Update: Hyperion PR explains their reasoning. (h/t Soylent)
Idaho Samizdat reports on nuclear startup Hyperion's recent conference presentation:
Dan Yurman calls this the "first release of reactor design information". Except the reactor design "released" appears to have very little to do with Hyperion as it was advertised. Googling into the past:
The key to the success of Hyperion will be its fuel – uranium hydride powder, which allows the hydrogen moderator to easily move in and out of the core. The physical characteristics of uranium hydride, a combined fuel and neutron energy moderator, are ideal for the generation of safe nuclear power. The reactor operates at an optimum temperature of 550°C, selected as the goal for the so-called Generation IV reactors by the US Department of Energy (DoE). At 550°C, the dissociation pressure for the hydrogen above the hydride is approximately eight atmospheres, which permits easy transportation of the gas without presenting significant high-pressure risk. The temperature-driven mobility of the hydrogen contained in the hydride can change the moderation, and therefore the reactor criticality, making the reactor self-regulating.
Yet what the slides on Samizdat blog describe are not this, but rather a fast reactor, using solid ceramic fuel elements (uranium nitride) with lead-bismuth coolant. This is completely different, and I think it very bizarre that this goes under the same 'Hyperion' name. It is no longer a thermal-spectrum reactor (there is no moderator). The 'unique' idea of the self-regulating uranium hydride fuel is discarded. Sure there are reasons for major redesigns (and this is still purely conceptual), but this isn't even the same idea.
Adding to the strangeness, the Hyperion website quitely erased its original advertisements of hydride fuel. Just look at Google's cache of the main product description. The current version is the same minus one paragraph:
The core of the HPM produces energy via a safe, natural heat-producing process that occurs with the oscillation of hydrogen in uranium hydride. HPMs cannot go “supercritical,” melt down, or get “too hot.” It maintains its safe, operating temperature without the introduction and removal of “cooling rods” – an operation that has the potential for mechanical failure.
Analogous excisions were made on the FAQ page.
And as far as the public-facing website goes, there does not seem to be any explanation for (or indication of) this complete reversal.
Incidentally, the new Hyperion seems conceptually similar to the Lawrence Livermore's SSTAR design - like Hyperion, it is a sealed, ~20 MWe, lead-cooled nitride-fuel fast reactor.