G.A. Esteban

The Surface Rate Constants of Deuterium in the Reduced Activating Martensitic Steel OPTIFER-IVb.

Abstract A gas permeation technique has been used to obtain the deuterium surface rate constants for adsorption σK 1 and recombination σK 2 in the martensitic steel OPTIFER-IVb. The measurements were performed over the temperature range 523–723 K with deuterium driving pressures ranging from 5×10 2 to 5×10 5 Pa. The deuterium surface rate constants obtained are: σK 1 ( mol m −2 s −1 Pa −1 )=2.998×10 −8 exp (−29230/RT) , σK 2 ( mol −1 m 4 s −1 )=2.838×10 −7 exp (−28679/RT) , R in J / K mol −1 . An intermediate gas transport regime has been accounted for over the experimental range. The transport regime was found close to the surface-limited regime as the deuterium driving pressure is lowered and the temperature increased. Permeability Φ has been derived together with surface rate constants: Φ ( mol m −1 Pa −1/2 s −1 )=5.311×10 −8 exp (−44988/RT) . This is in very good agreement with the permeability previously measured using a different gas evolution method, evidencing the consistency of the obtained results.

Tritium diffusive transport parameters and trapping effects in the reduced activating martensitic steel OPTIFER-IVb

Abstract A time-dependent gas-phase isovolumetric desorption technique has been used to obtain the hydrogen isotopes transport parameters between 423 and 892 K and driving pressures ranging from 4×104 to 1×105 Pa. For protium and deuterium the properties diffusivity (D), Sieverts’ constant (Ks), permeability (Φ), trapping energy (Et) and the trap sites concentration (Nt) are given. On the basis of ideal harmonic vibration of the hydrogen isotope atoms in a unique type of solution site, the values derived for the characteristic protium oscillation temperatures are: θ=1884 K, θ*=2387 K. These values lead to the following extrapolated tritium transport parameters: D ( m 2 s −1 )=4.166×10 −8 exp (−12 027/RT), K s ( mol m −3 Pa −1/2 )=0.271 exp (−27 905/RT) , Φ ( mol m −1 Pa −1/2 s −1 )=1.127×10 −8 exp (−39 933/RT), E t ( J / mol )=55 554, and N t ( sites / m 3 )=0.79×10 24 . The dynamics of the hydrogen isotopes transport and the origin of the trapping phenomenon are discussed in connection with the OPTIFER-IVb microstructure.

Diffusive transport parameters and surface rate constants of deuterium in Incoloy 800

Abstract A gas permeation technique has been used to obtain the complete set of deuterium transport parameters in Incoloy 800 with deuterium driving pressures ranging from 10 4 to 1.5×10 5 Pa and temperatures from 427 to 780 K. The deuterium diffusive transport parameters obtained are: D ( m 2 s −1 )=3.87×10 −7 exp (−47.8 ( kJ mol −1 )/RT) , K s ( mol m −3 Pa −1/2 )=0.102 exp (−7.8 ( kJ mol −1 )/RT) , Φ ( mol m −1 s −1 Pa −1/2 )=3.94×10 −8 exp (−55.6 ( kJ mol −1 )/RT) . The deuterium surface rate constants for a non-oxidized surface has been evaluated as: σk 1 ( mol m −2 s −1 Pa −1 )=2.67×10 −10 exp (−40.1 ( kJ mol −1 )/RT) , σk 2 ( mol −1 m 4 s −1 )=2.58×10 −8 exp (−24.5 ( kJ mol −1 )/RT) , and for an oxidized surface: ( σk 1 ) ′ ( mol m −2 s −1 Pa −1 )=4.14×10 −6 exp (−44.3 ( kJ mol −1 )/RT) , ( σk 2 ) ′ ( mol −1 m 4 s −1 )=4.00×10 −4 exp (−28.6 ( kJ mol −1 )/RT) .

Deuterium transport in SiCf/SiC composites

Abstract A time-dependent gas-phase isovolumetric desorption technique has been used over a temperature range of 675–1029 K and driving pressures ranging from 13 to 101 kPa, to obtain the deuterium transport parameters diffusivity, D, and solubility, S, in a 3-D SiCf/SiC composite. The values obtained are: D(m2s−1)=1.1×10−4 exp[−107.7 (kJ/mol)/RT], S( mol m −3 )=1.9×10 3 exp[−30.2(kJ/mol)/RT]. The set of measurements performed at the same temperature, 871 K, and different loading pressures 13, 33, 60, 101 kPa, has evidenced a power relationship of solubility versus loading pressure with exponent 0.22, departing from Sieverts’ law. These results are compared with the parameters previously obtained for different types of monolithic SiC, and explained on the basis of the physico-chemical phenomena foreseen within its particular structure. The same experiment has been performed with two sets of specimens manufactured using different variants of the hybrid CVI/PIP technique; a negligible variation of transport parameters has been accounted between both groups of specimens.

Characterisation of deuterium transport in the fibres and matrix of a 3D-SiCf/SiC composite

A non-stationary heterogeneous transport model has been used to simulate a series of deuterium absorption–desorption tests carried out with two sets of 3D-SiCf/SiC composite specimens over a temperature range of 675–1029 K and driving pressures ranging from 13 to 101 kPa. The deuterium transport parameters corresponding to each phase of the composite have been derived showing the following Arrhenius tendencies for the diffusivity and solubility in the matrix: Dm (m2 s−1)=9.0×10−8 exp(−39.0 (kJ mol−1)/RT), Sm (mol m−3)=1.9×105 exp(−70.7 (kJ mol−1)/RT), and the fibre: Df (m2 s−1)=1.6×10−11 exp(−91.0 (kJ mol−1)/RT), Sf (mol m−3)=2.1×101 exp(−28.5 (kJ mol−1)/RT), the solubilities being referred to 105 Pa. The different manufacturing procedures followed in the preparation of the specimens have not provoked a noticeable variation of the deuterium transport characteristics of the matrix or the fibres. The results are compared with the parameters previously obtained for different types of silicon carbide and the same material with a homogeneous transport model. The differences found are explained on the basis of the physico–chemical phenomena foreseen within its particular structure.

Study of the Isotope Effects in the Hydrogen Transport in Polycrystalline Tungsten

A time-dependent gas-phase isovolumetric desorption technique has been used to evaluate the diffusive transport parameters of hydrogen isotopes in polycrystalline tungsten in the temperatures range 673 to 1073 K and driving pressures from 1.3 104 to 105 Pa. Experiments have been run with both protium and deuterium obtaining their respective transport parameters diffusivity (D), Sieverts’ constant (Ks), the trap site density (Nt) and the trapping activation energy (Et). Isotope effects on these transport parameters are analysed and modelled. Because the classical isotope relation for diffusivity has not been fulfilled, quantum-statistical vibration theory has been applied to model the isotopic relation. A congruent isotopic variation of diffusion parameters related to the type of microstructure, bcc, has been confirmed.

Deuterium recycling rate constants derived from plasma implantation/desorption shots in a martensitic steel surface

The recombination (K 2 ) and dissociation rate constants (K 1 ) are essential magnitudes for the tracking of tritium at the First Wall (FW) of Fusion Reactors (FR). This paper presents our plasma implantation/recycling test, the modelling of the experiment and the results obtained for K 2 and K 1 in the case of a deuterium (D + 3 /D + 2 ) plasma in the martensitic steel DIN 1.4914 (MANET). Once parasitic contributions were accounted, the D 2 release from the target was seen to be surface limited. The values obtained for K 1 and K 2 show low dispersion on impinging flux and ion energies. For K 1 a roughly constant value of 7 x 10 -6 mol Pa -1 m -2 s -1 is derived. The obtained K 2 is written as: K 2 = 2.414 exp (-1571/RT) (m 4 mol -1 s -1 ), with R = 8.314 J mol -1 K -1 . Our activation energies agree with those existing in the literature derived from permeation experiments. High reflection coefficients are derived, which are in good agreement with the classical theory of ion scattering at low energy.