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US interest in water-cooling of reactors stemmed from the Hanford reactors and was furthered by the submarine PWRs. It was known that water allowed to boil is more effective in removing heat, but boiling was thought likely to trigger instabilities in a reactor core. The water in such a core serves also as moderator; if a steam bubble forms, the local effect on reactivity is swift and its consequences difficult to predict. But experiments in the mid-1950s demonstrated that water could indeed be allowed to boil in a reactor core. Accordingly, a new design of reactor was developed, which is by far the simplest in concept of all power reactors: the boiling water reactor, or BWR. BWRs and PWRs are often mentioned in the same breath, as 'light water reactors' or LWRs. In a BWR the water serves as moderator, reflector and coolant  - and in addition, when boiled, produces steam which is ducted directly to drive a turbo-generator. Once through the turbines, the coolant water...

Pressurized Water Reactors (PWRs) Like the first British power reactors, which were built to produce weapons-plutonium, the first US power reactors also began under military auspices, albeit specifically as power plants. The US Navy realized after the Second World War that a submarine powered by nuclear fuel would not need to resurface to replenish oxygen supply, since the 'burning' of nuclear fuel  - unlike that of oil - does not require oxygen. Spurred by this idea, and constrained by the space limitations in a submarine, US designers developed a reactor using a core of relatively high power density, with fuel elements immersed in a tank of ordinary water  - called 'light water' to distinguish it from heavy water - under sufficient pressure to keep it from  boiling. The 'first power reactor ever built', according to its builders, went critical on 30 March 1953 in a land-based mock-up of a submarine hull at the National Reactor Testing Station in I...

With different fuels, moderators, control systems, cooling arrangements, spatial configurations and so on, possible designs of nuclear reactor number in the hundreds. Early reactor designers had a field day, letting their imaginations run riot; some of their suggestions made colleagues' hair stand on end. Others seemed more feasible: amenable engineering, using manageable materials, controllable, safe, and – ultimately - even economic to build and operate. As we shall see, the main lines of development of such commercial actors sprang from the three partners in the Second World War 'atom-bomb' programme, the 'Manhattan Project'. The. UK in  due course developed gas-cooled, graphite-moderated reactors; the USA developed reactors cooled and moderated by ordinary 'light' water; and Canada developed reactors moderated by heavy water, variously cooled. Both the UK and the USA also began development of reactors using fast neutrons, with liquid metal co...

What is a Reactor? Atom and Nucleus If you take a pair of metal hemispheres and slam them together very fast face to face, one of two things may happen. You may get a loud clunk. Or you, the hemispheres and everything else in the vicinity may be almost instantly vaporized in a burst of incredible heat. If the latter happens, you can be sure that the metal was a particular kind of uranium, not that the confirmation will do you much good. What has vaporized you is raw energy, released from the innermost structure of the uranium. The energy in the interior of uranium was revealed to the world on 6 August 1945, in the sky above Hiroshima, Japan. Never has a source of energy made a more horrifying debut. Yet, paradoxically, the most overpowering energy humanity has learned to release comes from the tiniest reservoir we have yet learned to tap: the nucleus of an atom. What is an 'atom'? And what is its 'nucleus'? Suppose you take a lump of lead, and cut it int...