Influences of blast wave on dose field of delayed neutron
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摘要: 作为原子核裂变后的重要特征之一，裂变碎片发射的缓发中子在核技术及工程领域应用广泛。重大核反应堆事故（切尔诺贝利，福岛）通常伴随爆炸发生，为合理评估裂变产物形成的缓发中子剂量场，需考虑冲击波对裂变缓发中子输运的影响。本研究采用蒙特卡罗方法模拟缓发中子输运，建立质量厚度与缓发中子剂量的对应关系。使用基于镜像方法的LAMBR模型计算冲击波扰动下缓发中子源附近空气密度复杂分布。基于质量厚度等效衰减规律，结合LAMBR模型，计算给出地面测点处典型裂变核素缓发中子剂量场，分析冲击波对缓发中子输运的影响。研究表明，若冲击波源强确定，随着源高增加冲击波对缓发中子输运的增强效应也随之显著。此外，当源高接近地面且冲击波源强较大时，地面反射波可能会削弱缓发中子输运。Abstract:
Background Delayed neutron, as a key signature of nuclear fission, plays a significant role in nuclear technology and engineering. Major nuclear reactor accidents (e.g., Chernobyl, Fukushima) are often accompanied by explosions, which generated shockwave that may affects the transport of delayed neutron and consequently influence delayed neutron dose assessment. Understanding the influence of the shockwaves on the transport of delayed neutron is critical for accurate radiological evaluation in such scenarios.Purpose This study aims to investigate the influence of shockwave on the transport of delayed neutron released from fission products and to calculate the resulting dose field at ground-level monitoring points.Methods A correspondence between mass thicknesses and delayed neutron doses was established by using Monte Carlo method. The LAMBR model, based on a mirroring technique, was used to calculate the complex air density distribution arised by shockwave at around the delayed neutron source. By combing the mass-thickness equivalent attenuation law with the LAMBR model, the delayed neutron dose fields of typical fission nuclides were calculated.Results The results indicated that when the strength of the shockwave source is fixed, the enhancing effect of the shockwave on the transport of delayed neutron becomed more pronounced as the source height increased. Conversely, when the source is close to the ground and the strength of the shockwave source is sufficiently strong, ground-reflected shockwave may attenuate the transport of delayed neutron.Conclusions The transport of delayed neuron was significantly influenced by the shockwave, furthermore the influence is closely related to height and strength of the shockwave source. These findings provided valuable insights for improving dose assessment in accident conditions involving explosions.-
Key words:
- delayed neutron /
- Monte Carlo method /
- shock wave /
- mass thickness /
- dose
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图 1 基于质量厚度等效衰减规律的缓发中子剂量计算流程图
Figure 1. Diagram for calculating delayed neutron dose based on mass thickness attenuation law
图 2 235U裂变缓发中子能谱
Figure 2. Energy spectra of delayed neutron emitted from fission products of 235U
图 3 235U、239Pu和238U在1～2 s时间内的裂变缓发中子能谱
Figure 3. Energy spectra of delayed neutron emitted from fission products of 235U, 239Pu, and 238U at time range from 1 s to 2 s
图 4 冲击波源强为50 kt TNT当量，源高分别为200 m、400 m、600 m时，地面测点处缓发中子剂量
Figure 4. Ground-level delayed neutron doses for 50 kt TNT equivalent explosion at altitudes of 200 m, 400 m, and 600 m
图 5 冲击波源强为50 kt TNT当量，源高分别为200 m、400 m、600 m时，有无冲击波影响的缓发中子剂量相对偏差
Figure 5. Relative deviation of the delayed neutron doses with effects of blast and without effects of blast wave for 50 kt TNT equivalent explosion at altitudes of 200 m, 400 m, and 600 m
图 6 冲击波源强为100 kt TNT当量，源高分别为800 m、
1000 m、1 200 m时，地面测点处缓发中子剂量Figure 6. Ground-level delayed neutron doses for 100 kt TNT equivalent explosion at altitudes of 800 m,
1000 m, and 1 200 m
图 7 冲击波源强为100 kt TNT当量，源高分别为800 m、1 000 m、1 200 m时，有无冲击波影响的缓发中子剂量相对偏差
Figure 7. Relative deviation of the delayed neutron doses with effects of blast and without effects of blast wave for 100 kt TNT equivalent explosion at altitudes of 800 m, 1 000 m, and 1 200 m
图 8 冲击波源强为50 kt TNT当量，源高为200 m，时间分别为0.01 s、0.1 s、0.3 s、0.5 s，冲击波影响下空气密度分布
Figure 8. Distributions of air density under effects of blast wave of 50 kt TNT equivalent explosion at altitude of 200m for times at 0.01 s, 0.1 s, 0.3 s, 0.5 s
图 9 冲击波源强为50 kt TNT当量，源高为600 m，时间分别为0.01 s、0.5 s、1 s、2 s，冲击波影响下空气密度分布
Figure 9. Distributions of air density under effects of blast wave of 50 kt TNT equivalent explosion at altitude of 600 m for times at 0.01 s, 0.5 s, 1 s, 2 s
图 10 冲击波源强为500 kt TNT当量，源高为100 m，地面测点处缓发中子剂量
Figure 10. Ground-level delayed neutron doses for 500 kt TNT equivalent explosion at altitude of 100 m
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