The chamber is roughly 4m across, with the fuel rods itself being 2.5m long. Space is required to have uniform absorption of heat by propellant - scaled down versions tended to have cavitation problems. Sunshards operate at 3500K, but they can go up to 5000K (not that the core will withstand that). Delivers 4GW of power. The blue tint you see is from Cherenkov radiation.

K37 uses moving fuel rods design due to lower mass. There are numerous failsafes built into the reactor, but they are rarely actively maintained by private owners and many of them just don't work on a century old ship.