Introduction

Naturally occurring radioactive materials such as
uranium and thorium are common elements within the earth's crust. Natural background radiation from these
elements and other sources has always been present and is a constant feature of
life on earth. Spent
fuel from a nuclear reactor is highly radioactive, but over time this radiation
decreases and becomes less significant.
It would take many thousands of years for the radiation from the spent
fuel to fade away completely, but once it reaches the same level as natural
background radiation it no longer needs to be kept separate from the biosphere.

If spent fuel is directly
disposed of without reprocessing it will remain more radioactive than the
corresponding quantity of uranium ore for over 30,000 years. The principal objective of spent fuel
reprocessing is recovery of plutonium and uranium for recycling as reactor
fuel. There are also substantial waste
management advantagesremoval of plutonium and uranium reduces the period in
which the remaining high level waste will be more radioactive than the
corresponding uranium ore to around 2,000 years^[11].

2,000 years of course is
still a significant period. While
studies of natural areas of high radioactivity, such as the Oklo natural
reactors in Gabon^[12], and ore bodies in the
Alligator Rivers Region in the Northern Territory, show that radiotoxic
elements can be immobilised and isolated from the biosphere for many hundreds
of thousands of years, nevertheless it would be advantageous to reduce the
period of high radiotoxicityif for no other reason, to establish public confidence
in waste management programs.

Accordingly, a number of
countries have been carrying out research into the possibility of partitioning
radioactive isotopes from high level waste.
Partitioningin the context of spent
fuel management, refers to the processes that provide efficient separation of
long-lived radioactive isotopes (fission products and minor actinides) from
spent fuel and/or high level waste for further treatment and disposal.

If, for example,
reprocessing of spent fuel is modified to remove some of the minor actinides, such as neptuniumand americium, then the remaining waste will decay to a radioactivity
level similar to uranium ore in 1,000 years.
If the process is further refined to also remove certain long-lived
fission products, the waste will decay to a radioactivity level similar to
uranium ore in about 500 years.

Partitioning of minor
actinides and fission products will be more advantageous if there is a further
process in place for treating these elements to reduce their half-lives. Hence the concept of transmutationthe
return of the materials to reactors for transmutationthrough fission or
neutron captureinto elements with shorter half-lives.
In other words, transmutationrefers to the
process of gaining a substantial reduction in the period over which waste
arising from nuclear energy remains highly radiotoxic, by using the neutron
flux within a reactor or other intensive source of neutrons to turn (transmute)
long-lived radiotoxic elements into short-lived or stable elements. This transmutation step can substantially
decrease the time needed to render the partitioned material harmless.

Efficient transmutation
requires fast neutrons (neutrons not slowed down by a moderator). As there is only limited availability of
fast neutrons in thermal reactors
(such as light water reactors), research into partitioning and transmutation
arose in the context of expectations of the early deployment of fast breeder or
other fast neutron reactors. While the
delay in the introduction of fast neutron reactors has led to some diminution
of interest in partitioning and transmutation in the short term, nonetheless it
is a concept of considerable promise for the futureand for example is the basis of the
Russian concept of a transmutational fuel cycle (on page 68).

Neptuniumand americium

Two of the materials of interest for
partitioning and transmutation are neptunium and americium. Since these are fissionable materials (i.e. they can be fissioned by fast
neutrons), recycle in a fast neutron reactor would have the advantage that they
would contribute to the energy production in the reactor, in other words they
would be a useful component of the reactor fuel.

Neptunium and americium are produced in
very small quantities in irradiated fuel.
Typically (depending on the irradiation history) reactor spent fuel
would contain about 1 gram of neptunium for every 20 grams of
plutonium. Americium is produced in
irradiated fuel at a lower rate, roughly one quarter as much as neptunium, and
also arises in separated plutonium or spent fuel through decay of the isotope
plutonium-241.

Because neither material is fissionable by thermal neutrons, to date there has been
limited use for neptunium or americium, and generally they are not separated from
fission products: they are either contained within spent fuel or, if
reprocessing is undertaken, mostly end up in the waste stream. Both materials have been separated in
significant quantities only by the nuclear-weapon States (mainly the US and
Russia) for specialised applications.
Separated neptunium is used for the production of plutonium-238, which
is used in thermo-electrical generating systems for satellites and heart
pace-makers. Separated americium is
widely used in smoke detectors. Both
materials are also used as industrial radioisotopes, e.g. in borehole logging
equipment and in instruments for measuring the thickness of processed metals.

Only very small quantities of neptunium and
americium have been separated in the non-nuclear-weapon States. Separation in significant quantities would
require substantial quantities of spent fuel and a reprocessing programthere
are few NNWS in this situation, and there has been no incentive to separate
these materials, because the tiny amounts required for research or for the
commercial applications mentioned above have been available from NWS. Nonetheless, because these materials are
fissionable, and because of ongoing research into their possible separation for
transmutation, in recent years interested States and the IAEA have been
considering how they should be managed from the safeguards perspective. ASNO identified this issue early on and has
played an active part in the ensuing deliberations.

The matter was considered by the IAEAs
Board of Governors in September 1999.
In the case of neptunium, the Board decided it is of little
proliferation risk in current circumstances, where there are only very small
quantities of separated neptunium in the NNWS.
The Board decided to establish arrangements to monitor international
transfers of neptunium and to verify there is no undeclared separation of
neptunium in NNWS. If a significant
change in the current situation appears likely the Board will consider the
matter further, including whether formal extension of safeguards to neptunium
is warranted. The Board considered that
the proliferation risk posed by americium is even lower than for
neptunium. Not only are there very
limited quantities of separated americium in NNWS, but major heat and radiation
problems would make any attempted explosive use extremely difficult. Accordingly, the Board asked the IAEA
Secretariat to keep the situation under review and report to it if appropriate.

Australia agrees with other Board Members
that this is a pragmatic approach in current circumstances, considering the
limited quantities of these materials in separated form in NNWS and considering
also the uncertainty that significant quantities will be separated in the
future. Delays in the development of
fast neutron reactors obviously impacts on the interest in separating these
materialsand if transmutation programs do proceed, it is possible
transmutation could be effected without actually separating the materials, e.g.
they could be separated from fission products but remain in stream with
plutonium and uranium, covered by the safeguards measures on those materials.

Since all spent fuel contains neptunium and
americium, clearly a proportion of these materials in spent fuel is derived
from AONM. Accordingly Australia has discussed
this matter with relevant bilateral partners, i.e. those that reprocess
AONMUK, France and Japan. Discussions
have also been held with the US and with the IAEA. Through these discussions ASNO has established that no neptunium
or americium has been separated from AONM.
The situation will be kept under review, and Australia will take an
active part in any further IAEA Board consideration of this matter. While extension of our bilateral agreements
to include these materials is a possibility if they become safeguardable
materials, this is not expected to occur for many years, if at all.

[11]. Time periods taken from
Radioactive Waste ManagementAn IAEA Source Book, 1992 (figures 7 and 8).

[12]. The Oklo natural reactors
evolved 1.8 billion years ago, at a time when the content of the fissile
isotope uranium-235 in natural uranium was much higher than it is todayaround
3%, similar to the level in LEU used in light water reactors. Water saturation
of the uranium ore bodies created the conditions for a self-sustained chain
reactionthe resulting heat evaporated the water, bringing the chain reaction
to a halt. This process repeated itself over many thousands of years, creating
natural deposits of fission products and plutonium normally found only in spent
reactor fuel. The movement of these radiotoxic materials through the ore bodies
has been limited to only a metre or so, providing practical evidence that such
materials can be successfully isolated for periods well in excess of that
necessary for the protection of the biosphere.

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