The China Syndrome

While visiting the (fictional) Ventana nuclear power plant outside Los Angeles, television news reporter Kimberly Wells (Fonda), her cameraman Richard Adams (Douglas) and their soundman Hector Salas witness the plant going through an emergency shutdown (SCRAM). Shift Supervisor Jack Godell (Lemmon) notices an unusual vibration while grabbing his cup of coffee which he had set down. He then finds that a gauge is misreading and that the coolant is dangerously low (he thought it was overflowing). The crew manages to bring the reactor under control and can be seen celebrating and expressing relief.
Richard surreptitiously films the incident, despite being requested to not film the control room for security purposes. Kimberly's superior at work (Donat) refuses to permit her to report what happened or show the film, disgusting Richard, who steals the footage. He shows it to experts, who conclude that the plant came perilously close to the China Syndrome in which the core would have melted down into the earth, hitting groundwater and contaminating the surrounding area with radioactive steam.
During an inspection of the plant before it is brought back online, Godell discovers a puddle of radioactive water that has apparently leaked from a pump. Godell pushes to delay restarting the plant, but the plant superintendent denies his request and appears willing to let nothing stand in the way of the scheduled restart of the plant.
Godell investigates further and finds that a series of radiographs supposedly taken to verify the integrity of welds on the leaking pump are identical - the contractor simply kept submitting the same picture. He believes that the plant is unsafe and could be severely damaged if another full-power SCRAM occurs. He tries to bring the evidence to plant manager Herman DeYoung (Brady), who brushes off Godell as paranoid and states that new radiographs would cost at least $20 million. Godell confronts D.B. Royce, an employee of Foster-Sullivan, the construction company who built the plant, as it was Royce who signed off on the welding radiographs. Godell threatens to go to the Nuclear Regulatory Commission, but Royce threatens him; and later a pair of goons from Foster-Sullivan parks outside his house.
Kimberly also defies her bosses, determined to pursue the truth. She and Richard confront Godell at his home with what they know, and he voices his concern about the vibration he felt during the SCRAM and his anger about the false radiographs. Kimberly and Richard ask if he will testify at the NRC hearings, being held at Point Conception, where Foster-Sullivan is looking to build another nuclear plant. Godell agrees to obtain for them, through Hector, a set of the false radiographs to take to the hearings.
Hector's car is run off the road and the radiographs are taken from him. Godell leaves for the hearings but is chased by the goons waiting outside his home. He escapes by taking refuge inside the plant.
To his dismay, Godell finds that the reactor is being brought up to full power. He grabs a gun from a security guard and forces everyone out, including his friend and co-worker Ted Spindler (Brimley). Godell demands to be interviewed on live television by Kimberly. Plant management agrees to the interview, but only to buy time as they try to regain control of the plant.
Minutes into the broadcast, plant technicians deliberately cause a SCRAM so they can retake the control room, despite Spindler's warnings of Godell's concerns about safety. Godell is distracted by the alarms as a SWAT team forces its way into the control room. The television cable is cut and a panicky Godell is shot by the police. Before dying, he feels the unusual vibration again. The resulting SCRAM is only brought under control by the plant's automatic systems. True to Godell's predictions, the plant suffers significant damage as the pump malfunctions.
Plant officials try to paint Godell as emotionally disturbed. However, a distraught Spindler contradicts them when a question is posed to him on live television by Kimberly, saying that Godell was not crazy and would never have taken such drastic steps had there not been something wrong. A tearful Kimberly concludes her report as the TV signal abruptly cuts to color bars.

Question: What did the plant come periously close to?
Answer: China Syndrome