Abstract
In fusion energy systems (FES) high-energy neutrons born from burning plasma activate system components to form radionuclides. The biological dose rate that results from photons emitted by these radionuclides after shutdown—the shutdown dose rate (SDR)—must be quantified for maintenance planning. This can be done using the Rigorous Two-Step (R2S) method, which involves separate neutron and photon transport calculations, coupled by a nuclear inventory analysis code. The geometric complexity and highly attenuating configuration of FES motivates the use of CAD geometry and advanced variance reduction for this analysis. An R2S workflow has been created with the new capability of performing SDR analysis directly from CAD geometry with Cartesian or tetrahedral meshes and with biased photon source sampling, enabling the use of the Consistent Adjoint Driven Importance Sampling (CADIS) variance reduction technique. This workflow has been validated with the Frascati Neutron Generator (FNG)-ITER SDR benchmark using both Cartesian and tetrahedral meshes and both unbiased and biased photon source sampling. All results are within 20.4% of experimental values, which constitutes satisfactory agreement. Photon transport using CADIS is demonstrated to yield speedups as high as 8.5·105 for problems using the FNG geometry.
Original language | English |
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Pages (from-to) | 77-84 |
Number of pages | 8 |
Journal | Fusion Engineering and Design |
Volume | 106 |
DOIs | |
State | Published - May 2016 |
Externally published | Yes |
Funding
This work was funded in part by project DE-FG02-99ER54513 from the U.S. DOE Office of Fusion Energy Sciences and by the U.S. Nuclear Regulatory Commission Fellowship program. This research was performed using the compute resources and assistance of the UW-Madison Center For High Throughput Computing (CHTC) in the Department of Computer Sciences. The CHTC is supported by UW-Madison and the Wisconsin Alumni Research Foundation, and is an active member of the Open Science Grid, which is supported by the National Science Foundation and the U.S. Department of Energy's Office of Science. This work was funded in part by project DE-FG02-99ER54513 from the U.S. DOE Office of Fusion Energy Sciences and by the U.S. Nuclear Regulatory Commission Fellowship program. This research was performed using the compute resources and assistance of the UW-Madison Center For High Throughput Computing (CHTC) in the Department of Computer Sciences. The CHTC is supported by UW-Madison and the Wisconsin Alumni Research Foundation , and is an active member of the Open Science Grid, which is supported by the National Science Foundation and the U.S. Department of Energy's Office of Science .
Keywords
- CAD
- Shutdown dose rate
- Tetrahedral mesh
- Variance reduction