China’s Tsinghua University has unveiled the world’s first “meltdown-proof nuclear power plant,” according to a report in The Independent.
The design represents a major step forward for nuclear safety and could prevent disasters resulting from the extreme heat generated by nuclear fission. Overheating can result in an explosion and the release of dangerous radiation if not properly managed.
The Chinese plant uses an innovative design called a “pebble-bed reactor” to reduce the risk of meltdown. Older reactor designs such as Pressurized Water Reactors (PWR) require active intervention to shut down in an emergency, while their safety systems require an outside power source to operate pumps that circulate coolants.
But pebble-bed reactors are unique because their fuel rods are not cooled by circulating water. Instead, the reactor is essentially a big unpressurized hopper filled with spherical pebbles made of layers of enriched uranium fuel, carbon that acts as a moderator, and silicon carbide coating.
These billiard ball-sized spheres are provided by the German company SGL Group and are very resistant to heat. The coolant is helium gas which is chemically neutral and will remain gaseous at any temperature.
According to another report the pebbles are able to withstand temperatures of "up to 1,600°C (3,000 °F)". The pebbles’ heat causes the helium to naturally circulate when the pumps are turned off. Because of the high surface-to-volume ratio of the pebbles, heat loss exceeds heat generation.
The Chinese researchers tested the reactors by connecting them to a 210-MWe steam turbine which moderated the nuclear reactions and safe temperatures were maintained, with the core shutting down in a matter of minutes and both reaction and temperature stabilizing in about 35 hours.
On March 11, 2011, Japan experienced the Great East Japan Earthquake which was followed by a powerful tsunami, resulting in a severe nuclear accident at the Fukushima Daiichi nuclear plant. Three of six reactors at the plant sustained severe core damage and released hydrogen and radioactive materials.
The 1970s-era plant design was due to be phased out before its backup diesel generators were disabled by the tsunami, causing the meltdown. Rubble and debris prevented emergency crews from reaching the plant in time to prevent an explosion.