Columbia Generating Station recently hosted a Japanese delegation from the Hokuriku Electric Power Company, including the chief nuclear officer and the engineering manager for Shika Nuclear Power Station in Shika, Ishikawa.
The visit is part of a partnership between U.S. and Japan CNOs to exchange information and operating experience. During this meeting, hosts and visitors discussed probabilistic risk analysis (a method to determine station risk), risk management and risk communication.
“This was tremendously valuable,” said Brad Sawatzke, Energy Northwest chief nuclear officer. “We all understand that nuclear power is a global industry, and that our performance is linked. A challenge to any plant in the world is a challenge to our entire industry.”
“We appreciate your team coming here and spending time with us,” Sawatzke told the six-member delegation at the conclusion of the visit. “We are very impressed with the actions you have taken to improve the protection of your safety equipment.”
During the two-day visit the delegation toured Columbia and EN’s new FLEX facilities. FLEX is a nuclear industry response to the events at Fukushima Daiichi that adds to the industry’s defense-in-depth safety at nuclear plants across the U.S. (See more about EN’s response here.)
Akizumi Nishino, chief nuclear officer for Shika Power Station, noted the additional seismic support on plant equipment, calling it “impressive.” Toshihiro Aida, manager of engineering at Shika, said he was struck by the cleanliness of the plant. If you’ve been to Japan, you know that’s saying something.
The delegation also saw preliminary work for the hardened containment vent system that will be installed during Refueling and Maintenance Outage 23, which begins in May. The system is part of the Nuclear Regulatory Commission’s post-Fukushima actions, and will include a 164-foot vent pipe running up the south side of the reactor building. The system will provide a direct means of venting an area of the primary containment, known as the wetwell, to outside the secondary containment structure during beyond-design-basis accident conditions.
The tsunami at the Fukushima Daiichi nuclear power plant eliminated any onsite power at the plant after an earthquake removed all offsite power. Subsequent fuel melting led to hydrogen explosions that destroyed the reactor buildings (secondary containment) at three of the Fukushima Daiichi units. The loss of the various fission product barriers led to the release of radioactive materials, which further hampered operator efforts to mitigate the accident. The disaster claimed no lives, nor is it expected to, but today more than 80,000 people are still displaced from their homes.
One of the lessons directly taken from that series of events is the need for licensees with Mark I and Mark II containments to either upgrade or install a hardened containment venting system that will remain functional during beyond-design-basis severe accident conditions. Mark II containment systems were not designed with a “hardened” containment venting system, though the current design can employ other methods for reducing containment pressure. Columbia has a Mark II containment and, therefore, must design and install such a venting system to build-in additional protections in the event of a beyond-design-basis severe accident.
What is a “hardened” vent? From the Nuclear Regulatory Commission:
“Hardened” means these vents must withstand the pressure and temperature of the steam generated early in an accident. The vents must also withstand possible fires and small explosions if they are used to release hydrogen later in an accident.
The vent will provide a reliable method to ensure continued operation of reactor core isolation pump cooling operation and removal of decay heat during a beyond-design-basis event where all onsite and offsite power is lost. Along with our added FLEX safety equipment stored on site, it will further enhance Columbia’s safety margins.
As a continuous learning industry, the U.S. nuclear reactor fleet has put a lot of effort into reviewing what happened at Fukushima to make U.S. plants even safer. For Columbia, the NRC declared the plant “safe” regarding seismic hazards. New evaluations are taking place and will be completed soon. The Army Corps of Engineers recently completed its flood hazard evaluation and found that Columbia remains a “dry site,” in other words, the facility will not experience flooding to a level that would impact its safe operation should one or more Columbia River dams fail upstream of the station.
This continuous learning is making the industry safer – and more efficient. Nuclear energy is a full-time, or baseload resource. Capacity factors for the industry as a whole are rising; Columbia has operated at a more than 92 percent capacity factor over the past four years. As the threat of climate change becomes more real, carbon-free nuclear energy will become more relied upon to provide the clean-air energy that benefits the global environment while powering our homes and businesses, and sustaining our national standard of living.
(Posted by Kevin Shaub/John Dobken)