Rishel Jeremy P, Barnett J Matthew, Mozhayev Andrey V, Dutcher Elliott Dutch, Colby Scott A, Carter Gregory L, Patello Gertrude K, Steen Franciska H, Hanson Eric M
1Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352.
Pacific Northwest National Laboratory, PO Box 999, Richland, WA 99352.
Health Phys. 2018 Oct;115(4):531-538. doi: 10.1097/HP.0000000000000901.
The Pacific Northwest National Laboratory operates the Radiochemical Processing Laboratory, which is a multi-purpose, non-reactor nuclear research facility. Regulations require both continuous sampling and monitoring of radioactive particulates and tritium gas in the exhaust from the main stack. Releases of other radioactive gases, including planned releases of radon, are tracked separately in a database and reported. During the 2015 calibration of the Radiochemical Processing Laboratory stack continuous air monitor, measured alpha and beta background count rates were much higher than expected, especially when compared to count rates from previous calibrations. The source of the higher background count rates was examined by trending of historical continuous air monitor measurements and a comparison to the sampler data. The analysis revealed that the sample results showed no increase in emissions, whereas the continuous air monitor showed a steady increase in count rates. Ultimately, the continuous air monitor filter was analyzed and found to contain higher-than-normal background levels of Rn progeny. Assessments were performed to determine the cause of the increased background values, including reviews of building research activities, radioactive material usage and storage, adequacy of procedures, and the potential for internal continuous air monitor contamination. Project reviews determined that a research activity involving Th was left in an unsealed state, resulting in Rn being released from a hot cell into the exhaust system. The Th source material was subsequently repackaged and contained, resulting in a decrease of continuous air monitor background count rates. An estimate of the Rn release was made and the contribution to the annual offsite dose from the facility was calculated. The released activity and reported dose results were well below the permit limits for the facility.
太平洋西北国家实验室运营着放射化学处理实验室，这是一个多用途的非反应堆核研究设施。法规要求对主烟囱排放物中的放射性微粒和氚气进行连续采样和监测。其他放射性气体的排放，包括计划中的氡气排放，在数据库中单独跟踪并报告。在2015年放射化学处理实验室烟囱连续空气监测仪的校准过程中，测得的α和β本底计数率远高于预期，尤其是与之前校准的计数率相比。通过对历史连续空气监测测量数据的趋势分析以及与采样器数据的比较，对较高本底计数率的来源进行了检查。分析表明，样本结果显示排放量没有增加，而连续空气监测仪显示计数率稳步上升。最终，对连续空气监测仪的过滤器进行了分析，发现其中氡子体的本底水平高于正常水平。进行了评估以确定本底值增加的原因，包括审查建筑物研究活动、放射性物质的使用和储存、程序的充分性以及内部连续空气监测仪污染的可能性。项目审查确定，一项涉及钍的研究活动处于未密封状态，导致氡从热室释放到排气系统中。随后对钍源材料进行了重新包装和封装，导致连续空气监测仪的本底计数率下降。对氡的释放量进行了估算，并计算了该设施对年度场外剂量的贡献。释放的活度和报告的剂量结果远低于该设施的许可限值。
