Localisation and behaviour of caesium, molybdenium and barium in UO2 and MOX fuels. Consequences for fission product release - IRSN - Institut de radioprotection et de sûreté nucléaire Accéder directement au contenu
Rapport (Rapport De Recherche) Année : 2003

Localisation and behaviour of caesium, molybdenium and barium in UO2 and MOX fuels. Consequences for fission product release

Résumé

The behaviour of fission products during irradiation regime is of particular importance as it plays a significant role in the release of these fission products during a severe accident transient regime. Indeed, release kinetics and total amount released during severe temperature transient depend on the chemical form and localisation of these fission products in the fuel after some irradiation stage. It is shown that molybdenum takes a central place for other fission products behaviour during irradiation and that it is essentially localised in a MoO2 precipitate (with an increasing burnup) rather than in a Mo metallic precipitate. This particular form of Mo oxide has special volatilization properties (volatile over 1273K) in the fuel. This can lead to a Mo migration under this gaseous MoO2 form during irradiation when there is a temperature gradient in the pellet. MoO2 can recondense in colder parts of the fuel with a possible reaction with (Cs, Ba) oxides or uranates leading to (Cs, Ba) molybdates. The depletion of Mo from metallic phase with this mechanism implies also an increase of the other element activities in this phase. This can concern Ru for instance whose oxide vapour pressure should therefore be increased. This scheme is then used to analyse some accidental sequence experiments as Vercors tests and it is demonstrated that observed kinetics of release can be interpreted by the previous considerations. MFPR applications to the Vercors tests are finally presented, showing that the current assumptions adopted in the modelisation concerning Mo chemical state do not satisfy the physical arguments exposed before. Some short term improvements are then proposed.
Fichier non déposé

Dates et versions

irsn-04295674 , version 1 (20-11-2023)

Licence

Copyright (Tous droits réservés)

Identifiants

  • HAL Id : irsn-04295674 , version 1

Citer

Gregory Nicaise. Localisation and behaviour of caesium, molybdenium and barium in UO2 and MOX fuels. Consequences for fission product release. DRS/SEMAR/03-26, IRSN - Institut de Radioprotection et de Sûreté Nucléaire. 2003. ⟨irsn-04295674⟩

Collections

IRSN LARA
4 Consultations
0 Téléchargements

Partager

Gmail Facebook X LinkedIn More