双语阅读-福岛核事故之后的核安全反思

Nuclear Safety After Fukushima

Even with events at Japan's Fukushima Daiichi nuclear power complex still in a state of flux, attention is shifting from containment to assessment. The 9.0 magnitude earthquake, hundreds of aftershocks and ensuing tsunami were historic. But they can hardly be calledunforeseeable, and therein lies the nub of the critical questions this incident will raise for regulators everywhere: To what extent should nuclear safety regulation take account of all foreseeable contingencies, and should new technologies be required to apply to pre-existing facilities that were built to the standard of the industry at the time of construction?

The six-reactor Fukushima Daiichi facility was commissioned in 1971 and—by design—successfully withstood the March 11 earthquake and its aftershocks. But the tsunami topped the facility's sea wall, knocking out the back-up diesel generator and forcing the pump cooling systems and pressure ventilators to rely on batteries until mobile generators could be delivered to the site. Water also flooded the basement where switching equipment connected the pumping equipment, impeding repairs.

The result was overheating that caused pressure to build to over two times the designed limitations and led to explosions at three of the reactors. The outer buildings were designed to contain the reactor and

to withstand severe weather conditions, but not hydrogen explosions. Radiation leakages resulted, causing widespread concerns about threats to health and the environment.

Such a chain of events, however extraordinary, cannot be said to be unforeseeable. Japan's infrastructure and regulatory framework have anticipated earthquakes for 150 years; power outages, tsunamis and widespread demands that strain response efforts are all predictable consequences of earthquake risk.

Indeed, engineers have already designed solutions to mitigate the risks that materialized at Fukushima. Today's third-generation nuclear reactors anticipate the possibility of failed cooling systems and hydrogen pressure build-ups. The Westinghouse AP1000 reactor has a series of passive cooling systems that operate without external or

diesel-generated power or activation by its operators. It also has recombiners that prevent hydrogen explosions.

This design has been officially adopted in China for all inland nuclear projects where earthquake risks are more prevalent than on its coasts. Areva's EPR reactor under construction in Finland, France and China has four independent emergency passive cooling systems and extra core containment areas around the reactor. And Mitsubishi's new APWR has passive and active redundant cooling systems.