It was nominated for Academy Awards for Best Actor in a Leading Role (Lemmon), Best Actress in a Leading Role (Fonda), Best Art Direction-Set Decoration and Best Writing, Screenplay Written Directly for the Screen. The film was also nominated for the Palme d'Or (Golden Palm) at the 1979 Cannes Film Festival and Lemmon won Best Actor for his performance. The movie's script won the 1980 Writers Guild of America award.
The film was released on March 16, 1979, just twelve days before the real-life events at Three Mile Island, Pennsylvania. The Three Mile Island accident helped propel The China Syndrome into a blockbuster.
TV news reporter Kimberly Wells (Fonda) and her cameraman Richard Adams (Douglas) visit the Ventana nuclear power plant outside Los Angeles as part of a series of news reports on energy production. While viewing the control room from an observation room, the plant goes through a reactor SCRAM (emergency shutdown). Shift supervisor Jack Godell (Lemmon) notices what he believes to be an unusual vibration during the SCRAM. Checking their gauges, the control room staff finds that water levels in the reactor core have risen to high levels; they begin opening relief valves in an effort to prevent too much water from damaging the plant. However, the needle in the water level gauge turns out to have been stuck, and when Godell taps the glass cover on the gauge, the needle rapidly drops to indicate that the water level is actually far too low, and the core has almost been uncovered. The staff begin restoring coolant systems, but for several agonizing minutes, the crew doesn't know whether the core is undergoing a meltdown or not. Eventually, backup systems are able to raise the water levels, and the reactor is brought under control.
In the observation room looking out over the control room, Adams began filming the activity below; when told he was not permitted to film the control room for security reasons, he surreptitiously tucks the camera under his arm and begins filming anyway. Because the glass is soundproof, the visitors can only guess as to what is happening.
When they return to the television station, the station's news director refuses to air the footage, fearing criminal prosecution. Adams, believing that there is more to the story than is indicated in the plant's official statement (which referred to the near-meltdown as an "unexpected transient"), steals the film from the station and shows it to a pair of experts, who are able to fill him in on what actually happened.
Meanwhile, Godell, suspecting there to be more to the strange vibration he felt at the beginning of the SCRAM, does some investigating of his own and uncovers evidence that the plant is unsafe. Specifically, he finds evidence to suggest that another reactor SCRAM at full power could cause the cooling system to be severely damaged. Godell asks the plant foreman to delay restarting the reactor until the main water pump can be disassembled and inspected, but he refuses, under pressure from the plant's owners. Godell then contacts Wells, asking her to help get his concerns heard. Wells and Adams agree to help get Godell's evidence entered at safety hearings for a new plant being built. Godell asks to remain anonymous, but when the original messenger (Wells' soundman) is run off the road by hit men (presumably hired by the plant's owners), he decides he must appear at the safety hearings himself. On the way there, he is chased by more hit men, and finds safe harbor at the Ventana power plant where he works.
When Godell arrives, he finds the plant has been brought up to full power. Now convinced of the danger, he grabs a gun from the control room's security guard and forces everyone out. Once alone and secured inside the control room, he brings the power down to a safer level around 75% of full. He also tells the plant's managers that if anyone attempts to take control of the reactor from the outside or break in, he'll open valves and flood the containment building with radiation, essentially ruining the plant. He then demands to be interviewed live on television by Wells.
While Wells and Adams set up their equipment, plant technicians find a way to cause a reactor SCRAM. In the middle of the live interview, the SCRAM is started, the camera's cables are physically cut, and a SWAT team forces its way into the control room and shoots Godell several times, killing him. Proving Godell's fears true, however, the SCRAM causes significant damage to the plant, as portions of the cooling system physically collapse. The reactor is eventually brought under control by the plant's automatic systems.
Outside the plant, a phalanx of reporters and television crews are awaiting word on the events inside. When the plant spokesman suggests that Godell was "emotionally disturbed" and that he "had been drinking", Wells confronts the spokesman in front of the other reporters, and eventually gets one of Godell's co-workers (Brimley) to admit that Godell was not a "loony" and would not have taken such drastic steps had there not been something to his belief in problems with the plant.