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Category Archives: Operating Reactors

When A Plant Changes Hands

Neil Sheehan
Public Affairs Officer
Region I

FitzPatrickTowerViewIn February, Entergy announced plans to permanently shut down the James A. FitzPatrick nuclear power plant on Jan. 27, 2017. However, there are indications – based on recent negotiations between Entergy and Exelon – that the facility may not cease operations after all.

On Aug. 9, Exelon announced it had reached a deal to purchase the Scriba (Oswego County), N.Y., boiling-water reactor from Entergy for $110 million. This agreement occurred after the New York State Public Service Commission approved Zero Emission Credits, or subsidies, which will help upstate N.Y. nuclear plants stay online amid historically low energy prices.

Challenging market conditions had earlier prompted Entergy to announce the plant’s closure. The NRC in 2008 had approved a renewal of FitzPatrick’s initial 40-year operating license, extending it until October 2034.

Before the sale of the plant can be completed, the transaction will undergo reviews by the NRC, as well as other regulatory agencies. NRC staff will evaluate Exelon’s technical and financial capabilities to ensure the plant’s safe operation and to provide reasonable assurance that adequate funding is available to safely decommission the unit after the final shutdown has occurred.

Exelon currently owns and operates 22 reactors at 13 plant sites in the U.S. The company also runs Fort Calhoun under a contract with the Omaha Public Power District.

We will publish on our website and in the Federal Register a notice of having received the license transfer application, dated August. 18, and the opportunity to request a hearing on the proposal. As for the process itself, such reviews generally take from six months to a year. For example, when the FitzPatrick operating license was transferred from the New York Power Authority to Entergy in 2000, the review was completed in about half a year.

As a footnote, Exelon already owns the Nine Mile Point nuclear power plant, which is located next-door to FitzPatrick.

NRC Keeps an Eye on Gulf Coast Flooding

Victor Dricks
Senior Public Affairs Officer
Region IV

Torrential rains have been battering the Gulf Coast since Friday, but have not adversely affected any of the nuclear power plants in Louisiana, Mississippi, or Arkansas.

louisiana map_sealThough skies have now cleared over Baton Rouge, the area has been especially hard hit by flooding. But this has had no significant impact on the River Bend nuclear power plant, about 25 miles northwest of the city, or the designated routes that would be used to evacuate the public in the event of a nuclear emergency.

The Waterford 3 nuclear plant, located in Killona (about 25 miles west of New Orleans), has been similarly unaffected. “We’ve had some heavy rain here over the weekend but there has not been any real impact on the plant,” said NRC Resident Inspector Chris Speer.

Flooding is one of the many natural hazards that nuclear power plants must be prepared for. Every nuclear power plant must demonstrate the ability to withstand extreme flooding and shut down safely if necessary. Most nuclear power plants have emergency diesel generators that can supply backup power for key safety systems if off-site power is lost.

All plants have robust designs with redundancy in key components that are protected from natural events, including flooding. These requirements were in place before the Fukushima accident in Japan in 2011, and have been strengthened since.

As of Tuesday, Arkansas Nuclear One, in Russellville, has gotten about five inches of rain since Friday, NRC Resident Inspector Margaret Tobin said. “It’s a little muddy at the site, but that’s about it.”

At Grand Gulf plant in Mississippi, 20 miles southwest of Vicksburg, only light rain has been reported. “We actually had very little rain at the site, compared to what was expected,” said Matt Young, the NRC’s Senior Resident at the plant.

The NRC is closely following events and getting periodic updates from the National Weather Service on conditions that might affect any of the Gulf Coast nuclear plants. Additionally, the resident inspectors are monitoring local weather conditions to remain aware of conditions that could affect continued safe operations of the plants.

REFRESH: The Power of Power Uprates

Since this blog post first ran in December 2011, the NRC staff has approved 16 additional power uprates, increasing the nuclear fleet’s output by an additional 1300 megawatts electric. An additional three are under review (for the three reactors at Browns Ferry), and the staff expects to receive an additional 10 uprate applications through the end of September 2017.  David McIntyre

Neil Sheehan
Public Affairs Officer
Region
I

refresh leafMuch news space has been devoted over the years to the prospects for new reactors in the U.S. However, new reactors are not the only way the nation’s share of nuclear-generated electricity can be increased — and it doesn’t involve earth-movers, the construction of new buildings or other changes visible to the casual observer.

Another option available to nuclear power plant owners is to pursue a power uprate, which essentially means an increase in the maximum amount of power a reactor can generate. But before a power uprate can be implemented, it must first undergo a thorough review by the NRC.

Take for example, the NRC’s approval of a 15 percent power uprate for the Nine Mile Point 2 nuclear power plant in upstate New York. That approval was the culmination of an NRC review that began with the submittal of the application on May 27, 2009.

During the course of the agency’s evaluation of the proposal, NRC staff scrutinized data regarding the proposal and posed dozens of technical questions to the plant’s owner, Constellation. They included queries about the effects of greater stresses on piping and the plant’s steam dryer, a component at the top of the reactor vessel, as a result of operations at higher power levels.

Power_Uprates_past-current-future (002)The NRC does not proceed to a final decision until all such questions are answered to our full satisfaction.

Uprates are not a new development. In fact, the NRC approved the first uprate back in 1977 and has to date approved 140 such applications. All told, the uprates have led to an increase in power output nationwide of about 6,000 megawatts electric.

There are three different kinds of power uprates: “measurement uncertainty recapture” uprates, “stretch” uprates and “extended” uprates. Here’s a brief description of each:

Measurement uncertainty recapture uprates – They involve an increase of less than 2 percent and are achieved by implementing enhanced techniques for calculating reactor power levels. State-of-the-art devices are used to more precisely measure feedwater flow, which is used to calculate reactor power.

Stretch uprates – The increases are typically between 2 and 7 percent and usually involve changes to instrumentation settings but do not require major plant modifications.

Extended uprates – Power boosts of this type have been approved for increases of up to 20 percent. They usually involve significant modifications to major pieces of non-nuclear equipment, such as high-pressure turbines, condensate pumps and motors, main generators and/or transformers. The Nine Mile Point 2 uprate would fall into this category.

For more information on power uprates, visit the NRC web site.

Part II: How the NRC Uses a Defense-in-Depth Approach Today to Protect the Public

Mary Drouin
Senior Program Manager
Division of Risk Assessment, Performance and Reliability Branch

Defense-in-depth is a central theme in the NRC’s regulatory oversight of the nuclear power industry. As our agency historian, Tom Wellock, discussed in Monday’s post, the concept of defense-in-depth emerged during the trench warfare of World War I. The idea of multiple lines of defense was applied to nuclear safety in the 1950s as the leading concept for protecting the public from the consequences of a nuclear reactor accident.

The NRC’s predecessor agency, the U.S. Atomic Energy Commission, spelled out defense-in-depth in a 1957 report called WASH-740, Possibilities and Consequences of Major Accidents in Large Nuclear Power Plants. “Should some unfortunate sequence of failures lead to destruction of the reactor core … no hazard to the safety of the public would occur unless two additional lines of defense were also breached,” the report said.

These words are at the heart of defense-in-depth as it has been practiced for six decades: multiple layers of defense to protect against accidents and their effects to ensure the risk to the public is acceptably low.

In a recent report issued this spring, Historical Review and Observations of Defense-in-Depth (NUREG/KM-0009), the NRC looks at how the concept has evolved in practice over the years. It also includes views from other government agencies and the international community.

As the report explains, defense-in-depth recognizes that our knowledge is imperfect. Although we plan for all conceivable accidents, the unexpected may still occur. Even if we have anticipated an event, its characteristics and impacts may be unpredictable. Our design and operation of nuclear plants need to be robust enough to compensate for this lack of knowledge. Defense-in-depth offers multiple layers of protection in case one or more layers fail.

So we don’t just rely on preventing an accident; we also need strong defenses to mitigate the effects of any accident that does occur. This applies to nuclear power plants, waste management and security as well.

In practice, defense-in-depth addresses three principles that should be factored into the design and operation of systems and components to provide additional confidence that an accident would not compromise the defensive layers:

  • Redundancy means more than one component performs the same function – for example, having multiple pumps instead of a single one;
  • Independence means these multiple components rely on separate and distinct attributes to function – the multiple pumps have separate piping from the water tank to where they discharge, and are housed in separate compartments; and
  • Diversity means the multiple components performing the same function rely on different design features to operate – motor-driven pumps versus steam-powered pumps.

dindgraphicIn reactor safety, the layers of defense might be:

  • Maintain reactor stability by limiting the ability of events to disrupt operation (with protective measures such as fire-safe or flood-tight doors, seismically designed buildings)
  • Protect the reactor should operation be disrupted (emergency reactor core cooling with redundant pumps)
  • Barrier integrity to guard against a release of radioactivity to the environment (leak-tight containment structures, filtered vents, containment sprays) and
  • Protect the public if a release does occur (emergency preparedness plans)

This versatile framework can apply whether the risk to the public comes from the reactor, spent fuel pool, nuclear waste or security threats.

Defense in Depth Part I: A War for Safety

Thomas Wellock
Historian

One hundred years ago the French and German armies of World War I devised a new defensive strategy called “defense in depth.” Its aim was to prevent an enemy breakthrough of an army’s frontline with a deep system of interconnected trench lines and strong points.

Defense in depth circa WWI. Photo courtesy of the Library of Congress

Defense in depth circa WWI. Photo courtesy of the Library of Congress

Popularized in all its desperation and grisly effectiveness in films such as All Quiet on the Western Front, defense in depth has become the NRC’s official metaphor in the battle to protect the public from radiation hazards. It is the key concept governing nuclear safety in using multiple strategies in safety-system design, operations, and emergency procedures and planning.

The NRC’s use of the term has roots in the Manhattan Project of World War II. Military metaphors seemed particularly apt for those charged with ensuring the safety of the early plutonium production reactors at Hanford, Washington. They worried about the potential for a reactor “catastrophe” from a radiation release of “explosive violence.” Their solution was to erect multiple “lines of defense” of trained operators and emergency personnel, carefully sealed fuel rods, shielding walls, backup cooling and power systems, and even a backup to the backup shutdown system—a final solution so drastic that it would destroy the reactor to save the operators lives. Fittingly, its moniker derived from another military term — the “last ditch” safety device.

After the war, the “lines of defense” in reactor safety were categorized into functions by Atomic Energy Commission safety committees:

  1. Features that made a reactor inherently safe;
  2. “Static,” or physical, barriers, such as containment buildings, were to halt the escape of radiation; and
  3. Active systems were to shut down and cool the reactor in the case of unusual conditions.

While the AEC’s safety approach became more coherent, there was no consensus among experts over the relative importance of each category. Some experts focused mostly on a design’s physical barriers, while others gave weight to all three categories and included reactor operation too.

Over time, “defense in depth” replaced the scattered concept of “lines of defense.” Its first use appears to have been in 1958 to describe safety design in the plutonium extraction processes at Hanford. In a 1965 letter to Congress, AEC Chairman Glenn Seaborg applied the term to civilian reactor safety as an accident prevention and mitigating strategy.

It provided, he wrote, “multiple safeguards against the occurrence of a serious accident, and for containment of fission product release.” The term stuck.

But the story continues. The Office of Nuclear Regulatory Research has published a report on the history of defense in depth up to the present, which covers the term’s application to the whole nuclear fuel cycle. It’s a fascinating look at how this bedrock safety concept has evolved under the influence of events and new knowledge. We’ll have more on this report on Wednesday.

 

 

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