March 11, 2012 | 2
A year ago today, a 9.0 magnitude earthquake rocked Northern Japan. In the wake of this earthquake, a massive tsunami would flatten the Northern Tohoku region, killing nearly 20,000 people and knocking out power to the Fukushima Daiichi Nuclear Power Plant. And, as the country rode through a large series of aftershocks, news of an explosion at this nuclear power plant would fill the world with the fear of another Chernobyl-like disaster.
Eventually, three of the boiling-water reactors at the Fukushima plant would experience full meltdowns, the result of a series of failures that started with the tsunami-induced power outage. After the plant lost its grid-based power supply, the diesel generators that were meant to provide back-up power also failed, and the battery back-up system’s 8-hour capacity would prove to be insufficient. As a result, cooling water could not be properly circulated through the reactors, and water levels fell dangerously low. Without adequate cooling water circulating through the plant, the nuclear fuel rods inside of the reactors started to melt and subsequent explosions (the result of hydrogen gas buildup) and fires resulted in the release of enough radioactive material to necessitate a 20-km “exclusion zone” around the power plant.
As a result of the Fukushima nuclear power plant disaster, the U.S. Nuclear Regulatory Commission (NRC) has spent significant man hours focusing on the lessons that can be learned from the disaster. On Friday, the NRC revealed some of their learnings as they issued three new orders designed to improve U.S. power plant safety. According to NRC Chairman Gregory Jaczko, these new orders “reflect a significant step forward on our post-Fukushima efforts…[but] there’s still a great deal of work ahead of us.’’
These three orders require additional safety equipment to be installed on all U.S. reactors, with additional requirements for those reactors with Mark I and II containment structures (like those found at Fukushima). Specifically, these orders require all U.S. commercial nuclear power plants, including the newly approved Georgia Vogtle reactors, to install new safety equipment. This equipment includes enhanced technology for monitoring water levels in each plant’s spent fuel pool. Additionally, all boiling-water rectors (BWRs) with Mark I or II containment structures are required to improve their venting systems in order to “prevent or mitigate core damage in the event of a serious accident.”
The U.S. commercial nuclear power plant fleet has until December 31, 2016 to complete any modifications needed to fulfill these three orders.
[For those interested in more information on the Mark I containment design and its role in the U.S. power plant fleet, see David Biello's recent piece on the safety of U.S. Nuclear Reactor designs.]