The SRE Accident
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.
A major portion of the radioactivity released from the fuel as a result of the cladding melting was contained in the sodium coolant, but some of the radioactive gases were collected in a hold-up tank. Over a period of two months these gases were vented to the atmosphere with the approval and oversight of the AEC. The releases were well below those permitted by regulations in existence in 1959 and also today.
Several reports were written shortly after the 1959 Sodium Reactor Experiment accident.
- NAA-SR-4488, "SRE Fuel Element Damage - Interim Report", November 1959 (2.4MB)
- NAA-SR-4488-Supl, "SRE Fuel Element Damage - Final Report", 1961
- NAA-SR-6890, "Distribution of Fission Product Contamination in the SRE", March 1962
In 2005, two independent studies were completed that confirmed Boeing's earlier findings that only small quantities of noble gases were released following the accident and that no iodine-131 or cesium-137 was released.
• "Chemical Behavior of Iodine-131 During the SRE Fuel Element Damage in July 1959. Response to Plaintiff's Expert Witness, Arjun Makhijani", Jerry D. Christian Ph.D., May 26, 2005
• "Investigation of Releases from Santa Susana Sodium Reactor Experiment in 1959", John A. Daniel Sr., May 27, 2005
Dr. Jerry Christian is a past Scientific Fellow from the Idaho National Engineering and Environmental Laboratory (INEEL) and is an expert in nuclear fuel chemistry and the behavior of fission products in nuclear fuel. John Daniel participated in the decontamination and recovery of the Three Mile Island (TMI) nuclear plant. He is an expert on nuclear power plant safety analysis and fission product transport and behavior.
The principal conclusions of these two independent studies were:
• Only very limited melting of an iron-uranium eutectic (alloy) occurred, causing failure of the steel cladding.
• Nearly all of the iodine-131 in the reactor stayed in the fuel as uranium tri-iodide, a solid. No elemental iodine-131 vapor was released.
• Approximately 1% of the iodine-131 (16 curies) was released from the fuel into the sodium coolant in the reactor core. It then formed sodium iodide, a solid, and stayed in the reactor coolant system.
• Approximately 1% of cesium-137 (28 curies) was released from the fuel into the sodium coolant in the reactor core, and all of this cesium-137 stayed in the reactor coolant system.
• Measurements of the reactor cover gas indicated only noble gases (xenon-133 and krypton-85) were present. No iodine-131 or cesium-137 was detected in the cover gas, which is contrary to the alleged pathway for release through the stack, as theorized by the Lochbaum Report.
• Only very limited quantities of noble gases (xenon-133 and krypton-85) were released to the environment from the stack.
2009 SRE Public Workshop
In response to stakeholder requests for more information about the SRE accident, DOE hosted an informational workshop on August 29, 2009 designed to explore the diverse expert and community perspectives on what occurred prior to, during, and immediately after the accident. Workshop materials and videos may be found on the SRE Workhop page.