Why Do VVER Reactors Use Horizontal Steam Generators?

[vietbilk]

please help.
i'm studying about VVER, but i meat dificult when i found document.
who can help me know: why VVER's Steam Generation has structure horizontal?
with this design what advantages and disadvantage when we compare with design that have vertical Steam Generation? (PWR or BWR)
thank so much.

 

[Astronuc]

why VVER's Steam Generation has structure horizontal?
with this design what advantages and disadvantage when we compare with design that have vertical Steam Generation?

These are good questions. The following article attempts to answer or at least explore these questions.

Steam generators – horizontal or vertical (which type should be used in nuclear power plants with VVER?). Atomic Energy - Volume 105, Issue 3, pp 165-174, September 2008
N. B. Trunov, B. I. Lukasevich, D. O. Veselov, Yu. G. Dragunov

http://link.springer.com/article/10.1007/s10512-008-9090-1

The steam generator is a very important component of a nuclear power plant. Historically, vertical steam generators came to be used abroad and horizontal steam generators in our country. Both types of steam generators operate successfully in nuclear power plants and satisfactorily fulfill their functions, enabling the production of electricity. Repeated attempts to re-examine the existing concepts in one or another country have been unsuccessful because there are no convincing arguments for this. Nonetheless, the question of using a different type of steam generator is raised periodically in our country and abroad. This article briefly reviews different concepts of steam generators. Their parameters, characteristics, and thermal efficiency are compared and ways to increase the latter are analyzed. It is shown that it is impossible to choose one or the other type of steam generator without making an exhaustive study and analysis of the layout of the reactor facility and its scheme, servicing, and operation as part of a nuclear power plant. A comparative analysis of layouts of reactor facilities with different types of steam generators is made.

 

[jim hardy]

I believe the reason for vertical steam generators is not a matter of performance , it's just they take less floor space than a horizontal steam drum. A big part of a plant's cost is the containment building. It is made however big it needs to be to contain the steam resulting from a worst case pipe rupture and no bigger. Recall the first PWR's had to fit inside a submarine hull.

The vertical steam generators in our PWR exhibit large changes in indicated level when pressure changes.
Look at page 13 here:
http://mitnse.files.wordpress.com/2011/03/pwr_plant_04.pdf
on the right side you'll see two instrument taps that are not far apart vertically. The level sensors connected there are called "Narrow Range" because they only cover the operating range not the full height of the steam generator.
So the narrow range level instrument reports the mass between those taps. That's what dp cells do, report the approximate mass that's between their taps.
A sudden pressure increase collapses steam voids and level falls. So even though total mass inventory of the steam generator hasn't changed, mass has moved down below the space between the narrow range taps so reported level moves down accordingly. That's called "boiler shrink "
The opposite happens on a pressure decrease, level rises, "boiler swell".
It takes operators quite a bit of practice to learn "that magic touch" of manual steam generator level control.

Wide range instruments that are connected between upper instrument tap and one way down by bottom drain nozzle(it's not shown on that sketch but that's where it is) do not show that pressure dependence, they report a more true picture of mass inventory.
It would be interesting to sense narrow range level from the wide range taps and electronically offset to get narrow range indication. But that'd be an experiment, and one at my low level just doesn't tinker .I suspect your horizontal steam generators are more control-friendly to the operator . I didn't know anybody had them. Do you know any VVER operators who could say if they're tricky to handle?

fascinating, this:

versus that:

Clearly a horizontal drum gives more surface area for the steam to dissociate itself from the water.
Look at those complex moisture separators and steam dryers in our PWRs, page 12 & 13 linked earlier.
There's a reason early boilers evolved horizontal steam drums.

You'll find an interesting article on evolution of boiler design here:
It's from "Steam" by B&W. After all, they literally wrote the book on steam.

http://www.gutenberg.org/files/22657/22657-h/chapters/evolution.html

I hope I didn't digress. We old guys do that a lot.

jim