Power Block

Overview
The power block is a micro nuclear reactor approximately 5 by 5 by 15 cm, with a Carnot port on one of the rectangular prism's faces. It is ideally suited to provide power for low intensity applications, such as extended EVA. It's uncharacteristic weight (12 Kg) is due to the shielding. The design still leaks radiation, but this is inconsequential compared to the environmental radiation encountered within the heliosphere.

Power blocks are one of the few remaining uses for fission technology. Fusion would be impractical at this scale, and it appears it will remain that way for the foreseeable future.

Design
The design features three core components; a neutron spaller, a nuclear core, and a Carnot port.

Neutron Spaller
As that Thorium is incapable of producing enough neutrons to ever reach critical mass--and the mass in the core of a power block is too small to efficiently absorb the neutrons it produces the way a much larger reactor could--power blocks need a device called a neutron spaller, which is basically a small particle accelorator. Hydrogen atoms strike a graphite barier, firing neutrons into the Thorium fuel. The amount of Hydrogen used like this is literally measured in atoms, so the power drain of the neutron spaller is very light, but if it turns off the reactor dies and must be restarted.

Nuclear Core
The nuclear core is a chunk of Thorium, placed as close to the Carnot port as possible. High temperature coolant runs from underneath the core, through a turbine, and along the Carnot port's capilaries before flowing back through the nuclear core.

Carnot Port
See Carnot Port

Power and Scope of Use
As that the power block's Carnot port is so small (75 cm2) and the temperatures it can reach are not particularly hot (about 1000 Kelvins) the power block is limited in its power production to approximately 50kW in the outer solar system, however that number can vary wildly. On a planet's surface a body of water can increase that number almost ten times, and in the inner solar system the block may only be able to manage 20kW. This amount of energy is significant and can run most personal applications in EVA, from a computer to a Courier to an Oxygen Recycler, but is shy by several orders of magnitude of the energy needed for larger applications. This has not stopped people from making ultralights which "run on double-A's."

In actual service, the Thorium tends to outlive the water, although in heavy use both need to be replaced every few months.

Power blocks constantly run at "maintenence power." As that Thorium is incapable of generating a sustained nuclear reaction on its own, the neutron spaller must be run constantly or else the power block will "die" and need to be kickstarted. As that the amount of energy needed to generate the nuclear reaction is trivial, a child with a dynamo can kickstart a power block.

Left to it's own devices, a power block can idle for approxamately 152 years before the supply of water finally exhausts. The only factor for storage once deactivated, though, is the radioactive decay of the Thorium, which is very slow. A power block is conceivably usable for twelve billion years if it has been properly deactivated.

See Also:
Carnot Port

Oxygen Recycler