OCCITANE
In the field of vessel steels for PWRs, irradiation experiments are carried out to substantiate the safety case of this second containment barrier and to improve its lifetime, thus the lifetime of the reactor itself.
The CEA has designed an out-of-core hosting system called OCCITANE for neutron ageing tests, making it possible to perform irradiation experiments in an inert gas from at least 230°C to 300°C.
The OCCITANE experimental device will be placed in the first ring of the JHR Material Test Reactor reflector. The neutron characteristics (a best estimate at the maximum flux plane, 100 MW, 27% 235U, and the core at equilibrium in mid-cycle) are expected to be:
⦁ Fast flux (E > 1 MeV) – about 8.1012 n/cm².s
⦁ Fast flux (E > 0.1 MeV) – about 2.1013 n/cm².s
⦁ mdpa/EFPD: 1.0
The neutron fluxes and the dpamust be multiplied by 0.7 to reach 70 MW.
The ratio between the neutron spectrum Rs = (E > 0.1 MeV) /(E > 1 MeV) and nuclear heating in the samples can be adapted by using neutron and gamma shields.
Various types of samples (creep, tensile, Charpy and microstructure) can be irradiated if they do not exceed 30 x 62.5 mm² in size. Samples can be stacked on top of each other up to 60 cm (see figure below), with an axial damage gradient due to variations in the fast neutron flux. The sample holder is rotated 180° in the device between each cycle to homogenise the damage in the experimental samples.
The multi-zone furnace controls the required irradiation temperature between 230°C and 300°C and compensates the axial thermal gradient due to the axial nuclear gradients mentioned above.
The related instrumentation includes at least several thermocouples and dosimeters positioned as close as possible to the samples.
The JHR has been designed with a full set
of experimental devices making
it possible to conduct the experiments
needed to characterise,
select and qualify new fuels and materials.
Some of these experimental devices
are capsules while others are loops,
which makes it possible to adjust
the experimental conditions in real time
to obtain even better results.
