The gamma dose rate caused by airborne radionuclides is a major concern in the mitigation of nuclear accidents. Unfortunately, there is no fast method for calculating the three-dimensional (3D) gamma dose rate field near the source, because the corresponding airborne radionuclide distribution is usually calculated on non-equispaced grids and existing fast methods are only suitable for equispaced grids. This paper presents a method that accurately calculates the 3D dose rate field on non-equispaced grids, accelerating the computation by around two orders of magnitude. This method splits the time-consuming 3D integral in the dose rate model into a large convolution with a regularized smooth function and a small correction term. A nonuniform fast Fourier transform (NFFT) is used to rapidly calculate the convolution, which significantly enhances the computational speed. Our approach is applied to different grids and is compared with the FFT-based convolution method in two complex air dispersion simulations and a field experiment. The results show that the proposed method is in good agreement with the original 3D integral method and avoids grid-dependent interpolation errors in the FFT-based convolution method. This method enables a coupled analysis of wind, radioactivity, and dose rate on arbitrary grids, which is important for simplifying the emergency response in the case of small modular reactors.

空中放射性核素引起的伽马剂量率是缓解核事故的主要考虑因素。不幸的是，没有快速的方法可以计算源附近的三维（3D）γ剂量率场，因为相应的机载放射性核素分布通常是在非等距网格上计算的，而现有的快速方法仅适用于等距网格。本文提出了一种在非等距网格上准确计算3D剂量率场的方法，将计算速度提高了大约两个数量级。该方法将剂量率模型中耗时的3D积分拆分为具有正则化平滑函数和较小校正项的大卷积。非均匀快速傅立叶变换（NFFT）用于快速计算卷积，这大大提高了计算速度。我们的方法适用于不同的网格，并在两个复杂的空气弥散模拟和现场实验中与基于FFT的卷积方法进行了比较。结果表明，所提出的方法与原始的3D积分方法具有很好的一致性，并且避免了基于FFT的卷积方法中依赖于网格的内插误差。这种方法可以对任意网格上的风，放射性和剂量率进行耦合分析，这对于简化小型模块化反应堆的应急响应至关重要。结果表明，所提出的方法与原始的3D积分方法具有很好的一致性，并且避免了基于FFT的卷积方法中与网格有关的内插误差。这种方法可以对任意网格上的风，放射性和剂量率进行耦合分析，这对于简化小型模块化反应堆的应急响应至关重要。结果表明，所提出的方法与原始的3D积分方法具有很好的一致性，并且避免了基于FFT的卷积方法中与网格有关的内插误差。这种方法可以对任意网格上的风，放射性和剂量率进行耦合分析，这对于简化小型模块化反应堆的应急响应至关重要。