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Workreport 2020-7



Testing and Quality Control of Full Scale Bentonite Buffer Block Manufacturing


Sjöblom, V., Rinta-Hiiro, V., Haapala, K.



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This report is only published for Posiva's internal use.

The quality control work for the isostatically compressed buffer blocks are important part of the manufacturing process. The research for this working report was carried out during 2015–2016 and it was built upon the work done in 2008–2015. The objective of this work was to do quality control work for the isostatically compressed buffer blocks what are going to be used in the buffer block installation tests and FISST-project. During the production process, focus was on monitoring of block circumstances (temperature and relative humidity), block green body properties and machining of the blocks. The purpose of this work was to gain better understanding about the consequences of isostatic compression for the production of bentonite buffer components. In this study large isostatic full scale blocks were compressed at 17% water content with various compression pressures.

The machining work for the buffer blocks was successful, resulting in blocks with accurate dimensions and good quality surfaces. Also, lifting of the blocks using either lifting slings or the vacuum lifting device worked in a proper way. Turning the blocks upside down was very successful with the turntable used in welding work for handling large parts. The production of buffer blocks was time-consuming. Time for machining one block, including lifting, turning and packing of the block, was usually 3–4 working days. The machining itself took quite a long time due to the large amount to be machined. For example, for the R2 ring block, about 36% of the green body volume was to be turned. The reason for the high machining volumes was the test mould made for the fabrication tests of the first isostatic blocks. Because of test purpose, a reservation had been made in the mould for machining and sample drilling. The shrinkage of the green body and the uniformity of the shape were not known at the beginning, so an extra volume was reserved for the mould. In addition, the diameter of buffer blocks were larger, 1.70 m instead of the present diameter 1.65 m. Handling of the blocks, including lifting and turning, as well as proper packing after machining was time-consuming, because final equipment for block handling had not been purchased.

There were some challenges in keeping the desired RH in the surrounding air. The RH was sometimes lower than the target which was due to cold outdoor air. Humidity management was hampered by large production facilities where the machining area could not be compartmentalized. Some minor cracking was found from some of the blocks. Water was sprayed into the air with a high pressure pump to increase the humidity in the air. Increasing the humidity was also useful to remove bentonite dust from the air, which is important for the cleanliness and safety of the work. Along with the moisturizing system, a proper dust collection system is needed during the machining. The results of this work will be used in the development and design of the bentonite buffer manufacturing process and quality control.


Bentonite block, quality control, isostatic compression, factory-scale, bentonite pellets, buffer



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