Refer to the following links for current progress in pebble bed reactor technology:
American Nuclear Society: Pebble Bed Reactor
INIS Web Services: Modular Pebble Bed Reactor
MIT Technology Review: The Next Nuclear Plant
Modular Pebble Bed Reactor (Pty) Ltd.
High Temperature Reactor Technology Network
Pebble Bed Reactor Technology in South Africa
Tsinghua University: High Temperature Gas-Cooled Reactor