Volanic Ash and Nuclear Power Plants

[Delta Force]

Trojan Nuclear Power Plant was located 12 miles north of St. Helens, Oregon. St. Helens, Oregon, is only 39 miles away from Mount St. Helens, which had a major volcanic eruption in 1980. The heaviest ash fell to the northwest of the volcano in Washington and to some extents Idaho, which respectively have nuclear reactors at Hanford Site and Idaho National Laboratory (although by 1980 only N Reactor was operational at Hanford). Were these reactors ever at risk during the 1980 eruption, or liable to be at risk if the wind had shifted?

Also, if completed, would Baatan Nuclear Power Plant have been at risk from the explosion of Mount Pinatubo in 1991? The plant was only a few miles away from Subic Bay, Clark Air Force Base, and Angeles City, all of which were buried under feet of volcanic ash.

 

[John Morrell]

Nuclear reactors don't require air-intake, so the ash in the air would make no difference. The only things that I think could really affect the reactors would involve seismic disturbances (damage to back-up generators or control rods or the like as happened in Japan) or a sudden and complete loss of water for use in cooling the reactor. I don't think that ash could do that very quickly, however, and reactors can be powered down safely given about a dozen hours.

On the whole I don't think the ash could really do anything significant. The earthquakes involves with a major eruption might, but I think that those eventualities would be engineered into the plant.

 

[etudiant]

The area of concern would be the heat exchangers that reject the excess heat to the environment.
While designs using ocean water would not be directly affected, I think air cooled systems would be impacted.
Afaik, Mt Pinatubo covered Subic Bay with over a foot of pretty dense ash. I don't think cooling towers would function well after such an ash fall.
We saw at Fukushima that even post shut down, reactor residual heat rejection requires ongoing effective cooling. That might be difficult if the cooling tower is down.

 

[Hiddencamper]

Columbia generating station has an ash fall procedure.

For those who worked there when St. Helens blew, they were putting coffee filters over their car air filters and changing them out half way to the plant, every 10 miles or so. There is a LOT of ash.

The ash will clog up filtration systems. The biggest concern is the emergency diesel generator air intakes. Columbia keeps a minimum number of filters on hand to ensure their emergency generator air intake filters can be replaced during a design basis ash fall without negatively impacting the unit.

The ash can clog regular ventilation systems. With no ventilation, the secondary containment will be placed into standby gas treatment mode, which exhausts air but does not cool or ventilate. This can potentially impact secondary containment vacuum over time. With no ventilation, various leak detection systems may trip on high temperature resulting in a unit scram.

Ash can impact circulating water systems as well. It's definitely not a negligible event, but it is a manageable one.

 

[etudiant]

Very interesting, had not considered such problems at all. Good to hear that the issue is getting thought and practical attention, even in water cooled facilities.
I'd still like to know how an air cooled installation might be impacted, by a major ash fall because it seems more vulnerable to me.

 

[John Morrell]

I don't think there are any "air cooled" nuclear reactors. The reactor generates power by running water over an internal heat-exchanger, boiling the water, and venting the steam through a turbine. It is that water, turned into steam and released through cooling towers, that does the cooling. They aren't pulling in air to cool any part of the reactor.

 

[jim hardy]

Buildup on insulators in switchyard and lines leaving the plant might make offsite power less reliable . Loss of offsite power for a few days is not a problem, though.

 

[etudiant]

I don't think there are any "air cooled" nuclear reactors. The reactor generates power by running water over an internal heat-exchanger, boiling the water, and venting the steam through a turbine. It is that water, turned into steam and released through cooling towers, that does the cooling. They aren't pulling in air to cool any part of the reactor.

It is the 'released through the cooling towers' aspect that seems iffy, when the cooling towers have been coated with a foot of ash.

 

[John Morrell]

Well, for that to be a problem you'd have to have so much ash that steam could not escape your reactor, and in that case I'd say that nuclear meltdown is only another small problem next to your entire world being covered in yards and yards of ash. #scadrial

 

[jim hardy]

It is the 'released through the cooling towers' aspect that seems iffy, when the cooling towers have been coated with a foot of ash.

Think of the cooling tower as just a heat exchanger.
Ash reduces its ability to transfer heat,
but when the reactor is shutdown there's not much heat to be transferred anymore,
so the heat exchanger can tolerate a lot if fouling.

I'd worry a whole lot more about my emergency diesels ingesting the stuff.

 

[Astronuc]

, which respectively have nuclear reactors at Hanford Site and Idaho National Laboratory (although by 1980 only N Reactor was operational at Hanford). Were these reactors ever at risk during the 1980 eruption, . . . .

The production reactors at Hanford used direct cooling from the river, and N reactor actually had both primary and secondary cooling systems.

Think of the cooling tower as just a heat exchanger.
Ash reduces its ability to transfer heat, but when the reactor is shutdown there's not much heat to be transferred anymore, so the heat exchanger can tolerate a lot if fouling.

Yes, as far as I know, when shutdown the draft cooling in the tower is not needed and the heat can be transferred through the heat exchanger to the river water.

 

[etudiant]

Think of the cooling tower as just a heat exchanger.
Ash reduces its ability to transfer heat,
but when the reactor is shutdown there's not much heat to be transferred anymore,
so the heat exchanger can tolerate a lot if fouling.

I'd worry a whole lot more about my emergency diesels ingesting the stuff.

No argument that keeping the diesel intakes clean is critical.
The concern I have is that the residual heat during the first few days after a shutdown is still considerable and that is the period in which the heat exchangers get coated with hot ash from the eruption.

 

[Benbenben]

I don't think there are any "air cooled" nuclear reactors. The reactor generates power by running water over an internal heat-exchanger, boiling the water, and venting the steam through a turbine. It is that water, turned into steam and released through cooling towers, that does the cooling. They aren't pulling in air to cool any part of the reactor.

Egads! No. That would be a huge amount of makeup water on a continual basis. Steam plant water chemistry is tightly controlled to avoid catastrophic failure from various aggressive corrosions possible.
Aside from the monumental cost of producing massive amounts of makeup water on a continual basis, turbines would be running against a backpressure at atmospheric. That would be a huge disadvantage. Condensers create a vacuum that is put to good use in improving plant output.
So, no, no one is running steam through a turbine and then venting it on a meaningful scale. There will invariably be a condenser, which is a heat exchanger. That will be cooled by water or water and air.
Whether water alone or water and air are used, fouling of tubes in the condenser/heat exchanger, depending on extent, can be a serious problem.