Investigation of Critical Heat Flux for Plutonium-Based Mixed Oxide Advanced Fuel Bundle Design

The critical heat flux performance of an advanced plutonium-based mixed oxide fuel for potential use in a pressure tube heavy water reactor has been studied experimentally at Canadian Nuclear Laboratories with an electrically-heated string simulator of 43-element fuel bundles. The fuel simulator has a uniform axial power profile and a radial power profile representative of the plutonium-based MOX fuel. The CHF measurements were made in the MR-3 heat transfer loop facility using R-134a refrigerant as the working fluid. The test matrix included system pressures from 1.47 to 2.11 MPa, mass flow rates from 12.7 to 14.7 kg/s and inlet temperatures from 31 to 59°C, which are representative of the water-equivalent reactor operating conditions of 9 to 12.5 MPa pressure, 13.5 to 21.3 kg/s mass flow rate and the desired inlet subcoolings. Compared to conventional natural uranium fuel, the radial power profile of a MOX fuel exhibits a steeper and uneven distribution across the fuel element rings, with a higher value in the outer ring. It was found that CHF values of the MOX fuel are significantly lower than those of the natural uranium fuel. Based on the experimental data, a correlation has been derived to account for the effect of radial power profile on CHF. This correlation can be used to evaluate the relative CHF values of advanced/non-conventional fuel designs with radial power profiles deviating from that of natural uranium fuel.

ПЕРСПЕКТИВЫ АТОМНОЙ ЭНЕРГЕТИКИ В ОБЕСПЕЧЕНИИ ЭНЕРГЕТИЧЕСКОЙ И ЭКОЛОГИЧЕСКОЙ БЕЗОПАСНОСТИ РОССИИ

Large-scale nuclear energetics can satisfy demands for all kinds of energy, i.e. it can secure energy safety of Russia and the whole humankind; however, this is associated with a number of daunting problems. With that, this approach is a priority for Russia. The State Corporation RosAtom is involved in the development of nuclear reactors in Russia and abroad on the conditions that the reactors will be supplied with nuclear fuel from Russia and the spent fuel will be returned to Russia for conversion into mixed uranium and plutonium oxide (MOX) fuel. In the city Zheleznogorsk near Krasnoyarsk, the first production line of a plant for treating 2000 tons of spent nuclear fuel annually has been already launched. The principal strategic plan of RosAtom, which has been being realized currently, is to develop nuclear power production based on fuel recycling using fast neutron reactors for generation of plutonium, which may be used in nuclear weapons and is most hazardous for the biosphere. The possibility of accidents associated with radioactive discharges cannot be excluded, and the hazardousness of such accidents in increased by using plutonium-based fuels. The nuclear power-based approach to energy production is costly but also dangerous not only for Russia.

Thorium-based CANDU qualification as plutonium burner

Converting the weapon grade Plutonium from the U.S.A., Russia, U.K. etc. to Mixed OXide fuel and using it in power reactors was seen as a feasible way to both dispose Plutonium and produce energy. Using Thorium-based fuels in CANDU has been investigated since early 1980’s, they were designed and tested in Canada as mixed ThO2 -UO 2 (both LEU and HEU) and mixed ThO2 -PuO 2, (both reactor- and weapons-grade) ([1]). In this respect, Thorium might also be seen as a valuable driver for weapon grade Plutonium annihilation. Our goal was to investigate ThO2 -PuO 2 MOX in the aim to propose a suitable fuel for the existing and future CANDU units in Romania. Both weapon grade and reactor grade Plutonium were considered as fissile drivers for Thorium. Since this is only an exploratory study, some key design parameters such as fuel pellet density and ThO2 /PuO 2 ratio were considered to span over a certain range imposed by MOX fuel fabrication technology and limited Plutonium availability. Eighteen fuel compositions were considered and cell calculations were performed for 37 and 43-element bundles using several computer codes.