Are the Japanese Nuclear plants melting down?

[navyasw02]

Can somebody tell me how a damned nuclear power plant can be cut off from electricity? It MAKES electricity. Why didn't they use the diesels to run the water pumps and fire the reactors back up to produce more energy?

When shutdown, it can't make electricity. The emergency cooling systems I know of require an external power source. Supposedly (based upon the varying rumors on TV), the backup power systems to run the pumps in case of emergency got taken out by the tsunami. Normally, this wouldn't be as big of a deal because you have a whole power grid to tap into, but in this case you're SOL since half the power grid is down. I suspect their next means of cooling the plant would be to draw off heat by bleeding as much steam as possible if there's a means of putting water back into the steam generators, which is doubtful considering there's no power. The next step would be to tap into the primary (reactor side) piping and pump in and circulate cooling water from an external source. That's pretty much a last resort. You can't fire the thing back up. Not only does it take a long time, but it probably also requires significant inspections to ensure everything is ok after a magnitude ridiculous earthquake.

 

[wilheldp_PE]

it probably also requires significant inspections to ensure everything is ok after a magnitude ridiculous earthquake.

This is what I wasn't getting. I can understand shutting the reactors down if you have alarms going off all over the place, but nobody really ever said that. It sounded like they just shut the reactors down for ***** and grins...going to emergency power for a short time. Wouldn't they have monitors/alarms on everything important (i.e., the stuff that would irradiate the population) if it had been damaged in the earthquake? It seems like they would have better generators/more fuel at something as important as a nuclear power plant.

 

[Flyer_PE]

If I read correctly, the units in question first went in service around 1970. The design standards have changed a LOT since then. I don't know about the Japanese fleet, but there were a whole lot of retrofits here in the states following the TMI event and a lesser known fire at Browns Ferry. The newer plants usually have one more emergency diesel generator (EDG) per unit than the older ones and a lot of the older ones in the states added EDGs in the mid 1980s. Sounds like they had diesel power for about an hour and then it failed for reasons unknown.

Nuclear plants are designed to withstand what is known as a Design Basis Event which is theoretically, the most severe earthquake/weather event that can be postulated. I'm wondering what their design basis is vs. what actually hit them.

As far as getting water in the vessel. These units are Boiling Water Reactors (BWR) and don't have the same primary/secondary systems you find on navy vessels. It's a simple primary loop that actually produces steam in the reactor vessel which is then sent to the main turbine. Without the EDGs, there are two emergency steam driven systems for getting water back in the vessel. The first is RCIC (Reactor Core Isolation Cooling and the second is High Pressure Core Injection (HPCI). If all they had is DC power, their batteries should be sized to control those two systems for a maximum of 8 hours. The theory is that you should be designed such that there are no credible events that will leave you without either off-site power or EDG power for more than either 4 or 8 hours depending on the site. Again, I'm wondering if they messed up the design or just got hit with something beyond what was considered credible when the place was built.

 

[navyasw02]

If I read correctly, the units in question first went in service around 1970. The design standards have changed a LOT since then. I don't know about the Japanese fleet, but there were a whole lot of retrofits here in the states following the TMI event and a lesser known fire at Browns Ferry. The newer plants usually have one more emergency diesel generator (EDG) per unit than the older ones and a lot of the older ones in the states added EDGs in the mid 1980s. Sounds like they had diesel power for about an hour and then it failed for reasons unknown.
Nuclear plants are designed to withstand what is known as a Design Basis Event which is theoretically, the most severe earthquake/weather event that can be postulated. I'm wondering what their design basis is vs. what actually hit them.

As far as getting water in the vessel. These units are Boiling Water Reactors (BWR) and don't have the same primary/secondary systems you find on navy vessels. It's a simple primary loop that actually produces steam in the reactor vessel which is then sent to the main turbine. Without the EDGs, there are two emergency steam driven systems for getting water back in the vessel. The first is RCIC (Reactor Core Isolation Cooling and the second is High Pressure Core Injection (HPCI). If all they had is DC power, their batteries should be sized to control those two systems for a maximum of 8 hours. The theory is that you should be designed such that there are no credible events that will leave you without either off-site power or EDG power for more than either 4 or 8 hours depending on the site. Again, I'm wondering if they messed up the design or just got hit with something beyond what was considered credible when the place was built.

I'd guess that for safety's sake, the plant would SCRAM in an extreme earthquake like this. Maybe the aftershocks/tsunamis/natural disasters delayed starting up again beyond the life of the batteries if the emergency diesels went out.

 

[wilheldp_PE]

I understand next to nothing about nuclear energy, but one thing I do know is that when the water stops flowing through the reaction chamber, the fuel rods heat up. When they heat up too much, they fuse together, the reaction runs out of control, and the core melts down (a la Chernobyl). I just don't understand why they shut down the reactors completely (stopping electricity production necessary to run the critical pumps, and allowing the heating process to begin) UNLESS there was some immediately detectable damage to the plant. In the case the there was damage, I completely understand the reason for shutting down...but I haven't found any reports that indicated that there was damage to the reactors.

Alright...I'm done talking out of my ass now. I'm just really tired of people that know even far less than me (i.e., the mainstream media) pitching a **** fit about all this when nothing worse than TMI has occurred yet. They are going to put a stop to all our domestic nuclear energy if they don't knock that **** off.

 

[Flyer_PE]

To get a nuke going, you need the grid. They aren't black-start capable. The reactor recirc pumps are several thousand horsepower alone and the turbines are so big they are damn near uncontrollable if the only load they see is the auxiliary power loads for the station. That, and any event like this, you want all rods in. The problem they have now is dealing with gobs of decay heat and they need power for the low pressure injection systems.

I've been at a station when we has a loss of offsite power and that was a giant PITA with the EDGs working as designed. I can only imagine what those operators are trying to deal with right now.

 

[cableguy]

I'm thinking that building a nuclear plant ON THE OCEAN in an EARTHQUAKE ZONE probably wasn't the best idea.

Call me "Captain Hindsight".

 

[benbo]

Where's Homer Simpson when you need him? Or as he's known in Japan - "Mr. Sparkle."

 

[MadDawg]

I'm thinking that building a nuclear plant ON THE OCEAN in an EARTHQUAKE ZONE probably wasn't the best idea.

Tell that to these guys:

http://en.wikipedia.org/wiki/SONGS

http://en.wikipedia.org/wiki/Diablo_Canyon_Power_Plant

This is all media hype...

 

[Flyer_PE]

Just got this from a friend of mine. Looks like I was wrong about the explosion. The source of the hydrogen was zirconium oxidation.

 

[navyasw02]

Just got this from a friend of mine. Looks like I was wrong about the explosion. The source of the hydrogen was zirconium oxidation.

Thanks for posting this. It looks like we were pretty close in our guesses about what happened. My only question is what caused the loss of coolant? Primary relief valve sticking? System integrity compromised during the quake?

 

[navyasw02]

I'm thinking that building a nuclear plant ON THE OCEAN in an EARTHQUAKE ZONE probably wasn't the best idea.
Call me "Captain Hindsight".

The whole country is an earthquake zone. Putting a nuke plant near a water supply is a great place to put it because you can pump seawater in easily in the event of an emergency. It's only a problem in a really complex event like an earthquake followed by a tsunami that ***** your whole power grid.

 

[navyasw02]

Here's another report with some pretty pictures

 

[Flyer_PE]

Just got this from a friend of mine. Looks like I was wrong about the explosion. The source of the hydrogen was zirconium oxidation.

Thanks for posting this. It looks like we were pretty close in our guesses about what happened. My only question is what caused the loss of coolant? Primary relief valve sticking? System integrity compromised during the quake?

Their losing water from it being converted to steam. They have to vent the steam occasionally to control the pressure in the RPV.

 

[navyasw02]

Just got this from a friend of mine. Looks like I was wrong about the explosion. The source of the hydrogen was zirconium oxidation.

Thanks for posting this. It looks like we were pretty close in our guesses about what happened. My only question is what caused the loss of coolant? Primary relief valve sticking? System integrity compromised during the quake?

Their losing water from it being converted to steam. They have to vent the steam occasionally to control the pressure in the RPV.

Gotcha. I'm still thinking of PWRs.

 

[Ble_PE]

Alright...I'm done talking out of my ass now. I'm just really tired of people that know even far less than me (i.e., the mainstream media) pitching a **** fit about all this when nothing worse than TMI has occurred yet. They are going to put a stop to all our domestic nuclear energy if they don't knock that **** off.

This is what I'm worried about. We're still taking baby steps with new-build nuclear and I'm afraid that this is going to set us back because of all the media coverage.

I just hope we've seen the worst of the nuclear problems over there and they get everything under control.

 

[wilheldp_PE]

This is what I'm worried about. We're still taking baby steps with new-build nuclear and I'm afraid that this is going to set us back because of all the media coverage.
I just hope we've seen the worst of the nuclear problems over there and they get everything under control.

There was a 2nd hydrogen explosion at the same plant where the first one happened, and they have reported that a third reactor is producing hydrogen at an accelerated rate. The US Navy moved an aircraft carrier that was 100 miles off the coast because of high radiation levels. That can't be a good sign.

 

[Capt Worley PE]

What percentage of Japan's reactors are now offline? I would suspect a good many were scrammed during the earthquake.

 

[Flyer_PE]

I haven't heard anything about the rest of their fleet. If the earthquake where any individual unit is wasn't large enough to trip it off-line, they're probably still running.

 

[wilheldp_PE]

I saw a map of their nuclear power plants (can't remember where). Only two of the plants are experiencing problems. I think the rest of them are still online, including the two nearest the epicenter (the two that are down are farther south of the epicenter).