Advantages of a safe nuclear energy
Nuclear energy is a concentrated energy source (adapted to
mega-cities), not very dependent of weather or climate (if
nuclear reactors are sited on the sea)
A well proved technology, which can be still largely improved
(life of reactor up to 60 years, load ratio up to 90%, BU up to 60
GWjt-1)
Important and diversified sources of natural and man-made
fissile nuclides (Pu isotopes). U ores are widespread and
abundant without competing uses and it is easy to store. More
than 50 years of production at the present level of production
can be achieved
A low cost of kWhe (“full life cycle cost” analysis).
A very low radiological impact for the environment and no
release of CO2 (but 6% of the world energy consumption).
A worldwide system of protection for workers
Extension of the present technology to produce electricity
(with reactors of 300 MWe) and high temperature heat
(metallurgical processes, H2 production). New technology
using all U isotopes (and Th) could provide fission energy
over a very long time (see later).
Disadvantages (drawbacks) of safe nuclear energy
A high investment costs with a long payback of money (10 years
for construction of a reactor and a large amount of money in
case of accident)
A difficulty to follow variable electricity demand (base load
generation only)
An accumulation of civil Pu. In average the world-wide
production is 75 tons a year. The status of Pu is peculiar
according of its use as a fuel or its management as waste. As
Pu239 has a lower  % of delayed neutron than U235 % the
quantity to be introduced in reactor is limited to 12 % (30 % of
MOX sub-assemblies in a 900 MWe PWR initially loaded with
UOX). The isotopic composition Pu MOX SF does not allow a
second recycle in PWR (too much even-even nuclides which
decrease the quantity of fissile nuclides by thermal neutrons).
Attached to the accumulation and separation of Pu from SF is
the question of dissemination of fissile material (nuclear
weapons proliferation)
A production of nuclear wastes difficult to manage in the long
term whatever they are, SF or packages of wastes from
reprocessing. LL-SLW packages (PF and AP), are disposed of in
ground or underground repositories. The HL-LLW and MLLLW packages, which contain LL radionuclides, are put in
interim storage waiting for a final destination, which is the
matter of hard discussions
A controversial appreciation by citizen (anti-nuclear people
against nuclear technocrats, very low risk can have tremendous
consequences, effects of radioactivity difficult to understand).
Real efforts, but too recent, have been done to give an objective
information on nuclear problems, but in general the dialogue is
difficult to be established (except in some countries)
Nuclear energy, environment and society. Is this energy
compatible with sustainable development?
Releases
The radioactivity of the gas or the aqueous solutions (called
ultimate effluents) which are released in atmosphere and
hydrosphere during operating reactors or facilities of the fuel
cycle are controlled according to the safety rules for radiation
protection. The authorisations of releases are calculated on the
basis of the dose for the most exposed people at the limit of the
site according to scenarios (and others regulations). The true
releases are only several per cent of the authorisations (T,
volatile FP,  emitters).
The case of accidents is special
The release of heat and chemicals by reactors and facilities of the
fuel cycle have no special status versus industrial rules.
Society
The links between nuclear energy and society are complex. The
concerns are all linked to the concept of radiological dose and
associated risk.
In short the hazard of nuclear energy comes from an exposure
to ionising radiations, appreciated by the calculated “dose” The
dose depend on scenarios of exposure. The risks depend on the
dose. A reference point is the natural dose.
The low doses (less than immediate lethal doses) are given in
Sievert (Sv). Natural dose is around 2.5 mSv/year.
The radiological risk, RR, associated to a dose is RR (t-1) = p
(Sv-1) i Pi (t-1) Ei (Sv-1) where p is the probability of occurrence
of the effects, Pi is the probability of the occurrence of an event
i, and Ei is the calculated dose given by the event i. For low dose
the unit of time is the year.
The basic hypothesis supporting the RR for low doses is called
the LNT (linear no threshold). The value of p = 0.073 Sv-1
(0.06 for a cancer leading to death and 0. 013 for hereditary
effect according to IRCP 60) means that 6 cancers per year
can appear in a population of 100 000 inhabitants, each
having got 1mSv. The value 0.073 is on debate. There are also
debates on LNT and the mechanisms of induced cancer by
ionising radiations
IRCP considers that an “acceptable risk” correspond to a dose
added to the natural dose of 1 mSv/year for any individual of
the public. This dose is considered to have any effect on the
“expected life”
IRCP considers that a “trivial added dose” is 1 microSievert
(1/100 of the natural dose).
For a given amount of radioactive matter (1 ton of SF for
instance or quantity of SF to produce 1 TWhe) the “inventory
of radiotoxicity”, in short the” radiotoxicity”, is defined as i
RRi calculated supposing that all radionuclides, i, are
incorporated. It represents a potential risk.
The “residual risk” is i RRi calculated for a given case of
exposure . It takes into account the management of the
radioactive matter (like in geological disposal for instance).
Doses due to the use of nuclear energy are low compared to the
natural doses and those given by medical diagnostic (1.5
mSv/year in average per person)
Sustainable development
Sustainable development requires to meet technical and
societal criteria. Here they are essentially discussed in the
context of the pursuit of the present technology of reactors
according to a moderate increase of the use of nuclear energy.
Up to 2050 nuclear energy will lie on U/Pu fissile nuclides
(impossibility to launch many fast neutron reactor to use
U238, lack of Pu and reprocessing SF facilities). Phase out of
nuclear energy is not considered (but is not a simple problem)
Forecasts are difficult (visibility on the demands of the open
market, safety rules) due to the complexity of the economy
and the changing feeling of the society on the nuclear energy.
Technological criteria
At least 4 technical criteria have to be fulfilled by nuclear energy
(and any source of energy) : providing adapted power to the
energy needs, safe technology, durability of resources (Unat), no
collateral damage (proliferation of nuclear material).
Management of nuclear wastes for the coming years rise some
technical problems but the main problems are of societal type
(see later).
As discussed the 3 first criteria are fulfilled (30 to 80% of
electricity depending countries, Generation III reactors will have
improved systems to reinforce safety, Unat resources are secure
for the next decades at known prices, Pu can be recycled once in
PWR without difficulty).
The proliferation is a question of technical and political means
controls. It is more easy to have fissile nuclides with high level
enriched Unat in U235 (ultra-centrifugation) than to produce
Social criteria
There are 2 important criteria : cost and wastes management,
the radiological impact being low (except in the case of
accidents)
Price is around 3 to 4 cents of Euro per kWhe (including
provisions for waste management and decommissioning)
whatever would be the interest of money (5 to 10 %) on the
next 40 years
Waste management of LLW is a major concern (U ores
mining, ML-LLW and HL-LLW). High isolation and
confinement or radioactivity over long periods of time is
necessary (105 time compared to toxic industrial wastes).
Actually 10 000 tons of SF are yearly unloaded in the world.
Nobody knows exactly if it will be possible to transmute on an
industrial scale the LL radionuclides, indefinite storage raise
the problem of the stability of society, sitting of deep geologic
disposal is difficult.
A geologic repository could be designed to dispose of around 80
000 tons of SF (or equivalent reprocessing packages). In 2020,
200 000 tons of SF will have to be managed. If geological
disposal is chosen, that will need 3 disposal sites (an increase of
the use of nuclear energy must be considered with respect to
the need of more repositories)
There are 4 characteristic periods of time in LL nuclear wastes
- 5 (to 10 ?) decades during which SF or HL-LLW must be
cooled (heat released by FP and SL actinides, Pu241, Cm244,
Cm243 for UOX and additionally Pu238 for MOX). During this
time either the way to change the type of wastes or to dispose of
the wastes is decided.
- several decades to implement the choice (no need of cooling)
The problems during these two periods are of national
relevance and solved by man-made technique (for geological
disposal heat released by Am241 and Pu238 lay down the size)a
- the third period extends to 100 000 years during which
radionuclides must be isolated/confined, for instance in
canisters and engineered barriers of high performances
(Pu239, Pu240, Pu242, Am241 and Np237). Concentration of
 emitters must be less than 10-10 M in environment, much less
than chemical pollutants (linked to 1mSv/year got by drinking
water).
- over 100 000 years the radionuclides (U isotopes, Np237 and
Pu242 and also long-lived FP) must be confined by natural
rocks
During these two last periods the problems can only be solved
by “geology”
Is nuclear energy renewable?
The question is a matter for the next half of this century and
later
The present yield for the utilisation of the energy of fission
contained in Unat is less than 1%. But when U238 is used as
fissile and fertile nuclide (fast neutrons) the period of time
during which energy can be produced is measured, as least in
theory, in thousands of years (renewable energy?)
In the case of lack of U, or in parallel for technical or social
reasons, the use of Th (thermal neutrons) can also be
considered on the same scale.
But the massive use of “new reactors” and new “nuclear
systems” is mandatory.
Resources in U
The stockpile of Udep is enormous (230 000 tons in France)
and will increase using Uenr as nuclear fuel. Udep is easy to
manipulate. The quantities of Urep are less (20 000 tons in
France) but will increase using MOX fuel. Declassified military
high enriched U (up to 90 % in U235) or fissile Pu239 could be
used.
According to some forecasts the need of Unat could be
important. For instance a power of 250 GWe in 2020 would
require 100 kt per year of Unat. So extraction of Unat both
from pure U ores and as by-product (industry of Cu, Au or P)
should be boosted
Reactors for the future (2050), valorisation of resources,
optimisation of waste management.
The nuclear energy for the future will be developed in the
direction of mixing this source of energy with other sources in an
“energetic mix” whatever the other objectives are.
The future “nuclear systems energy” including Generation IV
reactors and associated cycle facilities should have the objective
to valorise the resources in fissile nuclides and to optimise the
management of wastes.
Along the long way to launch these systems the most advanced
new reactors are HTR and FNR
Two international projects of HTR of low power (100 and 300
MWe) are developed (derived from experimental reactors
operated in USA and Germany in the sixties-seventies). Two
HTR are presently operated in China-10 MWth- and Japan -30
MWth)
The coming HTR will be fuelled with Uenr (8 to 10 %) or with
MOX made with military Pu239, moderated with C, cooled
with He and operated following an open cycle (75 % of loaded
Pu could be burnt). With He at 600°C directly associated with
a gas turbine a yield of 50 % is expected (Brayton cycle).
Their fuel will be based on micro-spheres of ceramic oxides
(or carbides) coated by several layers of C and by SiC and
embedded in C. This is a new fuel.
The layers will isolate FP and actinides from He (like cladding
of pins in PWR) up to 1600 °C. SF at high BU (100 to 150
GWjt-1) will be a waste because its reprocessing will be very
difficult (but not impossible).
FNR.
Fast neutrons allow the use of all isotopes of U, Pu and heavier
actinides (f/c of fast neutrons > f/c of thermal neutrons).
The resource of fissile nuclides is practically increased by a
factor of 50 (twice in theory). The technology of FNR cooled by
Na is known. They are fuelled with MOX of high content in Pu
(up to 20 %) and need to be launched 10 to 15 tons of Pu/GWe
(in fact with 9.6 tons of fissile Pu isotopes)
They can be operated giving as much Pu as they burn
(regeneration) or more (over-generation or breeding). But it
takes 2 to 3 decades to have sufficient Pu to launch a new FNR
(50 years for a PWR!).
Worldwide Pu production is around 75 tons (and 7.5 tons of
other actinides) which could allow to launch 5 to 7 GWe/year.
In 2030 the stockpile of Pu in SF will be around 3000 tons.
Transmutation of actinides (FNR and ADS)
FNR can burn actinides (Np, Pu, Am, Cm) if they are
included in U based fuel but in limited quantities (due to
safety problems raised by the decrease of available delayed
neutrons). Special fuel (metallic alloys, oxides, other
compounds) must be used of which preparation and
certification have to be implemented.
ADS (Accelerator driven system).
ADS are based, like FNR, on fission induced by fast neutrons.
But the core (U) is sub-critical (keff around 0.98 for instance)
and the fast neutrons needed to have  = 0 are given by a
spallation source.
In this device (cooled molten Pb-Bi alloy, diameter 0.5 m,
height 1 m) a beam of high energetic and high flux of proton
(1 GeV, 20 mA at the limits of present accelerators) is
transformed in fast neutrons (1 to 2 MeV) by nuclear
spallation reactions
The power of the reactor, Pr, is controlled by the power of the
accelerator, Pa (Pr/Pa = 6 / (keff/1-keff)).
The use of ADS is foreseen to transmute Am (and/or Pu)
embedded in inert target (without U). Transmutation with
ADS allows a load in actinide higher than in critical FNR
because operating the reactor does not need delayed
Other reserves of fertile nuclides
It is possible to launch thermal neutrons based reactors using
the fertile monoisotopic Th232 and fissile nuclides (U235 or
Pu isotopes) as a match. Fissile U233 is formed, which can be
recycled. U233 has very attractive nuclear properties. U233
can be, or could be, produced in PWR by irradiation of Th232
A molten salts reactor (MSR) in USA (7.5 MWth, U235 and
U233 fuelled) has shown, in the sixties, the possibility of
breeding. A modern version is under evaluation. MSR are
high temperature reactors (600 to 700 °C) where molten salts
(Li and Be fluorides) are both fuel and coolant and the
moderator is C. It needs 1.2 tons of fissile nuclide per GWe,
around 1/10 of a FNR-Na load. It does not produce heavy
actinides (U238 is not present)
Such reactor can transmute actinide in line.
Conclusion
Technology and economy make fission nuclear energy a
“sustainable energy”: Unat resources for decades (and
possible use of made-man fertile nuclides), safe technology
and possible improvement, low price of kWhe compared to
other sources (without considering CO2 emission tax),
environment friendless and no health impact by additional
low dose of radiation. A renew of nuclear energy could be
possible.
But problems remain: public antipathy (difficult to change),
waste management (problems identified, but not solved),
policy for international licensing (visibility for development),
ethical (intergeneration relationships).
It is reasonable to forecast that during the next 15-20 years
(say up to 2025) no drastic change will occur in nuclear
energy production.
This period will be for each country a period of” thinking” on
the use of nuclear energy, confirmation of phase out,
maintaining present level or increasing it in the “energetic
mix”.
This period will be also a test period for the implementation of
programmes set up to renew world-wide nuclear energy as for
instance the GNEP (Global Nuclear Energy Partnerships)
leaded by USA.
Finally this period will be devoted to test the will of countries
in developing international research to prepare possible
launching of reactors of “Generation IV”, and associated
nuclear fuel cycles, in the second half of the century according
to the objectives of GIF.
GIF (Generation IV International Forum, 11 partners) was
initiated in 2002. Several organisational steps have been
implemented up to 2005. It is aimed at developing 6 new types of
reactors based on fast and thermal neutrons for optimising the
use of fertile nuclides, producing less waste and opening new uses
of nuclear energy (high temperature heat production).
The GNEP organisational programme, launched in 2005 by USA,
proposes to complete the objectives of GIF as follows. In the
short term: encourage launching of new reactors particularly for
developing countries (low power reactor), in the long term:
develop new technologies proliferation resistant, for recycling Pu
and other actinides and develop advanced burners of Pu and
actinides. For both actions it is proposed to set up an
international system of nuclear services (enrichment,
reprocessing) under international control
What will happen after 2025 for nuclear energy is relevant to
prospective because choices on energy are subject to too
many parameters
In the countries where nuclear option will remain open one
can think that coexistence of Generation II and III of reactors
will exist. Indeed the Generation III reactors are designed for
a 60 years lifetime. These reactors, and associated fuel cycle
facilities, could finally dominate the nuclear landscape up to
the end of the century. This will not lead to a great change in
nuclear industry
In the case of positive tests for a possible development of
nuclear energy, which will mean that a drastic increase in
nuclear energy will have been accepted, research for “nuclear
energy for the future” will be boosted to prepare the use of
fertile nuclides (U238 and Th232) and to implement the