Editing Light-water reactor (section)

==History==

===Early concepts and experiments===
After the discoveries of [[Nuclear fission|fission]], [[Neutron moderator|moderation]] and of the theoretical possibility of a [[nuclear chain reaction]], early experimental results rapidly showed that natural uranium could only undergo a sustained chain reaction using graphite or [[heavy water]] as a moderator. While the world's first reactors ([[Chicago Pile-1|CP-1]], [[X-10 Graphite Reactor|X10]] etc.) were successfully reaching [[Critical mass|criticality]], [[uranium enrichment]] began to develop from theoretical concept to practical applications in order to meet the goal of the [[Manhattan Project]], to build a [[Nuclear weapon|nuclear explosive]].

In May 1944, the first grams of enriched uranium ever produced reached criticality in the [[Aqueous homogeneous reactor#History|low power (LOPO)]] reactor at [[Los Alamos National Laboratory|Los Alamos]], which was used to estimate the [[critical mass]] of U235 to produce the atomic bomb.<ref name="Federation of American Scientists - Early Reactors">{{cite web|url=https://fas.org/sgp/othergov/doe/lanl/pubs/00416628.pdf|title=Federation of American Scientists - Early reactor|access-date=2012-12-30}}</ref> LOPO cannot be considered as the first light-water reactor because its fuel was not a solid uranium compound cladded with corrosion-resistant material, but was composed of [[uranyl sulfate]] salt dissolved in water.<ref>It also can be noted that as LOPO was designed to operate at zero power, and no means for cooling were necessary, so ordinary water served solely as a moderator.</ref> It is however the first [[aqueous homogeneous reactor]] and the first reactor using enriched uranium as fuel and ordinary water as a moderator.<ref name="Federation of American Scientists - Early Reactors" />

By the end of [[World War II|the war]], following an idea of [[Alvin M. Weinberg|Alvin Weinberg]], natural uranium fuel elements were arranged in a lattice in ordinary water at the top of the [[X-10 Graphite Reactor|X10 reactor]] to evaluate the neutron multiplication factor.<ref name="Oak Ridge National Laboratory">{{cite web|url=http://info.ornl.gov/sites/publications/files/Pub20808.pdf|title=ORNL - An Account of Oak Ridge National Laboratory's Thirteen Nuclear Reactors|access-date=2012-12-28|page=7|quote=...&nbsp;Afterwards, responding to Weinberg’s interest, the fuel elements were arranged in lattices in water and the multiplication factors determined.&nbsp;...}}</ref> The purpose of this experiment was to determine the feasibility of a nuclear reactor using light water as a moderator and coolant, and clad solid uranium as fuel. The results showed that, with a lightly enriched uranium, criticality could be reached.<ref name="Oak Ridge National Laboratory - X10">{{cite web|url=http://www.ornl.gov/info/news/cco/graphite.shtml |title=ORNL - History of the X10 Graphite Reactor |access-date=2012-12-30 |url-status=dead |archive-url=https://web.archive.org/web/20121211023309/http://www.ornl.gov/info/news/cco/graphite.shtml |archive-date=2012-12-11 }}</ref> This experiment was the first practical step toward the light-water reactor.

After [[World War II]] and with the availability of enriched uranium, new reactor concepts became feasible. In 1946, [[Eugene Wigner]] and Alvin Weinberg proposed and developed the concept of a reactor using enriched uranium as a fuel, and light water as a moderator and coolant.<ref name="Oak Ridge National Laboratory" /> This concept was proposed for a reactor whose purpose was to test the behavior of materials under [[neutron flux]]. This reactor, the [[Materials testing reactor|Material Testing Reactor (MTR)]], was built in Idaho at [[Idaho National Laboratory|INL]] and reached criticality on March 31, 1952.<ref name="Idaho National Laboratory - Proving the principle">{{cite web|url=http://www.inl.gov/proving-the-principle/chapter_08.pdf |title=INEEL - Proving the principle |access-date=2012-12-28 |url-status=dead |archive-url=https://web.archive.org/web/20120305164231/http://www.inl.gov/proving-the-principle/chapter_08.pdf |archive-date=2012-03-05 }}</ref> For the design of this reactor, experiments were necessary, so a mock-up of the MTR was built at [[Oak Ridge National Laboratory|ORNL]], to assess the hydraulic performances of the primary circuit and then to test its neutronic characteristics. This MTR mock-up, later called the Low Intensity Test Reactor (LITR), reached criticality on February 4, 1950<ref name="INEL - History">{{cite web|url=http://ar.inel.gov/images/pdf/200608/2006080900743TUA.pdf|title=INEL - MTR handbook Appendix F (historical backgroup)|page=222|access-date=2012-12-31|archive-date=2006-09-30|archive-url=https://web.archive.org/web/20060930030110/http://ar.inel.gov/images/pdf/200608/2006080900743TUA.pdf|url-status=dead}}</ref> and was the world's first light-water reactor.<ref name="FirstReactor">{{cite web|url=http://www.osti.gov/COROH/ORNL/Transcripts/Beall-Haubenreich%20OH.pdf |title=DOE oral history presentation program - Interview of LITR operator transcript |page=4 |quote=...&nbsp;We were so nervous because there had never been a reactor fueled with enriched uranium go critical before.&nbsp;... |url-status=dead |archive-url=https://web.archive.org/web/20130514113353/http://www.osti.gov/COROH/ORNL/Transcripts/Beall-Haubenreich%20OH.pdf |archive-date=2013-05-14 }}</ref>

=== Pressurized water reactors ===

Immediately after the end of [[World War II]] the [[United States Navy]] started a program under the direction of Captain (later Admiral) [[Hyman Rickover]], with the goal of [[nuclear propulsion]] for ships. It developed the first pressurized water reactors in the early 1950s, and led to the successful deployment of the first nuclear submarine, the {{USS|Nautilus|SSN-571}}.

The [[Soviet Union]] independently developed a version of the PWR in the late 1950s, under the name of [[VVER]]. While functionally very similar to the American effort, it also has certain design distinctions from Western PWRs.

=== Boiling water reactor ===

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]].

===PIUS reactor===
PIUS, standing for ''Process Inherent Ultimate Safety'', was a Swedish design designed by ASEA-ATOM. It is a  concept for a light-water reactor system.<ref>National Research Council (U.S.). Committee on Future Nuclear Power, ''Nuclear power: technical and institutional options for the future''  National Academies Press, 1992, {{ISBN|0-309-04395-6}} page 122</ref> Along with the SECURE reactor,<ref>{{cite web |url=http://www.gdm-marketing.se/en/gdm-marketing |title=GDM Marketing |access-date=2018-02-16 |archive-date=2018-02-17 |archive-url=https://web.archive.org/web/20180217023945/http://www.gdm-marketing.se/en/gdm-marketing |url-status=dead }}</ref> it relied on passive measures, not requiring operator actions or external energy supplies, to provide safe operation. No units were ever built.

=== OPEN100 ===
In 2020, the [[Energy Impact Center]] announced publication of an open-sourced engineering design of a pressurized water reactor capable of producing 300 MWth/100 MWe of energy called [[OPEN100]].<ref>{{cite news | last=Proctor| first=Darrell| title =Tech Guru's Plan—Fight Climate Change with Nuclear Power| work=Power Magazine| date =February 25, 2020 | url =https://www.powermag.com/tech-gurus-plan-fight-climate-change-with-nuclear-power/| accessdate =October 6, 2021}}</ref>