Earthquake in nuclear power plant

[m.s.j]

After one sever earthquake happened in the hypothetical nuclear power plant area, following observations were reported by special investigation committee that were authorized to estimate earthquake demolition in power plant.
The mentioned Power plant has two units. Each unit has one control room. The control rooms have many quite similar electrical circuits integrated in protection and control panels. The panels are fixed on the floor of the rooms. According to the committee technical reports, one of the generator protection panels that were installed in unit 1 control room, broke from bottom of its base plate and fell down due to the strong vibration. On the other hand protection panels located in other control rooms (unit 2) withstood against mechanical stress. After more verification they found that the protective relays installed in inversed panel had operated correctly and related generator circuit breaker had received correct trip commands. But the protective relays located in other protection panels (unit 2) couldn’t have suitable reflection against earthquake.
Consequently, one of the panels damaged due to falling but it could protect relevant generator, vice versa other panel that withstood against vibration didn't do its assignments (generator protection).
Regardless similar electrical circuits, the method of devices installation in dedicated panel were different from the other panel. In the selfless panel, heavy equipments (e.g. matching current and voltage transformers) were installed on the top of the panel and main generator protection relays were located in the bottom side but in the other panels, heavy equipments were installed down and protective relay were fixed on the top of the panels.

How can you explain different behaviors of protection panels against earthquake waves?

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[jimbo]

Well, it is probably related to how they connected the framastat to the Fetzer valve.

[Bob NH]

The "hypothetical" was obviously written by an idiot who didn't know anything about nuclear power plants, their principles of operation, and their safety and control systems; and who failed his class in "English As a Second Language".

There are redundant safety systems to shut down the reactor and cool it to prevent any nuclear hazard such as the popular concept of a "meltdown".

When the reactor is shut down the generator will rapidly come to a stop for lack of steam to drive the turbine.

[m.s.j]

The specific seismic class shall be considered for important electro technical equipment, particularly for nuclear power stations, where the acceleration to which the equipment is subjected will be specified in the response spectrum.
As you know, the vibratory stresses to which the functional devices will be subjected must be evaluated, and there must be assurance that they would function correctly when put under these stresses. Therefore the nature of the transfer of ground seismic solicitation to functional cells (e.g. protective relays), must be taken into account at the design stage. The fragility threshold of functional devices (level of acceleration at which the equipment no longer performs its function) has to be determined be forehand.
When a structure (generator protection panels) undergoes floor acceleration"a (t)" (i.e. an earthquake) everything happens, supposing that the floor is fixed, as if each element of mass m of the structure was subject to an inertia load
Ft = -m . a (t)
The equation of motion for damped forced vibrations is
Ft =mx"+cx'+kx
In the first mode of vibration, the acceleration of mass increased by its displacement.
Therefore, the acceleration of mass in top of protection panel is more than its bottom portion. As a result, when generator protective relay installed in top of panel, it is possible to exceed acceleration of relay mass from its vibration withstand.

[Cookie]

I am just curious as to what is the question you are proposing here. My husband worked on Shippingport reactors and once, told me as safe as they are of course nothing is failproof. He is deceased so I can't ask him anything more. Food for thought look at Three Mile Island. Are you looking for mathematical formulas? I think they are pretty indepth, hard to understand and borders on theories in advanced mathematics.

[jimbo]

Just because the reactor scrams, does not mean the steam goes away.

In nuclear submarines, a specifice safety feature is that the main steam stops remain open in the event of a scram. If the boat is in extremis, the number one thing that can save it is the ability to drive to the surface. There is enough steam in the steam generators to do this, even after a scram.

There is an emergency ballast tank blow system, but if flooding is taking place, that may not be enough. Speed is the saviour. The amount of extra weight of water from flooding that could be suppored on my boat was 1000 pounds times the square of speed. So the difference between zero knots and 14 knots is 225,000 pounds of water. Speed is the saviour.

[CHH]

But if the reator scrams and the boat drives to the surface won't the tsunami from the earthquake get'em?

[jimbo]

Tsunamis are only about 1' in height in open ocean. Besides, as long as you keep the hatches shut, waves are not a problem. I have taken 100 footers in a Pacific typhoon. Rocks the boat, but no worries mate!

[CHH]

No worries? So you say. Look what happend to the Kursk. And a siesmic event was noted at the time it sank. How about that? I think folks just don't want it known that earthquakes sink submarines. So there.:)

[jimbo]

Going deep. It's safer down there.

[Bob NH]

Just because the reactor scrams, does not mean the steam goes away.

In nuclear submarines, a specifice safety feature is that the main steam stops remain open in the event of a scram. If the boat is in extremis, the number one thing that can save it is the ability to drive to the surface. There is enough steam in the steam generators to do this, even after a scram.

. . . . The amount of extra weight of water from flooding that could be suppored on my boat was 1000 pounds times the square of speed. So the difference between zero knots and 14 knots is 225,000 pounds of water. Speed is the saviour.

There is a bit of a difference between a submarine and a nuclear power station. They have never been able to get the Seabrook plant above 5 knots.

[jimbo]

I am from that neck of the woods ( Newbury,MA), back in the day....
A close school teacher colleague of my mother....her husband started at seabrook as a young whipper-snapper electrician, and retired before they ever lit it off, I think. We have long since buried both his wife and my mother, but Seabrook will always be Seabrook!