Hyperion Power has released the first technical details of the small 70MWt nuclear reactor that it is developing.

Hyperion Power Module core diagram. There are 24 assemblies of uranium nitride fuel, and 18 control rods. The centre of the core is hollow so that boron carbide marbles could be dropped in the centre to shut down the reactor in an emergency.

Although the company had originally been aiming to create a TRIGA reactor burning uranium hydride, it has decided for reasons of speed-to-market to focus on commercialising a liquid-metal-cooled fast reactor instead.

The Hyperion Power Module has a core of 24 assemblies of a metal fuel, uranium nitride, that is 20% enriched set in HT-9 cladding tubes. Flowing around the pins is liquid lead-bismuth eutectic coolant. Quartz is used as a radial reflector. A gas plenum is at one end of the 2-3m long fuel pins.

Two sets of boron carbide control rods keep the reactivity of the core under control. One set of 12 control rods advance about 0.5mm/day to moderate the reaction. A second set of 6 shutdown rods close to the centre of the reactor would automatically drop into the core in case of an accident. The centre of the core is hollow. Inside that void space marbles of boron carbide would be dropped in case of an emergency.

The hot (500 degrees C) coolant transfers its heat through an intermediate heat exchanger to another lead-bismuth loop, through another intermediate heat exchanger to a tertiary circuit with an undisclosed fluid, and then through a third heat exchanger to water (at about 200 degrees C). The reactor is not only designed to deliver electricity, but also process heat or co-generation. Hyperion Power president and CEO John 'Grizz' Deal told NEI that the configurations of the secondary and tertiary circuit would depend on the reactor's uses.

The reason why the 70MWt reactor has a relatively low electrical efficiency of 36%, or 25MWe, is because the steam loop does not run through the inside of the reactor, for simplicity and safety. The factory-built and factory-sealed reactor, which weighs 50 tons, would operate like a battery: it would be slotted into place in a power station built by an undisclosed partner company, connected, and generate power continuously for seven to 10 years without refuelling. Then it would be disconnected and left to cool down for up to two years (with water) before being removed and returned to the factory for dismantling.

Although no fuel has been tested or manufactured for the project, Deal said that fuel burns would begin before the end of the year. He said that Los Alamos National Laboratory, from whom Hyperion has licenced some of the technology, has researched uranium nitride. It said that the Russian military has used uranium nitride fuel and the lead-bismuth coolant.

Deal said in October that Hyperion is still planning to build a factory in the UK; but construction would be some way off. Initially he said that the company would rely on the supply chain for producing the first units.

He said that the company is looking to find six launch customers, some of which would run a prototype, including customers based in the US and UK. He said in mid-November that the company had signed 123 memorandums of understanding or letters of intent with customers.

Deal also said that in order to have operating units within four years, the company was also considering building its first pilot units in facilities that do not require approval from a nuclear regulator, such as US Department of Energy facilities, or military facilities.

In terms of suppliers, the company has signed up TetraTec as the architect-engineer-constructor, supported by Chamberlain.