Advanced Boiling Water Reactor
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The Advanced Boiling Water Reactor (ABWR) is a Generation III reactor based on the boiling water reactor. The ABWR was designed by General Electric. The standard ABWR plant design has a net output of about 1350 megawatts electrical.
Internal recirculation pumps inside of the reactor pressure vessel (RPV) are a major improvement over previous GE reactor plant designs (BWR/6 and prior). These pumps are powered by wet-rotor motors with the housings connected to the bottom of the RPV and eliminating large diameter external recirculation pipes that are possible leakage paths. Construction costs are also reduced. The 10 internal recirculation pumps are located at the bottom of the downcomer region (i.e., between the core shroud and the inside surface of the RPV).
Even though BWRs can operate using only the available natural recirculation thermal pumping head without forced recirculation flow, forced flow is desirable in order to increase the available output from the reactor and as a convenient method to change the reactor output by changing the flow.
Prior to the ABWR, all large commercial nuclear steam supply systems provided by GE from the BWR/3 through the BWR/6 designs used jet pump recirculation systems. These systems have two large recirculation pumps (each up to 9000 Hp) located outside of the reactor pressure vessel (RPV). Each pump takes a suction from the bottom of the downcomer region through a large diameter nozzle and discharges through multiple jet pumps inside of the RPV in the downcomer region. There is one nozzle per jet pump for the discharge back into the RPV and the external headers supplying these nozzles. Valves are required to isolate this piping in the event of a failure.
Consequently, internal recirculation pumps eliminate all of the jet pumps (typically 10), all of the external piping, the isolation valves and the large diameter nozzles that penetrated the RPV and needed to suction water from and return it to the RPV.
The first reactors to use internal recirculation pumps were designed by ASEA-Atom (now Westinghouse Electric Company by way of mergers and buyouts, which is owned by Toshiba) and built in Sweden. These plants have operated very successfully for many years.
The internal pumps reduce the required pumping power for the same flow to about half that required with the jet pump system with external recirculation loops. Thus, in addition to the safety and cost improvements due to eliminating the piping, the overall plant thermal efficiency is increased. Eliminating the external recirculation piping also reduces occupational radiation exposure to personnel during maintenance.
A nice operational feature in the ABWR design is electric fine motion control rod drives. Older BWRs use a hydraulic system to move the control rods in six-inch increments.
The ABWR is fully automated in response to a loss-of-coolant accident (LOCA), and operator action is not required for 3 days. These and other improvements make the plant significantly safer than previous reactors.
As of December 2006, four ABWRs were in operation in Japan: Kashiwazaki-Kariwa units 6 and 7, which opened in 1996 and 1997, Hamaoka unit 5, opened 2004 having started construction in 2000, and Shika 2 commenced commercial operations on March 15, 2006. Another two, identical to the Kashiwazaki-Kariwa reactors, were nearing completion at Lungmen in Taiwan, and one more (Shimane Nuclear Power Plant 3) had just commenced construction in Japan, with major siteworks to start in 2008 and completion in 2011. Plans for at least six other ABWRs in Japan have been postponed, cancelled, or converted to other reactor types, but three of these (Higashidōri 1 and 2 and Ohma) were still listed as on order by the utilities, with completion dates of 2012 or later.
Several ABWRs are proposed for construction in the United States under the Nuclear Power 2010 Program. However these proposals face fierce competition from more recent designs such as the ESBWR (Economic Simplified BWR, a generation III+ reactor also from GE) and the AP1000 (Advanced, Passive, 1000MWe, from Westinghouse). These designs take passive safety features even further than the ABWR does, as do more revolutionary designs such as the pebble bed modular reactor.
On June 19, 2006 NRG Energy filed a Letter Of Intent with the Nuclear Regulatory Commission to build two 1358-MWe ABWRs at the South Texas Project site. [1] On September 25, 2007, NRG Energy and CPS Energy submitted a Construction and Operations License (COL) request for these plants with the NRC. NRG Energy is a merchant generator and CPS Energy is the nations' largest municipally owned utility.
[edit] See also
- nuclear power
- Nuclear safety in the U.S.
- Economics of new nuclear power plants
- pressurized water reactor
- Advanced Heavy Water Reactor
[edit] External links
- Technical details and features of Advanced BWRs
- Advanced BWR General Description (PDF, 272KB): Table of Contents, with active links to text.
- ABWR Plant Economics and Project Schedule (old)
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