page_title: Reactor-grade plutonium
section_title: Reuse in reactors
hierarchical_section_title: Reactor-grade plutonium / Reuse in reactors
caption_attribution_description: English: Integral Fast Reactor concept. Fuel makes electricity and when spent, goes next door to be recycled as new fuel pins.
context_page_description: Reactor-grade plutonium 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.
  In contrast to the low burnup of weeks or months that is commonly required to produce weapons-grade plutonium, the long time in the reactor that produces reactor-grade plutonium leads to transmutation of much of the fissile, relatively long half-life isotope ²³⁹Pu into a number of other isotopes of plutonium that are less fissile or more radioactive.
  Generation II thermal-neutron reactors can reuse reactor-grade plutonium only to a limited degree as MOX fuel, and only for a second cycle. Fast-neutron reactors, of which there are a handful operating today with a half dozen under construction, can use reactor-grade plutonium fuel as a means to reduce the transuranium content of spent nuclear fuel/nuclear waste.
context_section_description: Today's moderated/thermal reactors primarily run on the once-thru fuel cycle though they can reuse once-thru reactor-grade plutonium to a limited degree in the form of mixed-oxide or MOX fuel, which is a routine commercial practice in most countries outside the US as it increases the sustainability of nuclear fission and lowers the volume of high level nuclear waste. 
  One third of the energy/fissions at the end of the practical fuel life in a thermal reactor are from plutonium, the end of cycle occurs when the U-235 percentage drops, the primary fuel that drives the neutron economy inside the reactor and the drop necessitates fresh fuel being required, so without design change, one third of the fissile fuel in a new fuel load can be fissile reactor-grade plutonium with one third less of Low enriched uranium needing to be added to continue the chain reactions anew, thus achieving a partial recycling. 
  A typical 5.3% reactor-grade plutonium MOX fuel bundle, is transmutated when it itself is again burnt, a practice that is typical in French thermal reactors, to a twice-thru reactor-grade plutonium, with an isotopic composition of 40.8% Pu-239 and 30.6% Pu-240 at the end of cycle (EOC). "MOX grade plutonium(MGPu)" is generally defined as having more than 30% Pu-240.
  A limitation in the number of recycles exists within thermal reactors, as opposed to the situation in fast reactors, as in the thermal neutron spectrum only the odd-mass isotopes of plutonium are fissile, the even-mass isotopes thus accumulate, in all high thermal-spectrum burnup scenarios. Plutonium-240, an even-mass isotope is, within the thermal neutron spectrum, a fertile material like uranium-238, becoming fissile plutonium-241 on neutron capture; however, the even-mass plutonium-242 not only has a low neutron capture cross section within the thermal spectrum, it also requires 3 neutron captures before becoming a fissile nuclide. 
  While most thermal neutron reactors must limit MOX fuel to less than half of the total fuel load for nuclear stability reasons, due to the reactor design operating within the limitations of a thermal spectrum of neutrons, Fast neutron reactors on the other hand can use plutonium of any isotopic composition, operate on completely recycled plutonium and in the fast "burner" mode, or fuel cycle, fission and thereby eliminate all the plutonium present in the world stockpile of once-thru spent fuel.  The modernized IFR design, known as the S-PRISM concept and the Stable salt reactor concept, are two such fast reactors that are proposed to burn-up/eliminate the plutonium stockpiles in Britain that was produced from operating its fleet of inefficient MAGNOX reactors and thus has generated the largest civilian stockpile of fuel-grade/"reactor-grade plutonium" in the world.
  In Bathke's equation on "attractiveness level" of Weapons-grade nuclear material, the Figure of Merit(FOM) the calculation generates, returns the suggestion that Sodium Fast Breeder Reactors are unlikely to reach the desired level of proliferation resistance, while Molten Salt breeder reactors are more likely to do so.
  In the fast breeder reactor cycle, or fast breeder mode, as opposed to the fast-burner, the French Phénix reactor uniquely demonstrated multi-recycling and reuses of its reactor grade plutonium. Similar reactor concepts and fuel cycling, with the most well known being the Integral Fast Reactor are regarded as one of the few that can realistically achieve "planetary scale sustainability", powering a world of 10 billion, whilst still retaining a small environmental footprint. In breeder mode, fast reactors are therefore often proposed as a form of renewable or sustainable nuclear energy. Though the "[reactor-grade]plutonium economy" it would generate, presently returns social distaste and varied arguments about proliferation-potential, in the public mindset.
  As is typically found in civilian European thermal reactors, a 5.3% plutonium MOX fuel-bundle, produced by conventional wet-chemical/PUREX reprocessing of an initial fuel assembly that generated 33 GWd/t
caption: IFR concept (Black and White with clearer text). The pyroprocessing cycle is not limited to sodium-fast-reactors such as the depicted IFR, many other conceptual reactors such as the Stable salt reactor are designed to rely on fuel from it, rather than PUREX.
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