The SRE accident occurred in July 1959 when there was an accidental blockage of sodium coolant in some of the reactor coolant channels. This resulted in the partial cladding melting of 13 of the 43 reactor fuel assemblies and the release of some fission products that contaminated the primary reactor cooling system and some of the inside rooms of the facility. Reactor safety systems functioned properly, and the reactor was safely shut down. The primary pressure vessel, containing the reactor core and sodium coolant, remained intact. Under the oversight of the Atomic Energy Commission (AEC), contamination within the building was cleaned up, and the damaged reactor fuel assemblies removed. A second fuel loading was inserted, and operations continued in September 1960 until the reactor was shut down in February 1964 due to termination of the project.
Detailed Account of Sodium Reactor Experiment (SRE) Partial Meltdown at Santa Susana (1959)