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Kaustubh Katdare
Kaustubh Katdare • Mar 12, 2011

Time & Steps To Shut Down Nuclear Power Plant?

With the recent news of blasts at nuclear plant in Japan, I'm wondering what's the typical time required to shut down a nuclear power plant?

Also, does anyone know the steps involved in the process?
maria flor
maria flor • Mar 12, 2011
Just what the ambassador of Japan in US said they're putting water on the Nuke plant to cool down the temperature.
ISHAN TOPRE
ISHAN TOPRE • Mar 13, 2011
Can we use other coolants? Apart from water?However water is the most practical coolant with whole sea at disposal.
Kaustubh Katdare
Kaustubh Katdare • Mar 13, 2011
I've absolutely no clue about Nuclear Power Plants and their operation. I believe they use Liquid Hydrogen as a coolant [just a guess!]- and it's the thing that caused the blast at the Japanese Nuclear Plant. However, the question remains : How long does it take to shut down a nuclear plant and steps involved in it.
maria flor
maria flor • Mar 13, 2011
Japanese have pumping sea water on plant. Don't you think it will create more hot temperature inside the plant since it is a salt water???
silverscorpion
silverscorpion • Mar 13, 2011
As far as I know, the coolant used depends on the type of the reactor. But mostly, it's heavy water (D[sub]2[/sub]O). Also, the blast might be due to any reason. It might also be due to some electrical short circuit, so to speak..

As for the actual process to shut down a nuclear plant, and the time it takes, I'm also clueless..
ISHAN TOPRE
ISHAN TOPRE • Mar 20, 2011
Nuclear power plants can be decommissioned using three methods:

1. Dismantling -- Parts of the reactor are removed or decontaminated soon after the plant closes and the land can be used.
2. Safe Storage -- The nuclear plant is monitored and radiation is allowed to decay; afterward, it is taken down.
3. Entombment -- Radioactive components are sealed off with concrete and steel, allowing radiation to “decay” until the land can be used for other purposes.
sachleen
sachleen • Mar 27, 2011
vry well said ishutopre.....
Chandrakiran
Chandrakiran • Jun 16, 2011
As a design engineer for N plant ( just the beginner of course) i can try to explain it:
1.In nuclear industry safety is primary concern rather than producing electricity. All safety and safety related equipments will have double and triple redundancy
2.In nuclear power plant electrical supply to its auxiliaries are classified as
Class IV normal power supply - from grid and from plant TG
Class III emergency power supply through Diesel Generators ( 30 sec duration)
Class II AC instrumentation and control supply through the UPS
Class I DC instrumentation and control supply through batteries and rectifiers
Normal condition Class IV power supplies power to all auxiliaries of the plant and Class II and Class I are called uninterrupted supply supplying power to safety systems
Shutdown time: In nuclear power plant unlike thermal plant cannot be shutdown and sleep, reactor can be shutdown by applying scram signal and shutdown rods shut the reactor in no time, However still the reactor is in shutdown condition decay heat is produced in the reactor (7% of full power eg 500MW reactor will have decay heat of 35MW generated even in shutdown state) This decay heat is because the gamama radiation and daughter nuclei radiations in the reactor.
This heat is to be removed else heat produced eventually melt the core. Shutdown cooling system should operate to remove the heat. ( Decay Heat can be removed by heat exchange at Steam generators or through outer environment by passive circuit (natural convection))

FUKOSHIMA: fukoshima is a Boiling Water Reactor ( BWR ); coolant and moderator is demineralized water (H20). In india mostly we have PHWRs and 1 BWR at Tarapur.
Due to earthquake Class IV supply was gone and reactor came to shutdown state, Due to Tsunami Diesel Generators were flooded results in failure of Class IV and Class III power supplies.
Shutdown cooling system didn't operate due to the failure of electric supply to the plant, water level in the reactor starts falling down and forms h2 gas ( reaction between zirc alloy fuel rod with steam) and h2 gas leaks from reactor vessel to containment building, pressure in containment building increases and h2 explosion occurs. Some amount of fuel also spilled out of reactor vessel. Later sea water is pumped into the reactor to cool it down.

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