The hydrogen-moderated self-regulating nuclear power module (HPM), also referred to as the compact self-regulating transportable reactor (ComStar), is a type of

nuclear power reactor A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from ...

using

hydride In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride of ...

as a neutron moderator. The design is inherently safe, as the fuel and the neutron moderator is

uranium hydride Uranium hydride, also called uranium trihydride (UH3), is an inorganic compound and a hydride of uranium. Properties Uranium hydride is a highly toxic, brownish grey to brownish black pyrophoric powder or brittle solid. Its density at 20 ° ...

UH₃, which is reduced at high temperatures (500–800 °C) to

uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weakly ...

and

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

. The gaseous hydrogen exits the core, being absorbed by hydrogen absorbing material such as

depleted uranium Depleted uranium (DU; also referred to in the past as Q-metal, depletalloy or D-38) is uranium with a lower content of the fissile isotope than natural uranium.: "Depleted uranium possesses only 60% of the radioactivity of natural uranium, ...

, thus making it less critical. This means that with rising temperature the neutron moderation drops and the

nuclear fission Nuclear fission is a nuclear reaction, reaction in which the atomic nucleus, nucleus of an atom splits into two or more smaller atomic nucleus, nuclei. The fission process often produces gamma ray, gamma photons, and releases a very large ...

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 (often shortened as Los Alamos and LANL) is one of the sixteen research and development laboratories of the United States Department of Energy (DOE), located a short distance northwest of Santa Fe, New Mexico, i ...

(LANL) in

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

. 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 Gen4 Energy, Inc (formerly Hyperion Power Generation, Inc.TRIGA TRIGA (Training, Research, Isotopes, General Atomics) is a class of nuclear research reactor designed and manufactured by General Atomics. The design team for TRIGA, which included Edward Teller, was led by the physicist Freeman Dyson. Design ...

research reactors, which are operated by research laboratories and universities around the world, as well as the

SNAP-10A SNAP-10A (Systems for Nuclear Auxiliary Power, aka Snapshot for Space Nuclear Auxiliary Power Shot, also known as OPS 4682) was a US experimental nuclear powered satellite launched into space in 1965 as part of the SNAPSHOT program.

Characteristics

According to the patent application the reactor design has some notable characteristics, that sets it apart from other reactor designs. It uses

(UH₃) "low-enriched" to 5%

uranium-235 Uranium-235 (235U or U-235) is an Isotopes of uranium, isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile ...

—the remainder is

uranium-238 Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However ...

—as the nuclear fuel, rather than the usual metallic uranium or

uranium dioxide Uranium dioxide or uranium(IV) 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 reac ...

that composes the

fuel rod Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission. Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing ...

s of contemporary

light-water reactor The light-water reactor (LWR) is a type of thermal-neutron reactor that uses normal water, as opposed to heavy water, as both its coolant and neutron moderator; furthermore a solid form of fissile elements is used as fuel. Thermal-neutron reac ...

s. In fact, within the application, the contemporary "rod" based design with fuel rods and

control rod Control rods are used in nuclear reactors to control the rate of fission of the nuclear fuel – uranium or plutonium. Their compositions include chemical elements such as boron, cadmium, silver, hafnium, or indium, that are capable of absorbing ...

s is completely omitted from the proposed reactor design in favor of a "tub" design with passive

heat pipe A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces. At the hot interface of a heat pipe, a volatile liquid in contact with a thermally conductive solid surface turns into a vapor ...

s conducting heat to the heat exchanger running through the "tub" of granulated uranium hydride. The likely

coolant A coolant is a substance, typically liquid, that is used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corros ...

to be used is

potassium Potassium is the chemical element with the symbol K (from Neo-Latin '' kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosp ...

. The reactor design in question begins producing power when

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 is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission. Most nuclear fuels contain heavy fissile actinide elements that are capable of undergoi ...

and a neutron moderator; 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 , 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 Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ...

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 Meltdown may refer to: Science and technology * Nuclear meltdown, a severe nuclear reactor accident * Meltdown (security vulnerability), affecting computer processors * Mutational meltdown, in population genetics Arts and entertainment Music * ...

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 Uranium zirconium hydride (UZrH), a combination of uranium hydride and zirconium(II) hydride, is used as the fuel in TRIGA reactors. UZrH fuel is used in most research reactors at universities and has a large, prompt negative fuel temperature coef ...

(UZrH) fuel and is the only reactor licensed by the

U.S. Nuclear Regulatory Commission The Nuclear Regulatory Commission (NRC) is an independent agency of the United States government tasked with protecting public health and safety related to nuclear energy. Established by the Energy Reorganization Act of 1974, the NRC began oper ...

for unattended operation. According to the reactor design specification, the uranium hydride core is surrounded by hydrogen-absorbing storage trays, made of

thorium Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...

. The storage trays can either desorb or absorb the hydrogen gas from the core. During normal operation (with the

operating temperature An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...

being approximately ), 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 from the uranium hydride core, deliver the nuclear generated heat from the core to a

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct conta ...

, which in turn can be connected to a

steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam turb ...

-generator set, for the production of electricity. The only hazards are those of all

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", con ...

s, namely those of

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, vi ...

, 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. In particular, the patent application for the design indicates that using a

thorium fuel cycle The thorium fuel cycle is a nuclear fuel cycle that uses an 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 t ...

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 In nuclear power technology, burnup (also known as fuel utilization) is a measure of how much energy is extracted from a primary nuclear fuel source. It is measured as the fraction of fuel atoms that underwent fission in %FIMA (fissions per init ...

, of up to 50%, in contrast to a

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 MW_e of electric power or 70 MW_th, 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 Monte Carlo N-Particle Transport (MCNP) is a general-purpose, continuous-energy, generalized-geometry, time-dependent, Monte Carlo radiation transport code designed to track many particle types over broad ranges of energies and is developed by Lo ...

. 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 (LLNL) is a federal research facility in Livermore, California, United States. The lab was originally established as the University of California Radiation Laboratory, Livermore Branch in 1952 in response ...

) 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, 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 (or hydrogen-2, symbol or deuterium, also known as heavy hydrogen) is one of two Stable isotope ratio, stable isotopes of hydrogen (the other being Hydrogen atom, protium, or hydrogen-1). The atomic nucleus, nucleus of a deuterium ato ...

(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 Gen4 Energy, Inc (formerly Hyperion Power Generation, Inc.lead-cooled fast reactor The lead-cooled fast reactor is a nuclear reactor design that features a fast neutron spectrum and molten lead or lead-bismuth eutectic coolant. Molten lead or lead-bismuth eutectic can be used as the primary coolant because especially lead, and ...

design for its power module, based on uranium nitride, citing the long development and regulatory licensing process for the uranium hydride reactor design.
Hyperion Power Generation news release, November 18, 2009

References

External links

Patent application
at the

United States Patent and Trademark Office The United States Patent and Trademark Office (USPTO) is an agency in the U.S. Department of Commerce that serves as the national patent office and trademark registration authority for the United States. The USPTO's headquarters are in Alex ...

* {{DEFAULTSORT:Hydrogen Moderated Self-Regulating Nuclear Power Module Nuclear power reactor types