Zirconium-95 Distribution in Bottom Sediments of the Techa River in 1952–1955

IF 0.9 Q4 CHEMISTRY, INORGANIC & NUCLEAR Radiochemistry Pub Date : 2024-03-12 DOI:10.1134/s1066362223070111

Yu. G. Mokrov

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Abstract

The study is aimed at the source-term reconstruction for the exposure of people to ionizing radiation who lived in 1949–1956 on the Techa riverside. It deals with the migration of γ-emitting nuclides (GENs), and specifically ⁹⁵Zr and ⁹⁵Nb, in the river system. It is known that ⁹⁵Zr exhibits abnormally high sorption properties and is virtually completely and irreversibly sorbed onto bottom sediments (BSs) and suspended material already near the liquid radioactive waste (LRW) discharge site. Therefore, its further migration is possible only with the solid runoff. It was shown previously that the large-scale radioactive contamination of the river occurred in the relatively short period from July to October 1951, when the water flow rate in the upper section was varied from 8 to 30 m³/s. Under such water runoff conditions, the most contaminated BSs near the LRW discharge site undergo intense stirring-up (erosion), and the resulting suspensions are transferred with gradual sedimentation of the suspended material throughout the river stretch. After October 1951, when the LRW discharge into the river decreased by 2–3 orders of magnitude, the ⁹⁵Zr distribution in BSs was determined only by the radioactive decay and transfer of suspended matters and saltation loads. Specific features of methods used in the 1950s for measuring the specific activity of the sum of β-emitting nuclides (BENs, A_Σ, μCi/kg) and sum of GENs (М_Σ, μg-equiv Ra/kg) are discussed. The use of the ratio R_Σ = М_Σ/А_Σ as a criterion furnishes new information on the ⁹⁵Zr activity concentration in BSs and allows picking out BS samples with prevalent contributions of ⁹⁵Zr (М_Zr) и ⁹⁵Nb (М_Nb) to М_Σ from the whole set of the archive data. Analysis of the measured archive data on the specific activity of BS samples taken from different sections of the Techa River in 1952, 1954, and 1955 using the criterion R_Σ = М_Σ/А_Σ allowed estimation of М_Σ ≈ М_Zr + М_Nb and recalculation of these results taking into account the radioactive decay as of November 1, 1951. The results of M_Σ measurements performed in 1952, 1954, and 1955 and converted to the level of November 1, 1951 appeared to be close, although the absolute activity level decreased by a factor of up to ~10 mln owing to radioactive decay. The ⁹⁵Zr specific activity in the river BSs as of November 1951 remained virtually constant throughout the river stretch. These results provide a new approach to reconstruction of the external dose for the Techa riverside population.

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1952-1955 年 Techa 河底沉积物中的锆-95 分布情况

摘要这项研究的目的是对 1949-1956 年期间生活在特查河畔的人们所受电离辐射的源期进行重建。研究涉及γ发射核素（GENs），特别是 95Zr 和 95Nb 在河流系统中的迁移。众所周知，95Zr 具有异常高的吸附特性，几乎完全不可逆地吸附在液态放射性废物（LRW）排放点附近的底层沉积物（BSs）和悬浮物质上。因此，只有固体径流才有可能使其进一步迁移。以前的研究表明，在 1951 年 7 月至 10 月这一相对较短的时间内，河流发生了大规模的放射性污染，当时上游河段的水流量为 8 至 30 立方米/秒。在这种径流条件下，轻轨污水排放点附近受污染最严重的沉降物受到强烈的搅拌（侵蚀），所产生的悬浮物随着悬浮物的逐渐沉降而转移到整个河段。1951 年 10 月以后，当 LRW 向河流中的排放量减少了 2-3 个数量级时，BS 中 95Zr 的分布仅由放射性衰变和悬浮物的转移以及盐化负荷决定。讨论了 20 世纪 50 年代用于测量 β 发射核素总和（BENs，AΣ，μCi/kg）和 GENs 总和（МΣ，μg-当量 Ra/kg）比活度的方法的具体特点。使用比率 RΣ = МΣ/АΣ 作为标准，可提供有关 BS 中 95Zr 活性浓度的新信息，并可从整套档案数据中挑选出 95Zr (МZr) и 95Nb (МNb) 对 МΣ 有显著贡献的 BS 样品。利用 RΣ = МΣ/АΣ 标准，对 1952 年、1954 年和 1955 年从泰恰河不同河段采集的 BS 样品比活度的实测档案数据进行分析，可以估算出 МΣ ≈ МZr + МNb 的值，并根据 1951 年 11 月 1 日的放射性衰变对这些结果进行重新计算。1952 年、1954 年和 1955 年进行的 MΣ 测量结果换算成 1951 年 11 月 1 日的水平，虽然由于放射性衰变，绝对放射性水平下降了约 10 百万分之一，但结果似乎很接近。截至 1951 年 11 月，河流 BSs 中的 95Zr 比活度在整个河段几乎保持不变。这些结果为重建 Techa 河沿岸居民的外照射剂量提供了一种新的方法。

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来源期刊

Radiochemistry CHEMISTRY, INORGANIC & NUCLEAR-

CiteScore

1.30

自引率

33.30%

发文量

期刊介绍： Radiochemistry is a journal that covers the theoretical and applied aspects of radiochemistry, including basic nuclear physical properties of radionuclides; chemistry of radioactive elements and their compounds; the occurrence and behavior of natural and artificial radionuclides in the environment; nuclear fuel cycle; radiochemical analysis methods and devices; production and isolation of radionuclides, synthesis of labeled compounds, new applications of radioactive tracers; radiochemical aspects of nuclear medicine; radiation chemistry and after-effects of nuclear transformations.

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