| An ambitious European project EURISOL DS (FP7) deals with the design of new generation RIB
production facility based on ISOL method. The future factory is characterized by a 4 mA proton
beam of 1 GeV (4 MW power) impinging on a liquid Hg target-converter, which in turn is
surrounded by a number of small actinide fission targets, each aiming at ~1015fissions/s. In this
context, Monte Carlo simulations using MCNPX version 2.5.0 were performed to optimize the bulk
shielding of this EURISOL Multi-MW target. Using the obtained neutron flux and energy spectra,
activation calculations with DCHAIN-SP2001 code were carried out to create an activation map of
the entire shielding structures. Some quantitative comparisons between DCHAIN-SP2001 and
CINDER’90 material evolution codes were also performed. Two approaches of the shielding
activation zoning were assumed for the radioactive wastes study: i) the activity estimates were done
at the level of a fine annular mesh grid with radius and height of 10 cm (FM approach) and ii) thick
layers of 100 cm thickness (TL approach) were used to derive the total activity. Finally, the
classification of the radioactive wastes based on IAEA clearance levels was further elaborated for
seven decay time periods after target operation shutdown. Comparison of the results obtained for
the two approximations used is discussed. Using the same procedure, an estimation of the produced
radioactivity inside the soil surrounding the shield (to be used as source term for the contaminant
transport) was further derived.
Estimates of the air activation in the shielding gap were also determined and the obtained
results are compared and discussed. The results of this study will contribute to the estimates of the
overall timescale and costs of the EURISOL facility having also a strong impact on the decision and
strategy to be adopted for the facility dismantling, waste classifications, and their final disposal. |
