The German state of North Rhine Westphalia, Federal Republic of Germany, and Hochtemperatur-Kernkraftwerk GmbH (HKG) financed the THTR-300’s construction.

[3] The electrical generation part of the THTR-300 was finished late due to ever-newer requirements and licensing procedures.

Consequently, radioactive helium containing aerosols was released to the environment via the feed system's exhaust air chimney.

The incident initially went unnoticed due to the overlap with radioactive fallout from the Chernobyl disaster, complicating attribution.

An anonymous informant from the THTR-300 workforce was the first to blow the whistle on the incident, and alleged that there was a deliberate attempt to conceal the radioactive emissions from authorities and environmental groups.

[6] Official investigations were delayed, and environmental monitoring stations eventually identified unusual levels of radioactive Protactinium-233 (²³³Pa) isotopes, inconsistent with fallout from Chernobyl.

[6] Repeated false and misleading statements by the operator quickly eroded trust of state and federal officials, as well as the public.

The presumptive cause of the fuel element damage was the frequent and overly-deep insertion of control rods during the commissioning process.

The nuclear power plant was plagued with shutdowns due to design issues, generating only 2891 GWh, far less than anticipated, never reaching the required availability of 70% (1988: 41%[10]).

In August 1989, the THTR company was almost bankrupted after a long period of shut down due to broken components in the hot gas duct.