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Reactor-grade plutonium
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Reactor-grade plutonium
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.
In contrast to the low burnup of weeks or months that is commonly required to produce weapons-grade plutonium (WGPu/239Pu), 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. When 239
Pu absorbs a neutron, it does not always undergo nuclear fission. Sometimes neutron absorption will instead produce 240
Pu at the neutron temperatures and fuel compositions present in typical light water reactors, with the concentration of 240
Pu steadily rising with longer irradiation, producing lower and lower grade plutonium as time goes on.
Generation II thermal-neutron reactors (today's most numerous nuclear power stations) 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. Russia has also produced a new type of Remix fuel that directly recycles reactor grade plutonium at 1% or less concentration into fresh or re-enriched uranium fuel imitating the 1% plutonium level of high-burnup fuel.
At the beginning of the industrial scale production of plutonium-239 in war era production reactors, trace contamination or co-production with plutonium-240 was initially observed, with these trace amounts resulting in the dropping of the Thin Man weapon-design as unworkable. The difference in purity, of how much, continues to be important in assessing significance in the context of nuclear proliferation and weapons-usability.
The DOE definition of reactor grade plutonium changed in 1976. Before this, three grades were recognised. The change in the definition for reactor grade, from describing plutonium with greater than 7% Pu-240 content prior to 1976, to reactor grade being defined as containing 19% or more Pu-240, coincides with the 1977 release of information about a 1962 "reactor grade nuclear test". The question of which definition or designation applies, that of the old or new scheme, to the 1962 "reactor-grade" test, has not been officially disclosed.
From 1976, four grades were recognised:
Reprocessing or recycling of the spent fuel from the most common class of civilian-electricity-generating or power reactor design, the LWR, (with examples being the PWR or BWR) recovers reactor grade plutonium (as defined since 1976), not fuel grade.
The physical mixture of isotopes in reactor-grade plutonium make it extremely difficult to handle and form and therefore explains its undesirability as a weapon-making substance, in contrast to weapons grade plutonium, which can be handled relatively safely with thick gloves.
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Reactor-grade plutonium AI simulator
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Reactor-grade plutonium
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.
In contrast to the low burnup of weeks or months that is commonly required to produce weapons-grade plutonium (WGPu/239Pu), 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. When 239
Pu absorbs a neutron, it does not always undergo nuclear fission. Sometimes neutron absorption will instead produce 240
Pu at the neutron temperatures and fuel compositions present in typical light water reactors, with the concentration of 240
Pu steadily rising with longer irradiation, producing lower and lower grade plutonium as time goes on.
Generation II thermal-neutron reactors (today's most numerous nuclear power stations) 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. Russia has also produced a new type of Remix fuel that directly recycles reactor grade plutonium at 1% or less concentration into fresh or re-enriched uranium fuel imitating the 1% plutonium level of high-burnup fuel.
At the beginning of the industrial scale production of plutonium-239 in war era production reactors, trace contamination or co-production with plutonium-240 was initially observed, with these trace amounts resulting in the dropping of the Thin Man weapon-design as unworkable. The difference in purity, of how much, continues to be important in assessing significance in the context of nuclear proliferation and weapons-usability.
The DOE definition of reactor grade plutonium changed in 1976. Before this, three grades were recognised. The change in the definition for reactor grade, from describing plutonium with greater than 7% Pu-240 content prior to 1976, to reactor grade being defined as containing 19% or more Pu-240, coincides with the 1977 release of information about a 1962 "reactor grade nuclear test". The question of which definition or designation applies, that of the old or new scheme, to the 1962 "reactor-grade" test, has not been officially disclosed.
From 1976, four grades were recognised:
Reprocessing or recycling of the spent fuel from the most common class of civilian-electricity-generating or power reactor design, the LWR, (with examples being the PWR or BWR) recovers reactor grade plutonium (as defined since 1976), not fuel grade.
The physical mixture of isotopes in reactor-grade plutonium make it extremely difficult to handle and form and therefore explains its undesirability as a weapon-making substance, in contrast to weapons grade plutonium, which can be handled relatively safely with thick gloves.