Denatured MSR demonstration

[katyhuff]

This issue can be closed when a denatured molten salt reactor design has been modeled with Moltres. Steady state and transient problems should both be demonstrated and verified.

One suggestion is the design discussed in : "Lattice optimization for graphite moderated molten salt reactors using low-enriched uranium fuel" http://www.sciencedirect.com/science/article/pii/S0306454917301627