Transmutation of 239Pu and other nuclides using spallation neutrons produced by relativistic protons reacting with massive U- and Pb-targets

First nuclear activation experiments using the new accelerator NUCLOTRON in Dubna

First nuclear activation experiments have been carried out using the new accelerator for relativistic particles NUCLOTRON in Dubna. The distribution of neutrons emitted during the irradiation with 0.65, 1.0 and 1.5 GeV protons from a lead target (∅ = 8 cm, l = 20 cm) and moderated by surrounding paraffin of 6 cm thickness was studied with radiochemical sensors along the beam axis on top of the moderator. Small 139Lasensors of approximately 1 g each were used to measure essentially the thermal neutron fluence at different depths near the surface: i. e. on top of the moderator, in 10 mm deep holes and in 20 mm deep holes, respectively. The reaction 139La (n, γ) 140La (τ1/2 = 40.27 h) was studied using standard procedures of gamma-ray spectrometry and data analysis. The induced activity of 140La increases strongly with the depth of the hole inside the moderator. Its activity distribution along the beam direction on top of the moderator has its maximum about 10 cm downstream the entrance of the protons into the lead and the activity increases about linearily with the proton energy. Some comparisons of the experimental results with model estimations based on the LAHET code are also presented. The experiments were carried out in the Veksler and Baldin Laboratory of High Energies of the Joint Institute for Nuclear Research in Dubna, Russian Federation.

Accelerator driven systems for transmutation and energy production: challenges and dangers

Accelerator Driven Systems (ADS) are an old technological idea: Relativistic proton accelerators deliver their beams onto massive heavy element targets, thus producing abundant neutron fluences. Placing this target into sub-critical nuclear fission assemblies is yielding substantial fission reactions, thus additional fission energy (Rubbia called such a system “Energy Amplifier”). This technology has recently attracted considerable attention due to advances in the construction of powerful accelerators. It allows the safe and cheap production of nuclear energy simultaneously with the destruction (Transmutation) of long lived radioactive waste, in particular plutonium and other minor actinides (neptunium and americium). The principles and the present-state-of-the-art are described, including first experiments to transmute plutonium this way. This technology needs, however, many more years of further “research and development” before large scale ADS's can be constructed. It may be even necessary to investigate the question, if all basic physics phenomena of this technology are already sufficiently well understood.

Transmutation experiments on 129I, 139La and 237Np using the Nuclotron accelerator

Transmutation experiments have been carried out using the NUCLOTRON, a new accelerator for relativistic particles. The experiments were carried out in the Veksler and Baldin Laboratory of High Energies of the Joint Institute for Nuclear Research in Dubna, Russian Federation. Earlier experiments using an 8 cm Ø Pb-target of 20 cm length and surrounded by 6 cm paraffin (GAMMA-2 target) have been continued to study the transmutation of 139La and the highly radiotoxic radwaste nuclides 129I and 237Np using spallation neutrons produced by relativistic protons with energies 0.5 GeV ≤ E p ≤ 4.15 GeV. Results of previous experiments were complemented with additional results, thus yielding data systematics with small uncertainties over the probably commercially relevant energy range of 0.5 GeV ≤ E p ≤ 1.0 GeV and also in the scientifically interesting range above 1 GeV. Moreover, neutron density distributions in irradiations with 0.65 GeV, 1 GeV and 3.7 GeV protons were determined on the surface of the paraffin moderator for two energy regimes of slow and intermediate/fast neutrons. A large set of high quality experimental data with small uncertainties has been generated that can serve as benchmark data for modelling purposes.

Enhanced production possibility of the therapeutic radionuclides 64Cu, 67Cu and 89Sr via (n,p) reactions induced by fast spectral neutrons

Spectrum averaged cross sections for the 64Zn(n,p)64Cu, 67Zn(n,p)67Cu and 89Y(n,p)89Sr reactions were measured using a 14MeV d(Be) neutron source. In each case a clean radiochemical separation was performed and the radioactivity of the product was determined via high-resolution γ-ray spectrometry or anticoincidence β - counting. The cross sections are three to five times higher than with a fission neutron spectrum. It is postulated that at an intense fast spectral neutron source, e.g. a spallation source, it would be advantageous to use an (n,p) reaction: GBq amounts of 64Cu and 67Cu could be produced in one hour irradiation and of 89Sr in about one day irradiation.

Detection of spallation neutrons and protons using the (nat)Cd activation technique in transmutation experiments at Dubna

Various spallation sources have been used to transmute long-lived radioactive waste, mostly making use of the wide energy neutron fluence. In addition to neutrons, a large number of protons and gamma rays are also emitted from these sources. In this paper (nat)Cd is proved to be a useful activation detector for determining both thermal-epithermal neutron as well as secondary proton fluences. The fluences measured with (nat)Cd compared with other experimental data and calculations of DCM-DEM code were found to be in reasonable agreement. An accumulation of thermal-epithermal neutrons around the center of the target (i.e. after approx. 10 cm) and of secondary protons towards the end of the target is observed.

Application of activation methods on the Dubna experimental transmutation set-ups

High spallation neutron fluxes were produced by irradiating massive heavy targets with proton beams in the GeV range. The experiments were performed at the Dubna High Energy Laboratory using the nuclotron accelerator. Two different experimental set-ups were used to produce neutron spectra convenient for transmutation of radioactive waste by (n,x) reactions. By a theoretical analysis neutron spectra can be reproduced from activation measurements. Thermal-epithermal and fast-super-fast neutron fluxes were estimated using the 197Au, 238U (n,gamma) and (n,2n) reactions, respectively. Depleted uranium transmutation rates were also studied in both experiments.