JCJC SIMI 8 - JCJC - SIMI 8 - Chimie du solide, colloïdes, physicochimie

Corrosion at solid/solution interface under alpha radiolysis – CISSRAD alpha

Corrosion at solid/solution interface under a radiolysis

Scientific purposes of this project are studying the alpha water radiolysis effect onto chemical mechanisms ate solid/solution interface. The main experimental technic used is the on line Raman spectroscopy onto the alpha beam line of the ARRONAX cyclotron facility.

Studies of the radiolytic corrosion onto the Water/UO2 system

Management of nuclear waste such as spent fuel resulting from nuclear industry is one of the major political, social and scientific concerns of our society. Among various management possibilities, the concept of direct disposal in deep geological vaults (500 to 1000 m of depth) is being seriously considered by several countries. The spent nuclear fuel will be stored within canisters and its disposal is planned to be made in presence of a series of natural and artificial barriers whose aim is to isolate the waste from the outside environment. However, it is admitted that groundwater will success within geological timescales (= 1000 years) to percolate the different barriers and arrive to the nuclear waste level. Considering the scenario of canister failure, groundwater will get then in direct contact with the spent fuel whose radioactivity will be limited at these timescales to alpha irradiation. Water in contact with the waste will be then irradiated and various oxidants species (e.g. OH·, H2O2, O2...) will be formed near the spent fuel surface (about 30-40 µm). This will lead to the oxidation of the spent fuel matrix, which is principally formed of UO2 (in its reduced form U(IV)), and the formation of oxidized uranium species (U(VI)). These latter are more soluble in water and may consequently lead to the migration of radionuclides dissolved in the spent fuel matrix from the repository to the biosphere. Then, the knowledge of the chemistry of the solid-liquid interface (oxidation, corrosion...) which controls the radionuclides release under the conditions encountered in deep geological repositories is then of a great importance in performing assessment and safety studies.

Technical purposes of this project are the experimental development of: the on line Raman spectroscopy for the solid surface analysis onto the alpha beam line of ARRONAX cyclotron facility, performing experiments under controlled atmosphere, the time resolved experiment in order to follow the surface species formation/consumption.

A first study was performed at Water/Iron interface in order to determine the H2, H2O2 species role (produced by the water radiolysis) onto the iron surface corrosion phase, in particular the Lepidocrocite [1]. For the second study about the radiolytic corrosion at the Water/UO2 interface, we need drastically improving the Raman system tool in order to increase the detection sensitivity. First results are the following of the studtite formation at the UO2 surface during the radiolytic corrosion [2].

The same experimental system Raman analysis will be applied for other solids involved into the nuclear fuel cycle: (1) Tc and Se oxides; (2) Borosilicate Glasses; (3) Cements; (4) Clays minerals; (5) Iron and steels into canisters. For each solid, we will be able to study the radiolytic corrosion at the solid/solution interface by the Raman system detection developed in this project.

[1] J. Vandenborre, F. Crumière, G. Blain, R. Essehli, B. Humbert, M. Fattahi, Alpha localized radiolysis and corrosion mechanisms at the iron/water interface: Role of molecular species, Journal of Nuclear Materials, 433 (2013) 124-131.
[2] J. Vandenborre, A. Traboulsi, G. Blain, J. Barbet, M. Fattahi, Radiolytic Corrosion of Grain Boundaries onto the UO2 TRISO Particle Surface, in: 1st Annual Workshop Proceedings, 7th EC FP – FIRST-Nuclides, Budapest, Hungary, 2012.

This work is dealing with the understanding of the corrosion mechanisms at solid/solution interface and taking into account the alpha irradiation effects on these mechanisms. These corrosion and alpha radiolysis phenomena append at solid/solution interface and will be studied at a µmetric scale by the Raman spectroscopy. The water radiolysis products are radical and molecular species. High TEL irradiation particles, like alpha ion beam, will be quickly stopped and his energy is set down onto a very short distance. The high density of radical products implies a high recombination of them under molecular species. On the contrary, low TEL irradiation particles, such as gamma beam, give his energy on a longer distance. Most of the corrosion studies under irradiation are been performed with gamma beam not localized with irradiation of solid, solution and interface between them. But, an a irradiation appends onto a few µm3 volume and let us to control the irradiated area (solution, solid or interface). Considering the nuclear waste management storage in deep geological site, we want to study uranium dioxide, as nuclear waste. Then, the chemical species induced by alpha radiolysis of water are such reactive and are involved in classical corrosion mechanisms of UO2. Moreover, we want to study the impact of the alpha radiolysis of water layers physisorbed into the iron surface onto corrosion mechanisms. That is the reason why we want to use a local irradiation, allowed by the alpha ion beam provided by the ARRONAX cyclotron, and not by a classical gamma irradiation. In this work an experimental apparatus will be performed in order to characterize solid/solution interface at µmetric scale by Raman spectroscopy under alpha irradiation provided by ARRONAX.

Project coordination

Johan VANDENBORRE (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE BRETAGNE ET PAYS- DE-LA-LOIRE) – johan.vandenborre@subatech.in2p3.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

SUBATECH CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE BRETAGNE ET PAYS- DE-LA-LOIRE

Help of the ANR 190,892 euros
Beginning and duration of the scientific project: September 2011 - 36 Months

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