Sodium Reactor Experiment
Sodium Reactor Experiment ( SRE ) is the first commercial nuclear power plant in the United States in the history of nuclear power. It was in operation from 1957 to 1964 and was located on the grounds of the Santa Susana Field Laboratory in California. The nuclear power plant presented a feasibility study on sodium -cooled reactors with liquid dar.
History
In 1954, the Atomic Energy Commission of the United States announced its intention to test different reactor concepts for civilian use. For this purpose was provided to build five nuclear power plants with different experimental reactors within five years. One of these power plants was the Sodium Reactor Experiment.
The construction of the plant began in June 1954. On April 25, 1957, the reactor went critical for the first time, the first network synchronization took place on 12 July of the same year. Construction and operation were performed by Atomics International.
Already in July 1959, there was an incident involving the release of radioactive gases. After the repair of the reactor that was started up again in September 1960 and operated until its final shutdown on February 15, 1964 without further incident.
The reactor and its auxiliary systems were dismantled by the year 1981, the complex was demolished in 1999.
The use of liquid sodium, which was tested in this reactor, did not sit through a large area. The in the plans of the Atomic Energy Commission also tested boiling water (tested in the Argonne National Laboratory) and pressurized water reactors (tested in nuclear power station Shippingport ) were promising. Only in breeder reactors, liquid sodium is still preferably used as the coolant, because it does not moderated neutrons.
Construction
In a liquid metal cooled SRE (sodium), graphite - moderated reactor was tested. In contrast to water, the liquid sodium used as a coolant has a relatively low vapor pressure, which could be largely dispensed with an elaborate interpretation of the power plant systems to high pressure at the operating temperatures of the reactor.
To avoid that the sodium expands during solidification and ensure that the plant could damage, it must be kept permanently liquid. In the power mode it reaches the thermal output of the reactor. Is this, however, shut down, take radiator at the bottom of the reactor pressure vessel warming of sodium.
The actual core of the reactor was sitting at the bottom of made of steel and filled with liquid sodium reactor pressure vessel. This core consisted of 43 fuel assemblies of seven fuel rods. The 1.8 m long fuel rods were also made of steel and each contained twelve balls of fuel to 2.78% enriched uranium metal.
Since the sodium is used as coolant, even activated by the neutron irradiation, it is exposed, was to reduce the radioactivity of the design of the nuclear power plant with two separate coolant circuits necessary. At full power, the sodium of the primary circuit flow at a temperature of about 260 ° C into the lower region of the reactor vessel and in the upper left of this area with a temperature of about 510 ° C. The coolant is circulated from the converted centrifugal pumps and transported according to the operating mode to a particular one of the two heat exchangers. In each of the sodium of the primary loop was from a portion of its heat to the secondary circuit of a sodium. For operation in the low power region of said secondary circuits was provided, which gave the thermal power generated by the reactor through a cooling air on the roof of the reactor building into the atmosphere. In normal operation, the heat output, however, was used to generate electricity: In the second secondary circuit, the liquid sodium circulated through a steam generator in which it was boiled by the heat energy of sodium water. The water vapor produced thereby drove a conventional steam turbine and generated via a generator so electricity that was fed into the network of the nearby town of Moorpark.
The reactor pressure vessel is not completely filled with liquid sodium. In the upper part there is helium gas, which is kept under a pressure of about 0.2 bar. This allows the coolant to expand due to temperature fluctuations during operation. Helium is well suited for this task because it is not activated by the occurring in the reactor neutron radiation. This gas bubble is connected by pipes with a sodium tank and four gas tanks. Changing the gas pressure in the reactor flows through the helium gas as in one of the four tanks, where any radioactive gases are retained. If their activity decayed to a safe level, they are diluted with ambient air and vented to the atmosphere.
Incident in 1959
As noted in the name of the power plant, this was not only the generation of electricity, but mainly as a platform for testing and experimentation in order to assess the behavior of these reactors in terms of suitability for use for energy can. Led to the engineering of multiple series of tests, the so-called " runs " in which the reactor has been in operation. While this was observed the behavior of the investment and any suggestions for the reactor and the power plant derived, which were implemented between the runs.
During Run 8 were incurred removed from the reactor fuel elements on black deposits. It was suspected that this decomposed tetralin, an oil-like liquid was. During the next runs, the engineers observed several unusually high temperatures in the individual fuel elements. Only towards the end of Run 13, as well as irregular Performance Parts occurred, it was noted that the heat distribution of the reactor was impaired irregular and strong. This has been attributed to the tetralin decomposing. Tetralin was used in the power plant for cooling various systems as well as in the seals of pumps and was apparently leaked from there into the primary circuit. There decomposed due to hot sodium and formed small lumps. This hampered the cooling of a total of 13 fuel assemblies, which have become corrupted. Most likely, it was also for the partial boiling of the coolant ( sodium boiling point: 883 ° C), which allows conclusions to the locally prevailing temperatures. The melting temperature of the metal uranium is used as the fuel has not been reached, only the fuel rod cladding started in a liquid state to pass. The exact date of the damage is unknown, but could be limited to the period between 12 and 26 July 1959.
The damage of the fuel rod cladding radioactive fission products are released into the primary circuit, which arise during normal operation and will be retained intact in these fuel rods. Solid fission products distributed in the liquid sodium of the refrigeration cycle, gaseous elements mingled with the helium used as a protective gas in the upper part of the reactor. This was then moved to the gas tanks to await the collapse of mainly contained xenon -135. Then the gases contained was mixed with air and released into the atmosphere.
The residual in the primary circuit tetralin was removed with 11,300 m³ nitrogen. For this, the 13 damaged and 17 more, remained intact fuel elements were removed from the reactor core to obstruct the flow of nitrogen inside the reactor as little as possible. In addition, the sodium level was lowered in the reactor in order to keep with the added is in the primary circuit amounts of nitrogen pressure still low. The helium contained as a protective gas in the reactor pressure vessel was led into the gas tank to ensure that there were no radioactive gases in the reactor. Was then started with the introduction of nitrogen through the reactor coolant pumps. After the primary circuit of tetralin was cleaned, the nitrogen had to be removed from selbigem. These continued to a gas mixture of helium and argon, which should replace the nitrogen in the upper part of the reactor pressure vessel. The displaced nitrogen was passed to two of the gas tank and there also controlled released into the atmosphere.