Tuesday, March 15, 2011

What is a Nuclear Melt Down?

The horrors in Japan bring us all such overwhelming grief and concern.

The article introduced here sheds great light on the basics concerning Japan's nuclear reactors that are at play following the earthquake and tsunami disaster. (Please note that, as a transcript there are grammatical errors.)

The interview is re-published on CFACT, and can be read in its entirety here:

A nuclear engineer's briefing on the emergency in Japan

This Q&A briefing provides a concise overview of much of what you need to know on the nuclear emergency in Japan. Nuclear engineer Mark Mervine gave this interview to his daughter Evelyn Mervine.
March 14, 2011
by Evelyn Mervine

This Q&A briefing provides a concise overview of much of what you need to know on the nuclear emergency in Japan. Nuclear engineer Mark Mervine gave this interview to his daughter Evelyn Mervine. It was originally posted on her blog, Skepchick. Mark and Evelyn Mervine are not associated with CFACT.

My name is Mark Mervine. I graduated from the US Naval Academy in 1981, and went into the Navy nuclear power program. I was in submarines, and while I was in the Navy I qualified on two different types of Navy nuclear power plants and served as an instructor in the Navy nuclear power program.

Q: OK, and then after you got out of the Navy?
A: After seven years of active duty, I went into the Reserves, and I stayed in the Reserves and I retired as a commander in the Navy Reserves. I went to work, initially, for Wisconsin Electric, which at that time had a 2-unit Westinghouse pressurized-water reactor in Turbridge, Wisconsin. While I was there, I completed my SRO certification, which allowed me to do senior review and oversight, as a member of the plant management staff. And I also qualified and served as a shift technical advisor, which is a position that was added in the nuclear power industry, after Three Mile Island, that is a degreed engineer position, that’s available to the on-shift crew on a 24-hour basis. Some plants do it on an 8 hour watch, at that time, Wisconsin Electric did it on a 24 hour watch, so I would actually stay at the plant for 24 hours; we had a place where we could sleep, and my job was to advise the crew whenever they needed advice on what was happening with the plant.

After a few years at Wisconsin Electric, I went to work for Vermont Yankee, where I also completed the SRO certification, Senior Reactor Certification, which allowed me to do senior level reviews as a member of the plant management staff, and I also served on the Outside Review Committee, which is a very high-level committee for the main Yankee nuclear plant, until it closed, and also Vermont Yankee.

Q: Excellent. So, you’re qualified to talk a little bit about nuclear power, it sounds like.
A: I can talk a little about nuclear power, yes.

Q: OK, excellent. So, my first question for you is really basic, since maybe people are not familiar with this, but what, can you just describe quickly, what is a nuclear power plant?
A: Yes I can, maybe what I’ll do first is explain what a power plant is.

Q: Sure.
The vast majority of power plants in the world generate steam, by some method, some by burning oil, some by burning coal, and heat up water, and make steam, that steam then powers a turbine, and attached to the turbine, you have a generator, and that generator generates electricity, and through transformers is connected to the electrical power grid.

So, in that respect, a nuclear power plant is a lot like other power plants, in that you have this turbine, that’s steam driven, with a generator, that’s attached to a transformer and then to the grid. The difference is, what a nuclear power plant does, is it generates, depending on the type of the plant, hot water or steam, by the fissioning of uranium.

Q: Right. And that’s providing the power, basically.
A: So, there’s two major types of nuclear power plants in the Western world. One is a pressurized water reactor where the water’s kept at high pressure and doesn’t boil; an there’s a heat exchanger, and on the other side of the heat exchanger, that water is allowed to boil which generates the steam. And then you have a boiling water reactor, where the water in the reactor actually boils and generates steam directly, and that steam is used to power the turbine.

Q: So, another question I have for you, is one of the main problems they’re having in Japan is that they’re not able to cool the power plant. So, can you explain why a nuclear power plant needs to be cooled?
A: Absolutely, so what happens in a nuclear power plant is that the atoms fission or split in half and that generates heat. There’s also other materials that are created (I don’t want to get into too much detail and confuse people) that continue to decay and that also generates heat. So for some period of time after you shut down a nuclear power plant you have to continue to cool the reactor core. Because you’re still, I mean, to begin with, it was very warm because you were generating hot water under a lot of pressure or steam and it needs to be cooled, obviously, down and because of the decay of these materials in the fuel they also continue to generate heat for some period of time until the decay trails off.

Q: So they’ve actually shut down the plant in Japan and they’re just trying to cool it?
A: Okay, well if you’re talking specifics, the plant that we’re aware of that is in the most difficulty right now is the Fukushima plant, Unit One. That plant is a General Electric boiling water reactor, it first achieved criticality in 1970, it’s similar to a couple of other plants that we have here in New England. It’s very similar to Pilgrim, which is down in Massachusetts, and Vermont Yankee, in Vermont.

And, that plant was automatically shut down, when the earthquake occurred, and for about the first hour, they were running on their diesel generator. Once a plant shuts down, it has two ways to get electricity, one is from the grid, and another is from emergency diesel generators that they have on site. In this case, because of the magnitude of the earthquake, the grid basically went dark, so they were operating on their diesel generators and everything was functioning as it should be. But then, based on news reports, about an hour after the earthquake and the shutdown, the tsunami hit, and flooded the plant, where the diesel generators were, and that caused them to lose their diesel generator power and reduced them to their emergency battery backup power only.

The interview is re-published on CFACT, and can be read in its entirety here:

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