Fort Saint Vrain Generating Station was built as Colorado's first and only nuclear power plant, which operated from 1979 until 1989.

[1] The plant was named after the historic front trading post Fort Saint Vrain, which was located about a mile north of it.

The reactor fuel was a combination of fissile uranium and fertile thorium microspheres dispersed within a prismatic graphite matrix.

[1] The Fort St. Vrain HTGR power plant was proposed in March 1965 and its application was filed with the Atomic Energy Commission in October 1966.

As one of the first commercial HTGR designs, the plant was a proof-of-concept for several advanced technologies, but had a number of early adopter problems that required expensive corrections.

In practice, the gas pressure varied more than expected, allowing excessive water to escape into the circulator.

The capacity of the gas cleaning system did not account for the excess water from the bearings, and assumed that high-temperature reactions in the graphite reactor core would reduce the impact of residual water in the helium, based on the porosity of typical core graphite.

The graphite used to construct Fort St. Vrain's core was higher grade and less porous, and thus did not present as much surface area for these reactions to occur.

The reserve shutdown system, which released borated graphite spheres into the core in the event of an Anticipated Transient Without Scram (ATWS), was sometimes unavailable because water had leached the boron to form boric acid, which softened the graphite spheres and caused them to clump together.

Rust flecks migrated into the coolant and lodged in critical machinery, including control rod drives.

[3] The design problems which led to the corrosion were partially the fault of the regulators, who were focused heavily on chemical reactions of steam with the high-grade core graphite and the impact on the gas cleaning system.

It was arguable that the memorandums from the Nuclear Regulatory Commission consumed excessive engineering resources and other design considerations had been overlooked as a result.

These unique design features resulted in water ingress to the core, the primary reason for poor plant availability.

Failures of transformers and consequent failure of backup power occurred on at least one occasion due to moisture infiltration into electric cables and subsequent ground faulting when the plant was at low power to remove water from previous moisture infiltration issues.

As a result, Public Service Company of Colorado began to question the economics of continued commercial operation.

[5] Following the reactor decommissioning, Fort St. Vrain was converted to a conventional natural gas powered combustion facility.