Ali Ahmad FLUKA code validation of nuclear data required for the spallation target design in Accelerator Driven Subcritical Reactors ThorEA Meeting – Daresbury 24 th November 2009

FLUKA  High energy physics and engineering Monte Carlo code  Different hadronic models for different energy intervals and different interactions  Hadron-Nucleus:  Glauber-Gribov cascade  PEANUT

Hadronic Models FLUKA  PEANUT model  GINC -Hadron-Nucleus interaction - Exact energy/momentum conservation - Stopping criterion: Time Geant4  More than one model  Bertini INC  Binary cascade -Hadron-Hadron interaction - Not exact energy/momentm conservation - Stopping criterion : Energy

PEANUT  Sophisticated GINC  16 radial nuclear zones  Curved nuclear potential  Exact energy & momentum conservation  Quantum effects included  Fermi gas model adopted

FLUKA de-excitation model  Pre-equilibrium  De-excitation  Evaporation  Fission  Fermi break-up  Gamma de-excitation Geant4 de-excitation model is quite similar to that of FLUKA

What has been done with FLUKA??  Neutron double differential cross section measurement  Neutron yield calculation  Residual fragments production  Neutrons, protons spatial distribution  Energy deposition

Double differential cross section  Target: solid Pb-208  Thickness: 1 cm  Beam: Protons  Energy: 1 GeV  Primaries: 100 million

Double differential cross section: USRYIELD vs USRBDX  USRYIELD  Fully dedicated card for cross section measurements  Can be used for both, extended and point targets  cross sections are measured with respect to a fixed axis (beam axis)  USRBDX  Detector card that measures surface crossing current  Cross sections measured using neutron counting method  Fluence is measured with respect to the surface normal axis

Double differential cross section: Neutron counting method For a thin target bombarded by high energy protons Assuming the number of detected neutrons is equal to that of protons caused the spallation reaction Apply natural logarithm

Double differential cross section: USRYIELD vs USRBDX (cont)

Double differential cross section: FLUKA vs Geant4

Neutron Yield  Target: Solid Pb-208  Shape: Cylinder  Length: 60 cm  Diameter: variable  Detector: usrbdx card

Neutron Yield (cont)

Residual fragments production  RESNUCLEi card used  Residual distribution plotted against production cross section  Production cross section calculation requires again thin target approach

Residual fragments production

Residual fragments production (cont)  Important for studying the irradiation damage in the target  Gives an idea about the activation of the target material

Neutron production distribution  Neutron fluence can be assumed spherically symmetric  Maximum neutron production is achieved few cms away from the impact point

Proton distribution  The protons beam is fully contained in a 60 cm length cylinder  The difference in the fluence is of order of 1/10000 between centre and peripherals

Energy distribution  Energy deposition depends  Density of the target  Atomic number of the material  Beam energy  Target dimensions  Important for  Cooling system  Thermal stresses analyis

Conclusion  The largest contribution to the neutron production comes from primary neutrons rather than primary protons  Materials with high atomic number are essential for high neutron multiplicity, however, issues like neutron absorption should be investigated  Excluding thermal properties, solid lead seems to be a good candidate for spallation target material  For a solid Pb target, a cylindrical shape (L=60 cm, R=25 cm) target seems to be convenient to contain 1 GeV proton beam power  The neutron production is forward biased, this opens a discussion about idea of having multiple targets/beams

Recommendations  FLUKA can be used efficiently for the design optimisation of the spallation target and other ADSR structural component  Extend the benchmarking to other target material candidate such as LBE  FLUKA has shown excellent agreement with Geant4 at high energies, low energies need to be more investigated

I would like to express my gratitude to Dr. Cristian Bangau for his support, encouragement and advice over the project period and for letting me use his Geant4 results

Thank you for your good listening!! Any questions/suggestions ?