A system was developed for the transmutation of actinides into shorter-lived isotopes using a spallation-generated neutron source. A 250 mA, 1.5 Gev proton linear accelerator was chosen as the reference accelerator. The target consisted of liquid lead which circulates to dissipate the heat released when the beam collides with the target and to allow for some energy recovery. The actinides are placed in ordinary PWR fuel rods are arranged into assemblies to form a heterogeneous lattice immersed in liquid lead. The spallation yield was calculated with a version of the code HETC, which utilizes the intra-miclear cascade model to predict neutron production and other spallation products as a result of extraneous particle bombardment. The code 05R was then used to spatially transport the neutrons and to determine the fission rate. It was determined that the system could transmute the actinides included in the study (Np-237 and Am-241) at approximately twenty times the rate that they are produced in a typical PWR reactor. Also, sufficient heat is released through fission that the system should be self-sufficient in power at realistic thermal conversion and accelerator efficiencies. However, in many problems exist for such a system including the facts that 1) the lead becomes highly radioactive due to the spallation products including the creation of the long-lived isotope Hg-194 (520 year half-life), 2) the transmutation process is highly localized around the point of impact of the protons with the lead, 3) a high degree of partitioning is required for transmutation of the actinides to be -efficient and partitioning increases the short-term radiological risk, and 4) the expense of the system might not be worth the health benefits gained.
展开▼
