In my setting, I have Fulminium crystal reactors. Fulminium decays emitting an electrical current spontaneously, but at a greater rate when stimulated by UV light, and it also emits UV and orange light plus heat as a byproduct. Fulminium reactors are therefore self-stimulating, requiring shutters to reduce UV cross-talk between the crystals as a means of controlling their output.
However, 'traditional' Fulminium reactors are air-cooled, which makes the reactors quite bulky. Failure to cool the reactors usually results in them self-destructing.
I'm looking for a liquid coolant that can be pumped around the Fulminium crystals that won't absorb the UV necessary for the operation of the reactor.
Unfortunately water won't do... it absorbs a significant amount of UV radiation, and using it as a coolant would effectively poison the reactor, making it useless.
What liquid with a reasonably high specific heat and relatively low reactivity and toxicity, that does not absorb significantly in the UV part of the EM spectrum would make the best coolant? Having a high boiling/decay temperature (>100°C) and a low freezing point (<0°C) would be an advantage.
While Fulminium is 'magical', I'm looking for a real-world substance to use as a coolant.
I'm also willing to consider alternative reactor designs that don't necessarily require an UV-transparent coolant. To that end, this is how Fulminium works:
Fulminium is a high-atomic-number transparent orange crystalline element that occurs only in magical environments. Fulminium atoms may spontaneously undergo atomic decay, producing paired electrons and electron holes, along with light in the UV and orange parts of the EM spectrum, plus heat. About 5 to 10% of the total energy output of Fulminium decay is heat (depending on the purity of the crystals), and the electromagnetic radiation output is about 1% of the total energy released.
Fulminium atomic decay stimulation is not all-or-nothing like U235 neutron capture. The more UV that a Fulminium atom absorbs per unit time, the greater the probability of it decaying. Fulminium has piezoelectric- and semiconductor- like properties, meaning that it produces a direct electric current when clamped between dissimilar metals, and if mounted upon one metal and struck by a dissimilar metal striker at the opposite end, it may release a higher voltage and current charge accumulated between strikes than that of clamped crystals.
A new Fulminium reactor is typically designed so that it produces its full rated design power output with its UV absorbent shutters set at about 25% open. As a reactor ages due to use, it becomes poisoned by its opaque decay products, and the shutters must be opened further in order to achieve the same output. When the maximum output drops below its rated design output despite the shutters being fully open, it is time for the Fulminium crystals to be melted down, purified and remanufactured.
If a Fulminium reactor has its shutters opened too far, the reaction may run away and the reactor may melt down or explode.
A traditional Fulminium reactor typically consists of a number of Fulminium crystals clamped between dissimilar metals within a mirror-lined box through which air is passed as a coolant. Moveable opaque shutters are placed between the crystals as a means of control. Because of the necessity of air cooling, the crystals must be relatively widely spaced.
An alternative design intended to produce very high voltage and current spikes over short periods of time are similar to the first type of reactor, save that the metal at one end of the crystal banks is not clamped to the crystals but designed to strike them, and the shutters are designed to open for a short period of time before closing again until the crystals are struck.
Fulminium crystals are relatively fragile, and have a tendency to shatter if subjected to a sufficiently great thermal gradient across their volume. Since a reactor relies upon the crystals being solid from one end to the other, a broken crystal would both reduce the output of the reactor and increase the probability of the reactor entering a failure mode.
The purpose of this question is to find a way to redesign a Fulminium reactor of a particular rated output to be smaller and lighter.