German and US nuclear safety specialists say that solid-fuel, high-temperature pebble-bed reactor may need additional features and an extended start-up phase. Pebble-bed reactors use a very different reactor core configuration from conventional pressurised water reactors. Instead of the fuel being packed into rods that are arranged in an array and surrounded by a liquid coolant, the fuel – which contains uranium enriched to lower degree than conventional nuclear fuel – is packed into spherical particles surrounded by layers of ceramic, and the coolant is helium under moderate pressure (around 30 atm). Originally developed in Germany in the 1960s to breed uranium from thorium fuel, they operate at a much higher temperature than PWRs – over 900°C at the reactor outlet compared with around 300°C for a PWR – and are often believed to be fundamentally safer than PWRs because they are immune to meltdown even in the event of total coolant loss. A new commercial-scale pebble bed reactor called HTR-PM, with a thermal capacity of 200MW, is set to come online in China at the Shidao Bay Nuclear Power Plant (on the east coast of the body of water that separates China from the Korean peninsula) later this year. It is believed to be the first “Generation IV” reactor to enter service.
The Engineer 24th Aug 2018 read more »