Michael Österlund

Nucleon-induced reactions at intermediate energies: New data at 96 MeV and theoretical status

Double-differential cross sections for light charged particle production (up to A=4) were measured in 96 MeV neutron-induced reactions, at the TSL Laboratory Cyclotron in Uppsala (Sweden). Measurements for three targets, Fe, Pb, and U, were performed using two independent devices, SCANDAL and MEDLEY. The data were recorded with low-energy thresholds and for a wide angular range (20 deg. -160 deg. ). The normalization procedure used to extract the cross sections is based on the np elastic scattering reaction that we measured and for which we present experimental results. A good control of the systematic uncertainties affecting the results is achieved. Calculations using the exciton model are reported. Two different theoretical approaches proposed to improve its predictive power regarding the complex particle emission are tested. The capabilities of each approach is illustrated by comparison with the 96 MeV data that we measured, and with other experimental results available in the literature.

The New Uppsala Neutron Beam Facility

A new quasi‐monoenergetic neutron beam facility has been constructed at the The Svedberg Laboratory (TSL) in Uppsala, Sweden. Key features include an energy range of 20 to 175 MeV, high fluxes, and the possibility of large‐area fields. Besides cross‐section measurements, the new facility has been designed specifically to provide optimal conditions for testing of single‐event effects in electronics and for dosimetry development. First results of the beam characterization measurements performed in early 2004 are reported.

Neutron Detection–Based Void Monitoring in Boiling Water Reactors

Abstract The ratio between the thermal- and fast-neutron fluxes in a boiling water reactor depends on the void fraction. The density of the steam-water mixture present in the core determines the efficiency of the moderation of fast neutrons born in fission; therefore, the void fraction could be determined by means of a simultaneous measurement of the thermal- and fast-neutron fluxes. Such measurement could also be used to investigate channel bow of the nuclear fuel bundles surrounding the detector because of sensitivity of the thermal flux to geometry changes. Calculations have been performed with both lattice and nodal codes to study the behavior of the void fraction correlation to the ratio of the thermal- and fast-neutron fluxes. The results prove the correlation to be nearly linear and robust. The rate of change of the correlation is insensitive to standard reactor operating parameters such as control rods and burnable absorbers; the sensitivity of the ratio to void fraction changes primarily depends on the geometry of the fuel bundles. A linear prediction model was used to represent the nodal code results. The absolute void fraction at over 792 positions in the core could be predicted with an absolute uncertainty of ±1.5%.

A New Neutron Beam Facility for SEE Testing

A new quasi-monoenergetic neutron beam facility has been constructed at The Svedberg Laboratory in Uppsala, Sweden. The new facility has been designed specifically to provide optimal conditions for testing of single-event effects in electronics. Key features include a neutron energy range of 20 to 175 MeV, high fluxes, user flux control, flexible neutron field size and shape, and spacious and easily accessible user area. Results of beam characterization measurements are reported.

Homogenization of Cross Sections and Computation of Discontinuity Factors for a Real 3-D BWR Bottom Reflector for Comparison with Lattice and Nodal Codes

Abstract Boiling water reactor (BWR) bottom reflector calculations in lattice codes such as CASMO are presently used only to produce accurate boundary conditions for core interfaces in nodal diffusion codes. Homogenized cross-section constants and discontinuity factors are calculated in one dimension (1-D) without the explicit presence of the control rod absorber. If the spatial flux in a BWR bottom reflector is required, for example, for depletion calculations of withdrawn control rods, the homogenization of the reflector must be based on a representation of the three-dimensional (3-D) geometry and material composition that is as true as possible. This paper investigates differences in cross-section and discontinuity factors from 1-D calculations in CASMO with 3-D Monte Carlo calculations of a realistic bottom reflector model in MCNP5. The cross-section and discontinuity factors from CASMO and MCNP5 are furthermore implemented in the nodal diffusion code SIMULATE5 to investigate the effect on the neutron fluxes in the bottom reflector. The results show that for the case investigated, the 1-D homogenization in CASMO5 produces a 26% overestimation of the homogenized thermal absorption cross section in the reflector and a 62% underestimation of the homogenized fast absorption cross section. These cross-section differences have essentially no impact on the neutron flux in the core but cause a 4.5% and 12.3% underestimation of the thermal and fast neutron flux, respectively, in the reflector region.

Study of pre-equilibrium emission of light complex particles from Fe and Bi induced by intermediate energy neutrons

We have measured double differential cross sections (DDX) for emission of hydrogen- and helium-isotopes in the interaction of 175 MeV quasi-monoenergetic neutrons with Fe and Bi using the Medley setup at the The Svedberg Laboratory (Uppsala, Sweden). We compared experimental DDX with calculations with the TALYS code, which includes exciton model and Kalbach systematics; the code fails to reproduce the emission of complex light ions, generally overestimating it. We propose an correction for the application of the Kalbach phenomenological model in the TALYS code by introducing a new energy dependence for the nucleon transfer mechanism in the pre-equilibrium emission region. Our results suggest also evidence for multiple pre-equilibrium emission of composite particles at 175 MeV.

LIGHT CHARGED PARTICLE PRODUCTION IN 96 MEV NEUTRON INDUCED REACTIONS ON OXYGEN

U. Tippawan , S. Pomp, A. Ataç, B. Bergenwall, J. Blomgren, S. Dangtip, A. Hildebrand, C. Johansson, J. Klug, P. Mermod, L. Nilsson, M. Österlund, N. Olsson, A.V. Prokofiev, P. Nadel-Turonski, V. Corcalciuc, and A.J. Koning. Department of Neutron Research, Uppsala University, Sweden Fast Neutron Research Facility, Chiang Mai University, Thailand Swedish Defence Research Agency (FOI), Stockholm, Sweden The Svedberg Laboratory, Uppsala University, Sweden Department of Radiation Sciences, Uppsala University, Sweden Institute of Atomic Physics, Heavy Ion Department, Bucharest, Romania Nuclear Research and Consultancy Group NRG, Petten, The Netherlands E-mail: udomrat@fnrf.science.cmu.ac.th

Investigation of Three‐Body Force Effects in Neutron‐Deuteron Scattering at 95 MeV

We have measured the neutron‐deuteron (nd) elastic‐scattering differential cross section at 95 MeV incident neutron energy, using both the Medley and the SCANDAL setups at TSL in Uppsala. The full angular distribution was covered by detecting recoil deuterons from thin CD2 targets, and the result was normalized to the neutron‐proton (np) cross section. Recent theories predict that three‐nucleon (3N) force effects, if present, would affect the cross section in the minimum region by about 30%. The results are compared with theoretical calculations and are well described if 3N forces are included.

Simulations and Models of Neutron Fluxes in Boiling Water Reactors Intended for Depletion Calculations of Withdrawn Control Rods

Abstract Models of the neutron flux shape in a withdrawn control rod in a boiling water reactor (BWR) bottom reflector have been constructed from simulations with the Monte Carlo code MCNP. These neutron flux models are intended for determining absorber depletion and fast fluence accumulation for withdrawn control rods with nodal codes. So-called G-factors are created for coupling the neutron flux models to a conventional nodal code via the core bottom neutron flux. The neutron flux models and G-factors are created for three different neutron energies, and their dependence on various parameters such as blanket enrichments, Hf and B4C control rod absorber, and depletion and reflector geometry is investigated. The neutron flux models and G-factors are found to be very insensitive; the neutron flux models predict the simulated neutron flux in the withdrawn control rod from MCNP over a variety of reflector configurations with an error < 3.0%. This implies that the neutron flux models constructed in this paper are generally applicable for BWR reflectors and control rods not fundamentally deviating from the designs investigated in this paper.

MCNPX simulations of the SCANDAL setup for measurement of neutron scattering cross section at 175 MeV

The Scattered Nucleon Detection Assembly (SCANDAL) setup at The Svedberg Laboratory has been used to produce neutron elastic scattering cross section data at 175MeV for bismuth and iron. This work ...