A startup neutron source is a neutron source used for stable and reliable initiation of nuclear chain reaction in nuclear reactors, when they are loaded with fresh nuclear fuel, whose neutron flux from spontaneous fission is insufficient for a reliable startup, or after prolonged shutdown periods. Neutron sources ensure a constant minimal population of neutrons in the reactor core, sufficient for a smooth startup. Without them, the reactor could suffer fast power excursions during startup from state with too few self-generated neutrons (new core or after extended shutdown).
The startup sources are typically inserted in regularly spaced positions inside the reactor core, in place of some of the fuel rods.
The sources are important for safe reactor startup. The spontaneous fission and ambient radiation such as cosmic rays serve as weak neutron sources, but these are too weak for the reactor instrumentation to detect; relying on them could lead to a "blind" start, which is a potentially unsafe condition. Blind startups were used in the early days of the American nuclear submarine program, before corrosion problems of the clading of startup sources were resolved. (Leaking of the first neutron sources contaminated the reactors, making maintenance dangerous.)[1] The sources are therefore positioned so the neutron flux they produce is always detectable by the reactor monitoring instruments. When the reactor is in shutdown state, the neutron sources serve to provide signals for neutron detectors monitoring the reactor, to ensure they are operable.[2] The equilibrium level of neutron flux in a subcritical reactor is dependent on the neutron source strength; a certain minimum level of source activity therefore has to be ensured in order to maintain control over the reactor when in strongly subcritical state, namely during startups.[3]
The sources can be of two types:[4]
Primary sources, used for startup of a fresh reactor core; conventional neutron sources are used. The primary sources are removed from the reactor after the first fuel campaign, usually after few months, as neutron capture resulting from the thermal neutron flux in an operating reactor changes the composition of the isotopes used, and thus reduces their useful lifetime as neutron sources.
Californium-252 (spontaneous fission)
Plutonium-238 & beryllium, (α,n) reaction
americium-241 & beryllium, (α,n) reaction
polonium-210 & beryllium, (α,n) reaction
radium-226 & beryllium, (α,n) reaction[5]
When plutonium-238/beryllium primary sources are utilized, they can be either affixed to control rods which are removed from the reactor when it is powered, or clad in a cadmium alloy, which is opaque to thermal neutrons (reducing transmutation of the plutonium-238 by neutron capture) but transparent to fast neutrons produced by the source.[2]
Secondary sources, originally inert, become radioactive and neutron-producing only after neutron activation in the reactor. Due to this, they tend to be less expensive. Exposure to thermal neutrons also serves to maintain the source activity (the radioactive isotopes are both burned and generated in neutron flux).
Sb-Be photoneutron source; antimony becomes radioactive in the reactor and its strong gamma emissions (1.7 MeV for 124Sb) interact with beryllium-9 by an (γ,n) reaction and provide photoneutrons. In a PWR reactor one neutron source rod contains 160 grams of antimony, and stays in the reactor for 5–7 years.[6] The sources are often constructed as an antimony rod surrounded by beryllium layer and clad in stainless steel.[5][7] Antimony-beryllium alloy can be also used.
The chain reaction in the first critical reactor, CP-1, was initiated by a radium-beryllium neutron source. Similarly, in modern reactors (after startup), delayed neutron emission from fission products suffices to sustain the amplification reaction while yielding controllable growth times. In comparison, a bomb is based on immediate neutrons and grows exponentially in nanoseconds.
^Atomic Energy of Canada (1997). Canada enters the nuclear age: a technical history of Atomic Energy of Canada Limited. McGill-Queen's Press - MQUP. p. 224. ISBN 0-7735-1601-8.
^ abU.S. patent 4,208,247 Neutron source
^"Microsoft Word - lecture25.doc" (PDF). Archived from the original (PDF) on June 29, 2011. Retrieved 2010-03-28.
^Ken Kok (2009). Nuclear Engineering Handbook. CRC Press. p. 27. ISBN 978-1-4200-5390-6.
A startupneutronsource is a neutronsource used for stable and reliable initiation of nuclear chain reaction in nuclear reactors, when they are loaded...
A neutronsource is any device that emits neutrons, irrespective of the mechanism used to produce the neutrons. Neutronsources are used in physics, engineering...
uranium-235 (U-235) accounting for about 0.7%. U-238 has 146 neutrons and U-235 has 143 neutrons. Different isotopes have different behaviors. For instance...
ISBN 9781510651784. S2CID 249056691. B. Lauss (May 2012). "Startup of the high-intensity ultracold neutronsource at the Paul Scherrer Institute". Hyperfine Interact...
Antimony-124 is assembled with beryllium to make laboratory neutronsources and startupneutronsources. Antimony-124 (half-life 60.20 days) emits β− and 1.690MeV...
subcritical reactor uses additional neutrons from an outside source. There are two general classes of such devices. One uses neutrons provided by a nuclear fusion...
description of the Soviet equivalent of the CP1 startup at the University of Chicago in 1942, the long waits for those tardy neutrons is described in detail...
which produced a 2.45 MeV neutron in half of the reactions. The IPA experiments claimed 300 km/s velocities, deuterium neutron production, and 2 keV deuterium...
containing neutron poisons directly into the reactor coolant. Neutron poison solutions are water-based solutions that contain chemicals that absorb neutrons, such...
ZGS were ultimately inherited by a spallation neutronsource program, the Intense Pulsed NeutronSource (IPNS). Significant portions of the 1996 chase...
Retrieved 2020-06-02. Bernhard Lauss (2012-03-02). "Startup of the high-intensity ultracold neutron sourceat the Paul Scherrer Institute" (PDF). CORE....
Energy Authority. Fusors have also been developed commercially, as sources for neutrons by DaimlerChrysler Aerospace and as a method for generating medical...
Collider. Several OpenStack projects changed names due to trademark issues. Neutron was formerly known as Quantum. Sahara used to be called Savanna. Designate...
pebble beds (HCPBs) are subjected to neutron fluxes to generate tritium to complete the fuel cycle. As a source of power, nuclear fusion has a number...
combine to form one or more different atomic nuclei and subatomic particles (neutrons or protons). The difference in mass between the reactants and products...
However, a fast neutron reactor must use relatively highly enriched uranium or plutonium at the reactor startup so that the neutrons have a better chance...
subtracted. These results were passed on to neutron scientist Jean Claude Nimal (CEA Saclay), who estimated the neutron flux received by the analyzed sample...
1974, along with a 300 kCi Co-60 gamma ray source and a 5.5 MeV Van de Graaff accelerator. The first startup was on January 2, 1975. A budget for the reactor...
=10^{12}-10^{13}} g cm−3, they serve as a major heat source. In the fusion processes of the inner crust, the burning of neutron-rich nuclei ( Ne 34 + Ne 34 ⟶ Ca 68 {\displaystyle...
water (ordinary H2O) is both a neutron moderator and a neutron absorber. This means that not only can it slow down neutrons to velocities in equilibrium...
reactors of third generation as well as small fast neutron reactors of fourth generation. Often, the startup companies developing unconventional SMR prototypes...
reactor-based sources of neutrons for condensed matter physics research in the United States, and it has one of the highest steady-state neutron fluxes of...
nuclear startup will fold after failing to deliver reactors that run on spent fuel". MIT Technology Review. Retrieved September 25, 2018. "Open Source". 25...
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