MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is a flexible experimental lead-bismuth cooled accelerator driven system currently being developed at SCK•CEN. The linear accelerator of MYRRHA will accelerate the protons up to 600 MeV.
During routine operation of the accelerator, the interactions of the primary protons with the structural materials will produce a radiation field combining secondary protons, neutrons, photons, electrons, and other particles (depending on the incident beam energy) along the whole length of the beam line. Radiation transport calculations are required to evaluate dose rates along the beam line. Proper assessment of the dose rates is one of the main targets concerning the design of the facility. To calculate dose rates in large geometries with highly absorbent material and large regions of the interest is the main challenge due to large uncertainties and none affordable computing time. To decrease the computing time and uncertainties of the calculations there are various variance reduction techniques implemented in commonly used radiation transport code, MCNP. However, these techniques are not useful for some shielding applications since they are locally oriented rather than covering the entire phase-space. One of the solutions to obtain estimates through the entire phase-space is to use the AutomateD VAriaNce reducTion Generator (ADVANTG) code based on deterministic calculation(s).
ADVANTG automatically generates space- and energy-dependent mesh-based variance reduction parameters for MCNP simulations of fixed-source neutron, photon, and coupled neutron-photon transport problems. It reduces both the user efforts and the computational time required to obtain accurate and precise results. However it also brings some challenges due to limitations in source particle distributions allowed in the code and to use it for the accelerator applications with protons as primary particles in case of the MYRRHA accelerator. To able to use ADVANTG code for accelerator applications , a neutron source must be created from primary proton interactions with the target (i.e beam dump, beam line, etc.).