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I've noticed that quite a few commercial nuclear reactors have an extended outage (they close down for several months) some time late in their third decade, and the maintenance works during the closure involve significant investment. This cost has been high enough in some cases that the reactor has permanently shut down rather than undergo the works (e.g. the Vermont Yankee, Dec 2014) because the business case just didn't stack up.

What are the works involved, in terms of scope and cost; how much do these vary depending on the type of reactor (PWR, BWR, ...)?

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  • $\begingroup$ I though VT Yankee was shut down for other economic and political reasons, not because there was a large investment coming up. $\endgroup$
    – Olin Lathrop
    Apr 24, 2015 at 13:21
  • $\begingroup$ @OlinLathrop much nonsense was talked in the press, but in the end, they did get their licence extension, and it really does look as straightforward as it not being economic for them to refurb and reopen, because depressed domestic gas prices have pushed down wholesale electricity prices in the area. Now, given nuclear is near-zero short-run marginal costs given the taxpayer bears the third-party indemnity risk, that's an interesting turn of events, and is partly why I'm asking this question. $\endgroup$
    – 410 gone
    Apr 24, 2015 at 14:59

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Here is a good short article on the topic.

It says that reactors can be refueled in as little as 10 days, but outages typically last an average of two months because non-critical maintenance work is typically differed until a refueling outage. This makes sense, as most systems are safer and easier to work on when they are not running.

Standard non-critical maintenance on a steam power station would include:

  • Bearing replacement
  • Replacement of corroded lines
  • Cleaning scale from pipes, valves and heat excahngers
  • Electrical breaker and relay replacement
  • Control system upgrades
  • VFD upgrades
  • Sensors and pressure gauge, replacements
  • Turbine inspection
  • Boiler inspection
  • Insurance inspections
  • Lots of paperwork

US NRC Regulations may be a good place to start looking for nuclear specific maintenance.

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  • $\begingroup$ Thanks, but that's the answer to a different question, not the question I asked. $\endgroup$
    – 410 gone
    Mar 15, 2016 at 9:11
  • $\begingroup$ Well I felt that knowing that the tasks are mostly steam plant related rather than nuclear specific was helpful. I have added to the answer. $\endgroup$
    – ericnutsch
    Mar 15, 2016 at 23:40
  • $\begingroup$ @EnergyNumbers Your question would take a lot of time and space to answer it entirely. $\endgroup$
    – Drew_J
    May 16, 2017 at 20:05
  • $\begingroup$ @Drew_J and yet no one has been able to use a paragraph or two to even start to address the actual question I asked, which is specifically about the major works happen when a plant's around 30-40 years old. $\endgroup$
    – 410 gone
    May 17, 2017 at 5:50
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I think this is a question better for the bean counters instead of Engineering. I worked as an Intern at a natural gas fired power plant (about 500 MW total capacity) and profits were the critical factor in determining what happens at a plant. Fuel was a pass-thru cost but capital and maintenance projects were different. Capital was considered re-investment but maintenance was an expense. Capital projects were approved if they invested enough value to the plant to be worth it, unplanned repairs counted against the plant. As Ericnutsch stated above, minor repairs and temp fixes and inspections are what make overhauls and nuke refueling take longer than you might think.

Things like a leaking tube in a heat exchanger are a good example. You can isolate the heat exchanger to keep the unit operational but at a loss of efficiency so you may downgrade or limit the power output until an overhaul can repair the tubes. In this example what they usually do is isolate the heat exchanger, plug the tubes then once a set percentage of tubes are plugged you have to downgrade the unit until the entire tube rack can be replaced.

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