Abstract:
Background Extreme nuclear events typically generate intense explosions and release radioactive fission products. Gamma radiation from fission products, emitted during radioactive decay of fission products, can affect radiation dose fields for 10 μs to 15 s. During this period, the source intensity, spectrum, and spatial distribution exhibit significant temporal variations. Concurrently, shock-waves induce complex atmospheric density changes, creating hydrodynamic enhancement effects.
Purpose This study aims to develop a computational model for simulating time-varying fission product γ transport in non-uniform atmospheres perturbed by shock-waves, specifically quantifying the hydrodynamic enhancement effect on γ radiation dose fields.
Methods A computational model for atmospheric density distribution was constructed using the LAMBR theory for shock-wave flow-field evolution. Based on radiation transport time-discrete theory, a transient variable-time-step Monte Carlo (MC) method was developed using the PHEN particle transport code.
Results A validation via 20 kt TNT-equivalent detonation simulations at 400 m altitude was conducted to evaluate the hydrodynamic enhancement effect of fission product γ of 235U. The results demonstrate that, compared to a uniform atmospheric model, the hydrodynamic enhancement effect can amplify the γ dose by 2—3 times at some locations.
Conclusions The proposed transient variable-time-step Monte Carlo simulation method can effectively capture the hydrodynamic enhancement effect of the shock wave-perturbed atmospheric density field on the fission product γ radiation fields.
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