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Investigations Supporting MOX Fuel Licensing in ESNII Prototype Reactors
The current generation of nuclear reactors (Gen IIâIII) guarantees a stable supply of nuclear energy for the
next 2â3 decades but additional development of nuclear technology is needed to reduce further potential
accident risks and above all to increase its sustainability. The development of next generation (Gen IV)
reactors, especially fast reactors, will greatly increase sustainability and mitigate long term impact of
nuclear waste, when combined with concomitant fuel recycling facilities, firmly establishing the circular
economy via closed fuel cycles.
Europe has defined as its priorities three fast reactor designs: the sodium fast reactor (SFR) as reference
technology, the lead (and leadâbismuth) fast reactor (LFR) and the gas fast reactor (GFR) as alternative
technologies. In 2010, Europe, under the umbrella of the Sustainable Nuclear Energy Technology Platform
(SNETP), launched the European Sustainable Nuclear Industrial Initiative (ESNII). The objective is to
demonstrate Gen IV fast reactor technologies with closed fuel cycle, to harness European research and
industrial capabilities to build advanced fast reactor prototypes and develop supporting infrastructure. Four
prototypes or demonstrators are being designed: ASTRID for SFR, MYRRHA (ADS/LFR pilot plant) and
ALFRED (demonstrator) for LFR and ALLEGRO for GFR.
The operating conditions envisaged for these future systems are extremely demanding: high temperature,
intense and prolonged irradiation, chemically aggressive environments. Therefore, the necessary nuclear
materials will be exposed to very taxing conditions while simultaneously needing to respect increasingly
high safety requirements. The performance of nuclear (structural and fuel) materials is therefore an essential aspect to make Gen IV reactors a reality.
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Materials with the required properties must be selected, optimized or developed, properly qualified, and
their behaviour in operation fully understood. In particular, nuclear fuel is at the heart of all nuclear reactor
systems and is exposed to the most stringent irradiation and temperature conditions (see Figure).
Mastering the understanding of its behaviour is excruciatingly challenging due to the complex coupled
phenomena (physical, chemical, radiation, thermal and mechanical) induced by fission. All occur in steep
temperature gradients and have consequences at a multitude of time and length scales e.g. from the
nanometre to the metre (e.g. elemental radial migration, fission gas bubble precipitation, fission product
migration and interaction with the cladding, grain restructuring, and cracking etc.).
Although there are significant differences between them in terms of TRL (technology readiness level), the
ESNII prototypes are now at advanced stages of definition and the real needs and challenges of reactor
designers are articulated firmly. In addition, experimental techniques and modelling methods are now ripe
for their application to nuclear fuels (including plutoniumâbearing compounds). It is now that the
harnessing of basic and applied science can truly bring significant advances to the licensing of MOX fuel
under normal and off normal conditions by resolving operational and safety issues. The ultimate aims of
the INSPYRE (INvestigations Supporting mox fuel licensing in esnii PrototYpe REactors) proposal are thus to
Maximise the information extractable from qualification irradiation tests and ultimately decrease their number
Decrease the time needed to qualify fuel
Accelerate up the learning curve
Improve safety and performance by reducing uncertainties
Sweep through or bypassing steps on the TRL ladder
To reach these aims, INSPYRE has set three overarching strategic objectives:
Establish major breakthroughs in the understanding and description of fast reactor (FR) MOX fuel
behaviour under irradiation in a large variety of conditions by coupling: (i) post irradiation examinations
on neutronâirradiated fuel from past campaigns with (ii) separate effect experiments (SEE) using mainly
ion implantation and (iii) multiscale modelling, from the atomic to the macroscopic scale, including
thermodynamic modelling, thereby greatly enhancing the situations to be covered.
Advance the predictive capabilities of fast reactor fuel performance codes by bringing them several
steps forward in terms of reliability and extended simulation by (i) transferring the knowledge acquired
from basic and technological research into operational tools and (ii) bringing together experts from
various areas of expertise to develop and capitalize on the synergy between the various approaches
(basic and technological research, modelling and experimental aspects). This will permit reduced
operational margins in pile, enhance safety and reach more reliable management procedures of offâ
normal situations.
Transfer the results and approach of the proposal to endâusers, develop training to prepare the next
generation of researchers on fuel performance codes and fast reactor fuel and initiate or participate in original and effective outreach activities to improve public acceptance of the next generation of reactors
and attract young minds to nuclear energy development.
