MEASUREMENT OF VOID VOLUME OF A FUEL-ROD AND THE EXCHANGE OF OCCLUDEDGASES FROM MIXED CARBIDE FUEL WITH FILLING GAS HELIUM

The presence of gaseous impurities in the filling gas of a fuel pin is detrimental to the thermal performance of a nuclear reactor fuel. The composition of the filling gas does not remain constant throughout th e life of the fuel pin. The gas exchange phenomena that occur between the cover gas and impurity gases affect the fuel performance more seve rely in (U, Pu)O-2 fuel pin due to its inherently poor thermal conduct ivity than in advanced fuels such as mixed carbides and nitrides. In t he present study the exchange phenomenon of the occluded gases present in our Fast Breeder Test Reactor (FBTR) fuel pellets [(U-0.03, Pu-0.7 0)C with 6500 ppm O] with the cover gas helium was observed as a funct ion of time and temperature. Quantitative analysis of the released gas es namely H-2, O-2 + Ar, N-2, CH4 and CO was carried out at subambient pressure by gas chromatography. The void volume of the fuel element i s determined experimentally by gas equilibration with known volume.