Burning and/or transmutation of transuraniums discharged from PWR-UO 2 spent fuel and power flattening along the operation period in the force free helical reactor

Abstract

The burning and/or transmutation (B/T) of transuraniums (TRUs) in the force free helical reactor (FFHR), which is a demo relevant helical type D–T fusion reactor, has been investigated for an operation period (OP) of up to ten years by 75% plant factor ( η) under a neutron wall load ( P) of 1.5 MW/m 2. The transmutation zone (TZ), containing the mixture of TRU nuclides discharged from uranium fueled pressurized water reactor spent fuel, has been located in the blanket of the FFHR to incinerate and/or transmute the TRUs effectively. The TRU mixture, including minor actinides (MAs) and Pu isotopes, has been spherically prepared and cladded with SiC to prevent the TRU nuclides from contacting the coolant and the fission products from contaminating the coolant. Helium has been used for the nuclear heat transfer in the TZ. The effect of the Pu volume fraction in the TRU mixture on the B/T has also been investigated for acquiring a quasi-constant fission power generation along the OP. The neutron multiplication coefficient ( k eff), relating to the fission rate ( R F), is less than 0.9 in all investigated cases during the OP. The tritium breeding ratio value is greater than 1.1 for all investigated cases so that tritium self-sufficiency is maintained for the (D,T) fusion driver. During the OP, in the case of a Pu fraction of 18.1%, the peak to average fission power density ratio ( Γ) value is about 1.09, and the R F is also quasi-constant (about 0.95) along the OP. At the end of the OP, the effective half lives of 237Np, 239Pu, 241Pu, 241Am and 243Am decrease to about 5, 6.5, 7.5, 10 and 7 years, respectively, and the net transmutation fractions for the whole TRUs and MAs are obtained as 46% and 69%, respectively. These consequences show that the blanket accomplishes the B/T of the TRUs effectively, and in the case of a Pu fraction of 18.1%, the TZ has a good flat fission power density profile and a quasi-invariable R F along the OP.