Kowarski and von Halban, showed that each fission event releases neutrons, which introduces the possibility of a chain reaction. This was something that had been foreseen by Leo Szilard in 1933 and even patented by him for the production of bombs. That same year, Niels Bohr had established that it was the isotope U-235 – constituting only 0.7% of natural uranium – which fissioned; in fact, the physics of the vibrating nucleus were such that it was only the odd numbered isotopes that could be fissioned by low energy neutrons.

Until 1939 progress in understanding fission and nuclear reactions generally had been slow. But with war in Europe, American scientists, many of them refugees, began working together secretly to see if fission could be put to military use. America entered World War II in December 1941 and the following year the work was brought together officially under the umbrella of the Manhattan project. Even as early as 1939, however, it was clear that, so far as bomb-making was concerned, kilogram quantities of U-235 would be needed and at that time there was no way of separating the isotopes. Based on Bohr’s work, however, it was realised that odd-numbered isotopes of element 94 (later named plutonium) should also be fissile and, unlike uranium isotopes, it should be possible to isolate this chemically. Experiments in which U-238 was bombarded with sub-atomic particles in the Berkeley cyclotron eventually led, in February 1941, to the separation of a minute quantity of plutonium. But in order to produce enough to manufacture a bomb, the nuclear chain reaction had first to be demonstrated.¹

Enrico Fermi and Leo Szilard had been working on arrays of graphite and uranium at Columbia University and, based on this work, they succeeded in creating the world’s first nuclear reactor at the University of Chicago in December 1942. Fermi’s reactor contained 349 tonnes of graphite, 36 tonnes of uranium dioxide and 5 tonnes of uranium metal; it had a power of 2 watts. Scaling this up to produce a reactor of 250 MW was a major undertaking but design and construction were completed in less than two years. Fermi and his team later (1946) formed the nucleus of the Argonne National Laboratory (ANL). The first of the three Hanford piles went critical in September 1944. The fuel was metallic natural uranium clad in aluminium and loaded into horizontal aluminium tubes within a graphite moderator. Cooling was provided by water from the Columbia River, which was pumped through the aluminium tubes. Such a reactor is capable of producing about 0.25 kg of plutonium per day. To limit formation of Pu-240 and higher isotopes, fuel was discharged at low burn up and this was facilitated by the ability to load and unload fuel at power. The plutonium was separated from the irradiated fuel and was then shipped in the form of plutonium nitrate slurry to Los Alamos, where it was reduced to plutonium metal.

Meanwhile, work had been progressing on isotopic separation of U-235. Four methods were investigated: gas centrifuge, gaseous diffusion, mass spectrometry and liquid thermal diffusion. Mechanical problems with the centrifuges caused this technique to be abandoned but the other three yielded useful quantities. This work was performed at Clinton Laboratories (later to become Oak Ridge National Laboratory, ORNL), Tennessee and quantities of U-235 were shipped from there to Los Alamos for construction of a gun-type device in which two sub-critical masses of U-235 are quickly brought together. For the plutonium bomb, however, it was discovered that the material supplied by Hanford contained small quantities of Pu-240, spontaneous fission of which would cause premature detonation. Consequently a more sophisticated implosion design was needed for which a test would be necessary. Enough plutonium had been shipped from Hanford to Los Alamos to create three bombs and it was decided to use one for a full scale trial in the Nevada desert. This was the Trinity test of 16 July 1945. Three weeks later (6 August) the uranium bomb (nicknamed ‘Little Boy’) was dropped on Hiroshima. Three days later, the second plutonium bomb (‘Fat Man’) was used to destroy Nagasaki; the third plutonium bomb was never used.¹

What is clear from this brief description is that much of the applied science and technology that, even today, underpins the exploitation of nuclear energy came about as a direct result of a concerted effort to make these fearful weapons. Small wonder then that the public has difficulty in disassociating nuclear power from nuclear weapons.

1.1.2 Development of commercial thermal reactors

Plutonium production reactors in the UK, France and Russia were, like those at Hanford, based on metallic natural uranium with a graphite moderator. As at Hanford the Russian reactor (at Chelyabinsk) was water cooled but in the UK (Windscale) and in France (Marcoule) the reactors were gas cooled and later formed the basis of the first generation of electricity-producing reactors in these two countries. Only the British went on to develop these into a more advanced gas-cooled commercial type although there were many experimental designs along the way, including high temperature reactors. France gave up gas-cooled designs in favour of light water reactors in the late 1960s. In the UK this did not happen until almost two decades later.

A year after the war had ended, the US Atomic Energy Commission (AEC) was established (August 1946) to control nuclear energy development and foster its peaceful use. Within the AEC programme under the direction of Rear-Admiral Hyman Rickover, ANL in collaboration with Westinghouse developed a reactor for use as a submarine propulsion unit.² The use of plutonium or highly enriched uranium fuel coupled with a pressurised water coolant allowed the requisite power to be generated from a reactor that was sufficiently small to fit inside the ship’s hull. The keel for USS Nautilus the world’s first nuclear-powered submarine was laid in June 1952 and the ship was launched January 1954. The reactor design was subsequently scaled up for a land-based pressurised water reactor (PWR) and a prototype was constructed at Shippingport, Pennsylvania (230 MW thermal, 60 MW electrical); this went critical in December 1957. This was a joint venture between AEC, Westinghouse (vendor) and Duquense Light Company (utility).

A series of five boiling water reactor experiments (known as BORAX I to V) were designed by ANL and tested at AEC’s Idaho National Reactor Testing Station starting in 1953 and running through to 1964.³ The third experiment (mid-1955) produced enough electricity to power the nearby town of Arco. The first commercial plant (5 MW(e)) was built in 1957 at Vallecitos near San Jose, California. Based on this work, General Electric constructed a 210 MW(e) BWR for Commonwealth Edison at Dresden, Illinois, which started operation in October 1959. It was notable for being the first US reactor to be built without government funding.

Canada has developed, operated and exported its own unique pressurised heavy water reactor (PHWR) design, known as CANDU (see Chapter 11). The original aim was to exploit the country’s large reserves of uranium and to avoid the complications, expense and proliferation risks that are inherent in enrichment and reprocessing. The resulting design maximises neutron economy through the use of a heavy water coolant cum moderator. With non-enriched fuel, maximum burn-up is around 8 GWd/tHM (significantly less than with enriched fuel) but the reactor can be operated with a range of fuel cycles and twelve have been sold and are in operation throughout the world. Two units were sold to India the first of which went into service in 1973 but support from Canada was withdrawn after the testing of India’s nuclear bomb in May 1974. Cooperation effectively began again in 2008 when, with the consent of the IAEA, India reached an agreement with the Nuclear Suppliers Group⁴ but, in the interim, India had developed its own PHWR variants and investigated their use with thorium fuel.

A particular attraction of the PHWR is the use of pressure tubes to avoid the need for a large, difficult to construct pressure vessel. Similar considerations drove the development of the Soviet RBMK (reaktor bolshoy moshchnosty kanalny, high-power channel reactor) design which, like the early gas-cooled reactors, was based on a military plutonium-producing reactor. The fuel was low enrichment uranium ...