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Default Thorium power has a protactinium problem

Thorium power has a protactinium problem
By Eva C. Uribe, Aug 6, 2018, Bulletin of the Atomic Scientists

In 1980, the International Atomic Energy Agency (IAEA) observed that
protactinium, a chemical element generated in thorium reactors, could
be separated and allowed to decay to isotopically pure uranium
233—suitable material for making nuclear weapons. The IAEA report,
titled “Advanced Fuel Cycle and Reactor Concepts,” concluded that the
proliferation resistance of thorium fuel cycles “would be equivalent
to” the uranium/plutonium fuel cycles of conventional civilian nuclear
reactors, assuming both included spent fuel reprocessing to isolate
fissile material.

Decades later, the story changed. “Th[orium]-based fuels and fuel
cycles have intrinsic proliferation resistance,” according to the IAEA
in 2005. Mainstream media have repeated this view ever since, often
without caveat. Several scholars have recognized the inherent
proliferation risk of protactinium separations in the thorium fuel
cycle, but the perception that thorium reactors cannot be used to make
weapons persists. While technology has advanced, the fundamental
radiochemistry that governs nuclear fuel reprocessing remains
unchanged. Thus, this shift in perspective is puzzling and reflects a
failure to recognize the importance of protactinium radiochemistry in
thorium fuel cycles.

Protactinium turns 100.

The importance of protactinium chemistry for obtaining highly
attractive fissile material from thorium has been recognized since the
1940s. However, the story really begins 100 years ago during the
earliest research on natural radioactivity. In 1918, Austrian-Swedish
physicist Lise Meitner and German chemist Otto Hahn were on a quest to
discover the long-lived isotope of “eka-tantalum” predicted to lie
between thorium and uranium in the periodic table. The isotope they
sought would decay to actinium, which was always found with uranium
but was known to be the parent of an unknown natural radioactive decay
chain distinct from that of uranium 238, the most common isotope of
uranium found in nature.

Meitner and Hahn discovered that treating pitchblende with nitric acid
yielded an insoluble fraction of silica that associated with tantalum
and eka-tantalum. After many years, they purified enough eka-tantalum
for identification and measured its properties. As discoverers of
eka-tantalum’s longest-lived isotope, Meitner and Hahn named this new
element protactinium. They had isolated protactinium 231, a member of
the uranium 235 decay chain. In 1938, they discovered that
protactinium 233 could be produced by neutron irradiation of thorium
232, the most abundant isotope in naturally occurring thorium.

For the next several decades, protactinium was shrouded in “mystery
and witchcraft” due to its scarcity in nature and its perplexing
chemical properties. We now know that protactinium’s peculiar
chemistry is due to its position in the periodic table, which lends
the element vastly different chemical properties than its neighbors.
Protactinium behaves so differently from thorium and uranium that,
under many conditions, their separation is inevitable.

Scientists did not investigate the macroscopic chemistry of
protactinium until the Manhattan Project. In 1942, Glenn T. Seaborg,
John W. Gofman, and R. W. Stoughton discovered uranium 233 and
observed its propensity to fission. Compared with naturally occurring
uranium 235, uranium 233 has a lower critical mass, which means that
less material can be used to build a weapon. And compared with
weapons-grade plutonium 239, uranium 233 has a much lower spontaneous
fission rate, enabling simpler weapons that are more easily
constructed. A 1951 report by the Manhattan Project Technical Section
describes extensive efforts devoted to the production of uranium 233
via neutron irradiation of thorium 232. Because the initial thorium
feed material was often contaminated with natural uranium 238, the
scientists obtained pure uranium 233 by using a variety of methods for
separating the intermediate protactinium 233.

By this time, advances in technology and projections of uranium
shortages stimulated interest in developing a breeder reactor, which
produces more fissile material than it consumes. In the late 1960s, a
team at Oak Ridge National Laboratory designed a Molten Salt Breeder
Reactor fueled by thorium and uranium dissolved in fluoride salts, but
it could only breed uranium 233 by continuously removing
impurities—including protactinium 233—from the reactor core. To
improve breeding ratios, the researchers investigated methods for
removing protactinium from the molten fluoride salts.

In 1977, President Jimmy Carter banned commercial reprocessing of
spent nuclear fuel, citing concerns with the proliferation of
technology that could be used to make nuclear weapons. And with the
high startup costs of developing new reactors, there would be no place
for the Molten Salt Breeder Reactor in the energy market. With the end
of research on thorium reactors came the end of ambitious research on
protactinium separations. Over time, the role of protactinium in
obtaining weaponizable uranium 233 from thorium was largely forgotten
or dismissed by the thorium community.

Thorium reactors born again.

Fast forward to 2018. Several nations have explored thorium power for
their nuclear energy portfolios. Foremost among these is India.
Plagued by perennial uranium shortages, but possessing abundant
thorium resources, India is highly motivated to develop thorium
reactors that can breed uranium 233. India now operates the only
reactor fueled by uranium 233, the Kalpakkam Mini reactor (better
known as KAMINI).

Thorium reactors have other potential advantages. They could produce
fewer long-lived radioactive isotopes than conventional nuclear
reactors, simplifying the disposal of nuclear waste. Molten salt
reactors offer potential improvements in reactor safety. Additionally,
there is the persistent perception that thorium reactors are
intrinsically proliferation-resistant.

The uranium 233 produced in thorium reactors is contaminated with
uranium 232, which is produced through several different neutron
absorption pathways. Uranium 232 has a half-life of 68.9 years, and
its daughter radionuclides emit intense, highly penetrating gamma rays
that make the material difficult to handle. A person standing 0.5
meters from 5 kilograms of uranium 233 containing 500 parts per
million of uranium 232, one year after it has been separated from the
daughters of uranium 232, would receive a dose that exceeds the annual
regulatory limits for radiological workers in less than an hour.
Therefore, uranium 233 generated in thorium reactors is
“self-protected,” as long as uranium 232 levels are high enough.
However, the extent to which uranium 232 provides adequate protection
against diversion of uranium 233 is debatable. Uranium 232 does not
compromise the favorable fissile material properties of uranium 233,
which is categorized as “highly attractive” even in the presence of
high levels of uranium 232. Uranium 233 becomes even more attractive
if uranium 232 can be decreased or eliminated altogether. This is
where the chemistry of protactinium becomes important.

Protactinium in the thorium fuel cycle.

There are three isotopes of protactinium produced when thorium 232 is
irradiated. Protactinium 231, 232, and 233 are produced either through
thermal or fast neutron absorption reactions with various thorium,
protactinium, and uranium isotopes. Protactinium 231, 232, and 233 are
intermediates in the reactions that eventually form uranium 232 and
uranium 233. Protactinium 232 decays to uranium 232 with a half-life
of 1.3 days. Protactinium 233 decays to uranium 233 with a half-life
of 27 days. Protactinium 231 is a special case: It does not directly
decay to uranium, but in the presence of neutrons it can absorb a
neutron and become protactinium 232.

Neutron absorption reactions only occur in the presence of a neutron
flux, inside or immediately surrounding the reactor core. Radioactive
decay occurs whether or not neutrons are present. For irradiated
thorium, the real concern lies in separating protactinium from
uranium, which may already have significant levels of uranium 232.
Production of protactinium 232 ceases as soon as protactinium is
removed from the neutron flux, but protactinium 232 and 233 continue
to decay to uranium 232 and 233, respectively.

The half-lives of the protactinium isotopes work in the favor of
potential proliferators. Because protactinium 232 decays faster than
protactinium 233, the isotopic purity of protactinium 233 increases as
time passes. If it is separated from its uranium decay products a
second time, this protactinium will decay to equally pure uranium 233
over the next few months. With careful attention to the relevant
radiochemistry, separation of protactinium from the uranium in spent
thorium fuel has the potential to generate uranium 233 with very low
concentrations of uranium 232—a product suitable for making nuclear
weapons.

Scenarios for proliferation.

Although thorium is commonly associated with molten salt reactors, it
can be used in any reactor. Several types of fuel cycles enable
feasible, rapid reprocessing to extract protactinium. One is aqueous
reprocessing of thorium oxide “blankets” irradiated outside the core
of a heavy water reactor. Many heavy water reactors include on-power
fueling, which means that irradiated thorium can be removed quickly
and often, without shutting the reactor down. As very little fission
would occur in the blanket material, its radioactivity would be lower
than that of spent fuel from the core, and it could be reprocessed
immediately.

Myriad possibilities exist for the aqueous separation of protactinium
from thorium and uranium oxides, including the commonly proposed
thorium uranium extraction (THOREX) process. Alternatively, once
dissolved in acid, protactinium can simply be adsorbed onto glass or
silica beads, exploiting the same chemical mechanism used by Meitner
and Hahn to isolate protactinium from natural uranium a century ago.

Another scenario is continuous reprocessing of molten salt fuel to
remove protactinium and uranium from thorium. Researchers at Oak Ridge
explored the feasibility of online protactinium removal in the Molten
Salt Breeder Reactor program. Uranium can then be separated from the
protactinium in a second step.

Sensible safeguards.

Protactinium separations provide a pathway for obtaining highly
attractive weapons-grade uranium 233 from thorium fuel cycles. The
difficulties of safeguarding commercial spent fuel reprocessing are
significant for any type of fuel cycle, and thorium is no exception.
Reprocessing creates unique safeguard challenges, particularly in
India, which is not a member of the Nuclear Non-Proliferation Treaty.

There is little to be gained by calling thorium fuel cycles
intrinsically proliferation-resistant. The best way to realize nuclear
power from thorium fuel cycles is to acknowledge their unique
proliferation vulnerabilities, and to adequately safeguard them
against theft and misuse.

https://thebulletin.org/2018/08/thor...tinium-problem

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Default Thorium power has a protactinium problem

Well thanks for cheering us all up then!
Brian

--
From the Sofa of Brian Gaff Reply address is active
Remember, if you don't like where I post
or what I say, you don't have to
read my posts! :-)
wrote in message
...
Thorium power has a protactinium problem
By Eva C. Uribe, Aug 6, 2018, Bulletin of the Atomic Scientists

In 1980, the International Atomic Energy Agency (IAEA) observed that
protactinium, a chemical element generated in thorium reactors, could
be separated and allowed to decay to isotopically pure uranium
233-suitable material for making nuclear weapons. The IAEA report,
titled "Advanced Fuel Cycle and Reactor Concepts," concluded that the
proliferation resistance of thorium fuel cycles "would be equivalent
to" the uranium/plutonium fuel cycles of conventional civilian nuclear
reactors, assuming both included spent fuel reprocessing to isolate
fissile material.

Decades later, the story changed. "Th[orium]-based fuels and fuel
cycles have intrinsic proliferation resistance," according to the IAEA
in 2005. Mainstream media have repeated this view ever since, often
without caveat. Several scholars have recognized the inherent
proliferation risk of protactinium separations in the thorium fuel
cycle, but the perception that thorium reactors cannot be used to make
weapons persists. While technology has advanced, the fundamental
radiochemistry that governs nuclear fuel reprocessing remains
unchanged. Thus, this shift in perspective is puzzling and reflects a
failure to recognize the importance of protactinium radiochemistry in
thorium fuel cycles.

Protactinium turns 100.

The importance of protactinium chemistry for obtaining highly
attractive fissile material from thorium has been recognized since the
1940s. However, the story really begins 100 years ago during the
earliest research on natural radioactivity. In 1918, Austrian-Swedish
physicist Lise Meitner and German chemist Otto Hahn were on a quest to
discover the long-lived isotope of "eka-tantalum" predicted to lie
between thorium and uranium in the periodic table. The isotope they
sought would decay to actinium, which was always found with uranium
but was known to be the parent of an unknown natural radioactive decay
chain distinct from that of uranium 238, the most common isotope of
uranium found in nature.

Meitner and Hahn discovered that treating pitchblende with nitric acid
yielded an insoluble fraction of silica that associated with tantalum
and eka-tantalum. After many years, they purified enough eka-tantalum
for identification and measured its properties. As discoverers of
eka-tantalum's longest-lived isotope, Meitner and Hahn named this new
element protactinium. They had isolated protactinium 231, a member of
the uranium 235 decay chain. In 1938, they discovered that
protactinium 233 could be produced by neutron irradiation of thorium
232, the most abundant isotope in naturally occurring thorium.

For the next several decades, protactinium was shrouded in "mystery
and witchcraft" due to its scarcity in nature and its perplexing
chemical properties. We now know that protactinium's peculiar
chemistry is due to its position in the periodic table, which lends
the element vastly different chemical properties than its neighbors.
Protactinium behaves so differently from thorium and uranium that,
under many conditions, their separation is inevitable.

Scientists did not investigate the macroscopic chemistry of
protactinium until the Manhattan Project. In 1942, Glenn T. Seaborg,
John W. Gofman, and R. W. Stoughton discovered uranium 233 and
observed its propensity to fission. Compared with naturally occurring
uranium 235, uranium 233 has a lower critical mass, which means that
less material can be used to build a weapon. And compared with
weapons-grade plutonium 239, uranium 233 has a much lower spontaneous
fission rate, enabling simpler weapons that are more easily
constructed. A 1951 report by the Manhattan Project Technical Section
describes extensive efforts devoted to the production of uranium 233
via neutron irradiation of thorium 232. Because the initial thorium
feed material was often contaminated with natural uranium 238, the
scientists obtained pure uranium 233 by using a variety of methods for
separating the intermediate protactinium 233.

By this time, advances in technology and projections of uranium
shortages stimulated interest in developing a breeder reactor, which
produces more fissile material than it consumes. In the late 1960s, a
team at Oak Ridge National Laboratory designed a Molten Salt Breeder
Reactor fueled by thorium and uranium dissolved in fluoride salts, but
it could only breed uranium 233 by continuously removing
impurities-including protactinium 233-from the reactor core. To
improve breeding ratios, the researchers investigated methods for
removing protactinium from the molten fluoride salts.

In 1977, President Jimmy Carter banned commercial reprocessing of
spent nuclear fuel, citing concerns with the proliferation of
technology that could be used to make nuclear weapons. And with the
high startup costs of developing new reactors, there would be no place
for the Molten Salt Breeder Reactor in the energy market. With the end
of research on thorium reactors came the end of ambitious research on
protactinium separations. Over time, the role of protactinium in
obtaining weaponizable uranium 233 from thorium was largely forgotten
or dismissed by the thorium community.

Thorium reactors born again.

Fast forward to 2018. Several nations have explored thorium power for
their nuclear energy portfolios. Foremost among these is India.
Plagued by perennial uranium shortages, but possessing abundant
thorium resources, India is highly motivated to develop thorium
reactors that can breed uranium 233. India now operates the only
reactor fueled by uranium 233, the Kalpakkam Mini reactor (better
known as KAMINI).

Thorium reactors have other potential advantages. They could produce
fewer long-lived radioactive isotopes than conventional nuclear
reactors, simplifying the disposal of nuclear waste. Molten salt
reactors offer potential improvements in reactor safety. Additionally,
there is the persistent perception that thorium reactors are
intrinsically proliferation-resistant.

The uranium 233 produced in thorium reactors is contaminated with
uranium 232, which is produced through several different neutron
absorption pathways. Uranium 232 has a half-life of 68.9 years, and
its daughter radionuclides emit intense, highly penetrating gamma rays
that make the material difficult to handle. A person standing 0.5
meters from 5 kilograms of uranium 233 containing 500 parts per
million of uranium 232, one year after it has been separated from the
daughters of uranium 232, would receive a dose that exceeds the annual
regulatory limits for radiological workers in less than an hour.
Therefore, uranium 233 generated in thorium reactors is
"self-protected," as long as uranium 232 levels are high enough.
However, the extent to which uranium 232 provides adequate protection
against diversion of uranium 233 is debatable. Uranium 232 does not
compromise the favorable fissile material properties of uranium 233,
which is categorized as "highly attractive" even in the presence of
high levels of uranium 232. Uranium 233 becomes even more attractive
if uranium 232 can be decreased or eliminated altogether. This is
where the chemistry of protactinium becomes important.

Protactinium in the thorium fuel cycle.

There are three isotopes of protactinium produced when thorium 232 is
irradiated. Protactinium 231, 232, and 233 are produced either through
thermal or fast neutron absorption reactions with various thorium,
protactinium, and uranium isotopes. Protactinium 231, 232, and 233 are
intermediates in the reactions that eventually form uranium 232 and
uranium 233. Protactinium 232 decays to uranium 232 with a half-life
of 1.3 days. Protactinium 233 decays to uranium 233 with a half-life
of 27 days. Protactinium 231 is a special case: It does not directly
decay to uranium, but in the presence of neutrons it can absorb a
neutron and become protactinium 232.

Neutron absorption reactions only occur in the presence of a neutron
flux, inside or immediately surrounding the reactor core. Radioactive
decay occurs whether or not neutrons are present. For irradiated
thorium, the real concern lies in separating protactinium from
uranium, which may already have significant levels of uranium 232.
Production of protactinium 232 ceases as soon as protactinium is
removed from the neutron flux, but protactinium 232 and 233 continue
to decay to uranium 232 and 233, respectively.

The half-lives of the protactinium isotopes work in the favor of
potential proliferators. Because protactinium 232 decays faster than
protactinium 233, the isotopic purity of protactinium 233 increases as
time passes. If it is separated from its uranium decay products a
second time, this protactinium will decay to equally pure uranium 233
over the next few months. With careful attention to the relevant
radiochemistry, separation of protactinium from the uranium in spent
thorium fuel has the potential to generate uranium 233 with very low
concentrations of uranium 232-a product suitable for making nuclear
weapons.

Scenarios for proliferation.

Although thorium is commonly associated with molten salt reactors, it
can be used in any reactor. Several types of fuel cycles enable
feasible, rapid reprocessing to extract protactinium. One is aqueous
reprocessing of thorium oxide "blankets" irradiated outside the core
of a heavy water reactor. Many heavy water reactors include on-power
fueling, which means that irradiated thorium can be removed quickly
and often, without shutting the reactor down. As very little fission
would occur in the blanket material, its radioactivity would be lower
than that of spent fuel from the core, and it could be reprocessed
immediately.

Myriad possibilities exist for the aqueous separation of protactinium
from thorium and uranium oxides, including the commonly proposed
thorium uranium extraction (THOREX) process. Alternatively, once
dissolved in acid, protactinium can simply be adsorbed onto glass or
silica beads, exploiting the same chemical mechanism used by Meitner
and Hahn to isolate protactinium from natural uranium a century ago.

Another scenario is continuous reprocessing of molten salt fuel to
remove protactinium and uranium from thorium. Researchers at Oak Ridge
explored the feasibility of online protactinium removal in the Molten
Salt Breeder Reactor program. Uranium can then be separated from the
protactinium in a second step.

Sensible safeguards.

Protactinium separations provide a pathway for obtaining highly
attractive weapons-grade uranium 233 from thorium fuel cycles. The
difficulties of safeguarding commercial spent fuel reprocessing are
significant for any type of fuel cycle, and thorium is no exception.
Reprocessing creates unique safeguard challenges, particularly in
India, which is not a member of the Nuclear Non-Proliferation Treaty.

There is little to be gained by calling thorium fuel cycles
intrinsically proliferation-resistant. The best way to realize nuclear
power from thorium fuel cycles is to acknowledge their unique
proliferation vulnerabilities, and to adequately safeguard them
against theft and misuse.

https://thebulletin.org/2018/08/thor...tinium-problem



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Default Thorium power has a protactinium problem

On Friday, 17 August 2018 18:15:52 UTC+1, Brian-Gaff wrote:
Well thanks for cheering us all up then!
Brian

--
From the Sofa of Brian Gaff Reply address is active
Remember, if you don't like where I post
or what I say, you don't have to
read my posts! :-)
wrote in message
...
Thorium power has a protactinium problem
By Eva C. Uribe, Aug 6, 2018, Bulletin of the Atomic Scientists

In 1980, the International Atomic Energy Agency (IAEA) observed that
protactinium, a chemical element generated in thorium reactors, could
be separated and allowed to decay to isotopically pure uranium
233-suitable material for making nuclear weapons. The IAEA report,
titled "Advanced Fuel Cycle and Reactor Concepts," concluded that the
proliferation resistance of thorium fuel cycles "would be equivalent
to" the uranium/plutonium fuel cycles of conventional civilian nuclear
reactors, assuming both included spent fuel reprocessing to isolate
fissile material.

Decades later, the story changed. "Th[orium]-based fuels and fuel
cycles have intrinsic proliferation resistance," according to the IAEA
in 2005. Mainstream media have repeated this view ever since, often
without caveat. Several scholars have recognized the inherent
proliferation risk of protactinium separations in the thorium fuel
cycle, but the perception that thorium reactors cannot be used to make
weapons persists. While technology has advanced, the fundamental
radiochemistry that governs nuclear fuel reprocessing remains
unchanged. Thus, this shift in perspective is puzzling and reflects a
failure to recognize the importance of protactinium radiochemistry in
thorium fuel cycles.

Protactinium turns 100.

The importance of protactinium chemistry for obtaining highly
attractive fissile material from thorium has been recognized since the
1940s. However, the story really begins 100 years ago during the
earliest research on natural radioactivity. In 1918, Austrian-Swedish
physicist Lise Meitner and German chemist Otto Hahn were on a quest to
discover the long-lived isotope of "eka-tantalum" predicted to lie
between thorium and uranium in the periodic table. The isotope they
sought would decay to actinium, which was always found with uranium
but was known to be the parent of an unknown natural radioactive decay
chain distinct from that of uranium 238, the most common isotope of
uranium found in nature.

Meitner and Hahn discovered that treating pitchblende with nitric acid
yielded an insoluble fraction of silica that associated with tantalum
and eka-tantalum. After many years, they purified enough eka-tantalum
for identification and measured its properties. As discoverers of
eka-tantalum's longest-lived isotope, Meitner and Hahn named this new
element protactinium. They had isolated protactinium 231, a member of
the uranium 235 decay chain. In 1938, they discovered that
protactinium 233 could be produced by neutron irradiation of thorium
232, the most abundant isotope in naturally occurring thorium.

For the next several decades, protactinium was shrouded in "mystery
and witchcraft" due to its scarcity in nature and its perplexing
chemical properties. We now know that protactinium's peculiar
chemistry is due to its position in the periodic table, which lends
the element vastly different chemical properties than its neighbors.
Protactinium behaves so differently from thorium and uranium that,
under many conditions, their separation is inevitable.

Scientists did not investigate the macroscopic chemistry of
protactinium until the Manhattan Project. In 1942, Glenn T. Seaborg,
John W. Gofman, and R. W. Stoughton discovered uranium 233 and
observed its propensity to fission. Compared with naturally occurring
uranium 235, uranium 233 has a lower critical mass, which means that
less material can be used to build a weapon. And compared with
weapons-grade plutonium 239, uranium 233 has a much lower spontaneous
fission rate, enabling simpler weapons that are more easily
constructed. A 1951 report by the Manhattan Project Technical Section
describes extensive efforts devoted to the production of uranium 233
via neutron irradiation of thorium 232. Because the initial thorium
feed material was often contaminated with natural uranium 238, the
scientists obtained pure uranium 233 by using a variety of methods for
separating the intermediate protactinium 233.

By this time, advances in technology and projections of uranium
shortages stimulated interest in developing a breeder reactor, which
produces more fissile material than it consumes. In the late 1960s, a
team at Oak Ridge National Laboratory designed a Molten Salt Breeder
Reactor fueled by thorium and uranium dissolved in fluoride salts, but
it could only breed uranium 233 by continuously removing
impurities-including protactinium 233-from the reactor core. To
improve breeding ratios, the researchers investigated methods for
removing protactinium from the molten fluoride salts.

In 1977, President Jimmy Carter banned commercial reprocessing of
spent nuclear fuel, citing concerns with the proliferation of
technology that could be used to make nuclear weapons. And with the
high startup costs of developing new reactors, there would be no place
for the Molten Salt Breeder Reactor in the energy market. With the end
of research on thorium reactors came the end of ambitious research on
protactinium separations. Over time, the role of protactinium in
obtaining weaponizable uranium 233 from thorium was largely forgotten
or dismissed by the thorium community.

Thorium reactors born again.

Fast forward to 2018. Several nations have explored thorium power for
their nuclear energy portfolios. Foremost among these is India.
Plagued by perennial uranium shortages, but possessing abundant
thorium resources, India is highly motivated to develop thorium
reactors that can breed uranium 233. India now operates the only
reactor fueled by uranium 233, the Kalpakkam Mini reactor (better
known as KAMINI).

Thorium reactors have other potential advantages. They could produce
fewer long-lived radioactive isotopes than conventional nuclear
reactors, simplifying the disposal of nuclear waste. Molten salt
reactors offer potential improvements in reactor safety. Additionally,
there is the persistent perception that thorium reactors are
intrinsically proliferation-resistant.

The uranium 233 produced in thorium reactors is contaminated with
uranium 232, which is produced through several different neutron
absorption pathways. Uranium 232 has a half-life of 68.9 years, and
its daughter radionuclides emit intense, highly penetrating gamma rays
that make the material difficult to handle. A person standing 0.5
meters from 5 kilograms of uranium 233 containing 500 parts per
million of uranium 232, one year after it has been separated from the
daughters of uranium 232, would receive a dose that exceeds the annual
regulatory limits for radiological workers in less than an hour.
Therefore, uranium 233 generated in thorium reactors is
"self-protected," as long as uranium 232 levels are high enough.
However, the extent to which uranium 232 provides adequate protection
against diversion of uranium 233 is debatable. Uranium 232 does not
compromise the favorable fissile material properties of uranium 233,
which is categorized as "highly attractive" even in the presence of
high levels of uranium 232. Uranium 233 becomes even more attractive
if uranium 232 can be decreased or eliminated altogether. This is
where the chemistry of protactinium becomes important.

Protactinium in the thorium fuel cycle.

There are three isotopes of protactinium produced when thorium 232 is
irradiated. Protactinium 231, 232, and 233 are produced either through
thermal or fast neutron absorption reactions with various thorium,
protactinium, and uranium isotopes. Protactinium 231, 232, and 233 are
intermediates in the reactions that eventually form uranium 232 and
uranium 233. Protactinium 232 decays to uranium 232 with a half-life
of 1.3 days. Protactinium 233 decays to uranium 233 with a half-life
of 27 days. Protactinium 231 is a special case: It does not directly
decay to uranium, but in the presence of neutrons it can absorb a
neutron and become protactinium 232.

Neutron absorption reactions only occur in the presence of a neutron
flux, inside or immediately surrounding the reactor core. Radioactive
decay occurs whether or not neutrons are present. For irradiated
thorium, the real concern lies in separating protactinium from
uranium, which may already have significant levels of uranium 232.
Production of protactinium 232 ceases as soon as protactinium is
removed from the neutron flux, but protactinium 232 and 233 continue
to decay to uranium 232 and 233, respectively.

The half-lives of the protactinium isotopes work in the favor of
potential proliferators. Because protactinium 232 decays faster than
protactinium 233, the isotopic purity of protactinium 233 increases as
time passes. If it is separated from its uranium decay products a
second time, this protactinium will decay to equally pure uranium 233
over the next few months. With careful attention to the relevant
radiochemistry, separation of protactinium from the uranium in spent
thorium fuel has the potential to generate uranium 233 with very low
concentrations of uranium 232-a product suitable for making nuclear
weapons.

Scenarios for proliferation.

Although thorium is commonly associated with molten salt reactors, it
can be used in any reactor. Several types of fuel cycles enable
feasible, rapid reprocessing to extract protactinium. One is aqueous
reprocessing of thorium oxide "blankets" irradiated outside the core
of a heavy water reactor. Many heavy water reactors include on-power
fueling, which means that irradiated thorium can be removed quickly
and often, without shutting the reactor down. As very little fission
would occur in the blanket material, its radioactivity would be lower
than that of spent fuel from the core, and it could be reprocessed
immediately.

Myriad possibilities exist for the aqueous separation of protactinium
from thorium and uranium oxides, including the commonly proposed
thorium uranium extraction (THOREX) process. Alternatively, once
dissolved in acid, protactinium can simply be adsorbed onto glass or
silica beads, exploiting the same chemical mechanism used by Meitner
and Hahn to isolate protactinium from natural uranium a century ago.

Another scenario is continuous reprocessing of molten salt fuel to
remove protactinium and uranium from thorium. Researchers at Oak Ridge
explored the feasibility of online protactinium removal in the Molten
Salt Breeder Reactor program. Uranium can then be separated from the
protactinium in a second step.

Sensible safeguards.

Protactinium separations provide a pathway for obtaining highly
attractive weapons-grade uranium 233 from thorium fuel cycles. The
difficulties of safeguarding commercial spent fuel reprocessing are
significant for any type of fuel cycle, and thorium is no exception.
Reprocessing creates unique safeguard challenges, particularly in
India, which is not a member of the Nuclear Non-Proliferation Treaty.

There is little to be gained by calling thorium fuel cycles
intrinsically proliferation-resistant. The best way to realize nuclear
power from thorium fuel cycles is to acknowledge their unique
proliferation vulnerabilities, and to adequately safeguard them
against theft and misuse.

https://thebulletin.org/2018/08/thor...tinium-problem


It's something TurNiP should know about.
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Default Thorium power has a protactinium problem

On 17/08/2018 16:21, wrote:
Thorium power has a protactinium problem
By Eva C. Uribe, Aug 6, 2018, Bulletin of the Atomic Scientists

In 1980, the International Atomic Energy Agency (IAEA) observed that
protactinium, a chemical element generated in thorium reactors, could
be separated and allowed to decay to isotopically pure uranium
233€”suitable material for making nuclear weapons. The IAEA report,
titled €śAdvanced Fuel Cycle and Reactor Concepts,€ť concluded that the
proliferation resistance of thorium fuel cycles €śwould be equivalent
to€ť the uranium/plutonium fuel cycles of conventional civilian nuclear
reactors, assuming both included spent fuel reprocessing to isolate
fissile material.

Decades later, the story changed. €śTh[orium]-based fuels and fuel
cycles have intrinsic proliferation resistance,€ť according to the IAEA
in 2005. Mainstream media have repeated this view ever since, often
without caveat. Several scholars have recognized the inherent
proliferation risk of protactinium separations in the thorium fuel
cycle, but the perception that thorium reactors cannot be used to make
weapons persists. While technology has advanced, the fundamental
radiochemistry that governs nuclear fuel reprocessing remains
unchanged. Thus, this shift in perspective is puzzling and reflects a
failure to recognize the importance of protactinium radiochemistry in
thorium fuel cycles.

Protactinium turns 100.

The importance of protactinium chemistry for obtaining highly
attractive fissile material from thorium has been recognized since the
1940s. However, the story really begins 100 years ago during the
earliest research on natural radioactivity. In 1918, Austrian-Swedish
physicist Lise Meitner and German chemist Otto Hahn were on a quest to
discover the long-lived isotope of €śeka-tantalum€ť predicted to lie
between thorium and uranium in the periodic table. The isotope they
sought would decay to actinium, which was always found with uranium
but was known to be the parent of an unknown natural radioactive decay
chain distinct from that of uranium 238, the most common isotope of
uranium found in nature.

Meitner and Hahn discovered that treating pitchblende with nitric acid
yielded an insoluble fraction of silica that associated with tantalum
and eka-tantalum. After many years, they purified enough eka-tantalum
for identification and measured its properties. As discoverers of
eka-tantalums longest-lived isotope, Meitner and Hahn named this new
element protactinium. They had isolated protactinium 231, a member of
the uranium 235 decay chain. In 1938, they discovered that
protactinium 233 could be produced by neutron irradiation of thorium
232, the most abundant isotope in naturally occurring thorium.

For the next several decades, protactinium was shrouded in €śmystery
and witchcraft€ť due to its scarcity in nature and its perplexing
chemical properties. We now know that protactiniums peculiar
chemistry is due to its position in the periodic table, which lends
the element vastly different chemical properties than its neighbors.
Protactinium behaves so differently from thorium and uranium that,
under many conditions, their separation is inevitable.

Scientists did not investigate the macroscopic chemistry of
protactinium until the Manhattan Project. In 1942, Glenn T. Seaborg,
John W. Gofman, and R. W. Stoughton discovered uranium 233 and
observed its propensity to fission. Compared with naturally occurring
uranium 235, uranium 233 has a lower critical mass, which means that
less material can be used to build a weapon. And compared with
weapons-grade plutonium 239, uranium 233 has a much lower spontaneous
fission rate, enabling simpler weapons that are more easily
constructed. A 1951 report by the Manhattan Project Technical Section
describes extensive efforts devoted to the production of uranium 233
via neutron irradiation of thorium 232. Because the initial thorium
feed material was often contaminated with natural uranium 238, the
scientists obtained pure uranium 233 by using a variety of methods for
separating the intermediate protactinium 233.

By this time, advances in technology and projections of uranium
shortages stimulated interest in developing a breeder reactor, which
produces more fissile material than it consumes. In the late 1960s, a
team at Oak Ridge National Laboratory designed a Molten Salt Breeder
Reactor fueled by thorium and uranium dissolved in fluoride salts, but
it could only breed uranium 233 by continuously removing
impurities€”including protactinium 233€”from the reactor core. To
improve breeding ratios, the researchers investigated methods for
removing protactinium from the molten fluoride salts.

In 1977, President Jimmy Carter banned commercial reprocessing of
spent nuclear fuel, citing concerns with the proliferation of
technology that could be used to make nuclear weapons. And with the
high startup costs of developing new reactors, there would be no place
for the Molten Salt Breeder Reactor in the energy market. With the end
of research on thorium reactors came the end of ambitious research on
protactinium separations. Over time, the role of protactinium in
obtaining weaponizable uranium 233 from thorium was largely forgotten
or dismissed by the thorium community.

Thorium reactors born again.

Fast forward to 2018. Several nations have explored thorium power for
their nuclear energy portfolios. Foremost among these is India.
Plagued by perennial uranium shortages, but possessing abundant
thorium resources, India is highly motivated to develop thorium
reactors that can breed uranium 233. India now operates the only
reactor fueled by uranium 233, the Kalpakkam Mini reactor (better
known as KAMINI).

Thorium reactors have other potential advantages. They could produce
fewer long-lived radioactive isotopes than conventional nuclear
reactors, simplifying the disposal of nuclear waste. Molten salt
reactors offer potential improvements in reactor safety. Additionally,
there is the persistent perception that thorium reactors are
intrinsically proliferation-resistant.

The uranium 233 produced in thorium reactors is contaminated with
uranium 232, which is produced through several different neutron
absorption pathways. Uranium 232 has a half-life of 68.9 years, and
its daughter radionuclides emit intense, highly penetrating gamma rays
that make the material difficult to handle. A person standing 0.5
meters from 5 kilograms of uranium 233 containing 500 parts per
million of uranium 232, one year after it has been separated from the
daughters of uranium 232, would receive a dose that exceeds the annual
regulatory limits for radiological workers in less than an hour.
Therefore, uranium 233 generated in thorium reactors is
€śself-protected,€ť as long as uranium 232 levels are high enough.
However, the extent to which uranium 232 provides adequate protection
against diversion of uranium 233 is debatable. Uranium 232 does not
compromise the favorable fissile material properties of uranium 233,
which is categorized as €śhighly attractive€ť even in the presence of
high levels of uranium 232. Uranium 233 becomes even more attractive
if uranium 232 can be decreased or eliminated altogether. This is
where the chemistry of protactinium becomes important.

Protactinium in the thorium fuel cycle.

There are three isotopes of protactinium produced when thorium 232 is
irradiated. Protactinium 231, 232, and 233 are produced either through
thermal or fast neutron absorption reactions with various thorium,
protactinium, and uranium isotopes. Protactinium 231, 232, and 233 are
intermediates in the reactions that eventually form uranium 232 and
uranium 233. Protactinium 232 decays to uranium 232 with a half-life
of 1.3 days. Protactinium 233 decays to uranium 233 with a half-life
of 27 days. Protactinium 231 is a special case: It does not directly
decay to uranium, but in the presence of neutrons it can absorb a
neutron and become protactinium 232.

Neutron absorption reactions only occur in the presence of a neutron
flux, inside or immediately surrounding the reactor core. Radioactive
decay occurs whether or not neutrons are present. For irradiated
thorium, the real concern lies in separating protactinium from
uranium, which may already have significant levels of uranium 232.
Production of protactinium 232 ceases as soon as protactinium is
removed from the neutron flux, but protactinium 232 and 233 continue
to decay to uranium 232 and 233, respectively.

The half-lives of the protactinium isotopes work in the favor of
potential proliferators. Because protactinium 232 decays faster than
protactinium 233, the isotopic purity of protactinium 233 increases as
time passes. If it is separated from its uranium decay products a
second time, this protactinium will decay to equally pure uranium 233
over the next few months. With careful attention to the relevant
radiochemistry, separation of protactinium from the uranium in spent
thorium fuel has the potential to generate uranium 233 with very low
concentrations of uranium 232€”a product suitable for making nuclear
weapons.

Scenarios for proliferation.

Although thorium is commonly associated with molten salt reactors, it
can be used in any reactor. Several types of fuel cycles enable
feasible, rapid reprocessing to extract protactinium. One is aqueous
reprocessing of thorium oxide €śblankets€ť irradiated outside the core
of a heavy water reactor. Many heavy water reactors include on-power
fueling, which means that irradiated thorium can be removed quickly
and often, without shutting the reactor down. As very little fission
would occur in the blanket material, its radioactivity would be lower
than that of spent fuel from the core, and it could be reprocessed
immediately.

Myriad possibilities exist for the aqueous separation of protactinium
from thorium and uranium oxides, including the commonly proposed
thorium uranium extraction (THOREX) process. Alternatively, once
dissolved in acid, protactinium can simply be adsorbed onto glass or
silica beads, exploiting the same chemical mechanism used by Meitner
and Hahn to isolate protactinium from natural uranium a century ago.

Another scenario is continuous reprocessing of molten salt fuel to
remove protactinium and uranium from thorium. Researchers at Oak Ridge
explored the feasibility of online protactinium removal in the Molten
Salt Breeder Reactor program. Uranium can then be separated from the
protactinium in a second step.

Sensible safeguards.

Protactinium separations provide a pathway for obtaining highly
attractive weapons-grade uranium 233 from thorium fuel cycles. The
difficulties of safeguarding commercial spent fuel reprocessing are
significant for any type of fuel cycle, and thorium is no exception.
Reprocessing creates unique safeguard challenges, particularly in
India, which is not a member of the Nuclear Non-Proliferation Treaty.

There is little to be gained by calling thorium fuel cycles
intrinsically proliferation-resistant. The best way to realize nuclear
power from thorium fuel cycles is to acknowledge their unique
proliferation vulnerabilities, and to adequately safeguard them
against theft and misuse.

https://thebulletin.org/2018/08/thor...tinium-problem

Interesting. I have always been somewhat sceptical of the claims made
for thorium on the grounds that if it really was that much better than
U/Pu, someone would have exploited it commercially by now.

Nothing short of bombs and/or invasion is going to stop a determined
rogue state from making "simple" fission weapons. Exploiting Thorium
from power reactors is going to require reprocessing, which is currently
no longer unfashionable. So I don't really see that a move to Thorium
poses much of a proliferation risk. That said, it is good to see
misleading claims being challenged.

Similarly, the claim that fusion power will produce "no nuclear waste".
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Default Thorium power has a protactinium problem

On 18/08/18 20:32, newshound wrote:
Similarly, the claim that fusion power will produce "no nuclear waste".



The world is made of nuclear waste.


--
New Socialism consists essentially in being seen to have your heart in
the right place whilst your head is in the clouds and your hand is in
someone else's pocket.



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Default Thorium power has a protactinium problem

On 18/08/2018 20:47, The Natural Philosopher wrote:
On 18/08/18 20:32, newshound wrote:
Similarly, the claim that fusion power will produce "no nuclear waste".



The world is made of nuclear waste.


Indeed. We are stardust, we are golden....
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