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Science 101 – What is Nuclear Fuel?

Kevin Heller
Reactor Systems Engineer, Division of Safety Systems

science_101_squeakychalkIn earlier Science 101 posts, we told you about nuclear chain reactions and how they are used to generate electricity in reactors. This post focuses on the fuel that reactors use to create those chain reactions.

You may recall that nuclear fuel rods get hot because of the nuclear reaction, and that heat is key to generating electricity. But what exactly are these fuel rods?

Nuclear fuel starts with uranium ore, which is found in the ground throughout the world. For now, we’ll just say that uranium ore goes through several steps to be processed and manufactured into nuclear fuel. In a future Science 101 post, we’ll talk more about the process of turning uranium ore into fuel pellets.

fuelpelletEach pellet is about the size of a pencil eraser. These pellets are stacked inside 12-foot long metal tubes known as fuel cladding. The tubes are sealed on each end to form a fuel rod, and between 100 and 300 fuel rods are arranged in a square pattern to form a fuel assembly. The number of fuel rods used to make a fuel assembly depends on the type of reactor the assembly will be used in and the company that makes the fuel.

fuelrodsWhile the assemblies are very long (about 12 feet), they are less than 1 foot wide. The assemblies have special hardware at the top and bottom and at intervals in between to keep the fuel rods firmly held and evenly spaced. Fuel assemblies are only slightly radioactive before they are placed into a reactor core. Typically, a reactor core will have between 150 and 250 fuel assemblies.

We talked before about the form of uranium that is important in commercial nuclear reactors. It is an “isotope,” or an atom with a very specific number of neutrons, known as U-235. Part of the process of turning uranium ore into nuclear fuel is enrichment—which increases the amount of U-235 relative to the other isotopes naturally found in uranium. Under the right conditions in a reactor, neutrons will cause U-235 atoms to fission, or split. This leaves two new, different atoms and a couple of neutrons. These new neutrons will then cause other U-235 atoms to fission, forming a chain reaction.

As U-235 atoms fission, energy is released in the form of heat. That heat creates steam which turns a turbine to create electricity. After a few years, there is considerably less U-235 in the fuel. If the amount of U-235 were to drop too low, there would no longer be enough to keep a chain reaction going. So every 18-24 months about one-third of the fuel in a reactor core is removed and replaced with new, fresh fuel. The used fuel is often called “spent fuel.”

Spent fuel is very hot and very radioactive. The atoms created by the fission process are unstable at first and emit particles that create heat. Therefore, spent fuel must be handled and stored carefully, and under controlled conditions. We’ll talk more about spent fuel and how it is managed in a future Science 101 post.

The Yucca Mountain Safety Evaluation Report: One Step of a Long Journey

David McIntyre
Public Affairs Officer

The NRC staff has now completed its safety evaluation report (SER) on the proposed nuclear waste repository at Yucca Mountain in Nevada, with the publication of Volume 2 and Volume 5. This is an important milestone – however, completion of the SER neither finishes the review process nor represents a licensing decision.

yucca

To recap: The NRC closed its review of the application in fiscal year 2011. (The full story is here.) The NRC staff published Volume 1 of its five-volume SER in August 2010. Volume 1 covered general information about the application. The NRC staff subsequently published three technical evaluation reports to capture the work it had already done on volumes 2, 3 and 4, though without any regulatory conclusions.

In August 2013, the U.S. Court of Appeals for the District of Columbia Circuit ordered the NRC to resume the licensing process using leftover money appropriated from the Nuclear Waste Fund. So the agency resumed its work on the formal safety evaluation report. We published Volume 3, covering repository safety after permanent closure, in October 2013. Volume 4, on administrative and programmatic requirements, was published in December. Volume 2, repository safety before permanent closure, and Volume 5, license specifications, complete the SER and the technical part of the licensing review.

That technical review concluded DOE’s application meets the safety and regulatory requirements in NRC’s regulations, except for DOE’s failure to secure certain land and water rights needed for construction and operation of the repository. These issues were identified in Volume 4.

Bottom line: the SER recommends that the Commission should not issue a construction authorization until DOE secures those land and water rights, and a supplement to DOE’s environmental impact statement (EIS) is completed.

The land DOE still needs to acquire is owned by three federal agencies: DOE’s National Nuclear Security Administration, the Department of the Interior and the Department of Defense. Legislation was introduced in Congress in 2007 to appropriate the land for the repository, but it did not pass. The water rights DOE needs are owned by the state of Nevada, which refused to appropriate the water in 1997. Litigation challenging that refusal is stayed.

yuccatunnelWhen the NRC resumed its licensing review in response to the appeals court, the agency asked DOE to supplement the EIS to cover certain groundwater-related issues. DOE declined to do so. The NRC staff is prepared to develop the supplement if the Commission tells it to.

Even if the EIS is completed, two more steps are needed before a licensing decision can be made. The adjudication of nearly 300 contentions filed by Nevada and other parties challenging the repository was also suspended in 2011. Reviving and completing this hearing will require more funding from Congress. Finally, the Commission must review issues outside of the adjudicatory context. Only then would the Commission decide whether to authorize construction.

So yes, completion of the SER is a major step, but there are many more ahead before the NRC can say yea or nay to Yucca Mountain.

 

Nuclear Power Plants Ready For Major Winter Storm

Neil Sheehan
Public Affairs Officer
Region I

winterstorm

Update: The Pilgrim nuclear power plant experienced an automatic shutdown, or scram, early Tuesday amid Winter Storm Juno (as dubbed by the Weather Channel). Here is additional information:

Entergy had sequestered staff on-site prior to the storm. The NRC also had an inspector stationed on-site overnight. Reactor power was reduced to 75 percent overnight, per procedures, as the grid experienced voltage fluctuations. Operators started the plant’s two emergency diesel generators and transferred electrical loads for safety systems to those on-site power supplies due to concerns with off-site power.

One of two 345-kilovolt offsite lines was deenergized due to weather concerns. At about 52 percent power, the second 345-kilovolt line that provides off-site power to the plant tripped, resulting in a reactor shutdown, or scram, at about 4 a.m. (Nuclear power plants not only generate power and send it to the grid, they also receive a certain amount of power from the grid for operational purposes.)

A third off-site power line, a 23-kilovolt line, remains available. However, the emergency diesel generators for now remain the primary source of power for safety systems. The reactor was safely shut down, with plant safety systems performing as expected. The exact cause of the loss of the 345-KV power lines is still being investigated.

Entergy intends to take the reactor to “cold” shutdown. NRC inspectors will continue to monitor plant activities and efforts to restore off-site power, as well as any troubleshooting and repair work.

 

The atmospheric stars have aligned once again to produce a powerful mid-winter storm aimed squarely at coastal areas in the Northeastern United States. Officials in a broad swath stretching from New Jersey to Maine have been warning residents to prepare for a blizzard that could produce prodigious amounts of snow, hurricane-force winds and dangerous travel conditions.

There are several nuclear power plants in the storm’s path and the personnel at those facilities will not be sitting back and simply awaiting its arrival. Plant procedures call for multiple checks and preparations in advance of such a winter blast.

Among other things, plant personnel will ensure that doors designed to prevent flooding are ready to perform their task; fuel oil tanks for emergency generators are appropriately filled; and the site grounds do not have loose objects which could become airborne amid strong winds and cause damage.

On a related note, the NRC will be monitoring those preparations and stationing inspectors to keep watch on the plants as they weather the storm. An inspection procedure and checklist dealing with adverse weather protections will guide the inspectors as they conduct those assessments.

It’s important to note that all nuclear power plants have technical specifications that dictate how they have to respond to a significant storm. As an example, if wind speeds are in excess of specified limits, a plant would have to shut down.

Safety at nuclear power plants is never taken for granted, and that is certainly true when storms can present additional challenges for operators. The NRC will be keeping watch until the most potent storm of the winter of 2014-15 to hit the Northeast thus far has headed out to sea.

 

Pursuit Of Metal Can be Costly, If Not Deadly

Neil Sheehan
Public Affairs Officer
Region I

Copper is a valuable metal that, increasingly in recent years, has been the target of thieves hoping to pocket some quick cash by selling it to scrapyards.

copperPiping made with the material has been stolen from unoccupied homes and businesses. Copper downspouts have been snatched from churches. Even cemeteries have not been immune, as copper flag holders placed at the graves of veterans have been plundered. Cable-TV network CNBC reported in 2013 that copper thefts were ‘like an epidemic’ sweeping the nation.

Unfortunately, the energy sector has not been immune. In early January of this year, the Orlando Sentinel reported that thieves in central Florida had made off with about 42 miles of copper wire.

Non-radioactive copper wire also has been stolen from or close to switchyards located near several U.S. nuclear power plants. (No thefts from the “Protected Area,” or high-security, zone at the plants have occurred, and robust security measures help ensure that should continue to be the case.)

Some examples of the metal pilfering:

  • More than 1,400 pounds of scrap copper were stolen from a storage building near a switchyard at the Beaver Valley nuclear power plant in April 2013. The building was located outside the security perimeter at the western Pennsylvania facility. Police subsequently arrested a mother and son in connection with the incident.
  • New York State Police announced in January 2013 that two workers at the Indian Point nuclear power plant had been charged with stealing several thousand pounds of copper and other scrap from the site. Tens of thousands of dollars from the sale of the spools of excess wire were pocketed by the now former employees, police said.
  • In August 2012, police arrested four individuals who made off with copper from multiple electrical substations in the Philadelphia suburbs, including one at the Limerick nuclear power plant. The theft almost cost one of the thieves his life in a near-electrocution.

Between security patrols and other NRC-required measures, U.S. nuclear power plants are among the most fortified parts of the energy infrastructure while switchyards have not been, generally speaking, subject to the same level of security attention. That said, the good news is the utilities that own and operate the switchyards have been taking steps to deter future thefts.

For instance, Con Edison, based in New York, announced last year that it had begun using markings on copper wire only visible under ultraviolet light, making it easier to track where the material originated and thereby identify theft suspects.

Also, Pennsylvania-headquartered PPL, which operates the Susquehanna nuclear power plant, said it was bolstering security measures at substations and notifying scrapyard owners to be on the lookout for large quantities of copper wire that could have been taken from switchyards. Further, FirstEnergy and Ohio Edison said last September that they planned to install security fencing and monitoring systems at some of its substations in an effort to deter metal thieves.

As with all issues that surface at U.S. power reactors, the NRC staff is always made aware when theft incidents occur, and the agency’s security and safety experts would engage plant operators on potential implications and preventive actions.

The sudden loss of power from a nearby switchyard could potentially impact the operations of a nuclear power plant, making it a very bad idea. But it’s also illegal and potentially fatal for the thief. As PPL put it when it rolled out its campaign, “Copper – It’s not to die for.”

 

Keeping Tabs on Diablo Canyon’s Evolving Seismic Situation

Lara Uselding
Public Affairs Officer
Region IV

diabloThe NRC has added two items to the growing list of documents on seismic issues related to the Diablo Canyon Power Plant, near San Luis Obispo, Calif. Our Region IV office in Arlington, Texas, sent the plant operator, PG&E, an inspection report and our headquarters Office of Nuclear Reactor Regulation in Rockville, Md. sent PG&E a letter about the plant’s seismic hazard reevaluation due in March 2015.

The Region IV inspection report discusses the agency’s independent assessment of the operability determination completed by PG&E associated with its September report on the Shoreline and other faults near the plant. PG&E provided the report to the state under California Assembly Bill 1632. That bill required the report so the California Energy Commission could assess if California’s largest baseload power plants are vulnerable to a seismic event as those plants age.

The NRC did not request this analysis, but PG&E committed to keep us updated on any new information that would indicate the Shoreline fault is more energetic or capable than was presented in the January 2011 Shoreline Fault Report. PG&E further committed to provide the NRC with an interim analysis of any new Shoreline-related information before the post-Fukushima evaluations are due in March 2015.

Our regional review of PG&E’s operability determination indicates there is considerable design margin for the plant’s systems, structure, and components. The staff did not identify any concerns with PG&E’s determination that the plant is operable. The analysis adds to the evidence that the plant’s systems, structures, and components would function properly after an earthquake and not pose undue risk to public health and safety.

Our letter from headquarters confirms PG&E will incorporate the September report’s findings into its ongoing, post-Fukushima, full seismic re-analysis due in March 2015. The NRC believes this more rigorous analysis will provide the most accurate assessment of faults affecting the site.

The bottom line is that the effect of earthquakes has been extensively evaluated during the construction, licensing, and operation of the plant. Diablo Canyon’s systems, structures, and components are designed to withstand the area’s earthquakes and perform their safety functions.

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