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Category Archives: Operating Reactors

NRC Inspectors Head to Indian Point 3’s Electrical Supply Room

Neil Sheehan
Public Affairs Officer
Region I

Dousing the fire that ensued after one of the Indian Point 3 nuclear power plant’s main transformers failed on the evening of May 9th required substantial amounts of water, as well as foam. The water was applied by the automatic fire-suppression system for the transformer and by the on-site fire brigade and firefighters from off-site who provided assistance.

indianpointOne of the follow-up concerns for the NRC is that during the event, some water was found on the floor of an enclosed room inside the plant housing electrical supply equipment. The power that flows through that equipment is used to operate plant safety systems and components.

The equipment was not affected by the water during the May 9th event, and the plant was safely shut down. The plant remains out of service while work to install a replacement transformer is carried out.

In order to better understand what occurred, the NRC is launching a Special Inspection at the plant today. The three-member team will evaluate, among other things, how the water – apparently totaling an inch or two on the room’s floor — ended up in the room; and the potential for a significantly larger volume of water to build up and adversely impact the electrical equipment.

The NRC applies risks insights and specific knowledge of plants when determining whether to perform a follow-up inspection and what type. In this case, the NRC decided it was appropriate to conduct a Special Inspection, the first level of “reactive” reviews performed in response to an event. The agency performs such inspections to independently evaluate and assess what occurred during an event, as well as any plans by the plant’s owner to fix related problems.

In addition to the Special Inspection, the NRC is continuing to review the transformer failure, operator and equipment response during the event, and other issues.

A report containing the findings of the Special Inspection will be issued within 45 days after the formal conclusion of the review.

Indian Point Transformer Fire

Diane Screnci
Senior Public Affairs Officer
Region I

NRC inspectors are following up on a transformer fire at Indian Point Energy Center over the weekend. The NRC Resident Inspectors for Indian Point – who work at the plant on a daily basis – are monitoring activities at the site while plant workers are troubleshooting and looking for the cause of the fire on the Unit 3 main transformer.

The transformer fire happened at about 6 p.m. on Saturday night. A sprinkler system initially extinguished the flames, but it reignited and was put out by the onsite fire brigade and local fire departments. The fire caused the reactor to automatically shut down, as designed. All safety systems worked as designed. There was no danger to the public and no release of radiation. The reactor is stable. Unit 2 continues to operate at full power.

Plant operators declared an “unusual event” – the lowest of the emergency classifications – in accordance with plant procedures. All plants have procedures, approved by the NRC, that dictate how events are classified to ensure appropriate steps are taken to respond to the event and to communicate the event to local and state agencies and the NRC.

In addition to cooling provided by fans, the main transformer is also cooled by oil flowing through it. On Saturday, oil from the transformer spilled into the plant’s discharge canal. Entergy has been working to determine how much oil was spilled.

The transformer that failed carries electricity from the main generator to the electrical grid. The same type of equipment can be found at any plant that generates electricity. It is on the electrical generation side of the plant – not the nuclear side.

As far as next steps go, plant employees will determine what happened and why. They will repair or replace any equipment that was damaged in the fire. The plant can restart when ready. NRC inspectors will be monitoring Entergy’s actions every step of the way, ensuring workers are taking all appropriate actions.

As we do with any event at a plant, we’ll continue to review what happened and how the plant responded. If need be, we’ll send additional inspectors to the site to look further into the event and its effects.

Plenty of Progress to Report on Fukushima-related Enhancements

Scott Burnell
Public Affairs Officer

fukushimaThe NRC’s technical staff, industry executives and a public interest group will brief the Commissioners Thursday on the agency’s efforts to implement what we’ve learned from the Fukushima nuclear accident. The bottom line is the NRC is ahead of schedule on several fronts.

Some of the best news involves U.S. reactors meeting requirements from two of the NRC’s Fukushima-related Orders issued in March 2012. By the end of this spring, almost a quarter of the U.S. fleet will comply with the Mitigation Strategies and Spent Fuel Pool Instrumentation Orders. We expect more than half the fleet will meet those Orders by the end of December, which is a full year before the Orders’ deadline.

Every U.S. reactor will comply with the instrumentation requirements by the December 2016 deadline. Every reactor will also comply by that time with a major Mitigation Strategies requirement – additional, well-protected onsite portable equipment to support key safety measures if an extreme event disables a plant’s installed systems. The U.S. industry has already set up two response centers with even more equipment that can be transported to any U.S. reactor within 24 hours. By the time we say good-bye to 2016, almost every reactor will also have made all modifications needed to use those portable systems. In preparing to meet the deadlines, U.S. reactors have already enhanced their ability to keep the public safe.

About a dozen plants will have made all those modifications except changes closely related to the third Order, which requires Hardened Vents for reactors with designs similar to those at Fukushima. These vents would safely relieve pressure in an emergency and help other systems pump cooling water into the core. All the reactors subject to the Order have completed plans for the first set of vent enhancements or installation of new vents.

The NRC staff finished reviewing these plans earlier this month, ahead of schedule, and issued written evaluations to each plant. The agency is also about ready to issue guidance on how these plants can meet the second part of the Order, which involves an additional vent or other methods to protect the structure surrounding the reactor.

The staff’s presentation will also cover topics including revising the NRC’s rules in these areas, as well as the ongoing effort to re-evaluate flooding hazards for all U.S. nuclear power plants. The NRC’s regional offices will provide their perspective on the overall implementation effort’s progress.

REFRESH — What is a Reactor Trip and How Does it Protect the Plant?

Samuel Miranda
Senior Reactor Systems Engineer

Note: Last week, the Prairie Island nuclear power plant “tripped.” So, it seemed like a good time to revisit a blog post we did two years ago on the subject.

refresh leafOn occasion, a nuclear power plant will “trip,” meaning something happened that caused the reactor to automatically shut down to ensure safety. In other words, a trip means a plant is doing what it’s supposed to do. Let’s look at the term a bit more closely.

Key operating parameters of a nuclear power plant, such as coolant temperature, reactor power level, and pressure are continuously monitored, to detect conditions that could lead to exceeding the plant’s known safe operating limits, and possibly, to damaging the reactor core and releasing radiation to the environment.

If any of these limits is exceeded, then the reactor is automatically shut down, in order to prevent core damage. In nuclear engineering terms, the automatic shutdown of a nuclear reactor is called a reactor trip or scram. A reactor trip causes all the control rods to insert into the reactor core, and shut down the plant in a very short time (about three seconds).

How do control rods do their job?

pwr[1]The control rods are composed of chemical elements that absorb neutrons created by the fission process inside the reactor. They are placed methodically throughout the nuclear reactor as a means of control. For example, as the control rods are moved into the reactor, neutrons are absorbed by the control rods and the reactor power is decreased. Inserting them all at the same time shuts down the reactor. Control rods can also be inserted manually, if necessary.

The plant operator then determines the reason for the trip, remedies it and, when it’s determined to be safe, restarts the reactor. So, while not common, a reactor trip is an important way to protect the components in a nuclear power plant from failing or becoming damaged.

REFRESH is an occasional series where we re-run previous blog posts. This post originally ran in December 2012.

 

 

Western U.S. Reactors are Completing Their Seismic Picture

Lauren Gibson
Project Manager
Japan Lessons-Learned Division

An ongoing lesson from 2011’s Fukushima Dai-ichi accident involves U.S. reactors better understanding their earthquake hazard. Reactor owners in the Western parts of the country have had to assemble a particularly complex jigsaw puzzle of seismic information. They’ve just sent the NRC their detailed re-analysis.

seismicgraphicThe graphic shows the three pieces of information U.S. reactor owners have used to analyze their specific hazard:

  • Where quakes are generated (seismic source)
  • How the country’s overall geology transmits quake energy, (ground motion/attenuation) and
  • How an individual site’s geology can affect quake energy before it hits the reactor building (site amplification).

Central and Eastern U.S. reactors benefitted from region-wide updated earthquake source information and a model of quake energy transmission for the first two pieces. Plants west of the Rockies, however, had to deal with the West’s more active and interconnected faults.

Columbia, Diablo Canyon Part I and Part II and Palo Verde used the Senior Seismic Hazard Analysis Committee (SSHAC) approach to develop site-specific source models and ground-motion models. This group of independent seismic experts develops guidance on major seismic studies such as this. The group has met several times the past few years to ensure the Western plants properly conduct and document their seismic activities.

The NRC carefully considers SSHAC comments and recommendations before the agency comes to its own conclusions on seismic issues. We’re currently evaluating the Western plants’ reports and will issue our short-term screening and prioritization review later this spring.

As for the Central and Eastern U.S. plants’ March 2014 submittals, we screened them to determine what other actions the plants might have to take. Plants that have more to do were grouped into three priority groups with staggered deadlines. Many of those plants submitted additional analyses in December 2014, and the NRC continues reviewing both that information and the March 2014 submittals.

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