U.S. NRC Blog

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What gets “upped” in an uprate?

Every year, a few nuclear power plants ask the NRC for permission to boost their power output in what’s called an “uprate.” The principles behind an uprate are fairly simple.

First of all, a plant’s NRC license sets a limit on how much heat the reactor core can generate. A hotter core creates more steam, which then runs a turbine at a higher rate to generate more electricity (we’ll get to how much more electricity in a moment). The basic heat limit is a key part of figuring out how the plant’s safety systems would protect the public in an emergency situation. The NRC carefully analyzes uprate requests to ensure the plant’s systems will continue to function properly at the proposed higher power level.

There are three uprate categories, starting with an increase of only a percent or two. A plant does this by installing more accurate instruments to determine how much water is going into the reactor. Plant operators must be sure they’re sending the correct amount of water through the core to maintain the proper power level. Since older instruments are slightly less accurate, a pre-uprate power level will be slightly lower to ensure safety. If plant operators are more certain how much water’s going into the core, they can be more certain how much power the core generates and therefore a slightly higher power limit is still safe and appropriate.

The second category is a “stretch” uprate, which increases the power level between two and seven percent. This is done by changing some instrument settings, along with redesigning the core to use slightly more of the type of uranium that undergoes a chain reaction. This redesign increases the core’s output.

An “extended” uprate, the third category, adds from seven to as much as 20 percent to a plant’s power output. It’s the most complex of the uprates, since it involves improving major systems such as pumps, turbines and generators, as well as using a revised core design. Updating so many systems with new parts requires the plant to do a lot of careful analysis to show the uprate can be done safely.

Several factors come into play when figuring out how much more electricity a nuclear power plant will produce after an uprate. Updating the non-nuclear side of the plant, such as the generator itself, can improve the plant’s ability to transform the reactor’s heat into electricity. A nuclear power plant also needs electricity to run its systems, and that comes from the transmission grid, offsetting some of the plant’s output. The plant’s needs can remain relatively steady after an uprate, however, so the increased output goes straight to the grid.

Putting all this together means that if a plant increases its reactor core output by 15 percent, for example, its net electricity output can actually increase a little more than 15 percent.

The NRC’s uprate reviews last at least nine months, and normally take about a year and a half for extended uprates. Our evaluations cover much more than changes to the fuel or large components such as pumps and turbines. We examine the uprate’s impact on the plant’s instruments and control systems, and we also look at how the increased power level comes into play for analyzing possible accidents and their consequences. We’ll also ensure the plant will appropriately revise its procedures and train its personnel.

Over the past few decades, uprates have safely and appropriately added the electricity generating equivalent of approximately seven new reactors to the U.S. power grid.

You can visit our website for more details on uprates. For an earlier post on the uprate at Nine Mile Point nuclear power plant, go here .

Scott Burnell
Public Affairs Officer

4 responses to “What gets “upped” in an uprate?

  1. Lorri December 29, 2012 at 10:51 am

    Very great post. I just stumbled upon your blog and wanted to mention that I’ve truly enjoyed browsing your blog posts. After all I will be subscribing on your feed and I hope you write again very soon!

  2. Bruce Behrhorst July 31, 2012 at 7:20 pm

    “There are no examples of U.S. nuclear power plants being licensed for co-generation, desalination or refining of hydrogen-based fuels.”

    I understand the statement above. If I may stay with the issue I raised about links to Nuke Co-Gen under cursory search for: “Co-Generation or NRC terms” & under NEUREG or ADAMS only see:
    [Next Generation Nuclear Plant Phenomena Identification and Ranking Tables (PIRTs) (NUREG/CR-6944)] 6 volume set.
    Many links low quality no relation to subject matter on searches. The Vol 6 set seem limited any links to Japanese evaluation studies for Next Gen NPP-PIRT??

  3. Bruce Behrhorst July 25, 2012 at 6:01 pm

    Hi, wanted to know if you have any links to NRC policy on Co-Generation such as for example; de-salination operation licenses (overview literature only) or Stream Methane Reformation (SMR) for H2 gas fuels.
    Does an uprate-extended category on a NPP fit Co-Generation license? Or is Co-Gen a mortal sin as far as NRC is concerned?

    thanks…

    • Moderator July 30, 2012 at 12:30 pm

      There are no examples of U.S. nuclear power plants being licensed for co-generation, desalination or refining of hydrogen-based fuels. If a plant wished to amend its license for any of those activities, it would have to provide the NRC a great deal of supporting information and analysis to prove such an activity could be done safely. The NRC would then take a significant amount of time reviewing such an application before deciding whether the activity would be acceptable.

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