> The water acts as neutron moderator, cooling agent and radiation shield. The layer of water directly above the reactor core shields the radiation so completely that operators may work above the reactor safely. This design has two major advantages: the reactor is easily accessible and the whole primary cooling system, i.e. the pool water, is under normal pressure. This avoids the high temperatures and great pressures of nuclear power plants. Pool reactors are used as a source of neutrons and for training, and in rare instances for processing heat but not for electrical generation....Most research reactors are of the pool type.
> But just to be sure, I got in touch with a friend of mine who works at a research reactor, and asked him what he thought would happen to you if you tried to swim in their radiation containment pool. “In our reactor?” He thought about it for a moment. “You’d die pretty quickly, before reaching the water, from gunshot wounds.”
There's no pressure vessel and a massive thermal inertia. Not child's play, but very safe.
The big issue is the waste.