气载放射性碘取样测量装置的设计与研究

Design and Study of Sampling and Measuring Device for Airborne Radioactive Iodine

气载放射性碘的准确监测是预警核事故、评价核事故等级、环境保护的必要前提之一。碘取样测量装置是气载放射性碘监测仪的关键部件,其设计的合理性直接关系到碘在取样盒内分布的均匀性、测量的准确性。为了分析气态碘在取样盒内的分布形式,通过测量得出取样盒中活性炭气体流速与压强降的关系,利用流行的计算流体动力学(computational fluid dynamics,CFD)软件Fluent仿真计算了所研制取样测量装置中气体在取样空间的压力分布及碘在取样盒内的吸附分布,并利用蒙特卡罗软件(monte carlo N particle transport code,MCNP)模拟计算了不同模型下的探测效率。对依据仿真所研制的放射性碘监测仪样机进行测试和校准,样机对低活度放射性碘测量的重复性为2%,对364.5 keV全能峰的能量分辨率为9.5%,参考响应的非线性为6%。结果表明:放射性碘取样测量装置的流道最优化设计时,取样盒入口面碘分布均匀,进而提高了探测效率标定的准确性,为气载放射性碘监测仪的设计提供了有效的理论基础。

Accurate monitoring of airborne radioactive iodine is one of the necessary preconditions for nuclear accident warning,nuclear accident grade evaluation and environmental protection.Iodine sampling and measuring device is the key component of airborne radioactive iodine monitor.The rationality of its design is related to the uniformity of distribution for iodine in the sampling box and the accuracy of measurement.To analyze the distribution of gaseous iodine in the sample box,the relationship between the flow rate of activated carbon gas and the pressure drop in the sampling box was obtained by measurement.The popular computational fluid dynamics(CFD)software Fluent was used to simulate the gas pressure distribution in the sampling space and the adsorption distribution of iodine in the sampling box,and monte carlo N particle transport code(MCNP)was used to simulate and calculate the detection efficiency under different models.The prototype of the radioactive iodine monitor developed by the simulation has been tested and calibrated.The prototype has 2%repeatability for low-activity radioactive iodine,9.5%energy resolution for full energy peak of 364.5 keV,and the nonlinear of reference response is 6%.The results show that:when optimizing the flow channel design,the iodine distribution at the inlet surface of the sampling box is uniform.The designed flow channel can greatly improve the homogeneity of iodine distribution in the sampling box and improve the accuracy of detection efficiency calibration,which provides an effective theoretical basis for the design of airborne radioactive iodine monitor.