Proceedings of ICAPP 2007
Nice, France, May 13-18, 2007
Paper 7446
THE NUCLEAR WASTE ISSUE: TOWARDS AN ASSESSMENT OF THE PARTITIONING AND
TRANSMUTATION OF ACTINIDES
Hervé Masson (AREVA NC/DRD), Dominique Grenêche (AREVA NC /DRD),
Pierre Chambrette (AREVA NC /BUT)
AREVA NC
1 Place de la Coupole
92084 Paris La Défense
France
Tel: 01.47.96.79.94, Fax: 01.47.96.79.99, Email: [email protected]
Abstract – First of all, this paper describes recent regulatory, scientific and technical developments in France concerning the
management of high level, long-lived radioactive waste. In this context, which culminated in parliament’s adoption of the
radioactive waste management bill, it analyses, from an industrial viewpoint, the motivation for separating and transmuting
minor actinides, as well as the technical and economic consequences for waste management, given the performance levels
that can be envisaged for the various options.
The new law underlines the need to reduce the harmfulness of radioactive waste and research into separation and
transmutation is continuing with a view to “an assessment in 2012 of the industrial perspectives for these technologies” that
makes allowance for the developments made with new reactors.
This very clearly marks a new departure since researchers are being required to contribute to the creation of consistent
industrial plans and to be fully part of them. These plans must include the separation of elements to be transmuted, the
fabrication of fuels or targets to be transmuted, and their treatment once they have been unloaded from the reactor.
As a world wide operator of the fuel cycle, AREVA intends to make available its experience and to be part of the evaluation
of the industrial plans. After all, plutonium recycling, fully mastered by AREVA, is an industrial reality and contributes
impressively in the reduction of the waste potential harmfulness.
It is admitted that the waste will not be eradicated by transmutation and therefore that the geological disposal is inevitable.
But destroying the waste, however partially, is worthy of consideration if it helps to simplify disposal and reduce costs. It
may also merely reduce safety assessment uncertainty or increase calculation margins.
The results of previous studies, which revealed the difficulty in transmuting long-lived fission products, have shown that
research has to focus on the minor actinides. On the one hand, they account for practically all the radiotoxicity of waste and
on the other hand, with the exception of two fission products with relatively short half-lives for which suitable interim
storage is to be envisaged, they are the main contributors to the thermal load.
We therefore examine the possible consequences of management through actinide separation and transmutation on the fuel
cycle as a whole, and the advantages to be gained for disposal or release.
For example, americium makes a considerable contribution to the thermal load and transmutation would appear possible.
Conversely, curium is known to be difficult to transmute and would complicate target or fuel fabrication operations.
The potential savings to be made in disposal costs should also make allowance for future optimization, notably thermal.
Separation/transmutation costs should include not only special separation workshops and target fabrication units, but also the
impact of the modifications required if actinides are to be burnt in power reactors.
These issues must be examined in detail now so that all the necessary information is available for the 2012 assessment. If a
prototype is to be commissioned before 2020, as envisaged in the law, the objective has to be perfectly clear, given that it will
be impossible to continue all the lines of research.
date. So it was that after the 1973 oil crisis, France’s
President Pompidou decided to launch a vast nuclear
reactor construction program. There are currently 58
Pressurized Water Reactors in operation in France, the
oldest of which has been running for only 25 years.
I. THE FIRST LAW ON WASTE MANAGEMENT
In the early days of the civil nuclear industry, the
overriding priority was to meet energy requirements.
Nuclear waste management was perceived as nothing more
than a technical problem that would be solved at a later
-1-
Proceedings of ICAPP 2007
Nice, France, May 13-18, 2007
Paper 7446
II.b. The energy debate.
Preparations for their succession are underway with the
construction of AREVA's European Pressurized Reactor in
Flamanville. The program to equip France with nuclear
reactors therefore went ahead more or less unopposed.
Conversely, the startup tests for a laboratory due to carry
out research into high level waste disposal met with such
hostility that the government asked Parliament to step in.
As a result, a law on waste management was passed in
1991. It is known as the “Bataille law” after its author and
principal architect.
The law stipulated that research into waste management
was to continue for 15 years along three lines:
• reducing the harmfulness of waste,
• deep geological disposal, reversible or not,
• packaging and interim storage of waste.
At the end of the 15-year period, the government was to
present Parliament with "a new bill authorizing, if
necessary, the construction of a waste repository"i.
The 15-year research period has now come to an end, the
results have been discussed and a new law was passed in
June 2006.
A debate on energy policy was held in France in the spring
of 2003. After considering the numerous contributions
provided by trade unions, political parties, professional
bodies and associations, the government produced a White
Paperii which confirms the challenges that will have to be
met in the 21st century, notably those linked to global
warming.
As far as this is concerned, nuclear’s position is assured
without in any way closing the door to alternative and
complementary forms of energy. The advantages of opting
for nuclear are clearly stated in the White Paper:
ƒ national energy independence,
ƒ energy with low carbon emissions,
ƒ competitive electricity price,
ƒ risks and drawbacks taken into account and
perfectly controlled.
Long-lived nuclear waste is often mentioned as one of the
drawbacks. However, it is generally accepted that it has
never posed any immediate threat to safety since the
radioactivity emitted is blocked by suitable barriers.
During the debate, AREVA demolished the myth that waste
was the “Achilles heel of the nuclear industry”. What
exactly do we do with this waste and where is it?
- it accounts for less than 1% of special industrial waste,
- only 5% is highly radioactive,
- it fits into just one half of a storage hall at La Hague,
- the plutonium and uranium are recycled (together they
account for 96% of the matter contained in the fuel),
- the civil plutonium is not weapons-grade.
Generally speaking, there is no risk at this stage but the
worst thing possible would be to demonize radioactive
waste and more especially to refuse to talk about it.
II. THE SITUATION IN 2006
II.a. A nuclear renaissance?
Over and above the simple question about the future of
nuclear waste, the sustainability of nuclear energy was also
an issue. When the debate started, several factors were
becoming increasingly predominant. One of the very
earliest was the conviction that the oil resources on which
France is still largely dependent will not last forever.
Furthermore, the almost uncontrollable shifting
geopolitical scene causes oil prices to fluctuate. Another
factor comes from the concern due to the CO2 releases that
are blamed for the global warming.
Part of the solution to the problem is to develop all forms
of CO2-free energy, notably nuclear. Numerous countries
are therefore investigating this option. China is talking
about building a huge number of nuclear power plants over
several years. Finland has ordered its 5th reactor. The US
is envisaging new builds, as are the UK and numerous
other countries that currently do not possess any nuclear
power reactors.
In this context, the availability of fissile material becomes
an issue and after a long period during which it was quite
simply dismissed in some countries, fuel treatment is being
discussed again. The US has launched the GEN IV
initiative which aims to create an international framework
for developing new generation reactors, most of them fast
breeders, and re-examining the possibility of fuel
treatment, long banned due to fear of proliferation.
III. THE DEBATE ON WASTE THAT PRECEDED
THE LAW
In early 2005, the French Parliamentary Office for the
Assessment of Scientific and Technological Choices
(OPECST) listened to what the various playersiii,
researchers, national representatives, political leaders and
associations had to say. Summaries of the work carried out
were published firstly by the French National Agency for
Radioactive Waste Management (ANDRA) and the French
Atomic Energy Commission (CEA), then by the National
Assessment Commissioniv(CNE, created by the
aforementioned law of 1991). The recommendations came
from the General Directorate for Energy and Raw
Materials at the Ministry for Industry and from bodies
representing the industry, including AREVA. It was
recognized that much had been learned and the three lines
of research (see Section 1) were revealed to be
complementary. It was also recognized that a deep
geological repository had been proved feasible and that
disposal in a clay formation such as that of the Bure
-2-
Proceedings of ICAPP 2007
Nice, France, May 13-18, 2007
Paper 7446
Consequently, the desire to separate out then transmute a
proportion of the long-lived radionuclides will be
meaningless unless other countries, and not to mention the
potential customers of the one treatment plant, think the
same way.
Lastly, it should be highlighted that a number of foreign
countries
particularly
concerned
about
nuclear
proliferation participated in the debate. This raised the
issue of the “proliferating” aspect of the fuel cycle
processes. It would appear that despite the general
agreement on the need to reduce these risks, feelings on
the subject and the technical approaches put forward vary
considerably. We can only hope here that the various ideas
of what constitutes non-proliferation are brought into line
in order to avoid any inconsistency that might introduce an
element of doubt.
laboratory could be used as a reference solution. Longterm interim storage was also proved to be feasible. And
since industrial interim storage facilities already existed
and could be used for a century, there is no need to rush.
To be more precise, the argilite rock in the Bure area offers
very low permeability and is highly capable of trapping
radionuclides, meaning that solutes are transferred
extremely slowly. The repository has a robust modular
structure. The maximum doses at the outlets calculated in
the safety analysis using highly pessimistic hypotheses are
far lower than those received from natural radiation and
will not occur for at least several hundreds of thousands of
years. Reversibility, i.e. the possibility of retrieving waste
was still considered indispensable.
All this provides a solid basis for coming out in favor of
disposal and the research required for work to continue is
focusing on qualification of a site.
Conversely, despite the fact that research into
separation has yielded satisfactory results, much
remains to be done regarding transmutation. More
especially, thought needs to be given as to whether or
not it is really worth pursuing. At this juncture, it is
worth recalling the terms used by the rapporteur,
Mr. Bataille, when he spoke before the Senate in favor of
the first law: “all the experts are of the opinion that
advanced treatment and transmutation will not do away
with the need for deep geological disposal”v. This opinion
has been confirmed several times since then.
Transmutation is not doing away with the need for a
repository, but would merely contribute in one way or
another to successful completion of the project.
During the debate, many very different opinions were
voiced on this subject:
ƒ Some thought that it was sufficient just to separate out
the minor actinides, package them and put them in a
repository. In their opinion, clay is an excellent trap.
ƒ Others emphasized that it was more important to focus
on the “residual” rather than the “potential”
radiotoxicity (see later).
ƒ The separation and transmutation scenarios must be
consistent with an industrial scenario that includes
nuclear power generation and management of fuel
cycle material. Separation cannot be continued on an
industrial scale as long as the future of the separated
products is uncertain. And it has been admitted that
transmutation is not feasible with the present
generation of Light Water Reactors.
The industrialists concerned, including AREVA, were
obviously keen to voice their concerns during the debate
and raised the question as to whether separation and
transmutation was of any real use. Since, at the end of the
day, the customer will pay, the idea of cost/benefit has to
be introduced when discussing this issue.
Another aspect of the problem must be taken into account:
France cannot be right alone, nor will any other country.
IV. THE 2006 LAW ON WASTE MANAGEMENT
The 1991 law aimed to create a number of research
options, that of 2006vi is designed to place all the actions in
an industrial context. The introductory articles recall the
responsibilities of waste producers and the basic principle
of waste management: protecting human health and the
environment without imposing undue burdens on future
generations. To comply with these principles, all categories
of waste whose final fate is still unknown will be the
subject of studies which should result in their disposal. In
particular, holders of legacy waste are now obliged to
package it by 2030.
Every three years, the government draws up and publishes
a national waste management plan. Used fuel continues to
be treated to reduce the “quantity and harmfulness” of
radioactive waste and enable it to be packaged.
Deep geological disposal has been confirmed as the final
destination for waste that cannot be stored above ground.
The conditions for opening a repository are detailed and it
must be guaranteed as being reversible.
ANDRA is responsible for updating the national waste
inventory, which was published for the first time in 1993,
and for continuing research and studies into disposal and
interim storage.
All operators are required to make the necessary financial
provisions for the disposal of their waste and the
dismantling of their facilities, and to account for them.
Focused as it is on industrial perspectives, the law not only
offers solutions but provides a timeframe for implementing
them. These solutions are as follows:
- opening of a deep geological repository,
- continuing with interim storage for as long as necessary.
The value of interim storage is that it allows packages to
lose some of their thermal power.
The three lines of research are maintained but the
parameters of the road map have been defined and
milestones placed precisely over time, especially for the
separation and transmutation of long-lived elements
-3-
Proceedings of ICAPP 2007
Nice, France, May 13-18, 2007
Paper 7446
V.c. Reducing potential radiotoxicity
(Article 3 of the law). Research is being conducted “in
relation with that being carried out on new generations of
nuclear reactors” and on “accelerator-driven reactors
designed for waste transmutation, so that an assessment of
the industrial prospects for these technologies can be made
by 2012, and a prototype facility put into operation by
December 31, 2020”.
Here too, the aim is to converge towards an applicable
objective whose road map is traced out. The decision
whether or not to implement an industrial separation and
transmutation process will be taken in 2012. Until then, it
should be taken advantage of the time available to assess
whether or not it is worth pursuing in terms of cost and
benefit.
The potential radiotoxicity of waste is sometimes known as
the source term of the repository. It is expressed as Sieverts
per metric ton of fuel and decreases over time due to
radioactive decay. It represents the total dose which,
although hypothetical, could be received by a group of
people ingesting the waste if it was dispersed and diluted
in the atmosphere as is and with no protection.
Obviously this never happens since nuclear waste, like any
other industrial waste, is not hazardous as long as it is
correctly treated and contained. This is exactly the purpose
of disposal, which is also intended to reduce the
consequences of any incidents or errors. Consequently,
there is no particular benefit to be gained from reducing
potential radiotoxicity, it is more a question of principle.
V. THE MOTIVES FOR SEPARATION AND
TRANSMUTATION
V.a .Introduction
1.E+09
It is worth recalling that the main reason for the fuel cycle
is to enable electricity to be generated and fuel therefore
has to be supplied and recovered at the right time in
compliance with specifications laid down by operators and
safety authorities. In addition, there must be enough fertile
and fissile material available to meet customers’
requirements. Lastly, waste has to be managed as it is
generated and removed to the appropriate interim storage
and disposal facilities.
As stipulated in the law, the national waste management
plan leaves no scope for anything else.
Fuel cycle operations therefore have to remain as safe and
reliable as they are at present. Since it is evident that the
management and recycling of actinides will put additional
constraints on the fuel cycle, it has to be justified by a clear
benefit.
In this respect, the motives for separation and
transmutation can stem from one of several wishes:
ƒ to reduce the toxicity of waste,
ƒ to facilitate the repository safety case,
ƒ to densify the repository by reducing the thermal
power of packages.
Grand total
Plutonium
Americium
Curium
Uranium
Neptunium
Fission Products
1.E+08
Sv per ton HM
1.E+07
1.E+06
1.E+05
1.E+04
1.E+03
1.E+02
1
10
100
1000
10000
100000
time (years)
Figure 1 - Radiotoxicity inventory of a used UOx fuel
element (45,000 MWd/t)
In any case, the curves in Figure 1 show that plutonium is
by far the largest contributor to the potential radiotoxicity.
Chance is that it is also recyclable and this is what happens
during fuel treatment. After plutonium come the minor
actinides, of which americium is the main contributor.
The contribution of curium decreases rapidly and that of
neptunium is lower than that of the initial uranium. After a
few hundred years, the contribution of the fission products
drops to a very low level. Furthermore, the first question to
be asked when seeking to reduce potential radiotoxicity is
this: how far is it reasonable to reduce it? There is more
than just one answer to this question. Some have suggested
reducing it by a factor of 100, others propose that the
potential radiotoxicity level should return to the same level
as that of the initial uranium, prior to irradiation, after a
period of 1000 years.
Separating out americium alone would go a long way to
reaching these targets. Curium separation would be of
limited advantage and the same benefits as transmutation
could be obtained through interim storage. There is
nothing to be gained from separating neptunium, or indeed
V.b.Reducing the toxicity of waste
There are two ways of looking at how to reduce the
toxicity of waste. Either we attempt to reduce some of the
absolute or “potential” radiotoxicity of waste before it is
put into the repository or we try to reduce only that very
small part which, according to the repository safety
assessments, could return to the biosphere after at least
50,000 years. This is known as residual toxicity.
Regardless of the option selected, it is generally accepted
that there is no known way of reducing the toxicity of
waste to such an extent that it becomes short-lived or low
level waste capable of being stored above ground.
-4-
1000000
Proceedings of ICAPP 2007
Nice, France, May 13-18, 2007
Paper 7446
authorized by ANDRA in the first assessment report are
very conservative to avoid the need to prove that clay is
not transformed irreversibly. Thus the criterion adopted is
that the temperature of the clay that comes into contact
with the packages must not exceed 90°C and this
temperature must, in all events, drop to below 70°C within
1000 years. The first constraint is the most difficult to
comply with. As things stand at present, it means leaving
the packages in interim storage to cool down and then
leaving sufficient space between them in the repository.
These two complementary actions will have to be
optimized from an economic point of view. For the
moment, the feasibility study adopts a 60-year cooling
period, i.e. two half-lives of caesium and strontium, and
envisages an average of 80 m² for each glass package. For
example, there would be eight glass packages, each 1.4
meters long, in a gallery 30 meters long.
This is mostly a case of economic optimization since the
reduction in the heat released from the packages would
allow them to be placed more tightly in the repository. It
should be noted that plutonium recycling also has an
advantage here since it reduces the thermal power of the
packages, provided that the impact of used MOX fuel
treatment is taken into account, since this is likely to give
rise to large quantities of americium. Decreasing the heat
source is also a way to increase sustainability by
contributing to save a very valuable resource: the disposal
site.
the fission products, especially since we now know that
they are difficult to transmute.
V.d .Reducing residual radiotoxicity
This is a totally different problem. In this case, separation
and transmutation would reduce the radiological impact of
the repository in the very long term, as calculated for the
various scenarios describing changes in repository
conditions that are part of the safety case. There are many
responses here too since the chemical species likely to
migrate vary from one geological environment to another.
The “ARGILE 2005”vii report published by ANDRA
shows that in clay, only anions such as iodine, chlorine or
selenium are likely to contribute to the dose at the outlet.
Furthermore, the calculated doses have been shown to be
extremely low and we now know that these radionuclides
cannot be transmuted. It should be noted here that the
results obtained for the Yucca Mountain repository in the
US are different due to the different chemical conditions in
which neptunium, plutonium and technetium are the
species which migrate first.
But, in any case, it will not be acceptable to increase risks
or doses taken by the personnel, even though it would
decrease the hypothetic dose at the outlet of the disposal in
a hundred thousands years.
V.e. Reducing the thermal power of packages
The experts agree that the size of the repository will
depend to a large extent on the thermal power of the
packages. In the case of high level waste, the thermal
power is high, due to the presence of two fission products,
caesium and strontium, and americium 241. No allowance
is made for plutonium since it will have been separated and
recycled according to French practice. The other actinides
are either too scarce or have a long half-life and dissipate
low thermal power (over a very long period).
V.f. Scenarios to be considered.
The following conclusions can be drawn from this brief
analysis:
ƒ The desire to reduce the residual radiotoxicity of a
repository in a clay environment is tantamount to
wanting to reduce doses that are already
infinitessimally low and to transmuting fission
products that cannot be transmuted. We will therefore
consider this to be impracticable.
ƒ Reducing the potential radiotoxicity means trying to
transmute the minor actinides, mainly americium and
curium, since the contribution of neptunium is very
small. For assessment purposes, we would need to
wait until 2012 to weigh the advantages to be gained
from separating and transmuting curium and
americium against the very real difficulties in getting
this process off the ground.
ƒ Reducing the thermal power of packages to be able to
pack them more tightly in the repository means
looking at caesium and strontium first, followed by
curium and americium. From this point of view,
keeping waste in interim storage appears to be a good
way of reducing the thermal power of caesium and
strontium, particularly since the thermal energy
released by the curium, whose isotopes have a shorter
half-life, is reduced at the same time. Therefore,
1000
Watts per ton of heavy metal
spent fuel
total (after reproc.)
fission products
100
Americium
Curium
Pu (after reproc.)
10
1
0.1
60
100
1000
Time (years)
10000
Figure 2 - Heat released by vitrified waste after 60 years
cooling (UOX 45,000 MWd/t).
In clay, heat is released slowly through conduction, with a
thermal conductivity of the order of 1.5 Watts/m*°K,
which corresponds to a thermal diffusion of between 10-6
and 10-7 m2/s. Furthermore, the temperature limits
-5-
Proceedings of ICAPP 2007
Nice, France, May 13-18, 2007
Paper 7446
and would also make destroying the actinide flow the only
problem.
Heterogeneous transmutation can be carried out in fast
reactors or in reactors specially designed for transmutation.
Technologies that are easier to automate can be studied for
target manufacture, especially since, in the case of fast
reactors, the specifications are less draconian than those
required for current water reactors. However, they will
require technological developments and qualification
programs.
reducing the thermal power of the glass packages
involves separating and transmuting americium.
All of this results in two alternatives: either separating and
transmuting americium and curium, or separating and
transmuting americium only. It can be done in several ways
that have to be integrated in the scenarios of development
of the nuclear energy.
VI. THE REALITIES OF THE FUEL CYCLE AND
TRANSMUTATION
VI.a .Separation
VI.c. Transmutation.
Transmutation involves either a fission of the nucleus of an
element or a neutron capture, transforming the element into
another element which can in turn undergo fission or
capture. Fission and capture depend on the nature of the
element and the energy of the neutrons. In the case of
actinides, preference should be given to fission since the
element can be transformed into elements with short halflives, which is exactly what we are aiming for. From this
point of view, it is generally accepted that fast reactors
encourage the fission of actinides, but in actual fact, there
is very often a large majority of captures, even in the fast
spectrum (for example 88% for americium 241). Only after
a certain number of captures do we obtain elements with a
higher atomic number; we know that their nuclei are less
stable and more inclined to fission. Furthermore, some of
the nuclei in the chain of evolution of the actinide to be
transmuted have relatively short half-lives and produce
lower elements which can, in turn, capture a majority of
neutrons.
The CEA has developed two process, DIAMEX and
SANEX, used to obtain a combined flow of americium and
curium and the DIAMEX 2 process which then separates
the two. A small-scale demonstration of these processes
was given in the Atalante laboratory at the end of 2005
using a solution of 15 kg of actual fuel. The experiment
showed that the separation performances were good and
that the processes were “technically” feasible. It is
expected that carrying out the R and D will draw up or
confirm the mass balances of these operations, including
waste, and will confirm the ability of the extractant to
retain its capabilities. It will also provide information on
the potential build-up of impurities and decomposition
products and enough matter will be produced for future
operations.
One aspect, which is often overlooked, concerns the
preparation of these new solvants. They will need to be
produced with a consistently high level of quality.
VI.b. Fabrication of targets or fuel for transmutation
Total transmutation (Am+Cm)
France is now fabricating MOX fuel (uranium +
plutonium) on a large scale, and has acquired a
considerable amount of experience, which also extends to
fast reactors. Part of this operation is done in glove boxes
and the americium content has to be kept very low. If
americium and curium were to be recycled on a large scale,
glove box technology could no longer be used since
americium is also a beta emitter and curium is a strong
neutron emitter.
Either the process would have to be totally automated or
shielded cells and remote handling equipment would have
to be provided, which would complicate all of the
operations involved, be it the safety case, fabrication on an
industrial scale or quality control.
If homogeneous transmutation were to be envisaged
(actinides diluted in the U-Pu fuel), the problem would
arise for the tons of fuel to be fabricated for reactors. The
entire process, including quality control, would need to be
automated, and the problem would become even worse.
Conversely,
transmutation
through
heterogeneous
recycling of specific americium or curium fuels would
offer greater flexibility by reserving options for fuel
fabrication that have already been qualified industrially
There are two possible scenarios for total transmutation:
ƒ Either the choice is to manufacture suitable targets, and
to carry out heterogeneous transmutation by continuing
to irradiate them until, through a succession of
captures, we obtain predominantly fissile elements
which eventually disappear almost altogether. The two
problems encountered would be the resistance of the
targets and removal of the fission gases. The fission
products from the transmuted targets would also have
to be treated and packaged.
ƒ Or the choice is to limit actinide irradiation and
therefore the proportion of split nuclei. To obtain high
transmutation rates, it is compulsory to recycle
actinides that have not been transmuted, which means
recycling considerable quantities of curium, americium
and the higher actinides. These quantities are so great
that homogeneous recycling seems impractical, and a
specific cycle has to be set up for manufacturing new
targets and treating used ones.
-6-
Proceedings of ICAPP 2007
Nice, France, May 13-18, 2007
Paper 7446
ƒ
Keep it flexible to be in a position to provide
MOX and UOX fuel for light water reactors, as
well as fuel for fast reactors and potential
incinerator reactors.
ƒ Build on past experience and keep product or
process qualification to a strict minimum, since
these are often lengthy, risky and expensive
operations (for example, it takes at least fifteen
years to develop and qualify a new fuel).
ƒ Maintain as simple a cycle as possible.
ƒ Synchronize as far as possible the major technical
options with the need to renew fuel cycle
facilities.
ƒ Do not increase the total quantity of radioactive
waste generated by facilities or the impact of
these facilities on the environment, or the total
exposure of people working there.
Applying these principles implies choosing heterogeneous
recycling to avoid having to requalify the fuel and
automate all the fabrication facilities. Furthermore, it
encourages the search for a type of transmutation which
fissions most of the actinides in just one operation, thereby
minimizing the need to recycle once more the residual
actinides. However, there is no way of avoiding the fact
that used targets need to be treated to stabilize them for
packaging prior to disposal.
The choice still has to be made between reactors dedicated
to transmutation and fast power reactors in which targets
are incinerated in the covers; this choice will depend on the
progress made with studies.
It can be seen that applying these principles makes
combined separation and transmutation of actinides
difficult. Lastly, the option involving the separation and
direct packaging of americium should be investigated
further since the drawbacks of transmutation would be
avoided.
Transmutation of americium 241
For the transmutation of americium 241 only, which is
recommended to reduce thermal power, it has been shown
possible to reach a transmutation rate over 90% in a single
operationviii, using moderated targets loaded into a fast
reactor. It should be said in passing that this shows that it is
not so much the energy of the neutrons that encourages
transmutation but the number of neutrons, i.e. the neutron
flux integrated over time. Americium 241 is transformed
mainly through capture into americium 242, an isotope
with a very short half-life (16 hours) and produces Cm 242
which decays fairly rapidly (with a half-life of 163 days)
into plutonium 238. At this stage, barely 30% of the
fissions have occurred, and the total radiotoxicity has
increased (via the curium 242 chain), as has the thermal
power which we would prefer to see decreasing. Indeed,
per unit mass, the thermal power of plutonium 238 is five
times higher than that of americium 241 and its 88-year
half-life makes interim storage difficult. The target
therefore has to be irradiated over a longer period to
increase the fission rate by transmuting plutonium 238, via
fissions of plutonium 239 which it produces through
capture. The entire transmutation process for americium
241 therefore requires a large quantity of neutrons (even if
the fissions go a small way to compensating for this
neutron consumption) and an assessment has to be made of
the matter produced, particularly the higher actinides.
A promising solution appears to be heterogeneous
transmutation in fast neutron reactors of moderated targets,
since it combines a high flux (and therefore a large
quantity of neutrons) and a spectrum of slow neutrons (and
therefore high effective cross-sections). It can be envisaged
recycling scenarios limited to a blanket fuel where the
Americium would be associated with an other fertile
element. However this kind of solution, less mature, would
require a complete evaluation.
VIII. CONCLUSIONS
When first mooted, separation and transmutation aroused
hopes that nuclear waste could be done away with
completely. But after the fifteen years of research provided
for by the law of 1991, the conclusion is that this objective
will never be fully met, at least as far as our scientific and
technical knowledge stands at present.
We also know that neither separation, and even less so
transmutation, will be easily implemented on an industrial
scale, and that they will be expensive and not without risk.
However, if, for reasons that are yet to be made clear, the
decision-makers should opt to go down this path, two
scenarios appear possible: either separate and transmute
americium and curium to reduce the total radiotoxicity
inventory, without any identified compensation in terms of
risk reduction, or separate and transmute americium to
reduce the amount of heat released by packages and pack
the repository more tightly, thereby reducing costs.
VII. INDUSTRIAL RECOMMANDATIONS
Generally speaking, industry will prefer solutions that first
of all ensure the competitiveness of its products and
services while offering the greatest flexibility and ease of
operation of its production tools. In any case, even if
separation and transmutation is society’s choice, the end
user will be required to meet any extra costs incurred by
these operations. It belongs to the different bodies in
charge of preparing the files for an evaluation in 20122015 to provide a complete assessment of the question. To
contribute to this debate, it is possible to give some basic
and simple principles that make sense from an industrial
point of view:
ƒ In as far as possible, make a distinction between
electricity generation and transmutation.
ƒ Avoid making the fuel fabrication process more
complex.
-7-
Proceedings of ICAPP 2007
Nice, France, May 13-18, 2007
Paper 7446
The waste management law of 2006 sets 2012 as the date
for assessing “the industrial perspectives for this
technology”. This leaves time to take stock of the situation
and assess the cost of the potential options, not forgetting
that an answer has to be found to the basic question as to
whether or not they are really of any advantage.
i
Law no. 91-1381 of December 30, 1991 on research into
radioactive waste management.
ii
White paper on energy -Presentation by Nicole Fontaine,
French minister of state for industry - November 7, 2003.
iii
C. Bataille and C. Birraux - Rapport sur l’état
d’avancement et les perspectives des recherches sur la
gestion des déchets radioactifs – (French ) National
Assembly no. 2159, March 16, 2005.
iv
Report by the (French) National Assessment Commission
(CNE) on research carried out within the framework of the
law of December 30, 1991. January 2006.
v
Report by Christian Bataille – Gestion des déchets
nucléaires à haute activité – (French) National Assembly
no. 1839 - December 1990.
vi
Law no. 2006-739 of June 28, 2006 on the program for
the sustainable management of radioactive waste and
materials.
vii
ANDRA – ARGILE 2005 report - December 2005.
viii
JP Nabot, F. Sudreau – CLEFS CEA – N° 53 – Hiver
2005-2006.
-8-