Study on tissue dose field of delayed gamma emitted from fission products under effects of blast wave

Abstract: One of the important features of the major nuclear accidents (severe reactor accident, radioactive terrorist attack) lies in the explosion caused by hydrogen or nuclear energy release, which means air around fission products should be influenced by blast wave of the explosion. Therefore, it is essential to consider the effects of blast wave in the calculation of delayed radiation transport. [Purpose]: This study aims to analyze the effects of blast wave on transport of the delayed gamma, and to calculate the tissue dose field of the delayed gamma emitted from fission products of 235U, 239Pu, and 238U under the effects of blast wave. [Methods]: Firstly, low altitude multiple burst revised (LAMBR) model based on the method of image was employed to simulate the distributions of air density around delayed gamma source. The mass thicknesses of air were calculated by using LAMBR model. Subsequently, the attenuation law based on mass thickness was applied to study the effects of blast wave on transport of the delayed gamma. By combining the attenuation law based on mass thickness with LAMBR model, a fast simulation method for the delayed gamma transport under the effects of blast wave was proposed to calculate the tissue doses of the delayed gamma. Then, the Monte Carlo method and the cavity method were also used to simulate the transport of the delayed gamma under the effects of blast wave, and to give the tissue dose rates of the delayed gamma. Finally, the empirical formulas of ground-level tissue doses of the delayed gamma under the effects of blast wave were proposed to illustrate the relationships between ground-level tissue doses of the delayed gamma emitted from fission products of 235U, 239Pu, and 238U. [Results]: The ground-level tissue doses of the delayed gamma emitted from fission products of 235U, 239Pu, and 238U are calculated by using the fast simulation method, the Monte Carlo method, and the cavity method, respectively. Considering the effects of blast wave, the max relative deviation of tissue doses of the delayed gamma reaches up to 45% at the altitude of 1000m for 500t TNT equivalents. The max relative deviation increased from 4% to 45% as the altitude increased from 100m to 1000m. The calculated results are broadly consistent with the simulations of the Monte Carlo method, but the computational time remains under 1 minute, which is orders of magnitude shorter than the simulations of the Monte Carlo method. The calculated tissue dose rates of the delayed gamma are, on average, two times higher than the results of the cavity method. Furthermore, the average relative deviations between ground-level tissue doses calculated by using the empirical formulas and the simulations remain within 13%. [Conclusions]: The results indicate that compared to the calculations without the blast wave, the transport of the delayed gamma is enhanced significantly as altitude of the delayed gamma source increase in the altitude range below 1000m. The calculated tissue dose rates based on the fast simulation method are basically agreed with the simulations of the Monte Carlo method, and higher than results of the cavity method. Moreover, the proportional relationships between ground-level tissue doses of the delayed gamma emitted from fission products of 235U, 239Pu, and 238U are found.