A. Supe

Basic study of influence of radiation defects on tritium release processes from lithium silicates

The radiolysis of Li2SiO3 and Li4SiO4 was studied using the chemical scavengers method (CSM), thermoluminescence, lyoluminescence, electron spin resonance and spectrometric methods. The influence of the absorbed dose and many another parameters such as: irradiation conditions, sample preparation conditions and concentration of impurities on the accumulation rate of each type RD and RP were studied. Several possibilities for reducing the radiolysis of silicates were discussed. It has been found that tritium localization on the surface and in grains proceed by two different mechanisms. Tritium thermoextraction from the surface proceeds as chemidesorption of tritiated water, but from the bulk as diffusion. The tritium retention processes were studied. It has been found that tritium retention depends on irradiation conditions. Tritium retention is due to the formation of chemical bonds LiT and thermal stable ≡SiT bonds. The accumulation of colloidal silicon and lithium can increase the tritium retention up to 25–35%.

Formation and properties of radiation-induced defects and radiolysis products in lithium orthosilicate

Abstract Formation and properties of radiation-induced defects and radiolysis products in polycrystalline powders and ceramic pellets of Li4SiO4 were studied under the effect of various types of ionizing irradiation (γ quants, accelerated electrons, reactor irradiation), humidity, temperature, impurities in the samples, etc. The content of radiation defects and radiolysis products poorly depends on irradiation type, dose rate, admixture elements. The concentration of defects highly depends on the temperature of irradiation, humidity, granural size. Empirical dependence of radiolysis degree α on the dose was found: α = 5 × 10−2 × D0.5 for γ and electron irradiation (Trad = 300−350 K) and α = 5 × 10−3 × D0.5 for reactor radiation (Trad = 700–800 K); α - matrix dissociation degree (in %); D - dose (in MGy). Colloidal litium and silicon, lithium and silicon oxides, and O2 are the final products of radiolysis. Radiation-induced defects change tritium thermo-extraction parameters, deteriorate mechanical, thermo-physical and electric properties of ceramics.

Influence of radiation defects on tritium release parameters from Li2O

Abstract The study of the influence of radiation defects on tritium release behavior from polycrystalline Li2O was performed by simultaneous measurements of the luminescence emission and tritium release. It was found that the radiation defects in Li2O introduced by electron irradiation cause the retention of tritium. It is thought that the tritium recovery is affected by the formation of a Li–T bond, which is tolerant of high temperatures. The retardation of tritium decreases with increasing absorbed dose in the dose range from 50 to 140 MGy. The aggregation of radiation defects at high irradiation doses is considered to be responsible for the decrease of the interaction of tritium with radiation defects. The mechanism of the interaction of radiation defects with tritium is discussed.

THE ROLE OF RADIOLYSIS PRODUCTS IN IN SITU LUMINESCENCE OF LI2O

Abstract A new phenomenon of an “excess luminescence” (EL) in Li 2 O observed at 4.5–2.5 eV under light ion (H + , He + ) irradiation during the rise of temperature (>573 K ) was studied. The essence of the EL is in the rapid pulse increase of the luminescence intensity. It is proposed that this phenomenon is based on the thermo-dissociation of colloidal Li into Li lattice ions, F + and F 0 centers, and oxygen vacancies. Formed oxygen vacancies capture electrons during the irradiation and form excited F-centers, whose relaxation gives the EL. This phenomenon was reproduced using X-ray irradiation and a sample containing colloidal Li introduced by irradiation with electron accelerator to an absorbed dose of 105 MGy.

RADIOLYSIS OF SOLID BLANKET MATERIALS

The radiolysis of oxy-compounds (Li4SiO4, Li4ZrO4, Li2SiO3, LiAlO2, et. al) which can be used as the alternative blanket materials for fusion reactor has been investigated. The mechanisms of radiation-chemical processes and the composition of formed radiation defects (RD) and radiolysis products (RP) are the same as for the radiolysis of powders, only the quantitative parameters of radiolysis are different. Ceramic materials usually have a higher radiation stability as powders. It has been shown, that the radiolysis of ceramics has two stages. Firstly proceeds the generation of RD on the structure defects and impurity centers, then the radiolysis of matrix. It was found, that the formation of RD at the second stage of radiolysis proceeds slowly in comparision with the radiolysis of powders. The radiation stability of ceramics increases with the number of covalent bonds - oxygen-heteroatom in the structural unit. The new ceramic blanket material (lithium orthosilicate pebbles) produced in the Kernforschungszentrum (Kfk) Karlsruhe has a high radiation stability and it is usable for blanket zone.