Military Warheads as a Source of Nuclear Fuel
Military Warheads as a Source of Nuclear Fuel
Nuclear Issues Briefing Paper 4
Weapons-grade uranium and plutonium surplus to military requirements in the USA and Russia is being made available for use as civil fuel.
Weapons-grade uranium is highly enriched, to over 90% U-235 (the fissile isotope). Weapons-grade plutonium has over 93% Pu-239 and can be used, like reactor-grade plutonium, in fuel for electricity production.
Highly-enriched uranium from weapons stockpiles is displacing some 10,600 tonnes of U3O8 production from mines each year, and meets about 13% of world reactor requirements.
For more than three decades concern has centred on the possibility that uranium intended for commercial nuclear power might be diverted for use in weapons. Today, however, attention is focused on the role of military uranium as a major source of fuel for commercial nuclear power.
Since 1987 the United States and countries of the former USSR have signed a series of disarmament treaties to reduce the nuclear arsenals by about 80%.
Nuclear materials declared surplus to military requirements by the USA and Russia are now being converted into fuel for commercial nuclear reactors. The main material is highly enriched uranium (HEU), containing at least 20% uranium-235 (U-235) and usually about 90% U-235. HEU can be blended down with uranium containing low levels of U-235 to produce low enriched uranium (LEU), typically less than 5% U-235, fuel for power reactors. It is blended with depleted uranium (mostly U-238), natural uranium (0.7% U-235), or partially-enriched uranium.
Highly-enriched uranium in US and Russian weapons and other military stockpiles amounts to about 2000 tonnes, equivalent to about twelve times annual world mine production.
World stockpiles of weapons-grade plutonium are reported to be some 260 tonnes, which if used in mixed oxide fuel in conventional reactors would be equivalent to a little over one year's world uranium production. Military plutonium can blended with uranium oxide to form mixed oxide (MOX) fuel.
After LEU or MOX is burned in power reactors, the spent fuel is not suitable for weapons manufacture.
Megatons to Megawatts
Commitments by the US and Russia to convert nuclear weapons into fuel for electricity production is known as the Megatons to Megawatts program.
Surplus weapons-grade HEU resulting from the various disarmament agreements led in 1993 to an agreement between the US and Russian governments. Under this Russia is to convert 500 tonnes of HEU from warheads and military stockpiles (equivalent to around 20,000 bombs) to LEU to be bought by the USA for use in civil nuclear reactors.
In 1994, a US$12 billion implementing contract was signed between the US Enrichment Corporation (now USEC Inc) and Russia's Technabexport (Tenex) as executive agents for the US and Russian governments. USEC is purchasing a minimum of 500 tonnes of weapons-grade HEU over 20 years, at a rate of up to 30 tonnes/year from 1999. The HEU is blended down to 15,259 t of LEU at 4.4% U-235 in Russia, using 1.5% U-235 (enriched tails), to restrict levels of U-234 in the final product. USEC can then sell the LEU to its utility customers as fuel.
In September 2005 this program reached its halfway point of 250 tonnes HEU, producing some 7500 t LEU. At the end of June 2006 some 275 tonnes had produced 8090 tonnes of low-enriched fuel, for which Tenex in Russia had received US$ 4.1 billion. USEC claimed the elimination of 11,000 nuclear warheads.
For its part, the US Government has declared just over 174 tonnes of HEU (of various enrichments) to be surplus from military stockpiles. Of this, USEC has taken delivery of 14.2 tonnes in the form of uranium hexafluoride (UF6) containing around 75% U-235, and 50 tonnes as uranium oxide or metal containing around 40% U-235. Downblending of the UF6 was completed in 1998, to produce 387 tonnes of LEU. Some 13.5 tonnes of the HEU oxide or metal had been processed by September 2001 to produce 140.3 tonnes of LEU. In 2004 the Nuclear Regulatory Commission issued a licence for downblending 33 tonnes HEU by Nuclear Fuel Services in Tennessee and in 2005 the first delivery was made to a power plant.
In mid 2006 USEC announced that it had arranged the downblending of some US high-enriched uranium for use in power generation, making a total of 50 tonnes of this US material producing almost 660 tonnes of low-enriched fuel.
In mid 2007 the US Department of Energy's National Nuclear Security Administration awarded contracts to Nuclear Fuel Services and Wesdyne International to downblend 17.4 tonnes of HEU. NFS will downblend the material in Tennessee to yield some 290 tonnes of LEU by 2010. Wesdyne, the prime contractor, will then store the LEU at the Westinghouse fuel fabrication plant in South Carolina to be available for the Reliable Fuel Supply program. The fuel will be available for use in civilian reactors by nations in good standing with the International Atomic Energy Agency (IAEA) that have good nonproliferation credentials and are not pursuing uranium enrichment and reprocessing technologies. The LEU will be provided to qualifying countries only in the event of an emergency, such as a disruption in supply that cannot be corrected through normal commercial means, and would be sold at the current market price. To cover the cost of the project, Wesdyne will sell a small part of the LEU on the market over a three to four year period.
In the short term most US military HEU is likely to be blended down to 20% U-235, then stored. In this form it is not useable for weapons.
A more detailed paper on the US-Russia HEU Agreement is on the WNA web site.
Overall, the blending down of 500 tonnes of Russian weapons HEU will result in about 15,000 tonnes of LEU over 20 years. This is equivalent to about 152,000 tonnes of natural U, or just over twice annual world demand.
From 2000 the dilution of 30 tonnes of military HEU is displacing about 10,600 tonnes of uranium oxide mine production per year which represents some 13% of world reactor requirements.
Under the 1994 Agreement, USEC recognised the need to release the diluted military uranium to nuclear utilities in such a way as not to impact negatively on the US uranium market.
How the Market Works
Normally, a utility buys natural uranium from a mining company as "yellowcake" (U3O8) and has it converted to UF6. It then supplies this feed to USEC, paying them for the enrichment component. USEC runs its energy-intensive enrichment plant to separate an appropriate amount of enriched uranium (eg at 3.5 - 5.0% U-235, leaving a lot of depleted uranium). USEC then returns the enriched uranium to the utility for its reactor.
A different, and somewhat complicated, system is used for the Russian material. The utility supplies the feed component of natural uranium as before and pays USEC for the enrichment component. But instead of running their plant, USEC pays the Russians for some blended-down weapons uranium and passes this on to the customer utility as "enriched" uranium fuel. The customers receive the blended-down Russian material, paid for as if it were their own uranium which had been enriched.
USEC pays Russia for the enrichment services component (basically energy) of the low-enriched product it receives. Russia takes ownership of the corresponding amount of natural uranium "feed" provided to USEC by its utility customers for toll enrichment services. The material remains in the US, and Russia receives the proceeds of its sale. The customers receive the Russian material, and pay as though it were their own uranium which had been enriched.
Problems arose because the natural uranium feed, now owned by Russia, could not be sold at a price satisfactory to its new owner, so some 11,000 tonnes has accumulated at USEC since January 1997.
1999 Market Agreement
After years of stalled negotiations on this matter, a US$ 2.8 billion deal was approved early in 1999 by the US and Russian governments. It involves 163,000 tonnes of U3O8 feed to be supplied over the remaining 15 years of the US-Russian HEU agreement.
Cameco, Cogema, and Nukem have signed the commercial agreement with Tenex of Russia, giving them "exclusive options to purchase" 118,000 tonnes of this, leaving the remainder "available to Tenex". One important stipulation is that stockpiles, each of some 26 000 tonnes U3O8, will be held by both Russian and US governments for ten years, to 2009. The US stockpile already exists, Russia¹s will be built up over the next few years from all HEU feed not purchased by Tenex or an associate, and Russia is free to sell only what exceeds this.
The new agreement does not change the overall supply and demand situation, but it removes some major uncertainties over how the material is released to the market. This should help stabilise the nuclear fuel market, albeit at a level which favours low-cost producers.
Plutonium and MOX
Disarmament will also give rise to some 150-200 tonnes of weapons-grade plutonium (Pu). Weapons-grade plutonium has over 93% of the fissile isotope, Pu-239, and can be used, like reactor-grade Pu, in fuel for electricity production. Options for its disposal include:
Immobilisation with high-level waste - treating plutonium as waste,
Fabrication with uranium oxide as a MOXfuel for burning in existing reactors,
Fuelling fast-neutron reactors.
In June 2000, the USA and Russia agreed to dispose of 34 tonnes each of weapons-grade plutonium by 2014. The US undertook to pursue a dual track program (immobilisation and MOX), self-funded, while the G-7 nations are to provide some US$ 1 billion to set up Russia's program, which is MOX-oriented.
In the USA there is wide support for burning plutonium as a MOX fuel in conventional reactors. A consortium has been retained and funded to implement the program to convert 25.5 tonnes of plutonium to MOX, and it has applied for a construction permit to build a MOX fabrication plant. The federal budget for 2002 has set aside $115 million for the MOX program. However, the Department of Energy has deferred the US$ 1.2 billion funding for construction of the facilities needed for the plutonium immobilisation (for 8.5 tPu).
After environmental and safety reviews, the Nuclear Regulatory Commission authorised construction of a mixed-oxide (MOX) fuel fabrication plant at the DOE Savannah River site in South Carolina by Duke, Cogema, Stone & Webster (DCS). Construction started late in 2005. It will make civil MOX from depleted uranium and weapons-grade plutonium, unlike other MOX plants which use reactor-grade plutonium having around one third non-fissile Pu isotopes. US reactors using the fuel will need to licensed for it. DCS is under contract to the National Nuclear Security Administration, which will own the plant.
In June 2005 the first four fuel assemblies with mixed oxide fuel made from US military plutonium (plus depleted uranium) started generating electricity in Duke Power's Catawba-1 nuclear power plant in South Carolina, on a trial basis. They incorporate 140 kg of weapons-grade plutonium. The plutonium was made into 2 tonnes of pellets at the Cadrache plant and then fabricated into fuel assemblies at the Melox plant in France.
Meanwhile the US has developed a "spent fuel standard". This specifies that plutonium should never be more accessible than if it were incorporated in spent fuel and thus protected from interference by strong gamma radiation. The plutonium immobilisation plant, when it is eventually built, will thus incorporate the Pu in a version of Synroc (artificial rock), and encase small discs of this in canisters of vitrified high-level radioactive waste.
Europe's well-developed MOX capacity suggests that weapons plutonium could be disposed of relatively quickly. Input weapons-grade plutonium might need to be mixed with reactor grade material, but using such MOX as 30% of the fuel in one third of the world's reactor capacity would remove about 15 tonnes of warhead plutonium per year. This would amount to burning 3000 warheads per year to produce 110 billion kWh of electricity.
Over 35 reactors in Europe are licensed to use MOX fuel, and 20 French reactors are licensed to use it as 30% of their fuel.
Russia intends to use its plutonium to fuel nuclear reactors, particularly fast neutron reactors such as its BN-600 at Beloyarsk. The USA earlier insisted that it duplicate US plans to make it into MOX fuel for late-model conventional reactors, and for this Russia insisted that the USA pay all costs. But after announcement of the Global Nuclear Energy partnership in 2006 with its use of fast reactors, US objection to Russian plans disappeared. The 34 tonnes of plutonium initially available for MOX would have been enough for 1350 fuel assemblies for light-water reactors.
Burning the plutonium in the BN-600 reactor would use only about 330 kg per year as MOX. The unit would be run from 2010 as a plutonium incinerator, with the breeding blanket of depleted uranium removed. The BN-800 reactor now under construction (but delayed by lack of finance) would improve on this.
Since the early 1990s Russia has had a program to develop a thorium-uranium fuel, which more recently has moved to have a particular emphasis on utilisation of weapons-grade plutonium in a thorium-plutonium fuel.
The program is based at Moscow's Kurchatov Institute and involves the US company Thorium Power and US government funding to design fuel for Russian VVER-1000 reactors. Whereas normal fuel uses enriched uranium oxide, the new design has a demountable centre portion and blanket arrangement, with the plutonium in the centre and the thorium (with uranium) around it*. The Th-232 becomes U-233, which is fissile - as is the core Pu-239. Blanket material remains in the reactor for 9 years but the centre portion is burned for only three years (as in a normal VVER). Design of the seed fuel rods in the centre portion draws on extensive experience of Russian navy reactors.
*More precisely: A normal VVER-1000 fuel assembly has 331 rods each 9 mm diameter forming a hexagonal assembly 235 mm wide. Here, the centre portion of each assembly is 155 mm across and holds the seed material consisting of metallic Pu-Zr alloy (Pu is about 10% of alloy, and isotopically over 90% Pu-239) as 108 twisted tricorn-section rods 12.75 mm across with Zr-1%Nb cladding. The sub-critical blanket consists of U-Th oxide fuel pellets (1:9 U:Th, the U enriched up to almost 20%) in 228 Zr-1%Nb cladding tubes 8.4 mm diameter - four layers around the centre portion. The blanket material achieves 100 GWd/t burn-up. Together as one fuel assembly the seed and blanket have the same geometry as a normal VVER-100 fuel assembly.
The thorium-plutonium fuel claims four advantages over MOX: proliferation resistance, compatibility with existing reactors - which will need minimal modification to be able to burn it, and the fuel can be made in existing plants in Russia - hence it could be used from 2006. In addition, a lot more plutonium can be put into a single fuel assembly than with MOX, so that three times as much can be disposed of as when using MOX. The spent fuel amounts to about half the volume of MOX and is even less likely to allow recovery of weapons-useable material than spent MOX fuel, since less fissile plutonium remains in it. With an estimated 150 tonnes of weapons Pu in Russia, the thorium-plutonium project would not necessarily cut across existing plans to make MOX fuel.
Ivanov, 2000, paper in Proceedings of 25th UI Symposium.
World Nuclear Association, 2001, The Global Nuclear Fuel Market, Supply and Demand 1998-2020.
NATO ASI series, 1994, Managing the Plutonium Surplus: Applications and Technical Options.
Underhill, D H, 1998, paper to U'98 Conference, Adelaide.
USEC, Megatons to Megawatts Program, Status Report 2001.
Thorium Power 2003, Weapons-grade Plutonium Burning Fuel for Russian VVER-1000 Nuclear Power Plants.
Morozov et al 2005, Thorium fuel as a superior approach to disposing of excess weapons-grade plutonium in Russian VVER-1000 reactors. Nuclear Future?