Uncontrolled reactivity insertion transients of a material test research reactor fuelled with high density U3Si2 dispersion fuels

The effects of using high density low enriched U3Si2 uranium dispersion fuels on the uncontrolled reactivity insertion transients of a material test research reactor were studied. For this purpose, the low density LEU fuel of an MTR was replaced with high density U3Si2 LEU fuels currently being developed under the RERTR program. Simulations were carried out to determine the reactor performance under reactivity insertion transients with totally failed control rods. Ramp reactivities of 0.25$/0.5 s and 1.35$/0.5 s were inserted with reactor operating at full power level of 10 MW. Nuclear reactor analysis code PARET was employed to carry out these calculations. It was observed that when reactivity insertion was 0.25$/0.5 s, the new power level attained followed the relationship:P(MW)=8.256+6.276ρU−0.714ρU2+26.667×10−3ρU3for4.0≤ρU(g/cm3)≤6.0When reactivity insertion was 1.35$/0.5 s, the feedback reactivities were unable to control the reactor which resulted in the boiling of the coolant; the one with the highest fuel density was the first to reach the boiling point. The time of ONB followed the relation:tONB(s)=359.4×10−3+4.4×10−3ρU+687.5×10−3ρU2for4.0≤ρU(g/cm3)≤6.0The magnitude of total feedback reactivity at ONB decreased as uranium density increased and followed the relation:ρfb($)=130.0×10−3+19.3×10−3ρU+2.4197ρU2for4.0≤ρU(g/cm3)≤6.0