A numerical component to evaluate the iodine corrosion in a nuclear fuel accounting for chemisorption mechanisms zirconia layer impact on SCC
Visualitza/Obre
Estadístiques de LA Referencia / Recolecta
Inclou dades d'ús des de 2022
Cita com:
hdl:2117/191323
Tipus de documentText en actes de congrés
Data publicació2015
EditorCIMNE
Condicions d'accésAccés obert
Tots els drets reservats. Aquesta obra està protegida pels drets de propietat intel·lectual i
industrial corresponents. Sense perjudici de les exempcions legals existents, queda prohibida la seva
reproducció, distribució, comunicació pública o transformació sense l'autorització del titular dels drets
Abstract
In PWR plants, nuclear fuel pellets (cylinders 1.2 cm length, 0.84 cm diameter) are
piled in nuclear fuel rods placed in assemblies, each containing 265 fuel rods. the fuel rod is a
tube manufactured in a zirconium alloyed material. Fuel cylinders are piled to form a fuel
stack shorter than the overall tube length to maintain a remaining upper volume called
plenum, able to allow fuel stack elongation and accommodation of the gaseous and volatile
fission products released during operation. The fuel stack (3.6-4 m depending on the design)
is typically maintained during handling operation by a spring placed in the plenum. The fuel
rod is closed at both ends by sealed end plugs after filling dead volumes with a neutral gas
(helium) with a pressure ranging from 1 to 34.5 bars. The cladding insures the first
confinement barrier against radionuclides dispersion. During severe power transients some
fission products, like iodine, are expected to assist cracks initiation and propagation at the
inner surface of the cladding. Our major concern here aims improving understanding the
involved mechanisms, accounting for the zirconia layer able to develop as soon as a closed
contact is locally established between the pellet fragments and the cladding inner surface.
In this work, we extend a specific numerical component, developed by EDF, coupling two
numerical software codes [1]. The first one aims simulating the evolution of the fuel isotopic
composition and the second one aims evaluating the fuel dioxide chemistry. The growth of
the zirconia layer has been modelled and integrated in the numerical tool [2]. The scenario of
Stress Corrosion Cracking (SCC) previously defined has been improved to consider the full
impact of the zirconia layer on SCC. The role of the zirconia layer can be mechanical, thermal
or even chemical. Assumptions and coupling of the phenomenon are discussed.
To make demonstration, a sensitivity analysis is performed. This study considers several zirconia layer thickness for two cases: a high burn-up fuel rod operated in normal PWR
conditions, and a fuel rod segment pre-irradiated in a power plant and then submitted to an
incidental power transient simulation in a MTR. The results demonstrated a protective effect
of the zirconia layer. As a consequence, the corrosive attack of the clad is delayed. The
logarithm function of the iodine chemisorption kinetic appears to be proportional to the
zirconia thickness. The simulation analysis validates the extension of the SCC scenario. The
results are in good agreement with experimental observations.
ISBN978-84-943928-3-2
Fitxers | Descripció | Mida | Format | Visualitza |
---|---|---|---|---|
Coupled-2015_74 ... component to evaluate.pdf | 665,9Kb | Visualitza/Obre |