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REFRESH — Where There’s Steam, There’s … a Steam Generator

Kenneth Karwoski
Senior Advisor for Steam Generators

refresh leafWhen the NRC talks about “steam generators,” we’re not talking about teakettles. Steam generators provide vital technical and safety functions at many U.S. nuclear power plants.

In the United States, steam generators are only found in pressurized-water reactors, one of the two types of U.S. reactors. There can be two to four steam generators for each reactor unit. The generators mark the spot where two closed loops of piping meet. The first loop sends water past the reactor core to carry away heat, and this loop is at such high pressure that the water never boils. The second loop is at a lower pressure, so the water in this loop turns to steam and runs the plant’s turbine to generate electricity.

The steam generator’s main technical job is to let the first loop pass its heat to the second loop as easily as possible. To do this, a steam generator packs thousands of small tubes closely together, allowing the maximum area for heat to pass through the tubes and into the second loop’s water.

At the same time, the steam generators provide an important safety barrier – the first loop can contain radioactive material, so the tubes must keep the two loops of water separate. NRC rules require plants to closely monitor the second loop and immediately shut the reactor down if a tube leak exceeds very strict limits.

pwr[1]The NRC’s rules for inspections, maintenance and repair of steam generator tubes help ensure the tubes continue providing the safety barrier. If an inspection shows a tube is starting to get too thin, the plant will repair or even plug a tube to maintain safety.

Steam generator tube material has improved over time. The first steam generators had tubes made from a type of stainless steel that experience showed could be corroded by the chemicals, temperatures and pressures in the first and second loop. Over time, plants have replaced those steam generators with ones using more advanced alloys that are less likely to corrode.

Steam generator replacement only happens when the reactor is shut down for refueling, and plant owners bring in hundreds of specialized workers to safely remove the old generators and install the new ones. The old generators have to be safely disposed of as low-level radioactive waste.

REFRESH is an occasional series where we revisit previous posts. This first ran in July 2013.

An Explanation of Capacity Factor

Neil Sheehan
Public Affairs Officer
Region I

Earlier this year, the nuclear power industry announced it had set a record for reliability in 2015. The measuring stick for this achievement is what is known as “capacity factor.” But what exactly is that?

Put simply, capacity factor compares how much energy was generated against the maximum that could have been produced at continuous full-power operation during a specific period of time. It’s similar to baseball’s on-base percentage, which counts how many times a hitter reaches base versus the number of opportunities in the batter’s box.

Nuclear is one part of the energy generation mix.

Nuclear is one part of the energy generation mix in the U.S.

The Nuclear Energy Institute, the industry’s trade organization, preliminarily pegged the capacity factor average for all of the nation’s reactors at 91.9 percent last year. It added that this was a new record, edging out the previous one set in 2007.

An update issued by the U.S. Energy Information Administration on June 24 upped the 2015 total to 92.2 percent. EIA also lists nuclear power’s capacity factor in 2014 as 91.7 percent and 2013 as 89.9 percent.

For comparison purposes, other segments of the energy production sector had the following reliability ratings in 2015 (according to the EIA): Coal – 54.6 percent; natural gas-fired combined cycle – 56.3 percent; conventional hydropower – 35.9 percent; wind – 32.5 percent; solar photovoltaic – 28.6 percent; solar thermal – 22.7 percent; landfill gas and municipal solid waste – 67.6 percent; other biomass, including wood – 52.9 percent; and geothermal – 71.7 percent.

EIA allows visitors to its website to check capacity factors dating back to 1973. A review of this data shows that reactor reliability rates started out in the upper 40s/low-to-mid-50s percent range during the U.S. commercial nuclear power fleet’s early days.

By 1991, the level had climbed to 70.2 percent and in 1998 to 85.3 percent. Since the start of the new millennium, the capacity factor average has been in the upper 80s/lower 90s range.

Then-NRC Chairman Nils Diaz, in congressional correspondence issued in March 2001, wrote that increases in capacity factor could be attributed to decreases in the amount of time that plants were shut down for repairs, refueling and maintenance.

For its part, the NRC focuses not on the number of operational hours for plants but rather that they remain safe whether or not they are operating. The agency does, however, track the number of unplanned shutdowns as a measure of plant performance.

Five Questions With Tom Rich

Tom Rich is head of the agency’s Information Security Directorate

  1. How would you describe your job in three sentences or less?

5 questions_9with boxMy job is to work with others to protect NRC’s information and information systems. This includes providing security training, performing security assessments, testing the vulnerability of our IT systems to phishing and penetration attacks, responding to security incidents and keeping up with situational awareness to see where we may need to strengthen our defenses.

  1. What is the single most important thing you do at work?

Communication with NRC managers and employees regarding threats to our IT systems and data. We do security briefings, security awareness events for staff, and daily meetings with the Chief Information Officer.

  1. What is the single biggest challenge you face?

tomrichThe dynamic pace of technology changes and the need for cyber defenders to keep up. With the “Internet of Things” becoming more and more a part of our daily lives, the devices we now use in virtually everything we do present security and privacy concerns and introduce a much larger avenue of attack. These devices want to communicate, in some cases sensitive data, through multiple channels with each other and cloud services. The challenge is that these devices do not have adequate security controls built into their design.

  1. What would you consider one of your biggest successes on the job?

We established a cyber security dashboard that measures the NRC’s improvements in security practices. This is an internal mechanism to let NRC stakeholders see what they are doing well and where improvements are needed. Since implementation, we have seen significant improvement in cybersecurity across the agency.

  1. What one thing about the NRC do you wish more people knew?

That we have Resident Inspectors at each of the nuclear plants. I think a lot of the public believe we regulate and inspect from a distance. I do not believe many know we have feet on the ground at the nuclear plants.

Five Questions With is an occasional series where we pose the same five questions to NRC staff.

ncsam-web_edited-1For more information on National Cyber Security Awareness Month, go here.

Hurricane Matthew and the NRC — UPDATE Part II

UPDATE 2:  The NRC’s Region II Incident Response Center was staffed throughout the weekend due to Hurricane Matthew. In all, three plants entered unusual event classifications for storm-related reasons, including electrical grid instability. In addition to the update below on the St. Lucie plant, two other plants, Harris and Robinson, experienced brief losses of offsite power due to the effects of the hurricane. At those two sites, the emergency diesel generators started automatically and provided power until the grid stabilized. — Joey Ledford

UPDATE: While our thoughts are with the people who lost power or suffered damages in the storm, the St. Lucie nuclear plant experienced winds below hurricane strength and did not lose off-site power. The plant’s safety equipment and systems were not affected by the storm and both units remain safely shut down pending a “Disaster Initiated Review.” The review will ensure that evacuation routes are clear and emergency services are available. The units cannot restart until that review is conducted jointly by the NRC and FEMA. The NRC continues to monitor Hurricane Matthew, and will decide later today whether to continue to staff its incident response center in Atlanta. — Joey Ledford

Joey Ledford
Public Affairs Officer
Region II

It’s hard to believe, but no major hurricane has made landfall in the continental United States since 2005. Hurricane Wilma came ashore in southwest Florida in October of that year as a Category 3 storm, but then skirted the peninsula and went back into the Atlantic.

pathDuring this record respite of 11 years, the NRC never stopped training and preparing for big storms, including major hurricanes. Storm preparations were an important part of the post-Fukushima enhancements that have made U.S. commercial nuclear plants safer.

This week, a mammoth storm known as Hurricane Matthew is stalking Florida’s East Coast, having already taken its toll on Haiti, the Dominican Republic, Cuba and the Bahamas. The NRC and the companies that operate nuclear facilities began preparations for Matthew long before its anticipated path was clear.

Late Tuesday, the staff at Florida Power and Light’s St. Lucie plant in Port St. Lucie, not far from the predicted landfall, declared an unusual event, the lowest of NRC’s emergency classifications, because of the hurricane warning. The plant staff began severe weather procedures, which include making sure any equipment or debris that could be affected by wind or water has been removed or secured. Staff also conducted walk downs of important plant systems and ensured emergency supplies were adequate.

Similar work was being done at Turkey Point, south of Miami, another FPL plant, and at Brunswick, a Duke Energy station near Southport, N.C.

The NRC’s resident inspectors at each plant, meanwhile, worked to verify the storm preparations were completed as expected, paying special attention to the condition of emergency diesel generators that would be used if the plants lose offsite power.

The NRC maintains 24-hour staffing at any plant expected to experience hurricane-force winds. Since the resident inspectors live near the plant and need to take care of their families and homes, other agency personnel are dispatched to storm sites to help with staffing. One resident inspector from Tennessee volunteered to drive to southeastern North Carolina to staff Brunswick. Some other inspectors at or near the plants on other inspection duties volunteered to stay and provide staffing.

The NRC’s Region II Incident Response Center in Atlanta will be staffed around the clock during the storm, monitoring its path while keeping in contact with plant operators, NRC on-site inspectors, state emergency officials in the affected states and NRC headquarters.

Previous hurricanes have shown that nuclear plants are robust facilities that can withstand extremely high winds and storm surges. As Matthew approaches, the NRC is working to ensure plant operators have taken actions to protect the plants, safely shut down if necessary and ensure power is available to keep the plants in a safe condition until the storm has passed.

REFRESH: On the Wild Side at U.S. Nuclear Power Plants

Update: At nuclear power plants in the southwest, snakes, scorpions and black widow spiders are not an unusual sight. Resident Inspectors have to be especially careful during their walkthroughs in those plants not to poke into areas between pipes or bundles of electrical cables where venomous critters may be nesting.  But the most exotic wildlife may be the denizens at the South Texas Project nuclear plant in Bay City, where alligators abound. “We usually have about 75 alligators roaming around on site here at any given time,” said Shelia Davis, a corporate communications specialist for the South Texas Project. “If they stray into areas where they shouldn’t be we have people who are specially trained and can move them safely to our 7,000 acre reservoir.” Victor Dricks

Neil Sheehan
Public Affairs Officer
Region I

refresh leafExamples abound of the ways in which nature abhors a vacuum. Raptors will set up shop on a skyscraper ledge, just as they will on a cliff, if it suits their needs. Coyotes have been increasingly spotted in urban settings, even roaming about the streets of Manhattan. Last year, surveillance cameras captured images of a mountain lion strolling the Hollywood Hills after dark.

Nuclear power plants are also home to a variety of wildlife. Despite the industrial nature of these facilities, they are usually situated on large tracts of land encompassing hundreds of acres. They are also adjacent to bodies of water in order to tap into that H20 for cooling purposes.

All of that property and access to water can entice a variety of animals and birds to take up residence on the sites. And they do just that.

Information supporting this can be found in the Post-Shutdown Decommissioning Activities Reports for U.S. nuclear power plants that have ceased operations.

In the report for the Vermont Yankee nuclear power plant, which was submitted to the NRC in December 2014, it’s noted that the main emissions stack includes an attached nesting box for peregrine falcons. The box was installed by the company in 2009 at the request of the Audubon Society.

It’s been a rousing success, as according to the report “there have been two consecutive years of four young born and successfully fledged since 2012.”

An alligator crossing sign at the South Texas Project nuclear power plant.

An alligator crossing sign at the South Texas Project nuclear power plant.

Current decommissioning plans call for the Vernon, Vt., plant to be placed in storage for several decades prior to the initiation of major dismantlement work. However, when the time comes to remove the stack, the plant’s owner will need to consult with the U.S. Fish and Wildlife Service prior to removing the nesting box since the peregrine falcon is protected under the Migratory Bird Treaty Act.

Peregrine falcons can also be found at the Three Mile Island nuclear power plant, in central Pennsylvania. The PSDAR for TMI-2, where a severe accident occurred in 1979 and which won’t be taken apart until the neighboring TMI-1 permanently shuts down and is also ready for that work, shows peregrine falcons have nested on the TMI reactor building since 2002.

Meanwhile, the plant’s meteorological tower, which collects important weather data, has been home to an osprey nest every year since 2004. Ospreys, also referred to as fish hawks (with a wing span from around 5 feet), like to be around water, so it’s not surprising that TMI, situated on the Susquehanna River, is a place they call home.

A variety of wildlife can be found in the vicinity of the Crystal River 3 nuclear power plant, located on the Gulf Coast of Florida. That plant’s PSDAR, which the NRC received in December 2013, identifies the following threatened or endangered species in the vicinity of the site: Two species of fish — Gulf sturgeon and smalltooth sawfish; five species of sea turtles — green turtle, hawksbill, Kemp’s ridley, leatherback and loggerhead; one crocodilian species — American alligator; and one marine mammal — Florida manatee.

But on the site itself, only one state-listed threatened species, the bald eagle, and one state-listed endangered species, the wood stork, are found, according to the report. The PSDAR adds that three other species can “potentially occur” on the property: the gopher tortoise, the eastern indigo snake and the piping plover.

In the case of all of these plants and the others around the country, precautions must be taken to minimize the impacts of operations and decommissioning activities on these species and their habitats, consistent with federal and state laws.

REFRESH is an occasional series where we rerun and/or update previous blog posts. This post first ran in August 2015.

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