Mitsubishi Heavy Signs MOU with PBMR Pty on Development of Small-size Nuclear Power Generation Plant

7 February 2010

Mitsubishi Heavy Industries, Ltd. (MHI) has signed a Memorandum of Understanding (MoU) with Pebble Bed Modular Reactor (Pty) Ltd (PBMR Pty) of the Republic of South Africa to study the area of collaboration in the development of the helium-cooled, High Temperature Reactor (HTR) Pebble Bed Modular Reactor (PBMR).

Based on the MOU, MHI will initially study the area for possible collaboration in the design of 200 MWt (megawatts thermal) plant, which PBMR Pty is currently developing. Going forward, the two companies will also probe further collaboration, including construction of plants and market exploration. With the newly concluded MOU, PBMR development will now move forward toward commercialization of a small size reactor.

MHI did the basic design and research and development of a helium-driven turbo generator system and Core Barrel Assembly, the major components of PBMR’s original 400 MW thermal, direct-cycle design. This concept was changed last year to a 200 MWt design which delivers super-heated steam through a steam generator.

The 200 MWt plant consists of a 200 MWt PBMR and a steam generator that provides hot steam at 750 °C (1,382 °F). The plant uses silicon carbide-coated uranium particles encased in graphite for the fuel spheres and helium as the coolant, making it free from risk of reactor core meltdown. The PBMR requires relatively low initial investment and is considered to be well suited to applications in areas lacking a fully developed power transmission grid.

The 200 MWt design is aimed at steam process heat applications, which provides the basis for penetrating the nuclear heat market as a viable alternative for carbon-burning, high-emission heat sources. In addition to generating electricity, this concept can also service potential customers such as the Next Generation Nuclear Plant (NGNP) project in the US, which is funded by the US Department of Energy, oil sands producers in Canada and the South African petro-chemical industry. A number of potential customers, including South Africa’s Sasol, have been studying the introduction of the plant, which is targeted to begin operation in approximately year 2020.

Specifically, when collaboration area has been agreed, MHI will conduct part of the research & development activities for the 200 MWt plant design. In the future, further collaboration possibilities will be probed, including construction of the 200 MWt plant and exploring market potential for the PBMR.

PBMR. The PBMR reactor has a vertical steel pressure vessel which contains and supports a metallic core barrel, which in turn supports the cylindrical pebble fuel core. This cylindrical fuel core is surrounded on the side by an outer graphite reflector and on top and bottom by graphite structures which provide similar upper and lower neutron reflection functions. Vertical borings in the side reflector are provided for the reactivity control elements. Two diverse reactivity control systems are provided for shutting the reactor down.

The PBMR uses particles of enriched uranium dioxide coated with silicon carbide and pyrolytic carbon. The particles are encased in graphite to form a fuel sphere or pebble about the size of a billiard ball. The core of the reactor contains approximately 360,000 of these fuel spheres.

Helium, which is used as the coolant, transfers the energy absorbed in the core to a secondary loop through a special heat exchanger. The helium in the primary circuit is circulated by a blower. The secondary side of the steam generator contains water. The heat absorbed changes the water to steam which, in turn, is used to drive a steam turbine connected to a generator to produce electricity in the same way conventional power stations operate. In this configuration, the reactor is an electricity producing plant.

The secondary side of the steam generator may also be directly coupled to a process plant to provide the energy as process heat. In this configuration, the reactor is a pure process heat producing plant. Another possibility is to configure the PBMR into a co-generation plant, i.e. one that produces both electricity and process heat.

Resources

• PBMR: Product Overview & Source Term Modelling (Nov 2009)