Hydrogen Moderated Self-regulating Nuclear Power Module

Hydrogen Moderated Self-regulating Nuclear Power Module

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The Hydrogen Moderated Self-Regulating Nuclear Power Module (HPM), also referred to as the Compact Self-regulating Transportable Reactor (ComStar), is a new type of nuclear power reactor using hydride
Hydride
In chemistry, a hydride is the anion of hydrogen, H−, or, more commonly, a compound in which one or more hydrogen centres have nucleophilic, reducing, or basic properties. In compounds that are regarded as hydrides, hydrogen is bonded to a more electropositive element or group...

 as a neutron moderator
Neutron moderator
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235....

. The design is inherently safe, as the fuel and the neutron moderator are uranium hydride
Uranium hydride
Uranium hydride, also called uranium trihydride is an inorganic compound, a hydride of uranium.-Properties:Uranium hydride is a highly toxic, brownish gray to brownish black pyrophoric powder or brittle solid. Its specific gravity at 20 °C is 10.95, much lower than that of uranium...

 UH3, which is with temperature reduced to uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

 and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

. The gaseous hydrogen exits the core, being absorbed by hydrogen absorbing material such as depleted uranium
Depleted uranium
Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...

, thus making it less critical
Critical mass
A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The...

. This means that with rising temperature the neutron moderation drops and the nuclear fission
Nuclear fission
In nuclear physics and nuclear chemistry, nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts , often producing free neutrons and photons , and releasing a tremendous amount of energy...

 reaction in the core is dampened, leading to a lower core temperature. This means as more energy is taken out of the core the moderation rises and the fission process is stoked to produce more heat.

The concept for this type of nuclear reactor was developed by the scientists Otis Peterson and Robert Kimpland of the Los Alamos National Laboratory
Los Alamos National Laboratory
Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...

 (LANL) in New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

. Dr. Otis G. Peterson received a Federal Laboratory Consortium Award in the notable technology development category for this reactor concept in 2002. This technology has since been licensed exclusively to Hyperion Power Generation
Hyperion Power Generation
Hyperion Power Generation, Inc. is a privately held corporation formed to construct and sell several designs of relatively small nuclear reactors, which they claim will be modular, inexpensive, inherently safe, and proliferation-resistant...

, under a technology-transfer program and a co-operative research and development agreement (CRADA) with the Los Alamos National Laboratory.

The reactor shares some characteristics with the TRIGA
TRIGA
TRIGA is a class of small nuclear reactor designed and manufactured by General Atomics. The design team for TRIGA was led by the physicist Freeman Dyson.TRIGA is the acronym of Training, Research, Isotopes, General Atomics.-Design:...

 research reactors, which are operated by research laboratories and universities around the world, as well as the SNAP-10A
SNAP-10A
SNAP-10A was the first and so far only known launch of a U.S. nuclear reactor into space . The Systems Nuclear Auxiliary Power Program reactor was developed under the SNAPSHOT program overseen by the U.S...

 reactor, which was developed for space applications.

Characteristics


According to the patent application the reactor design has some notable characteristics, that sets it apart from other reactor designs. It uses uranium hydride
Uranium hydride
Uranium hydride, also called uranium trihydride is an inorganic compound, a hydride of uranium.-Properties:Uranium hydride is a highly toxic, brownish gray to brownish black pyrophoric powder or brittle solid. Its specific gravity at 20 °C is 10.95, much lower than that of uranium...

 (UH3) "low-enriched" to 5% uranium-235
Uranium-235
- References :* .* DOE Fundamentals handbook: Nuclear Physics and Reactor theory , .* A piece of U-235 the size of a grain of rice can produce energy equal to that contained in three tons of coal or fourteen barrels of oil. -External links:* * * one of the earliest articles on U-235 for the...

 -- the remainder is uranium-238
Uranium-238
Uranium-238 is the most common isotope of uranium found in nature. It is not fissile, but is a fertile material: it can capture a slow neutron and after two beta decays become fissile plutonium-239...

 -- as the nuclear fuel, rather than the usual metallic uranium or uranium dioxide
Uranium dioxide
Uranium dioxide or uranium oxide , also known as urania or uranous oxide, is an oxide of uranium, and is a black, radioactive, crystalline powder that naturally occurs in the mineral uraninite. It is used in nuclear fuel rods in nuclear reactors. A mixture of uranium and plutonium dioxides is used...

 that composes the fuel rods of contemporary light-water reactors. In fact, within the application, the contemporary "rod" based design with fuel rods and control rods
Control rod
A control rod is a rod made of chemical elements capable of absorbing many neutrons without fissioning themselves. They are used in nuclear reactors to control the rate of fission of uranium and plutonium...

 is completely omitted from the proposed reactor design in favor of a "tub" design with passive heat pipe
Heat pipe
A heat pipe or heat pin is a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces....

s conducting heat to the heat exchanger running through the "tub" of granulated uranium hydride. The likely coolant
Coolant
A coolant is a fluid which flows through a device to prevent its overheating, transferring the heat produced by the device to other devices that use or dissipate it. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, and chemically inert, neither causing nor...

 to be used is potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

.

The reactor design in question begins producing power when hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gas at a sufficient temperature and pressure is admitted to the core (made up of granulated uranium metal) and reacts with the uranium metal to form uranium hydride. Uranium hydride is both a nuclear fuel
Nuclear fuel
Nuclear fuel is a material that can be 'consumed' by fission or fusion to derive nuclear energy. Nuclear fuels are the most dense sources of energy available...

 and a neutron moderator
Neutron moderator
In nuclear engineering, a neutron moderator is a medium that reduces the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235....

; apparently it, like other neutron moderators, will slow neutrons sufficiently to allow for fission reactions to take place; the U-235 atoms within the hydride also serve as the nuclear fuel. Once the nuclear reaction has started, it will continue until it reaches a certain temperature, approximately 800 °C, where, due to the chemical properties of uranium hydride, it chemically decomposes and turns into hydrogen gas and uranium metal. The loss of neutron moderation due to the chemical decomposition of the uranium hydride will consequently slow — and eventually halt — the reaction. When temperature returns to an acceptable level, the hydrogen will again combine with the uranium metal, forming uranium hydride, restoring moderation and the nuclear reaction will start again.

This makes the reactor a self-regulating, dynamic system, as with a rise in temperature, nuclear reactivity will substantially decrease, and with a fall in temperature, nuclear reactivity will substantially increase. Thus, this reactor design is self-regulating, meltdown
Nuclear meltdown
Nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating. The term is not officially defined by the International Atomic Energy Agency or by the U.S. Nuclear Regulatory Commission...

 is impossible, and the design is inherently safe. From a safety point of view, the design leverages the technology used in the TRIGA reactor, which uses uranium zirconium hydride (UZrH) fuel and is the only reactor licensed by the U.S. Nuclear Regulatory Commission for unattended operation.

According to the reactor design specification, the uranium hydride core is surrounded by hydrogen-absorbing storage trays, made of depleted uranium
Depleted uranium
Depleted uranium is uranium with a lower content of the fissile isotope U-235 than natural uranium . Uses of DU take advantage of its very high density of 19.1 g/cm3...

 or thorium
Thorium
Thorium is a natural radioactive chemical element with the symbol Th and atomic number 90. It was discovered in 1828 and named after Thor, the Norse god of thunder....

. The storage trays can either desorb or absorb the hydrogen gas from the core. During normal operation (with the operating temperature being approximately 550 °C), the storage trays are kept at a temperature high enough to expel the hydrogen gas to the core. The storage trays are heated or cooled by means of heat pipes and an external thermal source. Thus, in a steady state, the uranium hydride core is slaved to the temperature of the storage trays. Other heat pipes, protruding the uranium hydride core, deliver the nuclear generated heat from the core to a heat exchanger
Heat exchanger
A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact...

, which in turn can be connected to a steam turbine
Steam turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....

-generator set, for the production of electricity.

The only hazards are those of all nuclear material
Nuclear material
Nuclear material refers to the metals uranium, plutonium, and thorium, in any form, according to the IAEA. This is differentiated further into "source material", consisting of natural and depleted uranium, and "special fissionable material", consisting of enriched uranium , uranium-233, and...

s, namely those of radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...

, but this is significantly mitigated by the fact that the reactor design is intended to be buried underground and only dug up for refueling every five years, at which point, assuming proper safeguards are used, exposure to radioactivity is a comparatively trivial concern. Spent fuel is also a concern, but this is mitigated due to certain technologies and advantages that make the design in question's used fuel more suitable for nuclear recycling
Nuclear reprocessing
Nuclear reprocessing technology was developed to chemically separate and recover fissionable plutonium from irradiated nuclear fuel. Reprocessing serves multiple purposes, whose relative importance has changed over time. Originally reprocessing was used solely to extract plutonium for producing...

. In particular, the patent application for the design indicates that using a thorium fuel cycle
Thorium fuel cycle
The thorium fuel cycle is a nuclear fuel cycle that uses the naturally abundant isotope of thorium, , as the fertile material. In the reactor, is transmuted into the fissile artificial uranium isotope which is the nuclear fuel. Unlike natural uranium, natural thorium contains only trace amounts...

 instead of a uranium fuel cycle with this type of reactor will allow far greater recycling potential than presently is found in standard used fuel. Furthermore, the uranium hydride has the capability of a high fuel burnup
Burnup
In nuclear power technology, burnup is a measure of how much energy is extracted from a primary nuclear fuel source...

, of up to 50%, in contrast to a light-water reactor which usually achieves a burnup of 5%.

Reprocessing of spent fuel is simplified and more economical for the hydride reactor design, because the so-called process of zone refining can be used for separation.

Apparently, the proposed reactor design will be capable of supplying 27 MWe of electric power or 70 MWth, weigh 18–20 tons, measure approximately 1.5 meters in diameter, be mass-produced on an assembly line, and be capable of unattended, unrefueled operation for up to seven to ten years at a time. Costs are projected to be competitive with other established sources of energy, like coal, conventional nuclear, and natural gas.

No prototype of this type of reactor has been realized yet, although the nuclear processes have been modeled with MCNP. As the concept of a uranium hydride reactor is novel, further experimental work will be needed with regard to gas flow dynamics, materials selection and performance (especially with regard to hydrogen embrittlement and hydride pyrophoricity), radiation damage and fission fragment buildup. A further challenge will be posed by the remote temperature control of the storage trays as well as cooling these trays when it may be necessary, so they absorb hydrogen from the core (absorption itself releases heat which first must be evacuated before more hydrogen can be absorbed by the storage trays).

History


The HPM concept is based on work from the 1950s, when the University of California Radiation Laboratory (currently the Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...

) required a small nuclear fission device as the ignition charge for a thermonuclear weapon. The aim was to produce an explosion powerful enough to ignite it, while using only the minimum amount of fissile material. This was tried in operation Upshot-Knothole
Operation Upshot-Knothole
Operation Upshot-Knothole was a series of eleven nuclear test shots conducted in 1953 at the Nevada Test Site.Over twenty-one thousand soldiers took part in the ground exercise Desert Rock V in conjunction with the Grable shot...

, where hydrogen was used to reduce the critical mass. The test explosions codenamed Ruth and Ray used in the core uranium hydride. Ruth used the hydrogen isotope protium (1H) and Ray used the hydrogen isotope deuterium
Deuterium
Deuterium, also called heavy hydrogen, is one of two stable isotopes of hydrogen. It has a natural abundance in Earth's oceans of about one atom in of hydrogen . Deuterium accounts for approximately 0.0156% of all naturally occurring hydrogen in Earth's oceans, while the most common isotope ...

 (2H or 2D) as neutron moderators. The predicted yield was 1.5 to 3 kt TNT for Ruth and 0.5-1 kt TNT for Ray, however the tests produced only a yield of about 200 tons of TNT.

Commercialization


The HPM technology is being developed and commercialized by Hyperion Power Generation
Hyperion Power Generation
Hyperion Power Generation, Inc. is a privately held corporation formed to construct and sell several designs of relatively small nuclear reactors, which they claim will be modular, inexpensive, inherently safe, and proliferation-resistant...

, Inc. Hyperion is targeting the volume market for small to medium-sized applications in remote areas for industrial installations and residential installations serving 20,000 (typical US) to 100,000 (typical non-US) households. They claim the unit will be deliverable in a sealed container and will be mostly maintenance free, as the unit is not to be opened on site. The company wants to mass produce the units in a factory, deliver them by truck and take them back for re-processing after 5 to 10 years (depending on power drain).

However, in November 2009, Hyperion Power Generation decided to use a different lead-cooled fast reactor design for its power module, based on uranium nitride
Uranium nitride
Uranium nitride refers to a family of several ceramic compounds: uranium mononitride , uranium sesquinitride , which exists in either an alpha or beta phase, and uranium dinitride ....

, citing the long development and regulatory licensing process for the uranium hydride reactor design.

External links

  • Patent application at the United States Patent and Trademark Office
    United States Patent and Trademark Office
    The United States Patent and Trademark Office is an agency in the United States Department of Commerce that issues patents to inventors and businesses for their inventions, and trademark registration for product and intellectual property identification.The USPTO is based in Alexandria, Virginia,...