Boiling in a tank that is inside a vault 2

[johcatrac]

We have a vented tank inside containment that is not accessible during plant operation. There is a pressure gauge connected to the 14" inlet line connected to the tank. This gauge is outside the containment. If, because of conditions (unknown) inside the containment, the water inside the tank starts boiling, what is the best way to figure this out from outside the containment? Certainly, the gauge pointer would not jump around rapidly, would it?

This is in a nuclear power plant and hence cannot access the containment during normal operation.

 

[LittleInch]

errr a temperature transmitter / guage attached to the tank / immersed in the liquid.

Steam coming out of the atmospheric vent?

I don't think you'll see any movement in a pressure guage.

I'm not really liking the sentence "This is in a nuclear power plant " and you have random tanks boiling and you don't know about it....

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Also: If you get a response it's polite to respond to it.

 

[Compositepro]

Measure the temperature of the vapor in the vent line. When boiling starts this will rise suddenly to the boiling point.

 

[johcatrac]

Should have said 'cannot access the vault during an accident scenario'. Under such a scenario, we need to pump water into the tank from the outside, for obvious reasons. Measuring the vent temperature is not possible, as we are assuming no power available under such a scenario. Also, the temperature gauge would require lines to run through the containment, which would be a very tedious affair.

 

[LittleInch]

I'm liking this even less

- "during an accident scenario",
- "we need to pump water into the tank from the outside, for obvious reasons" - Not to me?
- "no power available under such a scenario" !!

You could always run the wires inside the pipe you already have going through containment.

Tedious or not, it's by far the best solution and you have other things going through the containment no?



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[johcatrac]

I guess now the nuclear plant design is being audited!
It is designed to meet the normal accident conditions which includes the max. postulated seismic.
The new conditions which are outside design basis that are being considered now are similar to 'what if a Fukushima like scenario?' although such a scenario impossible in our geographical terrain.

 

[jari001]

You could add a line from the vent to some accessible location that has an analog thermometer (a "tattle tale line" kind of idea). When boiling starts, it will affect the energy balance of the system, so you would need to pump more water to keep the reactor area cooled if the liquid in the core is boiling versus not boiling. This assumes the plant has some idea of how much water is required for different failure scenarios. Can you paint things with temperature sensitive paint?

If all indicator methods need to be functioning with no electricity, your team is limited to either coarse measurements or you're going to have to break out the engineering history books and see what they used in "the good 'ole days". Or you could invent something new!


You'll have to forgive me if I'm not using the right names for things in a nuclear reactor, hopefully you get the gist of what I'm trying to say!

 

[adammal44]

Nuclear power plant design engineer here.

Containment entries occur during at-power operation; it just is a pain-in-the-ass. Check with your Health-Physics department to see what the real expected dose rates in this area would be...alot of things get relaxed for off-normal scenarios.

What specific tank is this? Are you a PWR or a BWR? If BWR, are you referring to your torus?

Where is the tank vented to? Potentially, you could rely on area rad monitors at the discharge point or the level sensors in wherever in-containment drainage is directed - these should be powered with reliable power if you're implementing a leak-before-break program.

For post-Fukushima, beyond-design-basis scenarios, recall that you're allowed to use more best-estimate assumptions (think FSAR Chapter 19 type analyses, not Chapter 15).

What event are you actually trying to work against? An extended station blackout with SBLOCA?

 

[IRstuff]

"we need to pump water into the tank from the outside, for obvious reasons.

So, where are you getting the power to do THAT? Surely, you can spare a bit of that power to find out if you need to pump anything at all?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[adammal44]

He is in a bind.

In the scenario required by the US NRC to be considered, you can start crediting assistance from temporary equipment stored in a hardened building onsite after 24 hours. You can start crediting in equipment from offsite (via helicopter usually) after 72 hours. This usually includes diesel generators, fuel oil, and cables.

In the meantime though, he needs instrumentation that he can credit during the first 24 hours when he needs to assume that all on-site AC power sources are lost (including the highly-reliable, safety-related diesel generators).

One way to get around this would be to procure a small sensor with a high-pedigree battery (if you can't afford the additional capacity on your current safety-related DC power source.

Nonetheless, he needs to give us alot more information before we can help him assess his options.