After the 1979 Harrisburg (US) accident, the nuclear industry faced a serious decline in selling nuclear power plants. The 1986 Chernobyl disaster made it even worse. Several countries decided not to build any more nuclear power plants. Since the early eighties, industry has started with the development of so-called inherently safe reactors.
(492.4881) Laka Foundation - In 1985 the US nuclear reactor builder Westinghouse started the design of the Advanced Passive 600 MW (AP600) pressurized water reactor. A conceptual design was completed in 1989. Certification by the US Nuclear Regulatory Commission is hoped for in late 1999. In early May, the NRC approved the final safety evaluation report. Final Design Approval (FDA) is expected this September. Receipt of the FDA will position the AP600 for foreign orders. Only after NRC certification can it be offered to the domestic market.
History
In 1985 Westinghouse started the development of the new-type pressurized water reactor, the AP600. This new generation reactor would be more safe than earlier reactors. Several new emergency core cooling systems were planned in the model as well as a new containment cooling system, that is even revolutionary as criticized. In 1989 a first concept design was finished. It is expected that the US certification will be given in late 1999, after which the whole development will have cost US$237 million.
Safety
The basic design of the AP600 does not differ that much from a conventional PWR. The main system consists of a reactor with two cooling circuits, leading hot water under pressure to the steam generators. New in the design are the emergency core cooling systems designs, to prevent the overheating and melting of the reactor core in case of a Loss Of Coolant Accident (LOCA). These systems that contain thousands of cubic meters of water should supply emergency cooling when the normal cooling fails. However, the working of these systems is still dependent on activation by computers and man, Westinghouse speaks about "passive safety systems". Once they even described it as "walk-away safe", suggesting that nothing would happen when personnel would leave the plant after an accident. Later on they decided not to use this term as it might be misunderstood by the public.
Four tanks are located above the reactor with borated water. In case of a LOCA this water (about 50 cubic meters) would enter the reactor. The borated water would stop the fission reaction. However, some critics also say the entrance of cool water in a hot reactor might lead to an opposite effect, a power increase. Besides, a water tank with about 1,900 cubic meters is situated in the containment. This amount would be enough to flood the whole containment building above the level of the reactor core. In that way the reactor building would be changed into a kind of swimming pool in which the hot reactor could cool down. Most evolutionary and also most controversial is the "passive containment cooling system". After an accident it is important to keep the containment intact. With too much pressure on the steam, it would burst and release radioactivity. To keep the pressure low enough, the AP600 containment is constructed to lead away the heat by a water-and-air-cooled system. The AP600 is designed with a single containment. Conventional reactors are constructed with double containments, a steal and a concrete one. The AP600 has only one containment to provide maximum heat transport to outside air. Besides, above the building a watertank with 1,300 cubic meters is located to spray the iron containment to cool it down. This water would be enough to cool the containment for three days. A 1991 study on new generations for the Dutch government concluded that the AP600 would not meet Dutch safety regulations. The construction with a single containment would not provide protection to possible accidents from outside like an airplane crash, an explosion, etc. A double containment would affect the possibility to cool the containment by outside air.
In 1990 the US Union of Concerned Scientists published a study on three new generation models (AP600, HTR and breeder PRISM). Besides the conclusion that none of the three design could be called "inherently safe" it concluded that the AP600 does not provide truly passive emergency core cooling (see also WISE News Communique 342.3421: Study finds no reactor designs 'inherently safe'). The report also criticized the reactor builders for withholding key safety-related documents from the public by claiming that the information is "proprietary"--a policy not likely to earn public confidence in the designs. The Union of Concerned Scientists also pointed to high-level radioactive waste and decommissioning as unresolved issues.
Funding
In the US, an Advanced Light Water Reactor program was created under the Energy Policy Act of 1992. This program was due to be completed in fiscal year (FY) 1996 and received more than US$ 250 million. In 1996, however, the Department of Energy (DOE) wanted to continue ALWR funding in FY 1997. Several groups criticized the DOE, saying that the ALWR program was a "textbook example of corporate welfare" to the nuclear industry. Instead of being a subsidy to open domestic markets, the ALWR program transformed into an export-assistance effort. As one reactor concept had been cancelled for market reasons at that time (the Simplified BWR), it was doubted whether the one then remaining, the AP600, would have chances. The SBWR and the AP600 were of a size (600 MW) that was chosen as the most likely potential for US electricity utilities (see also WISE News Communique 453.4478: Nuke advocates: stop ALWR funding!). General Electric cancelled its SBWR and is now looking for a 1000 MW design.
ALWR funding continued in FY 1997, however. In FY 1997 an amount of US$8 million was allocated for the AP600`s completion. Westinghouse, however, claimed another US$6.3 million from the program, saying money was allocated to other programs incorrectly.
Conclusions
The year 1985 saw the start of the development of the Advanced Passive 600 which is expected to be completed in late 1999 when it is certified by the US NRC. At that time US$237 million shall have been used by the US government for this reactor. The AP600 is designed with some new emergency cooling systems containing more than 3,000 cubic meters of water to transport heat from the reactor in case of an accident. The choice for a single containment, also to transport heat from the building, makes the AP600 more vulnerable to influences from outside. The funding by the ALWR program can be seen as an export subsidy as there are no chances for a new reactor in the US, even if the program was set up for domestic market. Now Westinghouse hopes to find new markets in Southeast Asia, especially China.
Sources:
- Advanced Reactor Study, Union of Concerned Scientists, July 1990
- E-mail Public Citizen's Critical Mass Energy Project, 1 May 1996
- Results of a comparison study of advanced reactors (NL), Nucon/ECN/KEMA, June 1991
- Nuclear Engineering International, November 1991
- Nucleonics Week, 9 April 1998
Tel: +31-20-6168294; Fax: +31-20-6892179
E-mail: laka@antenna.nl
NEW GENERATIONS: FOURTH ARTICLE
This is the fourth article in a series on new-generation reactors. The first article (The High Temperature Reactor) was published in #481, on November 21, 1997, the second one (on the European Pressurised Water Reactor) in #483/4, on December 19, 1997. The third article (on the Advanced Boiling Water Reactor) was published in #487, February 27, 1998. The articles are written by the Laka Foundation, the documentation and research center on nuclear energy.
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