PSI Center for Nuclear Engineering and Sciences

Chalk River Unidentified Deposits (CRUD) are dissolved and suspended solids, product of the corrosion of structural elements in water circuits of nuclear reactors.  

The chemical composition of CRUD is variable as it depends on the composition of the reactor’s structural material, as well as the types of refueling cycles.  Recent internal investigations have found unexpected but significant Si-amount in CRUD. The chemical composition of CRUD holds key information for an improved understanding of CRUD formation and possible impact in fuel reliability and contamination prevention.

The standard analytical methods available in the hot laboratory did not allow an easy quantitative determination of the Si-amount in CRUD. A new innovative procedure has been developed and tested with synthetic CRUD name Syntcrud.

The adapted flex-fusion digestion method presented here is able to provide reliable concentrations of several elements within CRUD, including Si, which was not possible in methods used previously for ICPMS measurement.

Mobility of water, sodium and gas molecules within a smectite nanopore

Various gases are produced by metal corrosion and organic material degradation in deep gelological repository for nuclear waste. To ensure repository safety, it's important to demonstrate that gases can be dissipated by diffusion in host rocks and prevent pressure buildup in repository near field. Smectite mineral particles form a pore network that is usually saturated with water, making gas diffusion the primary transport mechanism. Molecular simulations have shown that the diffusion of gases through the pore network depends on various factors, including pore size and temperature. For instance, smaller pores and lower temperatures tend to reduce gas diffusion. Interestingly, hydrogen and helium have been found to diffuse faster than argon, carbon dioxide, and methane, possibly due to interactions with the clay surface and water molecules. Ultimately, the diffusion coefficients for different gases and pore sizes can be predicted using an empirical relationship, which is useful for macroscopic simulations of gas transport.

During the last decades, computing power has been subject to tremendous progress due to the shrinking of transistor size as predicted by Moore’s law. However, as we approach the physical limits of this scaling, alternative techniques have to be deployed to increase computing performance. In this regard, the next big advance is envisioned to be the usage of approximate computing hardware based on field-programmable gate arrays and/or digital-analogue in-memory circuits. Such approximate computing can provide disproportional gain (x1000) in energy efficiency and/or execution time for acceptable loss of simulation accuracy. This could be highly beneficial in order to accelerate computational intensive simulations such as reactor core analyses with higher resolution multi-physics models. On the other hand, the execution of programming codes on low-precision hardware may result in inadequate outcomes due to quality degradation and/or algorithm divergence. To address these questions, studies on the stability and the performance of advanced reactor simulation algorithms as function of reduced floating-point arithmetic precision are being conducted at the laboratory for reactor physics and thermal-hydraulics. Results obtained so far indicate a large room for the acceleration of nuclear engineering applications using mixed-precision hardware. Therefore, research is now being enlarged towards assessing multiprecision computing methods for reactor core simulations with higher spatial resolution.