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Fukushima Daini Demonstrates Value of Flexible Equipment

Scott Peterson, NEI's senior vice president of communications, speaks with a plant employee during a tour of the Fukushima Daini nuclear power plant.

Scott Peterson, NEI's senior vice president of communications, speaks with a plant employee during a tour of the Fukushima Daini nuclear power plant. (Click to enlarge.)

The following is a guest post from Scott Peterson, the Nuclear Energy Institute’s senior vice president of communications, who just recently returned to the United States following a trip to Japan.

FUKUSHIMA PREFECTURE–The safe shutdown of Japan’s Fukushima Daini plant could be instructive to the U.S. industry’s approach to adding flexible and diverse safety equipment at nuclear energy facilities.

“We have demonstrated through experience that the flexible approach works,” said Shinichi Kawamura, plant manager at the Daini site. “We used flexibility both in our systems and emergency operating procedures to safely stabilize the reactors after the tsunami.”

All four reactors at the Daini site were pumping enough electricity into Tokyo Electric Power’s grid to serve the needs of more than three million homes. Then a 9.0 earthquake hit the Eastern shore of Japan on March 11, 2011. The Daini reactors shut down automatically as designed, based on signals that ground motion from the temblor exceeded the level for safe operation. Despite the strength of the quake, the ground movement under the Daini reactors was mostly within the safety parameters of the boiling water reactors’ design.
Forty minutes after the quake, the unexpected occurred—the plant was hit by a tsunami so strong that its trail of damage still scars the otherwise pleasing seaside landscape adjacent to the Daini facility. The tsunami struck Daini from the South, with the brunt of its force flooding reactor 1. In fact, the high water mark 23 and a half feet above the foundation of Unit 1 is double that of reactor 3 just a stone’s throw away. It also was more than 6 feet higher than the strongest tsunami anticipated by scientists.

Peterson looks at the exterior of the Fukushima Daini nuclear plant. The plant's intake cooling water screens are in the background.

Peterson looks at the exterior of the Fukushima Daini nuclear plant. (Click to enlarge.)

Seawater poured into Daini 1 from many different outlets—ventilation systems, doors, exhaust systems—and caused damage both to critical safety systems and backup power supplies. With three of four power lines from the grid to Daini out of service and most plant cooling systems unavailable, TEPCO operators relied on innovation to safely cool the reactors.

Late on March 11 and into the next day, reactor operators at Daini undertook measures to cool and depressurize the reactors that gained them an additional 18 hours of time, and ultimately led to cold shutdown at the site. They first secured an uninterrupted cooling water supply to the reactor, using both an emergency spray system to cover the reactor fuel and then water from an extra storage tank to maintain that fuel cooling.

Plant operators used a lesson learned from analyzing the Chernobyl accident in 1986 to cool both the reactors and the suppression chamber below the reactor. The suppression chamber holds excess steam and hot water from the reactor so that the pressure of the core doesn’t go beyond required limits.

TEPCO devised a new emergency operating procedure that used a combination of plant systems to deliver cooling water. In an innovative step that underscores the flexibility of plant systems during challenging conditions, operators used a line normally used to discharge water from a system called a hydrogen recombiner to move water into the suppression chamber.

Peterson looks at new safety equipment at Fukushima Daini's reactor 1, including part of the plant's cooling system.

Peterson looks at new safety equipment at Fukushima Daini's reactor 1. (Click to enlarge.)

“Flexibly applying emergency operating procedures allowed the site time to verify equipment status, prioritize restoration targets, procure materials, and restore [systems] without falling into a critical situation,” Kawamura said.

Cooling capacity to the reactors was completed over the next few days and the plants placed in a stable condition called cold shutdown at around dawn on March 15.

“The integrity of the plant has been maintained,” said Daini superintendent Naohiro Masuda. Masuda will not forecast the long-term future of the plant, but he keeps his workforce motivated by focusing on short-term restoration goals—both for the plant and the communities that surround it.

In the months since the tsunami, 700 TEPCO workers and a contractor force of about 1,000 have replaced equipment, reworked motors, repaired locomotive-sized backup diesel generators, and installed temporary cabling to provide power to systems that were disabled because of the loss of electrical panels.

Placards of encouragement from trade union peers and others line walls of a walkway into one of the plant’s command centers. Among other positive signs: 51 key safety systems at the plant, the only one still inoperable will be repaired by the end of this year. Two others are unavailable until power cabinets are replaced.

One of the heroic efforts within days of the tsunami was the work of 200 plant employees who connected 5.6 miles of cable from power sources to plant systems at the site within one day—a task that normally takes 20 workers more than a month to accomplish.

A year ago, the Palo Alto-based Electric Power Research Institute identified 80 short- and long-term recommendations to help improve Daini’s protection against seismic and flooding threats. TEPCO has implemented all of the short-term recommendations and is well down the list of the long-term recommendations, many of which require continuous monitoring of the plant’s approaches.

TEPCO has added vehicle-based power supply units that can be used in the event of total loss of power at the site, three fire engines with high-pressure pumping capacity for backup cooling water injection into plant systems, and heavy water-tight doors to protect cooling systems from flooding.

For additional photos from Peterson’s tour, visit NEI’s Flickr photo album.

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Activity ID: 1002943 Activity Name: NEI Remarketing Safety Activity Group Name: Remarketing Safety First