The B&W mPower is a proposed small modular reactor designed by Babcock & Wilcox, and to be built by Generation mPower LLC, a joint venture of Babcock & Wilcox and Bechtel. It is a Generation III++ integral pressurized water reactor (light water reactor).
The reactor was unveiled by Babcock & Wilcox in June 2009. In July 2010, Babcock & Wilcox announced a formal alliance with Bechtel called Generation mPower LLC. At the same time, Babcock & Wilcox announced that it will build a test facility for the mPower reactor design at the Center for Advanced Engineering and Research in Bedford County, Virginia. In April 2011, Babcock & Wilcox received a $5 million grant from the Virginia Tobacco Indemnification and Community Revitalisation Commission for this test facility.
Generation mPower planned to apply to the Nuclear Regulatory Commission for design certification by 2013. Babcock & Wilcox announced on February 20, 2013 that they had contracted with the Tennessee Valley Authority to apply for permits to build an mPower small modular reactor at TVA's Clinch River site in Oak Ridge, Tennessee.
In November 2012, mPower won a US Department of Energy funding competition for new SMR designs. The competition was intended to accelerate development of SMRs. The award was funded at $79 million in 2013, from a total of $150 million over five years, with a possibility of total government grants reaching $226 million or more.
In 2013 Babcock & Wilcox had intended to sell a majority stake in the mPower joint venture, but in February 2014 announced it was unable to find a buyer. In April 2014, Babcock & Wilcox announced it was scaling back investment in the programme, projecting investment of up to $15 million annually. It stated:
without the ability to secure significant additional investors or customer engineering, procurement and construction contracts to provide the financial support necessary to develop and deploy mPower reactors, the current development pace will be slowed.
B&W mPower is a Generation III++ integral pressurized water reactor (light water reactor) with a modular design. The reactor and steam generator are located in a single integrated reactor vessel located in an underground containment facility that would store all of the spent fuel. The modular unit has diameter of 4.5 metres (15 ft) and it is 23 metres (75 ft) high. The reactor core is of 2 by 2 metres (6 ft 7 in by 6 ft 7 in). The steam generator is derived from naval designs. The unit has an air-cooled condenser giving 31% thermal efficiency, and passive safety systems.
The reactor will have a rated electrical output of 125–180 MWe. When originally announced, the reactor had planned capacity of 125 MWe. Later the power was increased to 160 MWe and then to 180 MWe. In its pre-application design certification interaction to the Nuclear Regulatory Commission, the reactor's rated capacity was described as 500 MWt of thermal power and 160 MWe of electrical power.
Fuel and refueling
B&W mPower uses standard fuel enriched to 5%, similar to the fuel loaded in the other PWRs. It is designed for a 4-year refueling cycle. In the process of refuelling, the entire core will be completely removed in a single evolution, and replaced in a second separate evolution, making the core nearly "plug and play", unlike traditional reactors, which require fuel handling and movement of individual fuel rods during a refueling outage. The entire used core, once removed, can be placed in storage in the spent fuel pool next to the IRV in the containment, which is designed to hold an entire 60 years worth of used fuel, and is accessible by the containment gantry crane located above the IRV within the containment.
The mPower incorporates several features of the boiling water reactor (BWR). Like a BWR, the mPower reactor's primary coolant/moderator is highly purified water (with no boric acid). The Reactor Water Cleanup System ensures that primary system water remains pure. Similar to the ABWR, the mPower reactor has integral coolant recirculation pumps inside the Integral Reactor Vessel (IRV). The mPower reactor control rods are inserted from the top of the core and insert upon scram under gravity. All of the primary coolant is in the liquid phase during normal operation.
The integral once-through steam generator is an advanced derivative of the steam generators used in older B&W designs (Davis Besse). Control rod drives do not penetrate the IRV, as in the light water reactors of today, but are instead wholly enclosed within the IRV. Burnable neutron absorbers within the fuel and control rod inventory are used to suppress hot excess reactivity. Cold shut-down is accomplished with control rod insertion (as in BWRs).
The mPower is designed to produce superheated steam and does not require steam separators and dryers prior to admitting steam into the high pressure turbine.
The mPower is designed to eliminate the potential loss of coolant accidents as the integral reactor vessel does not have large cold or hot leg piping; it contains the entire primary coolant loop within the reactor pressure vessel with automatic primary loop depressurization. If secondary cooling is lost, creating an effective loss of standard heat removal, there are water supplies located above and within the containment that can cool the vessel with gravity driven-cooling. Heat removal can be used in the event that these systems are exhausted, such as by flooding the containment and establishing natural circulation, as no electrically driven pumps are required.
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