Abstract
With regard to the long-term safety of repositories for spent nuclear fuel, tracer tests have commonly been used in site characterisation (SC) for finding information that can be later used for performance assessment (PA). The question arises as to whether data obtained in tracer tests performed over a time scale of weeks or months are relevant for PA calculations. As part of a study overseen by the Äspö Task Force, the mechanisms that determine the radionuclide residence time under SC and PA conditions are addressed, given that they influence the validity of data transference from SC to PA. The results show that radionuclide transport in SC and PA, although governed by the same retardation mechanisms, are dominated by different sub-processes. In a practical sense this means that the parameter values (typically fracture apertures and “in situ” apparent retention data) determined in tracer tests, performed as a part of the SC program, should not be used directly for making PA predictions. The emphasis in SC should focus more on the determination of other parameters of relevance at PA timescales. The PA-specific flow rate, flow connectivity, and flow-wetted surface to flow ratio are given here as examples.
Résumé
Dans la problématique des stockages de longue durée des combustibles nucléaires usages, les essais de traçage ont été communément utilisés pour la caractérisation du site (CS) afin d’acquérir les informations nécessaires pour l’évaluation des performances (EP) de ces stockages. La question qui se pose est la suivante : des essais de traçage réalisés sur quelques semaines ou quelques mois sont-ils représentatifs pour l’évaluation des performances ? Dans le cadre d’une étude supervisée par la Äspö Task Force, les mécanismes qui déterminent le temps de résidence des radionucléides selon les conditions de la CS et de l’EP sont examinés, étant donné qu’ils influencent le bien-fondé de la transmission des données de la CS à l’EP. Les résultats montrent que le transport des radionucléides considéré dans le CS et l’EP, bien que gouverné par les même mécanismes de transfert, sont dominés par différents sous-procédés. En pratique, cela signifie que les valeurs des paramètres (tels que les ouvertures de fractures ou la rétention apparente “in situ”) déterminés par les traçages et réalisé dans le cadre de la CS ne devraient pas être utilisés directement pour établir l’EP. Les efforts durant la phase de caractérisation CS devraient être davantage concentrés sur la détermination d’autres paramètres à l’échelle du stockage. Les débits, la connectivité des écoulements, et les surfaces mouillées rapportées aux débits sont données ici à titre d’exemple.
Resumen
Con respecto a la seguridad a largo plazo de repositorios de combustibles nucleares consumidos, las pruebas de trazadores se han usado comúnmente en la caracterización de sitio (SC) para la localización de información que pueda ser usada más tarde en la evaluación de rendimiento (PA). El problema se presenta si los datos obtenidos en las pruebas de trazadores realizadas en una escala de tiempo de semanas o meses son relevantes para la evaluación de rendimiento. Como parte de un estudio de control de la Äspö Task Force, los mecanismos que determinan el tiempo de residencia de los radionucleidos bajo las condiciones de caracterización del sitio (SC) a evaluación de rendimiento (PA) son identificados, dado que ellos influyen en la validez de la transferencia de datos de SC a PA. Los resultados muestran que el transporte de radionucleidos en SC y PA, aunque gobernados por los mismos mecanismos de retardo, están dominados por diferentes subprocesos. En un sentido práctico esto significa que los valores de los parámetros (aperturas típicas de fracturas y datos de retención aparente in situ) determinados en pruebas de trazados, llevados a cabo como parte de un programa SC, no deben ser usados directamente para efectuar las predicciones PA. El énfasis en SC se debe enfocarse más en la determinación de otros parámetros de relevancia en las escalas de trabajo de PA. El ritmo específico de flujo de PA, la conectividad del flujo y la relación superficie mojada-flujo son dados aquí como ejemplos.
摘要
为保证废核燃料处置库的长期安全, 示踪试验通常用在场地描述 (SC) 之中, 以寻找其后可用于性能评价的信息。问题是, 从时间尺度为数周或数月的示踪试验中得到的信息是否与PA的计算相关。作为Aspo任务组监察的研究的一部分, 阐述了决定SC和PA条件下放射性核素滞留时间的机理 (假定这些机理影响自SC到PA转换中数据的有效性) 。结果表明, SC和PA中放射性核素迁移虽然受相同阻滞机理的制约, 但由不同的次级过程主导。从实用意义来说, SC中由示踪试验确定的参数值 (典型地, 如裂隙张开度和场地尺度的表观保留数据) , 不可直接用来做PA预测。SC的重点应更多地放在确定其它与PA尺度相关的参数上。这里将决定于具体PA的流速、径流连通性及浸涊面与流量作为例子给出。
Resumo
No que diz respeito à segurança a longo prazo dos depósitos de combustíveis nucleares gastos, os ensaios de traçador têm sido vulgarmente utilizados na caracterização de sítios (CS) para encontrar informação a utilizar posteriormente na avaliação de desempenho (AD). Coloca-se a questão se os dados obtidos nos ensaios de traçador desenvolvidos numa escala de tempo de semanas ou meses são relevantes para os cálculos da AD. Como parte de um estudo supervisionado pela Äspö Task Force, são considerados os mecanismos que determinam o tempo de residência dos radionuclídeos sob condições de CS e de AD, atendendo a que eles influenciam a validade da transferência de dados da CS para a AD. Os resultados mostram que o transporte de radionuclídeos na CS e na AD, apesar de serem regidos pelos mesmos mecanismos de retardamento, são dominados por diferentes sub-processos. De forma prática, tal significa que os valores dos parâmetros (tipicamente dados da abertura das fracturas e de retenção aparente “in situ”), determinados nos ensaios de traçador desenvolvidos como uma parte do programa de CS, não deveriam ser utilizados directamente para fazer previsões da AD. A ênfase da CS deveria focar-se mais na determinação de outros parâmetros de relevância nas escalas de tempo da AD. São aqui apontadas como exemplos a taxa de fluxo específica da AD, a conectividade de fluxo e a razão entre a superfície de fluxo húmida e o fluxo.
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The support of the Swedish Nuclear Fuel and Waste Management Company (SKB) is gratefully acknowledged as a benefactor of this research.
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Moreno, L., Crawford, J. Can we use tracer tests to obtain data for performance assessment of repositories for nuclear waste?. Hydrogeol J 17, 1067–1080 (2009). https://doi.org/10.1007/s10040-008-0418-7
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DOI: https://doi.org/10.1007/s10040-008-0418-7