Degradation in steam of 60 cm-long B4C control rods

Cristina Dominguez (1) , Doris Drouan (1)

1 IRSN/PSN-RES/SEREX/LE2M - Laboratoire d'Expérimentation en Mécanique et Matériaux

In the framework of nuclear reactor core meltdown accident studies, the degradation of boron carbide control rod segments exposed to argon/steam atmospheres was investigated up to about 2000°C in IRSN laboratories. The sequence of the phenomena involved in the degradation has been found to take place as expected. Nevertheless, the ZrO2 oxide layer formed on the outer surface of the guide tube was very protective, significantly delaying and limiting the guide tube failure and therefore the boron carbide pellet oxidation. Contrary to what was expected, the presence of the control rod decreases the hydrogen release instead of increasing it by additional oxidation of boron compounds. Boron contents up to 20 wt.% were measured in metallic mixtures formed during degradation. It was observed that these metallic melts are able to attack the surrounding fuel rods, which could have consequences on fuel degradation and fission product release kinetics during severe accidents.

Mots clés: Boron carbide; steam; degradation; control rod; nuclear reactor; severe accident

Domaines: Physique [physics]

Cristina Dominguez, Doris Drouan. Degradation in steam of 60 cm-long B4C control rods. Journal of Nuclear Materials, 2014, 451 (1-3), pp.111-119. ⟨10.1016/j.jnucmat.2014.03.040⟩. ⟨hal-02614012⟩