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PostPosted: Jul 08, 2018 10:33 am 

Joined: Jan 14, 2012 5:49 am
Posts: 64
I ran across this patent from 1959 while searching for articles on Magnesium carbide as a moderator. US patent 3146172
Appears applicable to pressure tube designs that use light water as the moderator. The magnesium or lead in the moderator allows the designer to tailor the flux across the reactor. Increasing the distance between the fuel elements within the reactor due to the reduced moderation (less light water).
Could this concept be used to create a reduced moderation boiling reactor with Lightbridge style fuel? Increase the diameter of the fuel element with an added layer of magnesium around the fuel to decrease moderation. As long as the heat can travel through the magnesium metal without raising the fuel temp to the point that the magnesium melts, it may be possible. Lightbridge fuel is expected to operate at 380 C and magnesium melts at 650 C, so there should be some margin.
The fuel rod may need a redesign to incorporate the magnesium and still have good flow rates through the fuel bundle (replace two arms of the center of the fuel rod with magnesium, large knobs of magnesium at the tips of the central fuel element, Maltese cross with magnesium in the thickened arms). Rods could be designed that were only zirconium clad magnesium and placed in the fuel bundle with the fuel rods to remove some of the moderator.
Increasing the total fuel rod diameter or reducing the central fuel cross sectional area would increase ratio of surface area to fuel and allow for adequate thermal transfer to the light water. The zirconium clad magnesium would function as a radiator for the central fuel component.
The interlayer of magnesium could even be a design feature that allows for easier reprocessing. Pull the rod, let it age till you want to reprocess, heat the rod to the melting point of the interlayer, drain the interlayer and remove the central fuel for reprocessing.

Lightbridge-fuel-profile.jpg [ 23.09 KiB | Viewed 977 times ]
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