Evaluation of Shutdown Gamma-ray Dose Rates around the Duct Penetration by Three-Dimensional Monte Carlo Decay Gamma-ray Transport Calculation with Variance Reduction Method.

Abstract

For the evaluation of gamma-ray dose rates around the duct penetrations after shutdown of nuclear fusion reactor, the calculation method is proposed with an application of the Monte Carlo neutron and decay gamma-ray transport calculation. For the radioisotope production rates during operation, the Monte Carlo calculation is conducted by the modification of the nuclear data library replacing a prompt gamma-ray spectrum with a decay gamma-ray spectrum. By multiplying each correction factor, which is ratio of the actual activation level after shutdown to the production rate during operation, with each decay gamma-ray flux due to each radioisotope, the decay gamma-ray dose rate is evaluated. In order to improve the statistical error, a variance reduction method is proposed by the application of the weight window importance technique and the specification of the decay gamma-ray generation location. We identify the cell producing the decay gamma-ray which can contribute the decay gamma-ray flux in evaluation locations, and forcibly terminate the gamma-ray transport calculation in the cells except for the identified cells. In order to validate the effectiveness of the method, shielding calculation for actual ITER (International Thermonuclear Experimental Reactor) configuration is performed, and small statistical errors below criteria are obtained. The effectiveness of the proposed method for ITER design analysis is demonstrated.

Impact of Reflector on Calculation Accuracy of Tritium Production in DT Neutronics Blanket Experiment

“…In the Monte Carlo calculation, the history of each particle is tracked so that we can recognize each path which a particle passes through [9,10]. Here, only particles passing through a flagged cell are identified.…”

Superconducting properties and microstructure of MgB2wires synthesized with a low-temperature diffusion process

“…A magnetic confinement type fusion reactor, such as ITER, requires a higher magnetic field property to confine the burning plasma and maintain the fusion reaction for longer operation times, so that the superconducting magnet system is one of the most important components in the fusion reactor system. Burning plasma is sure to generate many 14 MeV fusion neutrons during the D-T reaction, and the 14 MeV neutrons will stream and penetrate the superconducting magnet through plasma heating and/or diagnostic ports [2]. In future, both radioactivation and degradation of superconducting properties by the streaming and penetration of neutron irradiation will have to be considered.…”

Annealing Effect on Microstructure and Superconducting Properties of the<tex>$rm V$</tex>-based Laves Phase Superconducting Wire Synthesized by a RHQ Process

“…It is well known that fast neutrons are always formed during fusion reaction between D and T, and then superconducting magnets of fusion reactor will be irradiated by streaming neutron from many ports which is installed various equipment in fusion device. There is the report which neutron irradiation has been modeled for ITER using Monte Carlo simulation, and it shows that neutrons of over 1 MeV will come out of a plasma vacuum vessel and reach to the superconducting magnets at the rate of over [1]. We think that the streaming of D-T neutron will be generated proportionally for the operation time of fusion reactor, and its fraction will affect to design and total operation schedule including shutdown.…”