Bushehr - Reactors
The reactor units at Bushehr were initially built by a German company, Siemens, and were built to a plan closely resembling that of the Biblis A unit in Germany. The Bushehr I reactor was 85 percent complete and the Bushehr II reactor was partially complete prior to the 1979 Iranian Revolution, after which construction of both reactors halted. Ayatollah Khomeini declared the project "anti-Islamic," and the government of Mehdi Bazargan soon abandoned it.
The dome of the reactor building consisted of a cylindrical shell and hemispherical shell placed on top, each measuring a 60 meter diameter. The steel containment shell was a spherical and measured 56 meters in diameter.
Much of the exterior remained unchanged including a gantry that was mounted to the outside of the dome and was designed to allow easy access for materials and parts to the reactor dome.
Inside, the reactor building was divided into two containment areas, one formed by the steel containment and the other an outer containment shield. Both were high-pressure parts of the nuclear steam supply system and the spent fuel storage pool and the new fuel store. The German design called for the steel containment shell to be 56 meters in diameter and designed for a pressure of 5.7 bar, it was capable of absorbing the full equilibrium pressure in the case of a design basis accident. The outer shell would act as a barrier against direct radiation from the reactor building and as a protective shield for the reactor plant from ecternal impacts.
The German designs indicated that the reactor auxiliary buildings consisted of horizontally and vertically arranged sections while the turbine buildings had frames that were constrained at the bottom with rafters of prestressed concrete. Unit I was intended to have a 1500 rpm saturated-steam condensing turbine-generator unit used for the generation of electricity, and one double-flow high presssure casing and three double-flow low pressure casings. Additionally, the external walls of the turbine building were solid to increase acoustic insulation. The German designs called for the building between the two units to contain workshops, stores, a water treatment plant, laboratory, welfare rooms, as well as the diesel emergency generators for Unit I.
The Biblis reactors in Germany had a peak work force of roughly 500 people onsite with an engineering office with less than 40 personnel.
In January 1995, Russia and Iran signed a contract under which Russia would provide one VVER-1000 (aka WWER-1000) 950-1,073 MWe (electrical) light water reactor at Bushehr. The VVER-1000 reactor would be similar in configuration to Unit Four of the Russian Balakovskaya plant at Balakovo, Saratov. The Russian reactors would be installed in the original structures designed for the German 1,200-1,300 MWe reactors. Since the horizontal VVER-1000 steam generators were larger than the original German design, the project would require an enlargement of the existing reactor building, though the finished reactor dome would still resemble the German design.
Though Soviet-designed nuclear power plants differed from Western nuclear power plants in many respects, including safety systems, only the VVER-1000 design had a containment structure like that of most nuclear power plants elsewhere in the world. Although it shared a basic engineering concept with its counterparts in the United States, France and Japan, the Soviet VVER pressurized water design was very different. VVER is an acronym for Vodo-Vodyannoy Energeticheskiy Reactor (water-cooled, water-moderated).
The VVER-1000 design was developed between 1975 and 1985 based on the requirements of a new Soviet nuclear standard that incorporated some international practices, particularly in the area of plant safety. The evolutionary design incorporated safety improvements over earlier VVER-440 Model V213 plants, including a steel-lined, pre-stressed, large-volume concrete containment structure similar in function to Western nuclear plants. With 4 primary coolant loops (providing multiple paths for cooling the reactor), each with a horizontal steam generator (for better heat transfer), this design was more forgiving than Western plant designs with 2, 3 or 4 large vertical steam generators.
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