PBMR

PBMR stands for Pebble Bed Modular Reactor, a design for a high-temperature gas-cooled nuclear reactor. The core uses thousands of spherical fuel pebbles containing TRISO-coated uranium fuel embedded in a graphite matrix. Pebbles circulate through the core, allowing refueling by adding fresh pebbles and removing spent ones. Helium is used as the inert coolant at high temperature and low pressure.

High outlet temperatures (roughly 700–900°C) enable efficient electricity generation and industrial process heat or hydrogen production, using either a Brayton gas-turbine cycle or a steam turbine cycle. The reactor relies on a graphite moderator and aims for a strong negative temperature coefficient, with passive heat removal via natural convection to address decay heat in many scenarios.

PBMR designs emphasize modular factory fabrication and scalable units that can be deployed in clusters to reach larger capacity. The concept is intended to offer inherent safety characteristics and potential for cogeneration, especially for markets requiring high-temperature heat alongside electricity.

Development and status: The PBMR program in South Africa sought commercialization of the Pebble Bed modular reactor concept in the 2000s. The project faced financing, regulatory, and market challenges, and by the mid-2010s the program was halted with the company wound down. No PBMR units have entered commercial operation. The PBMR concept remains part of broader HTGR discussions about safety and high-temperature applications, but it has not been deployed at scale.