Molten Salt Reactor 2D: Thermal Feedback & Drain-Tank Safety

This simulator models the two behaviors that make a circulating-fuel molten salt reactor fundamentally different from a solid-fuel one: delayed-neutron precursors drifting out of the core with the flowing fuel salt (which lowers the effective delayed-neutron fraction as flow increases), and a strong negative temperature feedback coefficient that makes the reactor self-regulating without any control action. A coupled neutron-population / precursor / core-temperature system is integrated live with RK4 every frame as you dial in control-drum reactivity and fuel-salt flow rate on a 2D cutaway of the vessel, external loop and heat exchanger. A dedicated "Open Freeze Valve" control reproduces the reactor's signature passive-safety feature: the fuel salt drains by gravity alone into a geometrically subcritical drain tank, shutting the reaction down without pumps, valves under active control, or operator intervention — the same mechanism validated in the 1965 Molten Salt Reactor Experiment.