Monday, June 29, 2015

How a Bias for Action Led to an Innovative Alternative to External Filtered Vents

Maria Korsnick
The following is a guest post by Maria Korsnick, NEI’s Chief Operating Officer.

During the five years that I was chief nuclear officer at Constellation Energy, my first priority was to ensure that our plants operated safely and reliably in order to protect public health and safety. On a day-to-day basis, I wanted to make sure that our operating crews and emergency personnel had multiple tools available to combat any situation that might arise. And when we identified gaps, we made sure to address them promptly. It’s this bias for action -- together with the oversight of a strong independent regulator, the U.S. Nuclear Regulatory Commission  -- that has helped the American nuclear energy industry become the safest and most reliable in the world.

Following the tragic accident at Fukushima Daiichi in Japan on March 11, 2011, the U.S. nuclear industry followed that same bias for action to ensure that our plants would continue to protect the public should a similar set of events occur here. This led to many innovative concepts, such as the diverse and flexible coping strategy (FLEX), to ensure that the fuel in the reactor and spent fuel pools would remain cool and safe and the containment integrity protected if a nuclear plant lost access to offsite power and loss of emergency diesel generators. FLEX also requires that portable emergency equipment be located at every site, and industry further established two national response centers stocked with multiple sets of backup generators, hoses, lighting and pumps in Memphis and Phoenix that could be transported anywhere in the U.S. within 24 hours. Altogether, these enhancements represent a $4 billion investment by industry in making our plants even safer than before.

A key lesson from Fukushima was that BWRs with Mark I & II containments (similar to those at Fukushima) must ensure that the reactor containment would maintain its integrity and protect the public even if the nuclear fuel was damaged and the power was out. The NRC issued an order to the industry that these plants install a reliable containment vent system to reduce pressure and remove heat from containment when the power is out even if the nuclear fuel was damaged.

While this order clearly improved safety, we believed we could obtain additional safety benefit if we could ensure water could be added to the reactor to cool the damaged core and also prevent containment failure.

Working with my counterparts in the industry and the Electric Power Research Institute (EPRI), we remedied this problem by including water addition under these conditions. This was included in the industry’s guidance for implementing the vent order and endorsed by NRC.

Interestingly, the same water to cool the core will also act as a filter in containment. As industry and NRC research show, because the external filters are just tanks filled with water, the water in containment can be just as effective as an external filter. Taken together, it’s a solution that is innovative, elegant and cost-effective, one that ought to be a model for nuclear safety around the world going forward.



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