Overview
The family of nuclear reactors known as light water reactors (LWR), cooled and moderated using ordinary water, tend to be simpler and cheaper to build than other types of nuclear reactor; due to these factors, they make up the vast majority of civil nuclear reactors and naval propulsion reactors in service throughout the world as of 2009. LWRs can be subdivided into three categories - pressurized water reactors (PWRs), boiling water reactors (BWRs), and supercritical water reactors (SWRs). Various agencies of the United States Federal Government were responsible for the initial development of the PWR and BWR. An effort by the United States Navy, starting immediately after the end of World War II, and led by (then) Captain Hyman Rickover, developed the first pressurized water reactors in the early 1950s, building the first nuclear submarine (the USS Nautilus (SSN-571)) while researcher Samuel Untermyer II led the effort to develop the BWR at the US National Reactor Testing Station (now the Idaho National Laboratory) in a series of tests called the BORAX experiments. The Soviet Union also independently developed their version of the PWR in the late 1950s, and it became known as the VVER; because of this, Russian-designed PWRs are known in the West as VVERs, to denote their independent origin, and certain national design distinctions from Western PWRs. The SWR remains hypothetical as of 2009; it is a Generation IV design that is still a light water reactor, but it is only partially moderated by light water and exhibits certain characteristics of a fast neutron reactor.
The leaders in national experience with PWRs, offering reactors for export, are the United States (which offers the passively-safe AP1000, a Westinghouse design, as well as several smaller, modular, passively-safe PWRs, such as the Babcock and Wilcox MPower, and the NuScale MASLWR), the Russian Federation (offering both the VVER-1000 and the VVER-1200 for export), the Republic of France (offering the AREVA EPR for export), and Japan (offering the Mitsubishi Advanced Pressurized Water Reactor for export); in addition, both the People's Republic of China and the Republic of Korea are both noted to be rapidly ascending into the front rank of PWR-constructing nations as well, with the Chinese being engaged in a massive program of nuclear power expansion, and the Koreans currently designing and constructing their second generation of indigenous designs. The leaders in national experience with BWRs, offering reactors for export, are the United States and Japan, with the alliance of General Electric (of the US) and Hitachi (of Japan), offering both the Advanced Boiling Water Reactor (ABWR) and the Economic Simplified Boiling Water Reactor (ESBWR) for construction and export; in addition, Toshiba offers an ABWR variant for construction in Japan, as well. West Germany was also once a major player with BWRs. The other types of nuclear reactor in use for power generation are the heavy water moderated reactor, built by Canada (CANDU) and the Republic of India (AHWR), the advanced gas cooled reactor (AGCR), built by the United Kingdom, the liquid metal cooled reactor (LMFBR), built by the Russian Federation, the Republic of France, and Japan, and the graphite-moderated, water-cooled reactor (RBMK), found exclusively within the Russian Federation and former Soviet states.
Though electricity generation capabilities are comparable between all these types of reactor, due to the aforementioned features, and the extensive experience with operations of the LWR, it is favored in the vast majority of new nuclear power plants, though the CANDU/AHWR has a comparatively small (but quite dedicated) following. In addition, light water reactors make up the vast majority of reactors that power naval nuclear powered vessels. Four out of the five great powers with nuclear naval propulsion capacity use light water reactors exclusively: the British Royal Navy, the Chinese People's Liberation Army Navy, the French Marine nationale, and the United States Navy. Only the Russian Federation's Navy has used a relative handful of liquid-metal cooled reactors in production vessels, specifically the Alfa class submarine, which used lead-bismuth eutectic as a reactor moderator and coolant, but the vast majority of Russian nuclear-powered boats and ships use light water reactors exclusively. The reason for near exclusive LWR use aboard nuclear naval vessels is the level of inherent safety built in to these types of reactors. Since light water is used as both a coolant and a neutron moderator in these reactors, if one of these reactors suffers damage due to military action, leading to a compromise of the reactor core's integrity, the resulting release of the light water moderator will act to stop the nuclear reaction and shut the reactor down. This capability is known as a negative void coefficient of reactivity.
Currently-offered LWRs include the following:
- ABWR
- AP1000
- ESBWR
- European Pressurized Reactor
- VVER
Read more about this topic: Light Water Reactor