EXPERIMENTAL STUDIES OF TRANSMUTATION OF 129 I BY SPALLATION NEUTRONS USING JINR DUBNA PHASOTRON
An intensive beam of 660 MeV protons was directed towards a lead target (not surrounded by shielding or neutron reflectors) for 10 minutes. On the top of the target were placed detectors and iodine samples. The neutron field and the transmutation of I were studied by the neutron activation analysis method. First simulations were compared to the experimental data. 1 Description of the experiment The collaboration ”Energy plus transmutation” works on benchmark experiments intended to test simulation programs, which shall be used in design of Accelerator Driven Systems. The work consist of a series of similar experiments, of which each is concentrated on a specific topic. Generally said, we study production of neutrons by spallation reactions on massive targets, their transport, and use for transmutation. Our experimental setups consist of heavy metal (Pb, W, Bi, U) targets of cylindrical shape to which a narrow beam of relativistic protons is directed. In the target protons cause spallations of heavy nuclei to nucleons, and smaller fractions of nucleus. Relativistic nucleons cause further spallations, and mostly neutrons of all energies from thermal up to the energy of the proton beam exit the target sideways. Such neutron production shall be used in the devices called ADS (Accelerator Driven Systems), which will be able to use a wider spectrum of nuclear fuel (Th, nuclear waste from thermal reactors), and their waste should be much less radioactive than the waste from thermal reactors. These systems cannot be built in smaller scale as a test model, and the accelerators to be added to the reactors will not be a cheap extension. That is why we need the precise descriptions of what will be going on in these systems. Our experiments are simplified setups of them, and are used as benchmark tests for the computer simulations that will be used to describe larger and more complicated systems. One of the experiments was held on Dubna Phasotron in December, 2003, and was focused on the studies of short-lived iodine isotopes production. We needed to make our measurements as soon as possible after the irradiation, and use as intensive proton beam as possible. The proton beam was provided by Dubna Phasotron, which accelerated the intensive proton beam to the energy 660 MeV. The beam was directed to the bare lead
Experimental Studies of the Spatial Distribution of Neutron Production Around a Thick Lead Target Irradiated by 0.9 GeV Protons
This study is part of a complex research of Accelerator Driven Transmutation Technologies (ADTT) carried out by a collaboration of the NPI ASCR in Řež with the JINR in Dubna. The aim of the experiment was to check the validity of the model descriptions and the cross-section libraries used in the corresponding Monte-Carlo simulations of spallation reactions, and the propagation of the produced high-energy neutrons passed through a thick target. The experiment was carried out at the synchrophasotron of the Laboratory for High Energies at the JINR. Relativistic protons with an energy of 885 MeV interacting with a massive cylindrical lead target produced the spallation neutrons. The spatial and energetic distributions of the produced neutron field were measured by the activation of Al, Cu and Au foils placed on the surface of and next to the target. The HPGe detectors then measured the activity of the foils. The resulting γ-spectra of the activated foils were analysed, the yields of the corresponding radioactive nuclei were determined, and compared with Monte-Carlo based simulations performed both with the LAHET+MCNP code and the MCNPX code.
Wall-to-bed heat transfer in circulating fluidized beds
Heat Transfer from the wall of a circulating fluidized bed to the fast bed suspension has been investigated for several materials. The range of investigation includes dense and dilute phase fast fluidization and pneumatic transport. The overall heat transfer coefficient was found to be a function mainly of cross-sectional average suspension density. Effects of superficial velocity and solids mass flux were obscured by their interrelationship to the suspension density. Two models from the literature are evaluated using present and published data.