The Multi-Step CADIS Method for Shutdown Dose Rate Calculations and Uncertainty Propagation

Oak Ridge National Laboratory Shutdown Dose Rate Code Suite

“…The ITER SDDR benchmark was selected to demonstrate the application of the MS-CADIS R2S method. This benchmark, which simulates an ITER upper port plug, has been presented in several papers [1,2,6,7,8,9].…”

“…The geometry of the benchmark problem is shown in Figure 3 of [1], Figure 2 of [2], Figure 2 of [6], Figure 10 of [7], Figure 7 of [8], Figure 1 of [9] and Figure 2 of this report. The geometry includes a steel cylindrical ring with an outer radius of 100 cm, an inner radius of 50 cm, and a length of 550 cm [2,7].…”

“…Shutdown dose rate (SDDR) calculations involve the determination of gammas emitted due to the decay of radionuclides in materials that become activated from operation of a nuclear system. The Oak Ridge National Laboratory (ORNL) SDDR code suite [1,2] is based on the rigorous two-step (R2S) method. The R2S method involves the following steps:…”

“…In the R2S method, determining variance reduction parameters for the neutron transport calculation may be challenging because an importance function that characterizes the neutron importance to the final SDDR is needed. The Multi-Step Consistent Adjoint Driven Importance Sampling (MS-CADIS) method [1,2] overcomes this challenge. In the MS-CADIS method, the adjoint neutron source to be used in generating weight windows for the neutron transport calculation is computed by multiplying the gamma adjoint function with the transpose of transition matrices.…”

“…In the MS-CADIS method, the adjoint neutron source to be used in generating weight windows for the neutron transport calculation is computed by multiplying the gamma adjoint function with the transpose of transition matrices. The transition matrices describe the nuclear transmutations, burnup by neutron irradiation, and decay of radioactive nuclides using the irradiation history of a system [1,2].…”