Study of radionuclide release in commercials uo2 spent nuclear fuels
- Autores: Ernesto Gonzalez Robles Corrales
- Directores de la Tesis: Joan de Pablo Ribas (dir. tes.), Daniel Serrano Purroy (codir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2011
- Idioma: español
- Tribunal Calificador de la Tesis: Ignasi Casas Pons (presid.), Francisco Javier Giménez Izquierdo (secret.), Pablo Zuloaga Lalana (voc.), Jean Paul Glatz (voc.), Volker Betz (voc.)
- Materias:
- Texto completo no disponible (Saber más ...)
- Resumen
The main problem of the nuclear industry, developed to provide energy in the middle of the XX century, is the treatment of the waste generated during irradiation process in nuclear power plants. This wasye is so-called Spent Nuclear Fuel (SNF).
Nowadays, the most common solution adopte by different countries such as Sweden, USA or Spain, to solve this problem foresee, to build-up a gelogical repository. The aim is to dispose permanently and safely the SNF isolated from the biosphere, by using a multibarrier system. One of the main concerns is to establish the consequences in case of canister failure. Once groundwater interacts with SNF, it will corroded and dissolved, producing the release of the radionuclides.
Assesing the SNF performance in a potential gelogical repository requires the understanding and the quantification of radionuclide release. In the past, radionuclide release was divided into three zones gap, grain boundary and matrix. Recently, new contributions have been considered such as the so-called rim structure which appears when the time of the fuel in the reactor is increased. Short term release due to segregation of a part the radionuclide inventoty to the gap, the fractures (relaesed in weeks) and also to grain boundaries (released during months). The degree of segregation is very dependent on reactor fuel operating parameters such as linear power ratingand burn-up (BU). This whole process is generally referred as Instant Release Fraction (IRF) and it is considered to govern the dose that might arise because of premature canister failure.
Database for these processes is scarce especially for SNF with high BU where is possible detect the rim structure which can be considered as High Burn-up Structure (HBS). For this reason a complete study was performed to provide new data. A total of four commercial UO2 SNF were selected: three PWR with BU's of 48, 52 and 60 MWd/kgU and one BWR with a BU of 53 MWd/kgU. Two powder samples were prepared, one from the internal part, called CORE and another from the external part, labelled OUT, both to provide information on grain boundary contribution. Results showed in both leaching solution (bicarbonate and granitic-bentonite waters) that CORE dissolved faster than OUT, the formation of HBS seems to have a protecteive effect on the radionuclide release. Information about gap contribution was obtained using segment cladded samples with the four fuels in bicarbonate water. Radionuclides that constituted the IRF in all the experiments were Cs, Rb and Sr, and in a conservative approach Mo and Tc. IRF values indicate that release from the gap is higher than in grain boundaries. Dynamic experiments performed with SNF 48 MWd/kg gave similar results to those obtained in static reactors.
