B&W mPower

The B&W mPower is a proposed 125 MW modular, advanced light water nuclear reactor. The reactor is to be built by Generation mPower LLC, a joint venture of Babcock & Wilcox Co. and Bechtel. The reactor's power output is approximately 125 MWe. The reactor's design includes an underground containment facility that would store all of the spent fuel the reactor would use during its expected 60 year operating lifetime. Babcock & Wilcox is planning to apply to the Nuclear Regulatory Commission for design certification by 2013, and plans to deploy the first unit by 2020 at the Tennessee Valley Authority's Clinch River Site.

Overview

The mPower's Integral Reactor Vessel is designed to be prefabricated in a factory and sold to a buyer at a fixed price, shipped to a power plant site by rail, and installed in a pre-built underground containment building. Current illustrations of mPower site concept drawings show that the reactor is to be installed at facilities of approximately four modules, representing a total of 500 MWe of generation capacity per site. Auxiliary buildings for steam turbines (for power generation) and dry cooling towers will also be on site.

According to Power Engineering, the mPower's design - the factory-built Integral Reactor Vessel and standardized containment design - is designed to provide cost and construction time certainty to a purchasing utility. This is unlike other reactor designs, which are often built on a cost-plus or cost-sharing basis and utilities may suffer delays or cost overruns in the event construction is held back.

Fuel and Refueling

Power Engineering reports that the mPower is designed for a 5-year refueling cycle, and has a core that can be completely removed in a single evolution, and completely replaced in a second separate evolution, making the core nearly "plug and play", unlike the reactors of today, 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 core will not be a "plug and play cartridge" due to source term concerns [if dropped]; rather the traditional PWR fuel is off-loaded one assembly at a time as is typical of operating reactors. This evolution will not take long since the core comprises 69 fuel assemblies. Every feature of the fuel assembly is conventional and based on proven technology; the mPower reactor fuel is exceedingly similar to the fuel loaded in the AP-1000, EPR, and many other PWRs. Although the mPower reactor is advertised to operate for 4[not 5]-years between refueling, customers may operate this reactor with more frequent refueling outages if they so desire.

Thermal Hydraulics

According to sources, 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 mPower reactor is an advanced, generation 3++ light water reactor. The pressurizer, steam generator, primary coolant loop piping and reactivity control components are contained within a single Integral Reactor Vessel (IRV). 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 is 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.

Safety

The mPower is designed so as to make loss of coolant accidents impossible due to the Integral Reactor Vessel which contains the entire primary coolant loop within the reactor pressure vessel. 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 be used to cool the IRV with gravity driven-cooling. Further advanced means of heat removal can be used in the event that these systems are exhausted, such as by flooding the containment and establishing natural circulation.

See also

• Hyperion Power Module
• NuScale MASLWR
• Toshiba 4S