Remix Fuel

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REMIX-Fuel (REgenerated MIXture of U, Pu oxides) was developed in Russia to simplify the reprocessing process, reuse spent fuel, reduce the consumption of natural uranium and to enable multi-recycling. [1] [2] [3]

Contents

Compared to "conventional" MOX-fuel

MOX or Mixed Oxide Fuel [4] as deployed in some western European and East Asian nations generally consists of depleted uranium mixed with between 4% and 7% reactor grade plutonium. Only a few Generation II and about half of Generation III reactor designs are MOX fuel compliant allowing them to use a 100% MOX fuel load with no safety concerns.

Nuclear physics background

However all moderated reactors using lightly enriched uranium fuel produce plutonium in the course of normal operation as Uranium-238 (typically 94% to 97% of the uranium content in lightly enriched uranium [5] ) captures neutrons and undergoes successive beta decays until it is transmuted to plutonium-239. This internally produced plutonium increases in percentage until it is common enough that a growing percentage of fission reactions within the fuel are actually within the plutonium generated during the fuel cycle. Approximately half of the plutonium-239 "bred" during the fuel cycle is fissioned and another 25% is transmuted through additional neutron capture into other plutonium isotopes, primarily Pu-240. Virtually all of the minor actinides present in spent nuclear fuel are produced by successive neutron capture of the plutonium produced and as decay products of the more short lived isotopes. As a consequence of these factors the fresh uranium oxide fuel initially generates all of its fission reactions from U-235 but at the end of the cycle this has shifted to 50% U-235/50% Pu-239 fission reactions. In total about 33% of the energy generated by uranium fuel at the end of its life cycle actually comes from the bred and consumed Pu-239. Because the thermal neutron spectrum is not very good for fissioning Pu-239 the fuel shifts from 100% uranium at start of cycle to 96% uranium, 1% plutonium and 3% mixture of transuranic minor actinides and fission products. The longer the fuel remains in the reactor undergoing fission the more the uranium percentage decreases while the other materials increase. In effect all power reactors have been long known to be capable of operating with a mixed fissionable core containing 1% reactor grade plutonium without issues arising like those caused by the more highly concentrated MOX fuel used in western reactors. [6] [7] Ultimately, the spent fuel is removed from power reactors long before all available "fuel" is actually consumed, as neutron poisons and minor actinides with undesirable properties build up to unacceptable levels and alter the reaction parameters too much. Nuclear reprocessing is primarily done to remove undesirable parts of the spent fuel and either re-use the other parts or store them as waste. Reprocessed uranium for example, which is derived from spent fuel, usually has a higher uranium-235 content than natural uranium.

Process

Russia spent nearly a decade developing techniques similar to nuclear pyroprocessing that allows them to reprocess spent nuclear fuel without separating the recycled uranium and plutonium as is done in the PUREX chemical reprocessing system used to manufacture MOX fuel. [8] [9] Small volumes of enriched uranium are added to this recovered mixture of non-separated uranium and plutonium so that it performs similarly to the fuel made only from freshly enriched uranium. [10] [3] [2] After extensive testing in a reactor starting in 2016 [11] Russia is now deploying Remix Fuel as replacement fuel for their VVER pressurized water reactors as of February 2020.

Experiments at Balakovo Nuclear Power Plant

Balakovo Nuclear Power Plant is used for the pilot program. In December 2024 the third final 18-month phase of the program has started with the goal to achieve closed nuclear cycle for VVER reactors. A mixture of enriched uranium with recycled uranium and plutonium received from the used nuclear fuel at VVER reactors is used instead of a standard enriched uranium. After the first 2 stages of 3, fuel elements were inspected and were approved for the 3rd final stage. The 3rd stage should conclude in 2026 when the fuel will be unloaded and further studied. Remix fuel has a lower plutonium content of up to 5% compared with MOX fuel. [12]

Related Research Articles

<span class="mw-page-title-main">Nuclear fuel cycle</span> Process of manufacturing and using nuclear fuel

The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in the back end, which are necessary to safely manage, contain, and either reprocess or dispose of spent nuclear fuel. If spent fuel is not reprocessed, the fuel cycle is referred to as an open fuel cycle ; if the spent fuel is reprocessed, it is referred to as a closed fuel cycle.

<span class="mw-page-title-main">Nuclear reprocessing</span> Chemical operations that separate fissile material from spent fuel to be recycled as new fuel

Nuclear reprocessing is the chemical separation of fission products and actinides from spent nuclear fuel. Originally, reprocessing was used solely to extract plutonium for producing nuclear weapons. With commercialization of nuclear power, the reprocessed plutonium was recycled back into MOX nuclear fuel for thermal reactors. The reprocessed uranium, also known as the spent fuel material, can in principle also be re-used as fuel, but that is only economical when uranium supply is low and prices are high. Nuclear reprocessing may extend beyond fuel and include the reprocessing of other nuclear reactor material, such as Zircaloy cladding.

Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alternative to the low-enriched uranium fuel used in the light-water reactors that predominate nuclear power generation.

<span class="mw-page-title-main">Fast-neutron reactor</span> Nuclear reactor where fast neutrons maintain a fission chain reaction

A fast-neutron reactor (FNR) or fast-spectrum reactor or simply a fast reactor is a category of nuclear reactor in which the fission chain reaction is sustained by fast neutrons, as opposed to slow thermal neutrons used in thermal-neutron reactors. Such a fast reactor needs no neutron moderator, but requires fuel that is relatively rich in fissile material when compared to that required for a thermal-neutron reactor. Around 20 land based fast reactors have been built, accumulating over 400 reactor years of operation globally. The largest was the Superphénix sodium cooled fast reactor in France that was designed to deliver 1,242 MWe. Fast reactors have been studied since the 1950s, as they provide certain advantages over the existing fleet of water-cooled and water-moderated reactors. These are:

<span class="mw-page-title-main">Integral fast reactor</span> Nuclear reactor design

The integral fast reactor (IFR), originally the advancedliquid-metal reactor (ALMR), is a design for a nuclear reactor using fast neutrons and no neutron moderator. IFRs can breed more fuel and are distinguished by a nuclear fuel cycle that uses reprocessing via electrorefining at the reactor site.

<span class="mw-page-title-main">PUREX</span> Spent fuel reprocessing process for plutonium and uranium recovery

PUREX is a chemical method used to purify fuel for nuclear reactors or nuclear weapons. PUREX is the de facto standard aqueous nuclear reprocessing method for the recovery of uranium and plutonium from used nuclear fuel. It is based on liquid–liquid extraction ion-exchange.

<span class="mw-page-title-main">Nuclear fuel</span> Material fuelling nuclear reactors

Nuclear fuel refers to any substance, typically fissile material, which is used by nuclear power stations or other nuclear devices to generate energy.

<span class="mw-page-title-main">Fertile material</span> Substance that can be converted into material for use in nuclear fission

Fertile material is a material that, although not fissile itself, can be converted into a fissile material by neutron absorption.

<span class="mw-page-title-main">Plutonium-239</span> Isotope of plutonium

Plutonium-239 is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in thermal spectrum nuclear reactors, along with uranium-235 and uranium-233. Plutonium-239 has a half-life of 24,110 years.

Plutonium (94Pu) is an artificial element, except for trace quantities resulting from neutron capture by uranium, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long before being found in nature, the first isotope synthesized being 238Pu in 1940. Twenty-two plutonium radioisotopes have been characterized. The most stable are 244Pu with a half-life of 80.8 million years; 242Pu with a half-life of 373,300 years; and 239Pu with a half-life of 24,110 years; and 240Pu with a half-life of 6,560 years. This element also has eight meta states; all have half-lives of less than one second.

<span class="mw-page-title-main">Thorium fuel cycle</span> Nuclear fuel cycle

The thorium fuel cycle is a nuclear fuel cycle that uses an isotope of thorium, 232
Th
, as the fertile material. In the reactor, 232
Th
 is transmuted into the fissile artificial uranium isotope 233
U
 which is the nuclear fuel. Unlike natural uranium, natural thorium contains only trace amounts of fissile material, which are insufficient to initiate a nuclear chain reaction. Additional fissile material or another neutron source is necessary to initiate the fuel cycle. In a thorium-fuelled reactor, 232
Th
 absorbs neutrons to produce 233
U
. This parallels the process in uranium breeder reactors whereby fertile 238
U
 absorbs neutrons to form fissile 239
Pu
. Depending on the design of the reactor and fuel cycle, the generated 233
U
 either fissions in situ or is chemically separated from the used nuclear fuel and formed into new nuclear fuel.

<span class="mw-page-title-main">Spent nuclear fuel</span> Nuclear fuel thats been irradiated in a nuclear reactor

Spent nuclear fuel, occasionally called used nuclear fuel, is nuclear fuel that has been irradiated in a nuclear reactor. It is no longer useful in sustaining a nuclear reaction in an ordinary thermal reactor and, depending on its point along the nuclear fuel cycle, it will have different isotopic constituents than when it started.

<span class="mw-page-title-main">Weapons-grade nuclear material</span> Nuclear material pure enough to be used for nuclear weapons

Weapons-grade nuclear material is any fissionable nuclear material that is pure enough to make a nuclear weapon and has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium in grades normally used in nuclear weapons are the most common examples.

Uranium-236 is an isotope of uranium that is neither fissile with thermal neutrons, nor very good fertile material, but is generally considered a nuisance and long-lived radioactive waste. It is found in spent nuclear fuel and in the reprocessed uranium made from spent nuclear fuel.

In nuclear power technology, burnup 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 or %FIFA as well as, preferably, the actual energy released per mass of initial fuel in gigawatt-days/metric ton of heavy metal (GWd/tHM), or similar units.

Reactor-grade plutonium (RGPu) is the isotopic grade of plutonium that is found in spent nuclear fuel after the uranium-235 primary fuel that a nuclear power reactor uses has burnt up. The uranium-238 from which most of the plutonium isotopes derive by neutron capture is found along with the U-235 in the low enriched uranium fuel of civilian reactors.

The Reduced-Moderation Water Reactor (RMWR), also referred to as the Resource-renewable BWR, is a proposed type of light water moderated nuclear power reactor, featuring some characteristics of a fast neutron reactor, thereby combining the established and proven technology of light water reactors with the desired features of fast neutron reactors. The RMWR concept builds upon the Advanced Boiling Water Reactor and is under active development in theoretical studies, particularly in Japan. Hitachi and the Japan Atomic Energy Agency are both involved in research.

<span class="mw-page-title-main">Balakovo Nuclear Power Plant</span> Nuclear power plant in Saratov Oblast, Russia

Balakovo nuclear power station is located in the city of Balakovo, Saratov Oblast, Russia, about 900 kilometres (560 mi) south-east of Moscow. It consists of four operational reactors; fifth and sixth unit construction cancelled. Owner and operator of the nuclear power station is Rosenergoatom.

Reprocessed uranium (RepU) is the uranium recovered from nuclear reprocessing, as done commercially in France, the UK and Japan and by nuclear weapons states' military plutonium production programs. This uranium makes up the bulk of the material separated during reprocessing.

<span class="mw-page-title-main">Nuclear transmutation</span> Conversion of an atom from one element to another

Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.

References

  1. ↑ "TVEL outlines innovation in nuclear fuel : Uranium & Fuel - World Nuclear News". www.world-nuclear-news.org.
  2. 1 2 Teplov, Pavel S.; Alekseev, Pavel N.; Bobrov, Evgeniy A.; Chibinyaev, Alexander V. (2016-10-28). "Physical and economical aspects of Pu multiple recycling on the basis of REMIX reprocessing technology in thermal reactors". EPJ Nuclear Sciences & Technologies. 2: 41. doi:10.1051/epjn/2016034.
  3. 1 2 Thonney (2021-06-08). "Russia begins pilot production of Remix fuel assemblies". Nuclear Engineering International. Archived from the original on 2024-10-19. Retrieved 2024-10-19.
  4. ↑ "MOX, Mixed Oxide Fuel - World Nuclear Association". www.world-nuclear.org.
  5. ↑ "Nuclear Fuel Facts: Uranium".
  6. ↑ "Nuclear Fuel Fabrication - World Nuclear Association". www.world-nuclear.org.
  7. ↑ "REMIX fuel pilot testing starts at Balakovo reactor - World Nuclear News". www.world-nuclear-news.org.
  8. ↑ Simpson, Michael; Law, Jack (2024-10-20). "Nuclear Fuel Reprocessing" (PDF). INL Research Library Digital Repository.
  9. ↑ "Rosatom has launched facility for REMIX-fuel fabrication". rosatom-asia.com. Archived from the original on 2024-10-19. Retrieved 2024-10-19.
  10. ↑ "REMIX fuel ready for final test". World Nuclear News. 2021-11-11. Archived from the original on 2021-11-13. Retrieved 2024-10-19.
  11. ↑ "Russia loads REMIX fuel into MIR research reactor - World Nuclear News". www.world-nuclear-news.org.
  12. ↑ "Final cycle of REMIX nuclear fuel trial under way". World Nuclear News. 3 December 2024. Retrieved 4 December 2024.
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