During the high-level radioactive waste (HLRW) disposal experiment, the temperature of butter materials is generally thought to be less than 100 degree centigrade.
A thermal limit of about 100 C or lower is preferable in order to eliminate the risks associated with chemical alteration of the buffer and backfilling materials and the subsequent changes in swelling and hydraulic properties. My question is "is it possible for the temperature of buffer materials (mainly clays) are larger than 100 degree centigrade during the HLRW disposal? "
FYI:
Article Performance of the bentonite barrier at temperatures beyond ...
Up to now, most HLW repository concepts are based on a design criterion of 100 C for the maximum temperature of the bentonite buffer. This may be applied to the bentonite/canister interface or an outer annulus. There is a common agreement that this conservative criterion ensures that no adverse temperature-induced effects will occur. On the other hand, the application of such a 100 C criterion is not cost-effective, since it requires large spacings and large amounts of buffer material between the canisters, and may not be practical, since it severely limits design and emplacement options for some host rock settings. As is discussed in this contribution, the maximum temperature of 100 C is ill justified from a scientific perspective. This is revealed from the existing data on bentonite materials exposed to higher temperatures over time frames that are relevant for repository conditions. In this review, we focus on irreversible temperature-induced effects on mineralogical and macroscopic physical properties (swelling pressure, permeability, plasticity), since these are most relevant for the bentonite performance with respect to its barrier roles. The aspect of bentonite–cement interactions at higher temperatures, although of potential relevance for the bentonite buffer (Savage et al., 2002), is not treated in this contribution.
”Besides some slight negative effects of heating clay up to ∼80°C, a temperature increase up to 150°C leads, amongst others, to increases in thermal conductivity, mechanical strength, and stiffness of the clay, as well as to limiting microbial activities as soon as the environmental temperature exceeds 122°C by several degrees. Thus, heating clay host rocks does not necessarily compromise but may actually improve the barrier performance.” See details in refference: https://www.researchgate.net/deref/https%3A%2F%2Fpubs.geoscienceworld.org%2Fminmag%2Farticle-pdf%2F79%2F6%2F1389%2F2925513%2F1389.pdf
FYI:
All disposal concepts throughout the world, despite their differences in design, unanimously impose a temperature limit of about 100oC (Hicks et al., 2009). However, Wersin et al. (2007), after reviewing a number of data sets, concluded that the criterion of 100oC for the maximum temperature within the bentonite buffer is overly conservative. Their conclusion was based on their findings that no significant changes in bentonite hydraulic properties occur at temperatures of up to 120oC under wet conditions and that bentonite is chemically stable to much higher temperature under dry conditions. The impact of high temperature on bentonite and clay host rock behavior, and consequences on repository performance, remain largely an open question for a clay repository system. While various studies have shed light on certain aspects of this question, there is no study that integrates the relevant THMC processes while considering the interaction between EBS and host rock.
The performance of bentonite barriers in the
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