Abstract
In fusion energy systems (FES) neutrons born from burning plasma activate system components. The photon dose rate after shutdown from resulting radionuclides must be quantified. This shutdown dose rate (SDR) is calculated by coupling neutron transport, activation analysis, and photon transport. The size, complexity, and attenuating configuration of FES motivate the use of hybrid Monte Carlo (MC)/deterministic neutron transport. The Multi-Step Consistent Adjoint Driven Importance Sampling (MS-CADIS) method can be used to optimize MC neutron transport for coupled multiphysics problems, including SDR analysis, using deterministic estimates of adjoint flux distributions. When used for SDR analysis, MS-CADIS requires the formulation of an adjoint neutron source that approximates the transmutation process. In this work, transmutation approximations are used to derive a solution for this adjoint neutron source. It is shown that these approximations are reasonably met for typical FES neutron spectra and materials over a range of irradiation scenarios. When these approximations are met, the Groupwise Transmutation (GT)-CADIS method, proposed here, can be used effectively. GT-CADIS is an implementation of the MS-CADIS method for SDR analysis that uses a series of single-energy-group irradiations to calculate the adjoint neutron source. For a simple SDR problem, GT-CADIS provides speedups of 200 ± 100 relative to global variance reduction with the Forward- Weighted (FW)-CADIS method and 9 ± 5 . 104 relative to analog. This work shows that GT-CADIS is broadly applicable to FES problems and will significantly reduce the computational resources necessary for SDR analysis.
| Original language | English |
|---|---|
| Pages (from-to) | 27-48 |
| Number of pages | 22 |
| Journal | Nuclear Science and Engineering |
| Volume | 187 |
| Issue number | 1 |
| DOIs | |
| State | Published - Jul 2017 |
| Externally published | Yes |
Funding
This work was funded in part by project DE-FG02-99ER54513 from the U.S. Department of Energy (DOE) Office of Fusion Energy Sciences and by the U.S. Nuclear Regulatory Commission Fellowship Program. This research was performed using the computer resources and assistance of the University of Wisconsin (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 DOE Office of Science.
| Funders | Funder number |
|---|---|
| DOE Office of Science | |
| Department of Computer Sciences | |
| UW-Madison | |
| University of Wisconsin | |
| National Science Foundation | |
| U.S. Department of Energy | |
| Wisconsin Alumni Research Foundation | |
| U.S. Nuclear Regulatory Commission | |
| Fusion Energy Sciences |
Keywords
- Hybrid Monte Carlo/deterministic radiation transport
- Nuclear transmutation
- Shutdown dose rate analysis
