LNF:Technology: Difference between revisions

==Materials for fusion applications==

The radiation effect is one of the critical aspects concerning fusion reactor development. The neutron and gamma radiation produced in the reactors´vessels generates displacement defects and transmutations. Such micro-structural damage leads the materials to suffer degradation of its mechanical and physical properties. Embrittlement, swelling, stress corrosion cracking, hardening loss of optical transmission and of electrical isolation are some examples of the problems that radiation will cause on structural and functional materials used in [[ITER]] and DEMO.

[[Laboratorio Nacional de Fusión|LNF]] drives fundamental research activities to approach the understanding of radiation effects in structural and functional materials of interest for fusion.

*Structural Materials: Candidate steels to build the reactor vessel while resisting loads, high temperatures, high radiation fluxes and intense magnetic fields.

*Materials for solid breeder blankets: For the HCPB (Helium Cooled Pebble Bed) design.

==Material Irradiation Facilities==

===2 MeV ELECTRON VAN DE GRAAFF ACCELERATOR===

[[File:Foto1electrones.png|500px|thumb|right|Electron Accelerator]]

This facility permits material irradiation either by a 2 MeV electron beam or by Bremsstrahlung induced by stopping the electron beam. In this way, radiation testing that is normally carried out using a Co-60 source can be undertaken more rapidly (producing a larger and better controlled dose rate) while allowing in-situ measurements. Irradiation parameters (temperature, vacuum pressure, gas environment, dose rate and beam energy) are well controlled. Moreover, irradiation of relatively large components or material samples is possible. The accelerator staff can design and develop different irradiation chambers and experimental set-ups depending on irradiation requirements. Such experimental systems permit performing optical, electrical and dielectrical measurements during irradiation ("in-beam"). This makes it a unique experimental radiation facility in which simultaneous optical, electrical and dielectrical measurements can be made in the range of Hz to GHz. For this, systems to measure optical absorption and radioluminescence, electrical conductivity and dielectric properties during irradiation (in-situ) are mounted on the accelerator beam line.  

Beam characteristics;

For insulator studies typical dpa rates range from about 10^-12 to 10^-8 dpa/s while ionization rates (Bremsstrahlung or direct electron irradiation) up to ≈ 10⁴ Gy/s

For steels, about 10^-3 dpa/day can be achieved in samples of approximately 3x3x1 mm³.

Flexibility

===60 keV DANFYSIK ION IMPLANTER===

[[File:Foto0045.jpg|500px|thumb|right|60 keV ion implanter beam line at CIEMAT]]

This facility permits ion implantation at energies up to 60 keV. For instance, helium, hydrogen and duterium ions have been implanted for a range of studies related with fusion research. The implanter staff have designed and developed different irradiation chambers and experimental set-ups depending on the study requirements. The developed experimental systems permit in-situ optical, electrical and desorption measurements. For instance simultaneous ionoluminescence and surface electrical conductivity measurements can be made thus allowing correlation between macroscopic material degradation and defects produced by implantation.  

Beam characteristics;

*Type of source: 12 Co-60 cylindrical sources (15 mm diam. x 135 mm long) are distributed in a circle to provide an inner cylindrical irradiation volume.

*Two distributions are available: High flux; ≤ 8.3 10³Gy/h within a 60mm diam. x 100 mm high volume. Low flux; ≤ 1.2x10² Gy/h within a 200 mm diam. x 100 mm high volume (in the low flux configuration the sources can be rotated along an outer circle for uniform dose).

*Irradiation at controlled temperatures and atmospheres, together with in-situ testing of electrical properties, is also possible.

*Irradiation can be carried out at controlled temperature up to 300ºC. Gas flow (such as dry air or nitrogen) can be used during irradiation to minimize humidity. The uncertainty in the dose rate is better than 20% for a volume of about 283 cm³.

Irradiation rigs to perform in-situ measurements at different dose rates and under different conditions are routinely fabricated at Ciemat workshops. Sensors, cabling, laboratory equipment, feedthroughs, and environmental monitors (temperature, pressure, humidity, radiation) are available.

*Dosimetry system

Routine gamma dosimetry is performed using commercially available Red Perspex™ 4034 Harwell dosimeters. These are widely used polymethylmethacrylate (PMMA) dosimeters. When exposed to ionising doses that exceed 1 kGy, the Red 4034 polymer starts to darken due to the formation of a new absorption band extending from 600 nm to beyond 700 nm (it peaks at 615 nm). The absorbed dose is therefore determined by measuring radiation-induced absorbance in the 630nm-650 nm range where post-irradiation fading is minimal. For this the 640 nm wavelength is used as measurement wavelength. The absorbance per unit thickness, expressed in cm^-1, is the dose-dependent quantity measured against air as reference. These dosimeters has been shown to be valid in the range of 5 to 50 kGy and their accuracy is better than 10 per cent. The Red 4034 dosimeters are pre-conditioned in a fixed humidity environment and hermetically sealed in polyester/aluminium foil/polyethylene laminate pouches, as absorbed water concentration was identified as a parameter which could influence the spectrophotometric response and hence the dose readout. Keeping the dosimeter in its packaging is mandatory to use the calibration curves (absorbance at 640nm (cm-1) related to dose) supplied by the manufacturer. The temperature sensitivity of the dosimeter is the most important environmental dependence. From a practical point of view, the Red 4034 dosimeters are temperature-independent up to 40ºC, provided that measurements are made as soon as possible after ending an irradiation

These dosimeters have been also used to measure gamma dose in BR1 graphite-moderated, air-cooled nuclear reactor (SCK·CEN MOL), in mixed gamma neutron fields at a temperature below 40º.