In May 1966, Consumers Public Power District rejected their option to purchase the facility from the Atomic Energy Commission (AEC).

The sodium-cooled graphite-moderated reactor (SGR) design (of which HNFP was a demonstration) targeted economical commercial nuclear electricity.

The graphite moderator was clad in stainless steel hexagons with each corner scalloped to make room for the process tubes, which contained the fuel clusters and control rods.

Hallam was proposed in March 1955 in response to the first round of invitations by the Atomic Energy Commission's Power Demonstration Reactor Program.

[6] It used technology being developed in the smaller Sodium Reactor Experiment (SRE), also built by Atomics International.

Difficulties that arose during operation and required plant shutdown and correction included leaking control rod thimbles, seizure of secondary sodium pumps, leaking steam generator instrumentation and pipe flanges, difficulty of adjusting fuel channel flow orifices, and failure of primary and secondary sodium throttle valves.

The ruptures and subsequent absorption of sodium into the graphite reduced the thermal neutron flux in the core and caused a reduction in local power.

Examination disclosed that failure was caused by low ductility stress-rupture leading to a one-inch-long crack about three inches below the top of each element.

Chauncey Starr, the president of Atomics International, testified that they had identified and claimed to have fixed the issue with the moderator can.

He proposed a repair operation involving attaching snorkels to each moderator can into the cover gas space, which would cost $1.8M and require 6–9 months.