Researchers advise caution as a commercial-scale nuclear reactor known as HTR-PM prepares to become operational in China. The reactor is a pebble-bed, high-temperature gas-cooled reactor (HTGR), a new design that is ostensibly safer but that researchers in the U.S. and Germany warn does not eliminate the possibility of a serious accident. Their commentary, publishing August 23 in the journal Joule, recommends continued research, additional safety measures, and an extended startup phase that would allow for better monitoring.
n addition to generating electrical power more efficiently, pebble-bed HTGRs such as HTR-PM avoid some of the safety challenges that earlier reactor designs faced. They use graphite- and ceramic-coated grains of uranium fuel that can withstand the core’s very high temperatures and passive cooling systems, which together should eliminate the possibility of a core meltdown. “Pebble-bed reactors have been described by their supporters as ‘free from catastrophes’ and ‘walk away safe,'” he says.
What this means in practice, however, is that the soon-to-be-operational HTR-PM has been built without the safeguards that nuclear reactors in operation today are usually equipped with: it does not have a high-pressure, leak-tight containment structure to serve as a backup in case of an accidental release of radioactive material. It also does not have a redundant active cooling system.
“No reactor is immune to accidents. The absence of core meltdown accidents does not mean that a dangerous event is not possible,” Moormann says. He and his coauthors, Scott Kemp and Ju Li of the Massachusetts Institute of Technology, argue that with new technology, there is always a higher chance of user error. And prototype HTGRs have surprised their operators in the past by forming localized hot spots in the core and unexpectedly high levels of radioactive dust. The pebble-bed design also produces a larger volume of radioactive waste, which is challenging to store or treat.