ABSTRACT

Determining the completeness of nuclear reactor decommissioning is an important step in safely utilizing nuclear power. For example, ¹³⁷Cs from the Fukushima Daiichi Nuclear Power Station (FDNPS) accident can be treated as background radioactivity, so determining the origin of ¹³⁷Cs is essential. To accomplish this, measuring the ¹³⁵Cs/¹³⁷Cs isotope ratio can be useful, so this study optimized a solvent extraction method with calix[4]arene-bis(t-octylbenzo-crown-6) [BOBCalixC6] in 1-octanol to purify Cs. This optimized method was applied to Cs purification in soil samples collected near the FDNPS, and the ¹³⁵Cs/¹³⁷Cs isotope ratios were measured using both thermal ionization mass spectrometry (TIMS) and triple quadrupole induced coupled plasma mass spectrometry (ICP-QQQ). The results of each of these measurements were compared, and we found that Cs isotope ratios obtained by TIMS were more precise, by an order of magnitude, while the ICP-QQQ results possessed good abundance sensitivities. A slightly higher ¹³⁵Cs/¹³⁷Cs ratio in the northwest area of the FDNPS was observed, while other areas exhibited similar values, all within the measurement error range, which indicated different origins of radiocesium. These results agreed with previously reported ¹³⁴Cs/¹³⁷Cs activity distributions, suggesting that this ratio may be useful in identifying radiocesium origins for evaluating future nuclear reactor decommissions.

摘要

确定核反应堆退役的完整性是安全利用核电的重要步骤。例如，  ^137和从福岛第一核电站（FDNPS）事故铯可以被视为背景放射性，所以确定的原点 ^137个Cs的是必不可少的。为此，测量 ¹³⁵ Cs/ ¹³⁷ Cs 同位素比可能会很有用，因此本研究优化了一种溶剂萃取方法，使用杯 [4] 芳烃-双（t-辛基苯并冠-6）[BOBCalixC6] 在 1-辛醇中得到净化 Cs。该优化方法应用于 FDNPS 附近采集的土壤样品中的 Cs 纯化，  ¹³⁵ Cs/ ¹³⁷使用热电离质谱 (TIMS) 和三重四极杆诱导耦合等离子体质谱 (ICP-MS/MS) 测量 Cs 同位素比率。对每项测量的结果进行了比较，我们发现 TIMS 获得的 Cs 同位素比值更精确一个数量级，而 ICP-MS/MS 结果具有良好的丰度灵敏度。略高 ¹³⁵ CS / ¹³⁷，观察到FDNPS的西北区域Cs的比率，而其他区域表现出相似的值，则所有的测量误差范围内，这表明放射性铯的不同来源内。这些结果与先前报道的 ¹³⁴ Cs/ ¹³⁷Cs 活动分布，表明该比率可能有助于确定放射性铯的来源，以评估未来的核反应堆退役。