Here comes the AP1000

New Toshiba reactor model gets U.S. nod | The Japan Times Online

I meant to post about this before Christmas, but forgot:

The U.S. Nuclear Regulatory Commission has approved Toshiba Corp.'s AP1000 reactor design, paving the way for the first new reactor construction license to be issued in more than 30 years.

The five-member agency voted unanimously Thursday in favor of certifying the reactor's design.Southern Co. and Scana Corp. are seeking permission to use the next-generation reactors to expand nuclear power output at existing sites in Georgia and South Carolina. The certification "marks an important milestone toward constructing the first U.S. nuclear reactors in three decades," Energy Secretary Steven Chu said Thursday in a statement.

Well, they certainly take their time with new reactor approvals. As the report goes on to note:

The biggest difference between the AP1000 and existing reactors is its safety systems, including a massive water tank on top of its cylindrical concrete-and-steel shielding building. In case of an accident, water would flow down and cool the steel container that holds critical parts of the reactor — including its hot, radioactive nuclear fuel.

An NRC taskforce examining the Fukushima nuclear crisis said licensing for the AP1000 should go forward because it would be better equipped to deal with a prolonged loss of power — the problem that doomed the Fukushima No. 1 plant.

Good to see better passive safety being considered so important in new designs, but I would assume you could better than having a water tank on top.

Anyway, you can have a detailed look at the design at the reactor's own Westinghouse/Toshiba website. It's full of reassuring statements like this:

The AP1000^® pressurized water reactor works on the simple concept that, in the event of a design-basis accident (such as a coolant pipe break), the plant is designed to achieve and maintain safe shutdown condition without any operator action and without the need for ac power or pumps. Instead of relying on active components such as diesel generators and pumps, the AP1000 relies on the natural forces of gravity, natural circulation and compressed gases to keep the core and containment from overheating. However, many active components are included in the AP1000, but are designated as non safety-related.

Multiple levels of defense for accident mitigation are provided, resulting in extremely low core-damage probabilities while minimizing occurrences of containment flooding, pressurization and heat-up.

The AP1000 meets the U.S. NRC deterministic-safety and probabilistic-risk criteria with large margins. Results of the Probabilistic Risk Assessment (PRA) show a very low core damage frequency (CDF) that is 1/100 of the CDF of currently operating plants and 1/20 of the maximum CDF deemed acceptable for new, advanced reactor designs.

I hope they are right.