[1] Although once estimated to be 97% complete, poor construction and quality assurance (QA) led to the plant being converted to coal-fired generation.

The project was announced in 1969 with a cost of $420 million to construct two 840 MW nuclear power units with completion dates set for 1975 and 1976.

[9] In 1980 the Chicago Sun-Times reported accusations of a cover-up by CG&E of time-card falsifications and the installation of defective piping in one of the plant's safety systems.

[10] As a result, the Nuclear Regulatory Commission (NRC) fined CG&E $200,000 for a faulty quality assurance program in 1981.

[11][12] The constructor was Kaiser Engineering whereas the primary owner, CG&E, did its own procurement, awarding contracts for equipment, and quality assurance requirements.

[12] The NRC, under pressure from the Government Accountability Project (GAP) to reopen the investigation, eventually ordered work on the nuclear reactor to halt in 1982.

The utilities sought $400 million in damages asserting the defective equipment caused extra costs for the construction of Zimmer.

[27] In March 2020, Vistra Energy would settle with the Environmental Protection Agency (EPA) over a period of two decades of exceeding its emission operating limits.

[29] On July 19, 2021, Vistra announced the plant will shut down five years earlier, on May 31, 2022, because they failed to secure any capacity revenues in the May 2021 wholesale electricity market auction held by the grid operator, PJM Interconnection.

[citation needed] The boiler, designed by Babcock & Wilcox, is a supercritical steam generator with a maximum pressure of about 3,845 psi (26,510 kPa) and temperature of about 1,010 °F (543 °C).

[35] The plant also uses several environmental controls such as selective catalytic reduction (SCRs) to reduce nitrogen oxide (NOx) emissions, electrostatic precipitators to remove fly ash, and a flue-gas desulfurization (FGD) system which removes up to 98% of the sulfur dioxide (SO2) emissions.