Rouanet Maxime.The confining matrice : how to protect the world to radiations of high-activity radioactive waste

Confining matrices are materials that trap radionuclides (cesium, strontium, actinides...) by incorporation and long-term stability in their structure. The objective is to effectively isolate these radionuclides from the biosphere for many tens of thousands of years until their decay. Our concern in particular radionuclides from reprocessing of spent nuclear fuel (final waste). INTRODUCTION

SUMMARY Introduction I/ Some definitions about the radionuclides 1/Different kind of radiation 2/High-activity radioactive waste II/ Confining Matrice 1/ Definition of a confining matrice 2/Utilisation of glass as confining matrice 3/Utilisation of ceramic as confining matrice Conclusion

-A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy which is available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron (see internal conversion). Radionuclides may occur naturally, but can also be artificially produced. Some definitions about the radionuclides

- Alpha and beta radiation consist of tiny particles, much smaller than an atom. They move incredibly fast, perhaps thousands of kilometres per second. - Gamma radiation is a sort of invisible, very high-energy light. What are the impact of this radiations on the human body ? - Alpha particles cause lots of ionization in a short distance - Beta goes further than alpha but is less damaging - Gamma rays can pass through lead but aren't very damaging → Ionization is very dangerous for the human body so we have to isolate the nuclides even after their utilisation.

Some definitions about the radionuclides - High-activity radioactive waste : - From the power industry, they are the radioactive elements not recoverable from the reprocessing of spent fuel. - 2 kinds of product : - The fission products are body chemicals produced by the fission of an element that stabilizes the form of new atoms. These are the "ashes" of the nuclear reaction, which constitute the ultimate nuclear waste. → Radiation gamma mainly. - During irradiation in the reactor, the uranium atoms of fuel can capture a neutron without undergoing fission. He then forms minor actinides (neptunium - Americium - Curium). The rating reflects the minor fact that these elements are present in much less than major actinides: uranium and plutonium. --> Radiation alpha which is very dangerous.

Confining Matrice - What is a confining matrice ? - As we say in the introduction, confining matrices are materials that trap radionuclides (cesium, strontium, actinides...) by incorporation and long-term stability in their structure. - It can be considered to contain all final waste in glasses (40 elements), or some radionuclides individuals (those long-lived) from an enhanced separation in glass-ceramic or ceramic matrix specific more durable than glasses.

Confining Matrice Utilisation of glass as confining matrice -Due to a share of the coercion of long range order and the multiplicity of possible reception sites in their structure and secondly to their ease of manufacture (casting + merger), the oxide glasses appear to be the best type of matrix for containing nuclear waste is not separated.

Confining Matrice Utilisation of ceramic as confining matrice In the case of actinide wastes not separated or separated but containing high amounts of actinides, ceramic matrices are also prepared and studied in the laboratory. Such matrices are obtained by controlled heat treatment of glass leading to the crystallization of actinide host phases highly durable (zirconolite, apatite) in the glass. In this case, the radionuclides trapped in the crystal structure have a double barrier containment by both the crystal and the glass surrounding the crystals. This also allows, because of its flexible structure, to accommodate impurities or other elements present in the waste.

Conclusion

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