Purged Graphite Elements

Calculations indicate that a large HTGR operating with a fuel permitting rapid withdrawal of the gaseous fission products could achieve a breeding ratio as high as 1.1. 

Beryllium oxide is used as a diluent for the UO2 to increase the diameter of the fuel rod and its thermal conductivity for improved thermal performance and also to improve fission product retention in the BeO-UO2 matrix over that possible with UO2 alone. 

In-pile loop tests of this type of element were successfully carried out for 5700 hr at a maximum fuel surface temperature of 1500° to 1700°F and for appropriate burnup conditions (45). A full core loading of these fuel elements was manufactured for the EBOR reactor. 

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The fuel for the Peach Bottom reactor consisted of a uranium-thorium dicarbide kernel, overcoated with pyrolytic carbon and silicon carbide which were dispersed in carbon compacts (see Section 5), and encased in graphite sleeves [37]. There were 804 fuel elements oriented vertically in the reactor core. Helium coolant flowed upward through the tricusp-shaped coolant channels between the fuel elements. A small helium purge stream was diverted through the top of each element and flowed downward through the element to purge any fission products leaking from the fuel compacts to the helium purification system. The Peach... 

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