Recently environmental radionuclide signals were observed in the atmosphere which could be associated with undeclared nuclear activities, not directly connected with development of nuclear weapons. Large-scale contamination of European air with Ru-106 observed in 2017 may represent such an accident, which was probably associated with the Mayak nuclear fuel reprocessing facility in the Chelyabinsk region of Russia. A recently announced nuclear accident at Nyonoska in the Archangelsk region may represent an undeclared nuclear activity associated with the development of a nuclear jet engine which could be based on radionuclide energy generator or a small nuclear reactor. It is concluded that environmental radioactivity impacts associated with recent nuclear activities create new challenges for fast and reliable national and international monitoring systems which would require development of new monitoring strategies.

中文翻译：

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与未申报的核活动有关的近期核事故的环境放射性方面，并提出了新的监测策略的建议。

最近在大气中观察到环境放射性核素信号，这可能与未申报的核活动有关，与核武器的发展没有直接关系。2017年观察到Ru-106大规模污染了欧洲空气，可能代表了这样的事故，这可能与俄罗斯车里雅宾斯克州的Mayak核燃料后处理设施有关。最近宣布的阿尔汉格尔斯克地区尼翁奥斯卡发生的核事故，可能代表着未开发的核活动，该活动与开发可能基于放射性核素能量发生器或小型核反应堆的核喷气发动机有关。