Activation calculations for the target of a spallation ultra-cold neutron source at PSI

A spallation ultra-cold neutron source—UCN source—is scheduled to start operation at PSI in 2006 using up to 2 mA 590 MeV protons from the ring cyclotron. It will be operated in a pulsed mode with an average current of 20 μA. For safe maintenance, during operation as well as handling, transport and storage of the UCN target assembly after its lifespan, detailed knowledge about the activation induced by the impinging protons and secondary radiation fields is required. The Monte Carlo transport code MCNPX was coupled with the European Activation System—EASY—to calculate the residual nuclide production in the UCN target assembly. The nuclide inventory is finally used to design the shielded exchange flask that is needed to safely remove and transport the UCN target assembly after its lifespan to a hotcell for dismantlin

Po-production in lead: A benchmark between Geant4, FLUKA and MCNPX

On the last SATIF a comparison between the measured activities of the polonium isotopes Po-208, Po-209 and Po-210 and the simulated results using MCNPX2.7.0 was presented. The lead samples were cut from the SINQ spallation target at the Paul Scherrer Institut (PSI) and irradiated in 2000/2001 by 575 MeV protons. The Po-isotopes were separated using radiochemical methods by the group of D. Schumann at PSI and measured. Choosing the default model in MCNPX, Bertini-Dresner, the prediction underestimated the measured activities by up to several orders of magnitude. Therefore the Li\`ege intranuclear-cascade model (INCL4.6) coupled to the de-excitation model ABLA07 were implemented into MCNPX2.7.0 and very good agreement was found to the measurement. The reason for the disagreement was traced back to a suppression of alpha reactions on the lead isotopes leading to Po and neglecting the triton capture on Pb-208, which leads to Pb-210 and decays into Po-210 with a much longer life time (22.3 years) than the decay of Po-210 itself (138 days). The prediction of the Po-isotope activities turns out to be a sensitive test for models and codes as it requires the accurate treatment of reaction channels not only with neutrons, protons and pions but also with alphas and tritons, which are not considered in intra-nuclear cascade models of the first generation. Therefore it was decided to perform a benchmark by comparing the results obtained with MCNPX2.7.0 using INCL4.6/ABLA07 to the predictions of FLUKA and Geant4. Since the model of the SINQ spallation source requires an elaborate geometry a toy model was setup. The toy model has a simplified geometry preserving the main features of the original geometry. The results for the activities of the three Po-isotopes and Pb-210 as well as the energy spectra for alphas and tritons obtained with the three particle transport Monte Carlo codes are presented.Comment: 15 pages, 11 figures, Presented paper at the 13th Meeting of the task-force on Shielding aspects of Accelerators, Targets and Irradiation Facilities (SATIF-13), HZDR, October 10-12, 2016, Dresden, German

Radiochemical determination of 129I and 36Cl inMEGAPIE, a proton irradiated lead-bismuth eutectic spallation target

The concentrations of the long-lived nuclear reaction products 129I and 36Cl have been measured in samples from the MEGAPIE liquid metal spallation target. Samples from the bulk target material (lead-bismuth eutectic, LBE), from the interface of the metal free surface with the cover gas, from LBE/steel interfaces and from noble metal absorber foils installed in the cover gas system were analysed using Accelerator Mass Spectrometry at the Laboratory of Ion beam Physics at ETH Zürich. The major part of 129I and 36Cl was found accumulated on the interfaces, particularly at the interface of LBE and the steel walls of the target container, while bulk LBE samples contain only a minor fraction of these nuclides. Both nuclides were also detected on the absorber foils to a certain extent (≪ 1% of the total amount). The latter number is negligible concerning the radio-hazard of the irradiated target material; however it indicates a certain affinity of the absorber foils for halogens, thus proving the principle of using noble metal foils for catching these volatile radionuclides. The total amounts of 129I and 36Cl in the target were estimated from the analytical data by averaging within the different groups of samples and summing up these averages over the total target. This estimation could account for about half of the amount of 129I and 36Cl predicted to be produced using nuclear physics modelling codes for both nuclides. The significance of the results and the associated uncertainties are discussed

Experimental studies of a single flexibly-mounted rod in a triangular rod bundle in cross-flow

Experiments on flow-induced vibrations using a closely-packed triangular rod array with a pitch-todiameter ratio of 1.1 in water cross-flow was carried out at Paul Scherrer Institute. The bundle consists of 21 row of five rods in each one. Single flexibly-mounted test rod (TR) is in the fourth row in an otherwise fixed array. The test rod can freely move in the transverse and in-line direction. Two accelerometer sensors were attached at both ends of the TR to measure the rod response on the fluid flow. The effect of flow rate on the stability of the flexibly-mounted TR has been analysed. During experiments, it reveals a set of conditions and tendencies for the flow-induced vibration in the closely-packed multi-rod system

Experimental studies of a single flexibly-mounted rod in a triangular rod bundle in cross-flow

Experiments on flow-induced vibrations using a closely-packed triangular rod array with a pitch-todiameter ratio of 1.1 in water cross-flow was carried out at Paul Scherrer Institute. The bundle consists of 21 row of five rods in each one. Single flexibly-mounted test rod (TR) is in the fourth row in an otherwise fixed array. The test rod can freely move in the transverse and in-line direction. Two accelerometer sensors were attached at both ends of the TR to measure the rod response on the fluid flow. The effect of flow rate on the stability of the flexibly-mounted TR has been analysed. During experiments, it reveals a set of conditions and tendencies for the flow-induced vibration in the closely-packed multi-rod system

Induced radioactivity studies of the shielding and beamline equipment of the high intensity proton accelerator facility at PSI

The Paul Scherrer Institute (PSI) is the largest national research center in Switzerland. Its multidisciplinary research is dedicated to a wide ↓eld in natural science and technology as well as particle physics. The High Intensity Proton Accelerator Facility (HIPA) has been in operation at PSI since 1974. It includes an 870 keV Cockroft-Walton pre-accelerator, a 72 MeV injector cyclotron as well as a 590 MeV ring cyclotron. The experimental facilities, the meson production graphite targets, Target E and Target M, and the spallation target stations (SINQ and UCN) are used for material research and particle physics. In order to ful↓ll the request of the regulatory authorities and to be reported to the regulators, the expected radioactive waste and nuclide inventory after an anticipated ↓nal shutdown in the far future has to be estimated. In this contribution, calculations for the 20 m long beamline between Target E and the 590 MeV beam dump of HIPA are presented. The ↓rst step in the calculations was determining spectra and spatial particle distributions around the beamlines using the Monte-Carlo particle transport code MCNPX2.7.0 [1]. To perform the analysis of the MCNPX output and to determine the radionuclide inventory as well as the speci↓c activity of the nuclides, an activation script [2] using the FISPACT10 code with the cross sections from the European Activation File (EAF2010) [3] was applied. The speci↓c activity values were compared to the currently existing Swiss exemption limits (LE) [4] as well as to the Swiss liberation limits (LL) [5], becoming e↑ective in the near future. The obtained results were used to estimate the total volume of the radioactive waste produced at HIPA and have to be reported to the Swiss regulatory authorities. The comparison of the performed calculations to measurements is discussed as well