Why aren't the reactors and cooling tanks of nuclear power plants built below water level?

What would keep that water in once the area was flooded? If you open a dam, remove a levy, or open some kind of gate that water can flow both ways.

A pump would allow you to control what comes and goes.

Keeping water out when you don’t want it can be a bit tricky in basements; perhaps it’s something similar.

Because if they ruptured, radioactivity could spread more quickly through the water table destroying the water for miles and miles and endangering wildlife.

Ok, but if there’s a full-blown meltdown, surely the radiation contamination would be many orders of magnitude greater than if it was just limited to the local water table? I mean in a meltdown situation the local water table is fucked anyways right? Wouldn’t it be infinitely better to have a contaminated lake and water table than a Fukushima type disaster that has rendered the land useless in a radius of at least 20km for a very long time?

@Nullo I don’t think having industrial sump pumps is that big of a deal when you’re talking about how massive a project it is to design, build and run a nuclear facility.

Essentially, they are. They’re not built below a “ground water” elevation, because the construction itself would be so problematic at that point. But if you look at a simple diagram of a pressurized water reactor (the most common commercial nukes in the USA), they are built with:

1. Concrete “reactor pools” (including the primary piping to the steam generators, and the bottom section of the steam generator itself) that are normally filled with water during operation anyway (that is, the reactor, primary loop piping and steam generators are built to operate inside a pool filled with water) and

2. Safety injection tanks, which are massive suspended tanks of borated water (because boron stops the fission reaction by absorbing the fission particles) within the containment building that in the event of a severe LOCA (loss of coolant accident) are gravity-fed to continue to flood the reactor pool.

In the case of the most severe and dire failures on the PWR plants I’m familiar with, when the operators / owners are ready to sacrifice the plant to prevent catastrophe, then the entire lower half of the containment vessel itself can be flooded, which also includes the reactor pool (say if the pool integrity itself had been somehow damaged in a catastrophic failure of the reactor, for example). At that point, all of the plant equipment in the bottom of the containment would be sacrificed as unusable, but the vessels themselves should be prevented from continuing to produce unmanageable heat and fission.

The entire point of the “containment vessel” (a separate steel pressure vessel inside the concrete shell that you see in public photos and driving by on the road) is to separate ALL of the fission products and keep them inside at all times. There is a 100% commitment to NOT mix groundwater with products of radiation, and the plants are strictly evaluated on that basis through multiple testing points within and outside the plant boundaries.

No one wants ground water in a containment vessel / building, or to have anything escape containment into the groundwater. Either of those is a big fail.

@CWOTUS “the entire lower half of the containment vessel itself can be flooded”

Is this via gravity, or does it require pumps though? I guess that’s the main question. Everything you describe makes a lot of sense (particularly the stored borated water). Thanks for your enlightening response. I’ll be sure to let my friend know.

I think it takes a constant flow of water, doesn’t it?

The safety injection tanks are large tanks (I forget how many, either 4 or 6) suspended at the top ring of the containment vessel (where the cylinder is joined to the dome). As I recall (I only know about these because of the general plant design; I wasn’t involved with their design, construction or operation) the contents were held with valves in the powered-closed position. If the valves failed due to loss of power (and were not immediately re-powered by some other means), then the valves would fail-open and the tanks would immediately flood the pool. In other words, it’s a gravity-fed system that requires constant power to keep the water “up”. (The reactor control rods were the same way: They required constant power to keep them lifted out of the reactor vessel. If the power failed, the solenoid failure tripped the latch, and the boron rods would drop into the vessel and kill the reaction, no matter whether the operators wanted that or not.)