A prototyping failure on a fission reactor is a little different than a rocket exploding on the launchpad...

SpaceX blowing up a Crew Dragon capsule wouldn't be good either, but can you do the fast development testing and expect some failures, and don't go near nuclear material until much later in the process.

Even ignoring the radiation, how do you test that it keeps working with a 100 MW heat source inside it without putting nuclear material in?

Edit: where did I get the idea it’s 100MW from? Title talks of 1MW. That makes it a lot easier.

If 1MW is the actual design limit, it should be possible to test the loop with a mock heat source. At this scale, you could pay for grid power ($40-60/hr).

100MW would be a lot trickier to test due to infrastructure limitations, but you could probably figure something out with natural gas or propane burners.

By putting enough resistors inside, and pumping 100 MW of electricity in? If you're a utility trying this out, you can probably handle that (for some hours, maybe not for weeks).

Are there any resistors that would not melt under this situation?

Good question. There are two issues, the power and the temperature. The power is easy(ish) - just put enough resistors in there, and you're good. (If you physically can put enough resistors in that space, which... I don't know.)

But you also want to run it at reactor temperatures. I don't know what that is, but finding resistors that won't melt may be anywhere from difficult to impossible.

These prototypes don’t contain radioactive material though.

Unfortunately there are only two ways get a nuclear reactor working, one is for research, the other full on production. In the US regulatory system there is no in-between.

That is why all the reactor companies go for a fully functional production design with the first try. Without such a plan and reactor built, you do not get access to fissile material. Since you have to build many of them to ever have a hope of making money fast iteration is gone be difficult.

In general they all want to use the same basic design with different fuel and different operations to create a different type of reactor. Uranium fast burners are the easiest, thorium breeders are much further away.

For Molten Salt Reactors, the most advanced in development is probably IMSR by Terrestrial Energy, after that SSR by Moltex Energy are both currently in Canadian regulatory process.

Flibe energy is trying in the US but that is longer term, there is not even a regulatory process in the US yet. Flibe is by Kirk Sorensen the guy who basically restarted Thorium hype.

If the US government was serious about wanting to let nuclear power development happen in the US, they should set up a location where companies could work with live nuclear material while developing reactors. Workers could be required to have some type of security clearance and each company could have its own building(s) to avoid "mistakes" at one company from effecting other companies people and worksites. OSHA rules could be relaxed to allow quicker development, as everyone working there will be well informed of the radiation risks. The former nuclear test site in Nevada would seem to be a great location for this.

The list of things the government could do, even without a huge investment, to make nuclear happen is incredibly long. Sadly non of it is gone happen.

In my opinion, humanity should have long been living in the nuclear age and its kind of crazy that we are not.

If you can fund them.

There are many!