Hydrologic Transport of Dissolved Inorganic Carbon and Its Control on Chemical Weathering

Chemical weathering is one of the major processes interacting with climate and tectonics to form clays, supply nutrients to soil microorganisms and plants, and sequester atmospheric CO2. Hydrology and dissolution kinetics have been emphasized as factors controlling chemical weathering rates. However, the interaction between hydrology and transport of dissolved inorganic carbon (DIC) in controlling weathering has received less attention. In this paper, we present an analytical model that couples subsurface water and chemical molar balance equations to analyze the roles of hydrology and DIC transport on chemical weathering. The balance equations form a dynamical system that fully determines the dynamics of the weathering zone chemistry as forced by the transport of DIC. The model is formulated specifically for the silicate mineral albite, but it can be extended to other minerals, and is studied as a function of percolation rate and water transit time. Three weathering regimes are elucidated. For very small or large values of transit time, the weathering is limited by reaction kinetics or transport, respectively. For intermediate values, the system is transport controlled and is sensitive to transit time. We apply the model to a series of watersheds for which we estimate transit times and identify the type of weathering regime. The results suggest that hydrologic transport of DIC may be as important as reaction kinetics and dilution in determining chemical weathering rates

Efficient Refinement Checking in VCC

We propose a methodology for carrying out refinement proofs across declarative abstract models and concrete implementations in C, using the VCC verification tool. The main idea is to first perform a systematic translation from the top-level abstract model to a ghost implementation in VCC. Subsequent refinement proofs between successively refined abstract models and between abstract and concrete implementations are carried out in VCC. We propose an efficient technique to carry out these refinement checks in VCC. We illustrate our methodology with a case study in which we verify a simplified C implementation of an RTOS scheduler, with respect to its abstract Z specification. Overall, our methodology leads to efficient and automatic refinement proofs for complex systems that would typically be beyond the capability of tools such as Z/Eves or Rodin

Modeling of a radionuclide transport experiment in granitic rock matrix at the Grimsel Test Site (Switzerland). The role of advection

Within the framework of the GTS-LTD project (Grimsel Test Site – Long-Term Diffusion), a radionuclide transport experiment in unfractured granitic rock matrix was performed. Grimsel groundwater containing several radionuclide tracers (3H as HTO, 36Cl−, 22Na+, 134Cs+, 133Ba2+) was continuously circulated through a packed-off borehole interval. The decrease in tracer concentrations in the solution was monitored for a period of 1266 days (March 05, 2014–August 22, 2017). Additionally, tracer breakthrough was monitored in an observation borehole at a distance of 18.6 cm. Initial modeling of the experiment (1D radial), considering transport only by diffusion, showed that the evolution of tracer concentrations departed from the expected trend after some time, with concentrations in the injection borehole decreasing faster than expected. Additional 2D calculations (section normal to the boreholes) were performed to check the possible effect of advection through the rock matrix. Advection could explain the evolution of concentrations in the injection borehole, but concentrations in the observation borehole were overestimated. Core samples from new boreholes were collected immediately after the end of the experiment, allowing the measurement of tracer distributions in the rock. The observed patterns for the non-sorbing tracers (HTO, 36Cl−) showed clear preferential transport directions, consistent with advective flow towards the gallery from which the boreholes were drilled. Final 3D modeling of the experiment can explain the measured concentrations in the boreholes and in the rock. Tracer transport for the conservative tracers (HTO, 36Cl−) is affected by both diffusion and advection through the granitic rock matrix. Also, in situ accessible porosities deduced from the modeling (0.0014) are smaller than those measured in rock samples (about 0.009), pointing to unloading and destressing of the rock samples after drilling. At the spatial and temporal scales of the experiment, the effect of advection for the weakly sorbing 22Na+ is only minor, and it is practically negligible for the strongly sorbing tracers (134Cs+, 133Ba2+).The GTS-LTD project is financed by its partner institutions: JAEA (Japan), NUMO (Japan), UJV (Czech Rep.), SURAO (Czech Rep.), NAGRA (Switzerland) and BASE (Germany). IDAEA-CSIC is a Severo Ochoa Center of Research Excellence (Spanish Ministry of Science and Innovation, Project CEX 2018-000794-S). JMS acknowledges support from the Catalan Government through project 2021SGR00308. JJH acknowledges support from Grant RYC-2017-22300 funded by MCIN/AEI (10.13039/501100011033) and the European Social Fund “Investing in your future”. Finally, the constructive comments from two anonymous reviewers are gratefully acknowledged.Peer reviewe

Refinement-Based Verification of the FreeRTOS Scheduler in VCC

We describe our experience with verifying the scheduler-related functionality of FreeRTOS, a popular open-source embedded real-time operating system. We propose a methodology for carrying out refinement-based proofs of functional correctness of abstract data types in the popular code-level verifier VCC. We then apply this methodology to carry out a full machine-checked proof of the functional correctness of the FreeRTOS scheduler. We describe the bugs found during this exercise, the fixes made, and the effort involved