Forum: Author Hangout

Heard a BBC broadcast about the nuclear power plant in Ukraine - saying the plant shut down yesterday for a while when power from the grid was shut off. The danger, the report said, was that even if the nuclear plant is turned off, the "core" will continue to be hot and power from the outside is necessary to keep it cool. Without power from the outside, there was danger of a meltdown.
I'm not sure I'm remembering all of those details correctly. But the question is - is that true at U.S. nuclear power plants as well. In the event of a nuclear or solar event that knocks out the grid, how long could a nuclear plant go without meltdown?

m remembering all of those details correctly. But the question is - is that true at U.S. nuclear power plants as well. In the event of a nuclear or solar event that knocks out the grid, how long could a nuclear plant go without meltdown?

There are several nuances they left out. Chief among them is design. The Ukrainian plants are all Russian design VVER. There are four generations of those as well. The Gen3+ is considered safe by the west and has been installed in several countries outside the former USSR.

It is a form of pressure water reactor or PWR.

All PWR's require cooling water, particularly borated water and power to pump that water.

They also require cooling water for the spent fuel pool. Again, the need for power.

In the states, the NRC regards loss of offsite power as a special event. If it's gone more than 24 hours, federal regulations require the plant to shut down.

All US reactors have emergency diesel generators. However, that is not considered enough by the NRC.

ETA:In theory, they could go on as long as they have fuel for the generators, but the regulations will have them shut down long before that.

You can review all event notifications here.
https://www.nrc.gov/reading-rm/doc-collections/event-status/event/index.html

Just a titbit from the Northeast blackout of 2003:
There were some unaffected regions within the area of the blackout.
one of it was

the Buffalo, NY area, excluding southern Erie county, along the shore of Lake Huron via a feeder line to Owen Sound from Bruce Nuclear Generating Station. Three of the four Bruce B units were able to throttle back their output without a complete shutdown, then reconnect to the grid within five hours

Depending on the grid structure around a nuclear power plant, there may be enough demand to throttle down the unit without a complete shutdown. All depends on the ability to disconnect parts from the grid. In the case of Bruce this was possible and the shutdown fourth unit got the power for the cooling pumps from the running other units.

HM.