New method speeds up calculation of neutron transport

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Dr. ZHENG Yu from the Hefei Institutes of Physical Sciences of the Chinese Academy of Sciences, in cooperation with researchers from the Karlsruhe Institute of Technology in Germany, proposed a new method to accelerate the large-scale shielding simulation of Monte Carl.

The new global variance reduction method, also called On The Fly (OTF), makes Monte Carlo (MC) codes applicable to the shielding analysis of large-scale and complex fusion reactors. Relevant results have been published in Nuclear Fusion.

MC is one of the most accurate methods in the field of nuclear analysis for fusion and fission reactors. However, calculating fusion device shielding using Monte Carlo transport codes remains challenging due to the complexity and heavy shielding of fusion reactors. The slow convergence rate of rendering the MC method in analog simulations is computationally prohibitively expensive.

The researchers introduced a new idea of ​​timely updating of the weight window throughout the transport process in this method. They also proposed an innovative solution based on the automatic dynamic adjustment of the upper limits of the weight window, which solved the problem that has long plagued the neutron particle transport calculation of MC.

When they applied the OTF method to nuclear analysis of the International Thermonuclear Experimental Reactor (ITER) and the neutron source-oriented accelerator IFMIF-DONES at the International Fusion Materials Irradiation Facility-DEMO, acceleration effects remarkable were obtained.

Compared to the Automated Variance Reduction Generator (ADVANTG) variance reduction method developed by the Oak Ridge National Laboratory, the acceleration effect of the OTF method is 13 to 20 times greater than that of ‘ADVANTG.

In addition, the OTF is also used for the calculation of the global radiation field of the Chinese fusion engineering test reactor, which provides an important basis for evaluating the safe operation of key components such as magnets and vacuum vessels under nuclear radiation.

Geometric configuration of the ITER C model (left), normalized neutron flux maps (middle) and relative error maps (right) calculated by the OTF method. (Image by WANG Guohe)

Geometric configuration of IFMIF-DONES (left), normalized neutron flux maps (middle) and relative error maps (right) calculated by the OTF method. (Image by WANG Guohe)

Neutron flux distribution of horizontal slice (left) and vertical slice (right) calculated by OTF method. (Image by WANG Guohe)

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