Analysis of Chengdu earthquake

France's radiation protection authority has published an analysis of the possible effects of the earthquake that occured on 12 May in China's Sichuan province on nuclear plants.

A document posted by the Institut de Radioprotection et de Sûreté Nucléaire (Institute for Radiological Protection and Nuclear Safety, IRSN) on its website describes the magnitude 7.9 earthquake that struck on 12 May at 2.28pm. Its epicentre was 80 km northwest of Chengdu, capital of Sichuan province. The violent tremors caused devastation and huge loss of life. In an area of Minyang prefecture around 80% of homes were destroyed, while 1000 people died at once when a college collapsed. Overall, some 12,000 people are thought to have been killed, while around 18,000 are still missing.

In the city of Shifang, two chemical plants collapsed and spread more than 80 tonnes of ammonia into the environment, according to the Chinese government's Xinhua news agency. An official spokesman said that the Three Gorges Dam, 600 km away from Chengdu, was not damaged while the Chinese State Grid Corporation said the load on the grid dropped by 5500 MWe as blackouts occurred in Sichuan and Shaanxi provinces.

The earthquake relative to Tianwan, Qinshan, Daya Bay, Ling Ao and assorted non-power-generating nuclear facilities (Source: IRSN)

China's four nuclear power sites, Tianwan, Qinshan, Daya Bay and Ling Ao, were all between 1400 and 1500 km from the earthquake's epicentre. IRSN's analysis of US Geological Survey data shows those sites would not have experienced ground acceleration rates of more than 20 cm/s². IRSN said, "It is likely that these reactors have not suffered significant damage," although confimation of this at the end of inspections has not yet come.

However, several research reactors and nuclear fuel manufacturing sites were much closer to the earthquake - including some less than 100 km away from the epicentre. IRSN said: "Given the sharp acceleration observed 70 km from the epicentre (250 cm/s²), it is not possible at this stage to rule out that these facilities have been subjected to damage."

Nuclear power plants are among the most robust structures in the world, featuring heavy reinforced concrete construction. Each plant is certified to withstand certain ground acceleration rates with no significant damage, while maintaining nuclear safety during significantly greater rates of motion. In July 2007 Japan's Kashiwazaki Kariwa nuclear power plant was shaken by an earthquake with effects between those two standards. The seven reactors on site all remained safe, but suffered widespread light damage. Checks to those units are ongoing.