|A look inside the Indian Point Energy Center Turbine Hall. Entergy has spent around $1 million on portable equipment at Indian Point since the disaster in Japan. Photo courtesy Entergy|
By Brian Wheeler, Senior Editor
Almost one year after the meltdowns at the Fukushima Daiichi nuclear power plant, the U.S. Nuclear Regulatory Commission issued the first post-Fukushima orders to U.S. operators. The orders begin the implementation of several recommendations for enhancing safety at U.S plants based on lessons learned from the disaster in Japan.
The first two orders apply to every U.S. reactor, including those under construction. The first order requires the plant operators to better protect safety equipment installed after the 9/11 attacks and to obtain sufficient equipment to support all reactors at a site simultaneously. The second requires plants to install enhanced equipment for monitoring water levels in spent fuel pools.
The third order applies only to boiler water reactors that have GE Mark I or Mark II containment. These reactors are required to improve venting systems that help prevent or mitigate core damage in the event of an accident.
Also in response to the Fukushima Daiichi accident, the Nuclear Energy Institute in February said nuclear plant operators approved an initiative to purchase additional on-site portable equipment. Operators have acquired or ordered more than 300 pieces of major equipment to supplement layer upon layer of safety at U.S. sites. Operators also set a deadline of March 31 to place orders. The equipment ranges from diesel-driven pumps, electric generators, ventilation fans, hoses, fittings, cables and communications gear.
"Pumps to pump water and diesel generators to provide electricity are the heart of safety equipment," said Jay Thayer, vice president of operations at Entergy Nuclear.
NEI said the approach, known as FLEX, adds flexible coping capability that will provide a backup to permanently installed plant equipment that would be available following extreme events. Based on the industry's response to 9/11, in which additional portable equipment was procured, the FLEX approach will provide multiple means of obtaining power and water needed to fulfill key safety functions by providing an additional layer of protection on top of the safety systems already in place. Although there is not a specific cost set in place, NEI estimates the initiative could cost utilities about $1 million for each plant.
|NRC Senior Resident Inspector Karla Stoedter (right) talks to NHK Japanese public television station on June 28, 2011, about her work at the Prairie Island nuclear power plant in Minnesota. Photo courtesy of NRC.|
Charles Pardee, chief operating officer at Exelon Generation Co. and chairman of the industry's Fukushima Response Steering Committee, said the U.S. industry's defenses would be best improved by going to the same event that occurred in Japan; the loss of all AC electrical power and loss of heat sink, meaning there are no systems functioning that would allow those nuclear power plants to reject heat.
"An extended loss of AC power is critical to being able to cope with," said Tony Pietrangelo, senior vice president and chief nuclear officer at the Nuclear Energy Institute.
The industry also looked at a multi-unit response strategy. Most of the nuclear power plants' protection schemes are based on a single-unit basis, even the actions taken after 9/11. The disaster in Japan was a single event that impacted multiple units simultaneously.
"We recognized pretty soon that we were going to have to deal with multi-unit effects here in the U.S.," said Pietrangelo.
Exelon Nuclear, operator of the largest nuclear power fleet in the U.S. with over 19,000 MW, has added seven mobile, diesel-driven pumps at its plants. The operator completed thousands of purchases, upgrades and validations at its plants, including the 2,300 MW Byron Generating Station 100 miles west of Chicago.
Exelon experts have also verified the readiness of more than 1,700 pieces of equipment, inspected more than 1,900 flood barriers and seals, and invested more than 43,000 worker hours checking and testing equipment that may be needed in an unexpected emergency.
|Xcel Energy has purchased three additional pumps at the Prairie Island plant (pictured) and two additional at the Monticello plant. Photo courtesy of Xcel Energy.|
"We have additional safety measures planned for Exelon and the entire U.S. nuclear industry in the months ahead with additional guidance being issued by the U.S. Nuclear Regulatory Commission," said Mike Pacilio, president and chief nuclear officer of Exelon Nuclear.
At the Byron Station, the plant is protected from flooding by watertight doors, elevation of equipment above flood levels, and specifically-engineered flood barriers. Exelon said equipment purchases over the past year have only strengthened those barriers and systems. The two reactors and other critical components are protected by concrete walls up to four feet thick.
Minneapolis-based Xcel Energy, owner and operator of two nuclear plants in Minnesota, plans to spend between $25 million and $50 million to address all NRC recommendations, such as seismic and flooding design basis. Following 9/11, the utility, along with all nuclear operators, purchased additional on-site equipment in case of an event in which permanently installed equipment would not be available.
Building off the approach following 9/11 to procure additional portable equipment, Xcel has now purchased three additional pumps at Prairie Island and two additional pumps at Monticello. Before, each site had one pump.
"We identified all of those things that we could learn immediately from what happened at Fukushima," said Terry Pickens, director of Nuclear Regulatory Policy for Xcel Energy.
Xcel purchased pumps from Xylem Dewatering Solutions, a company that works with multiple electric utilities. Godwin, a brand of Xylem, designs, builds, sells, rents and services equipment. The Godwin Dri-Prime centrifugal pumps are self-priming pumps designed to prime from dry. Per Ohstrom, vice president of Marketing and Business Development, said the priming is always engaged, so if water is available from a surface or pressurized source, the pump will draw water into it with pressures in excess of 250psi.
Utilities are also looking to procure additional diesel generators in the event of a prolonged station blackout. Caterpillar Power Solutions, which has tailor-made solutions in about half of the current operating nuclear plants in the U.S., said they have received multiple inquiries on diesel generator sets. Caterpillar does offer a range of power solutions from small mobile units to qualified, permanently installed generator sets.
"We also have a dedicated team that focuses exclusively on developing power solutions for nuclear applications and supporting utilities with the considerable documentation and quality assurance mandated by regulatory agencies," said Bill Giunta, electric power commercial manager for Caterpillar. "Every utility is going through the process of reviewing their action plans for emergencies and assessing what they need to do if something like Fukushima happened at their facilities, and we are working with them to develop concepts to address those possibilities."
Giunta said the solutions can range from a mobile, commercial-grade emergency generator set that sits on a trailer next to other emergency vehicles all the way to a bunkered standby power solution that's impervious to almost anything.
|Workers roll up berm at the Fort Calhoun plant as flood waters recede. Photo courtesy of the Omaha Public Power District.|
"The ideal solution depends on the utility, design of the site, application, and geographical location," he said.
The Tennessee Valley Authority, owner and operator of the Browns Ferry, Sequoyah, and Watts Bar plants, has spent about $10 million over the past year to add more portable emergency equipment, according to the Chattanooga Times. In March, the paper reported that the federal utility ordered 3 MW diesel generators. TVA also ordered seven 150,000 watt diesel generators for use in recharging the plants' backup batteries.
Operators also have emergency plans in place to respond to any extreme events. The primary function of an emergency plan is to get the plant in a safe condition and, as importantly, to communicate the condition of the plant to the appropriate authorities. The industry took a leap forward in emergency planning following the Three Mile Island accident in 1979, said Entergy's Thayer.
"Emergency plans are mature," he said. "We have been fine-tuning these plans over the past 25 to 30 years."
Entergy, along with all U.S. operators, are required to conduct drills and exercises of each site's emergency plans on a quarterly basis. Operators are also graded during exercises conducted by the NRC and the Federal Emergency Management Agency.
Utilities aren't alone in making safety enhancements.
Westinghouse Electric Co., manufacturer of the AP1000 reactor that is being built at both Plant Vogtle and V.C. Summer, developed the Shield passive thermal shutdown seal. The Shield prevents a loss of reactor coolant system water inventory should an event occur that causes a loss of seal cooling. Westinghouse said with the Shield shutdown seal installed, operators do not need to implement an immediate cooldown to address reactor coolant pump seal leakage at the onset of a station blackout event and are able to focus their efforts on other critical tasks, such as power recovery and maintaining a heat sink.
While the Shield passive thermal shutdown seal was already in Westinghouse's portfolio of products, the company said utilities began looking at new ways to enhance safety.
"Clearly, looking at events and lessons we are addressing today it has an even more important role," said Rita Bowser, Westinghouse vice president of Major Projects.
Westinghouse said the Shield shutdown seal has been installed in one two-unit plant and the company has received orders from five more utilities for a total of 37 reactor coolant pump (RCP) installations.
Westinghouse partnered with Southern Nuclear Co. to install the Shield passive thermal shutdown seal in each reactor coolant pump at the Joseph M. Farley Nuclear Power Plant in Alabama.
The NRC has approved 24-hour survivability of the Shield seal under station blackout conditions and testing is underway to extend the mission time for the Shield shutdown seal to seven days.
Our Own Set of Challenges
Pardee said the tsunami, which was the cause of the disaster at Fukushima Daiichi, was a localized event. Plants in the U.S. have a very low, if not non-existent, risk of a tsunami impacting the facility. After Fukushima, the U.S. nuclear industry examined the lessons learned from the tsunami in Japan and applied those lessons for events that may take place in the U.S., such as earthquakes, tornadoes, hurricanes and flooding.
In 2011, plants in the U.S. dealt with many extreme events. In April, tornadoes tore through northern Alabama, resulting in the loss of off-site power at TVA's Browns Ferry plant.
In June, both the Fort Calhoun and the Cooper nuclear power plants in Nebraska were on flood alert as water continued to rise in the Missouri River. A 2,000-foot long berm did collapse at the Fort Calhoun station, allowing floodwaters to surround auxiliary and containment buildings and main electrical transformers.
Hurricane Irene made its way up the east coast in August, prompting the NRC to dispatch additional personnel at 10 plants from North Carolina to New Hampshire. Also in August, a 5.8 magnitude earthquake roughly 11 miles from Dominion's North Anna station in Virgina caused the two-unit plant to automatically shut down.
"The earthquake shook the reactors more strongly than the plant's design anticipated, so Dominion had to prove to us that the quake caused no functional damage to the reactors' safety systems," said Eric Leeds, director of the NRC's Office of Nuclear Reactor Regulation, at the time. NRC did allow both units to restart in November.
In all cases, which nuclear plants are designed for, the plants and plant operators responded as they were expected to. Diesel generators were activated to provide backup power when needed and the reactors automatically shut down.
"It was a good reminder for us that we have to be prepared for anything," said Pietrangelo. "Even beyond-external events."
In the U.S., though, there was only one instance of a station blackout, according to Pietrangelo. In 1990, a unit at Plant Vogtle in Georgia was in the midst of an outage when a truck backed into a transformer in the plant's switchyard. One diesel generator was down for maintenance and another failed to start. After 37 minutes, operators were able to get the available generator started. The U.S. industry possesses about 3,500 reactor years of operation and this case is the history of station blackouts in the U.S.
"This speaks to the operational experience we have. The plants are very robust from external events and natural events," Pietrangelo. "But that doesn't mean it can't happen here. So we have to ready for anything." That is what the FLEX approach is designed to do for the U.S. nuclear fleet.
NEI on April 16 said the indsutry met the deadline for ordering all on-site portable equipment to be used in emergencies.
"Procurement of this equipment strengthens every facility's ability to respond to and mitigate the impact of extreme events, no matter what causes them," said Pietrangelo.
Operators have until Dec. 31, 2016 to complete modifications and requirements from the NRC-issued orders.
At 2:30 p.m. ET on June 13, join Brian Wheeler, senior editor of Power Engineering magazine and editor of Nuclear Power International magazine, as he moderates a discussion with experts from the Nuclear Energy Institute and Entergy Nuclear. Learn about the best strategies for complying with new safety rules from Adrian Heymer, NEI's senior director of Strategic Programs, and how Entergy is preparing to make improvements to its fleet of nuclear reactors. Register at www.power-eng.com
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