Sodium Reactor Experiment

The Sodium Reactor Experiment facility was situated in a northwestern administrative section (known as Area IV) on a mountaintop known as The Hill of the Santa Susana Field Laboratory, about northwest of downtown Los Angeles in Simi Valley. When the Sodium Reactor Experiment was active, the Santa Susana Field Laboratory was operated by two business divisions of the North American Aviation company. The Rocketdyne division conducted liquid-propellant rocket engine testing and development at the site, while the Atomics International division focused on the development of commercial nuclear reactors and compact nuclear reactors for outer-space applications. == History ==

In 1954, the United States Atomic Energy Commission announced plans to test the basic nuclear reactor designs then under study by building five experimental reactors in five years. The Sodium Reactor Experiment, designed by Atomics International, was one of the chosen reactors. Design of the Sodium Reactor Experiment began in June 1954, and construction was underway in April 1955. A local utility company, Southern California Edison, installed and operated a 6.5 MW electric-power generating system. Controlled nuclear fission began on April 25, 1957. The Los Angeles Times published a front-page story when Moorpark was supplied with nuclear-generated electricity. Edward R. Murrow’s television program See It Now featured the event as a special news report, broadcast on November 24, 1957. In July 1958, Atomics International produced a film describing the construction of the Sodium Reactor Experiment facility. The Sodium Reactor Experiment used sodium as a coolant. Heat generated in the reactor was transported by liquid sodium through the reactor facility piping system. The pumps used to move the sodium were hot-oil centrifugal pumps modified for use in a sodium system. A support system used tetralin (an oil-like fluid) to cool the pump seals, which prevented leakage of hot sodium at the pump shaft. In July 1959, tetralin seeped into the primary coolant system through a pump seal and was decomposed by the high-temperature sodium. The decomposed tetralin clogged several narrow cooling channels used by the sodium system to remove heat from the reactor fuel elements. As the tetralin residues clogged the reactor's internal cooling channels, 13 of the reactor's 43 fuel elements overheated and were damaged. The exact date of the fuel damage is unknown, but is believed to have occurred between July 12 and 26. At the time, operators were aware of unusual reactor behavior but were unaware of the damage. They continued operations for several days before shutting down the reactor for examination. When the operators attempted to remove the fuel elements from the reactor, most elements were removed normally but some were found to be jammed. Pieces of the damaged fuel elements fell to the bottom of the reactor. During the following months, Atomics International personnel removed all the jammed fuel elements, retrieved the pieces of dropped fuel elements, cleaned the sodium system and installed a new reactor core. The Sodium Reactor Experiment was restarted on September 7, 1960, nearly fourteen months after the accident. In 1961, Atomics International produced another movie explaining the accident and the recovery operation. The Sodium Reactor Experiment operated until February 15, 1964. In 1964, several modifications were made to the reactor. These modifications were completed in May 1965, but the Atomic Energy Agency and Atomics International decided to close the reactor rather than restart it. The facility decommissioning began in 1976 with the removal of the reactor core, support systems and contaminated soil under the structure. The source of the contaminated soil underneath the building does not appear related to the 1959 reactor incident. Decommissioning was completed in 1981. In 1982, Atomics International produced a film on the decommissioning and decontamination of the Sodium Reactor Experiment. A group of certified health physicists from the Argonne National Laboratory conducted independent sampling to determine if the then-current minimum cleanup standards for radioactive residue were met. In 1985, the United States Department of Energy completed its evaluation of the survey reports and certified “…that there is no evidence the facilities pose a radiological threat to either personnel or the environment”. In 1999, the remaining structures were demolished and removed from the site. == Principles ==

The purpose of the Sodium Reactor Experiment was to demonstrate the feasibility of a sodium-cooled reactor as the heat source for a commercial power reactor to produce electricity. A secondary objective was to obtain operational data on slightly enriched fuel and uranium-thorium fuel mixtures. The reactor was designed as a flexible development facility, and was considered a development tool emphasizing the investigation of fuel materials. Compared to water, sodium has a relatively low vapor pressure at the operating temperatures of the reactor. The Sodium Reactor Experiment design utilized sodium as a coolant so high-pressure water systems would not be required. The reactor did not have a containment pressure vessel, because the maximum credible accident would not release enough gas volume to require pressure containment. It was designed to retain gases at about atmospheric pressure and reduce diffusion leakage from potentially contaminated gas. The gases used as a cover gas in the sodium systems (such as the reactor and fuel-assembly wash cells) are potentially radioactive. The design of the Sodium Reactor Experiment support facilities was to collect all such gases into a tank, compress them and put them into a gas holding tank until they had decayed sufficiently to allow discharge into the environment from an outdoor stack. == 1959 incident ==

Limited experience The Sodium Reactor Experiment was designed and constructed to gain experience in the use of uranium fuel in a reactor used to produce electricity. The fuel elements in the Sodium Reactor Experiment were operating under untried conditions. Fuel-design limits were based on theoretical limits, not operating experience. Cladding materials were untested, with little or no operating experience. Before the incident During the operation of the Sodium Reactor Experiment, its operators conducted several test cycles (known as “runs”) to correct and modify facility support systems, conduct reactor physics experiments and generate electricity. During run three, the Sodium Reactor Experiment became the first nuclear reactor in the US to produce power for a commercial power grid. During Run eight, a black residue (believed to be decomposed tetralin) was noticed on fuel elements removed from the reactor. The fuel elements were washed in the wash cell, and returned to the reactor. The reactor returned to operation for high-temperature testing. Several anomalous temperature readings were occasionally noticed during the next few runs, while the operators attempted to understand the behavior and its cause. At the end of run 13, it was obvious that something had occurred which impaired the heat-transfer characteristics of the system. It was decided that a tetralin leak had reoccurred, and was the cause of the trouble. The reactor sodium was purged with gaseous nitrogen, to remove volatile contamination. The excursion required the operators to manually override a malfunctioning automatic-control switch, and the reactor was shut down. The switch was repaired, and the reactor was slowly restarted. On July 29, 1959, an ad hoc investigative committee was established to study the incident and make recommendations. On August 21, 1959, The Van Nuys News published a story with the headline “Parted Fuel Element seen at Atomics International”. The article stated, “…a parted fuel element was observed” and “The fuel element damage is not an indication of unsafe reactor conditions. No release of radioactive materials to the plant or its environs occurred”. The investigative committee released “SRE Fuel Element Damage, An Interim Report” on November 15, 1959; the final report was made in 1961. The introductory material in both documents includes the statement, ”This report has been distributed according to the category ‘Reactors-Power’ as given in Standard Distribution Lists for Unclassified Scientific and Technical Reports", also noting that a total of 700 copies were printed. The documents were not labeled “secret”. == Radioactivity release ==

The Sodium Reactor Experiment core, high bay, reactor gas and exhaust stack were routinely monitored with particle detectors. Monitoring was underway at the time of the incident. Two sets of documentation appear to exist concerning the release of radioactive gases in the 1959 incident. The first set of documents include incident reports, technical analysis and radiation monitoring reports prepared by Atomics International personnel shortly after the incident. The second set of documents was primarily prepared to support a defense against a lawsuit against the current property owner (Boeing) about 45 years after the incident. Following the incident, Atomics International personnel documented an analysis of the distribution of radioactive materials released into the reactor by the damaged fuel elements. The analysis reviewed the radioactive materials released into the sodium and cover gas above the reactor. The researchers determined the amount of radioactive materials released into the sodium, and noted the materials were removed with cold traps; the sodium was reused when the reactor returned to service. The document states that only radioactive xenon-133 and krypton-85 were found in the cover gas. Attempts to detect radioactive iodine-131 were unsuccessful; this was not explained by Atomics International at the time. Internal Atomics International memoranda show the gases were removed from the reactor following the incident and stored in tanks, where they were allowed to decay and then slowly released into the atmosphere. A summary of radioactive gases released from the Sodium Reactor Experiment over a two-month period was prepared by Boeing. The document notes that 28 curies of fission gases were released into the environment through a stack, in a controlled manner which met federal requirements. Other expert estimates indicate that the available documentation does not resolve the uncertainties about how fission gases were released following the accident, and that the total amount of radioactivity released could be higher. == Controversy ==

Following the original July 1959 incident, it was next referenced in a 1976 report on nuclear activity in Los Angeles in a little-noticed In February 2004 a class action lawsuit was filed against the landowner, Boeing, alleging (in part) that the Sodium Reactor Experiment caused harm to nearby residents. The plaintiffs produced an analysis of the incident prepared by expert witness Arjun Makhijani, who is the head of an anti-nuclear organization. Makhijani's analysis of the Sodium Reactor Experiment estimated the incident at the Sodium Reactor Experiment may have released up to 260 times more radioactive iodine-131 than the official estimates for the Three Mile Island Nuclear Generating Station release. The "260 times worse than Three Mile Island" assertion has been widely quoted. The "Three Mile Island" conclusion presented in the legal filing did not agree with data and documents prepared at the time of the SRE incident. In August 2004 ground water under the former Sodium Reactor Experiment was sampled to determine the presence of tritium, which was undetected. The results were presented at a DOE-sponsored community meeting in June 2005 and in handouts at the meeting. In May 2005 a response to the Makhijani analysis was prepared for the defense by Jerry Christian, who provided a technical analysis disputing Makhijani’s claim of iodine release following the incident. Christian noted that Atomics International personnel attempted to monitor iodine-131 without success, and reactor temperature conditions did not permit a significant formation of iodine. A more-detailed analysis was prepared for the plaintiffs by John A. Daniel. Daniel focused on evaluating plant conditions, radiation monitoring and documentation to determine the amount of radioactivity released. His analysis concluded that a smaller amount of radioactive gases were released from the SRE. Christian and Daniel's technical analyses contrasted with that prepared by Makhihjani. The case was settled, reportedly with a large payment by Boeing to the plaintiffs (residents near the Santa Susana Field Laboratory who had cancer and other injuries from past site activities, including the SRE incident). The Engineering Disasters segment did not mention the technical analyses prepared for Boeing. In October 2006 California legislators, responding to community calls for independent health studies in the wake of revelations about the site, established the Santa Susana Field Laboratory Advisory Panel. The panel consisted of independent experts from around the country (and one from Britain) and community representatives. It was a project of the Tides Center, funded by the US Department of Energy and later by the California Environmental Protection Agency (as mandated by the California State Legislature). The panel released a set of documents analyzing events at the Santa Susana Field Laboratory. Five reports by consultants focused on the analysis of the radiological impacts of the July 1959 Sodium Reactor Experiment incident. One, by David Lochbaum, concluded that contrary to Rocketdyne's claim that no radioactivity was released into the environment, "as much as 30% of the most worrisome of the radionuclides, iodine-131 and caesium-137, may have been released, with a best estimate of 15% of each". In another report, Jan Beya attempted to provide an exposure estimate to epidemiologists interested in evaluating the effectiveness of radiation-induced-disease studies around the Santa Susana Field Laboratory. Beya noted that some meteorological information was withheld by the plant owner (Boeing). The estimates in the report were limited to scoping calculations with a wide range of uncertainty, but represented the current state of knowledge about the accident and its consequences according to experts who have analyzed the event. In September 2008, Daniel Hirsch presented testimony in the U.S. Senate to the Committee on Environment and Public Works, chaired by California senator Barbara Boxer. Hirsch called the July 1959 event “one of the worst nuclear accidents in nuclear history” and testified that the government “covered up the seriousness of the accident”. In December 2012, the EPA released the results of testing done at the site. The Agency noted that it took 3735 soil samples during the study and of those samples more than 10% contained radioactivity higher than background level. In July 2009, local media recognized the 50th anniversary of the July 1959 SRE incident. Local media reported that a former employee, John Pace, "broke his 50-year vow of secrecy" to describe his role in the reactor incident and recovery. A local newspaper featured photographs of Pace conducting activities at the SRE (monitoring the reactor, turning the top of the reactor core, placing sealer on asbestos piping, and seated at a console operating the reactor). The claim of secrecy contrasts with a press release, a motion picture and reports to the public following the 1959 incident. Jan Beyea was interviewed by a local newspaper; he reaffirmed his assertion that iodine-131 was released during the SRE incident, but it would "probably" not have produced a widespread effect on health. An electronic library of over 80 technical documents describing the design, operation, the 1959 incident and the activities taken to repair and restart the SRE is maintained by the DOE. Videos of the introductions, presentations, community comments and the question-and-answer session are available for viewing. == Aftermath ==

As a result of the incident, changes were made to the Sodium Reactor Experiment. Tetralin was eliminated, the sodium system was modified, the wash-cell cleaning process used steam instead of water, instrumentation was improved and the fuel-element geometry was modified. In September 1960, following recovery and cleanup operations, the Sodium Reactor Experiment began operation with a new reactor core. At the time of the July 1959 incident, the Sodium Reactor Experiment had operated for 10,344 hours. After the repairs were made and a new core loaded, the Sodium Reactor Experiment operated for an additional 26,716 hours and generated a total of 37 GWh of electricity. In 1966, the Energy Technology Engineering Center was established at the Santa Susana Field Laboratory by the U.S. Atomic Energy Commission for the development and non-nuclear testing of liquid metal reactor components. The testing and development notably improved the safety and reliability of sodium pump seals. The Energy Technology Engineering Center designed, developed and performed full-scale testing for a wide variety of sodium components (such as cold traps, flow meters and valves) from 1965 to 1998. == References ==