Korolevych Volodymyr
Canadian Nuclear Laboratories, Chalk River, ON, K0J 1J0, Canada.
J Environ Radioact. 2025 Aug;288:107739. doi: 10.1016/j.jenvrad.2025.107739. Epub 2025 Jun 14.
Recovery phase following the shutdown of the National Research Universal (NRU) nuclear reactor at Canadian Nuclear Laboratories' (CNL's) Chalk River site is studied here. In 2009, NRU was shut down for a period longer than a year during reactor vessel repair and then was shut down permanently in 2018. In both cases, tritium was sampled in the atmosphere, precipitation, vegetation, and soil. Tissue free water tritium (TFWT) and organically bound tritium (OBT) were collected in plants and in tree leaves at 1 m and 2 m above the ground. Two transects connecting dry uphill locations and neighbouring swamps downhill were sampled. These study transects are located away from the reactor site and waste management areas, and as such, are expected to represent pure recovery due to dilution of local tritium in the regional geophysical compartments of atmospheric water vapour and near-surface groundwater (aided by incoming precipitation). Trends in environmental tritium at CNL following the NRU reactor shutdown were assessed and the environmental half-life of tritium was derived for near-surface strata (atmosphere, biosphere/plants, and rhizosphere/groundwater). It appears that in 4 years, pure local (pure recovery-phase) dilution of historical tritium has reached the level at which it is now tangibly affected by remote atmospheric tritium plumes coming from CNL waste management areas with southeast (SE) winds. Exclusion of episodes associated with SE wind and with remote tritium plume results in more coherent trends across sampled near-surface geophysical strata. Trend-line exponents provide T = 1.30 ± 0.24 years of environmental half-life of tritium. The role of microclimate may require further investigation, but insignificant differences between wet and dry locations observed in TFWT already imply applicability of the environmental half-life of tritium to other sites in recovery. Features of the site-specific recovery process at CNL include insensitivity of OBT and groundwater HTO trends (half-life exponents) to exclusion of samples collected under the remote tritium plume, whereas atmospheric HTO and especially precipitation HTO trends (exponents) appear affected by as much as 49 % and 267 %, respectively. The sensitivity of trend for TFWT (environmental half-life exponent) was less tangible, because of only moderate 35 % decrease in exponent after exclusion of remote plume episodes. In summary, in 4 years after the NRU reactor shutdown, the drivers of tritium transfer (atmospheric HTO and precipitation HTO) are already under substantial influence of the tritium plume from remote sources at CNL, but recipient compartments of environmental tritium are either not, or are only slightly affected by the remote tritium plume. This implies recovery phase completion in the CNL atmosphere (and in precipitation washing tritium out of it), but yet unfinished recovery of recipient compartments of OBT and groundwater HTO where quasi-stationary phase has not yet started.
本文研究了加拿大核实验室（CNL）乔克河基地的国家研究通用（NRU）核反应堆关闭后的恢复阶段。2009年，NRU在反应堆容器维修期间关闭了一年多，然后于2018年永久关闭。在这两种情况下，都对大气、降水、植被和土壤中的氚进行了采样。在地面以上1米和2米处的植物和树叶中收集了无组织水氚（TFWT）和有机结合氚（OBT）。对连接干燥上坡位置和相邻下坡沼泽的两条样带进行了采样。这些研究样带远离反应堆场地和废物管理区，因此预计由于大气水汽和近地表地下水等区域地球物理隔层中局部氚的稀释（受降水影响）而呈现出纯粹的恢复情况。评估了NRU反应堆关闭后CNL环境中氚的趋势，并得出了近地表地层（大气、生物圈/植物和根际/地下水）中氚的环境半衰期。似乎在4年内，历史氚的纯粹局部（纯粹恢复阶段）稀释已达到这样一个水平，即现在受到来自CNL废物管理区东南风携带的远程大气氚羽的显著影响。排除与东南风及远程氚羽相关的情况后，整个采样的近地表地球物理地层的趋势更加连贯。趋势线指数给出氚的环境半衰期T = 1.30 ± 0.24年。小气候的作用可能需要进一步研究，但在TFWT中观察到的湿区和干区之间的差异不显著，这已经意味着氚的环境半衰期适用于其他处于恢复阶段的场地。CNL特定场地恢复过程的特点包括，排除在远程氚羽下采集的样本后，OBT和地下水HTO趋势（半衰期指数）不敏感，而大气HTO尤其是降水HTO趋势（指数）分别受到高达49%和267%的影响。TFWT趋势（环境半衰期指数）的敏感性不太明显，因为排除远程羽流事件后指数仅适度下降了35%。总之，在NRU反应堆关闭4年后，氚转移的驱动因素（大气HTO和降水HTO）已经受到CNL远程源氚羽的重大影响，但环境氚的接受隔层要么没有受到影响，要么仅受到远程氚羽的轻微影响。这意味着CNL大气（以及将氚冲刷出大气的降水中）的恢复阶段已经完成，但OBT和地下水HTO的接受隔层的恢复尚未完成，准稳态阶段尚未开始。
