André M, Malmström M E, Neretnieks I
Department of Chemical Engineering and Technology, Royal Institute of Technology, KTH, Stockholm, Sweden.
J Contam Hydrol. 2009 Nov 3;110(1-2):1-8. doi: 10.1016/j.jconhyd.2009.05.003. Epub 2009 May 15.
Permanent storage of spent nuclear fuel in crystalline bedrock is investigated in several countries. For this storage scenario, the host rock is the third and final barrier for radionuclide migration. Sorption reactions in the crystalline rock matrix have strong retardative effects on the transport of radionuclides. To assess the barrier properties of the host rock it is important to have sorption data representative of the undisturbed host rock conditions. Sorption data is in the majority of reported cases determined using crushed rock. Crushing has been shown to increase a rock samples sorption capacity by creating additional surfaces. There are several problems with such an extrapolation. In studies where this problem is addressed, simple models relating the specific surface area to the particle size are used to extrapolate experimental data to a value representative of the host rock conditions. In this article, we report and compare surface area data of five size fractions of crushed granite and of 100 mm long drillcores as determined by the Brunauer Emmet Teller (BET)-method using N(2)-gas. Special sample holders that could hold large specimen were developed for the BET measurements. Surface area data on rock samples as large as the drillcore has not previously been published. An analysis of this data show that the extrapolated value for intact rock obtained from measurements on crushed material was larger than the determined specific surface area of the drillcores, in some cases with more than 1000%. Our results show that the use of data from crushed material and current models to extrapolate specific surface areas for host rock conditions can lead to over estimation interpretations of sorption ability. The shortcomings of the extrapolation model are discussed and possible explanations for the deviation from experimental data are proposed.
几个国家正在研究将乏核燃料永久储存在结晶基岩中。对于这种储存方案，基岩是放射性核素迁移的第三道也是最后一道屏障。结晶岩基质中的吸附反应对放射性核素的迁移具有很强的阻滞作用。为了评估基岩的屏障特性，获得代表未受扰动基岩条件的吸附数据非常重要。在大多数已报道的案例中，吸附数据是使用破碎岩石测定的。研究表明，破碎会通过产生额外的表面来增加岩石样品的吸附能力。这种外推存在几个问题。在解决这个问题的研究中，使用将比表面积与粒径相关联的简单模型将实验数据外推到代表基岩条件的值。在本文中，我们报告并比较了使用氮气通过布鲁诺尔-埃米特-泰勒（BET）法测定的破碎花岗岩五个粒径级分和100毫米长岩芯的表面积数据。为BET测量开发了能够容纳大型样品的特殊样品架。此前尚未发表过与岩芯一样大的岩石样品的表面积数据。对这些数据的分析表明，从破碎材料测量中获得的完整岩石的外推值大于岩芯测定的比表面积，在某些情况下超过1000%。我们的结果表明，使用破碎材料的数据和当前模型来外推基岩条件下的比表面积可能会导致对吸附能力的高估解释。讨论了外推模型的缺点，并提出了与实验数据偏差的可能解释。
