Monte Carlo analysis of accelerator-driven systems: Studies on spallation neutron yield and energy gain

The neutron yield in the interaction of protons with lead and uranium targets has been studied using the LAHET code system. The dependence of the neutron multiplicity on target dimensions and proton energy has been calculated and the dependence of the energy amplification on the proton energy has been investigated in an accelerator-driven system of a given effective multiplication coefficient. Some of the results are compared with experimental findings and with similar calculations by the DCM/CEM code of Dubna and the FLUKA code system used in CERN.

Mass Spectrometric Investigations of the Evaporation of Crystalline Compounds of the System Cs2O-Al2O3-SiO2 Part II: The Compounds CsAlSiO4 and CsAlSi5O12

Abstract The evaporation of the synthetic compounds CsAlSiO4 and CsAlSi5O12 was studied by high temperature mass spectrometry. The measurements were carried out under equilibrium conditions with Knudsen cells in the temperature ranges 1242 to 1567 K (CsAlSiO4) and 1542 to 1803 K (CsAlSi5O12). The obtained Cs partial pressures are given by the equations

log p (Pa)=-18497/T(K)+11.85(CsAlSiO4)and

log p (Pa)=-26 974/T(K)+14.6(CsAlSi5012).

The probable uncertainty of the vapor pressures is ± 43%. The following enthalpies of sub­limation of Cs (g) were computed:

⊿Sub H°1405 (CsAlSiO4) =353.6 ± 9.8 kJ mol-1 and

⊿Sub H°1673 (CsAlSi5O12) =516.3 ± 18 kJ mol-1.

The Cs partial pressures over CsAlSiO4, CsAlSi5O12 and CsAlSi2O6 (see part I of this work [1]) are discussed with respect to their consequences for the final storage of high level radioactive waste.

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

Experimental studies on the transmutation of some long-lived radioactive waste nuclei, such as 129I, 237Np, and 239Pu, as well as on natural uranium and lanthanum were carried out at the Synchrophastron of the Laboratory for High Energies at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia. The radioactive targets (I, Np and Pu) were contained in weld-sealed aluminium holders produced by the Institute of Physics and Power Engineering, Obninsk, Russia. Spallation neutrons were produced by relativistic protons with energies in the range of 0.5 GeV≤E p≤1.5 GeV interacting with 20 cm long uranium or lead target stacks. The metallic targets were surrounded by 6 cm thick paraffin moderators. The uranium and lanthanum samples were positioned on the outside of the moderator surface and typically contained approximately 0.5 to 1.0 gram of uranium or lanthanum. The highest fluence of spallation neutrons was observed in the region of 5 to 10 cm downstream the entrance of the primary beam into the metallic target, rather independent of the target material or the proton energy. The results obtained by nuclear chemistry methods were supplemented by SSNTD (Solid State Nuclear Track Detector) studies. Consistent and systematic results of B-values and spectral distributions for neutrons have been found. From the experimentally observed transmutation rates one can extrapolate that in a subcritical nuclear power assembly (or "energy amplifier") using a 10 mA proton beam of 1 GeV onto a Pb-target as used here, one can transmute within one month in one gram of sample about 3 mg 129I, 21 mg 237Np, 3.3 mg 238U, and 200 mg 239Pu. Rather similar results have been found by another group for 129I and 239Pu. Observations show that the transmutation rates increase almost linearly with the proton energy in the energy interval 0.5 GeV up to 7.4 GeV. These findings are largely confirmed by model calculations using the LAHET- and DCM/CEM-codes.