You simply flood the containment building. They're designed for that. Shutdown, a PWR needs only sufficient cooling water circulating to remove the small amount of heat from long-term radioactive decay that is occurring. After 14 days, give or take a few, all the short-term decay has occurred.
The absolute worst-case scenario with a reasonably managed PWR is Three-Mile Island. The core suffers a partial meltdown, remains in the reactor vessel, and everything is inside the containment building.
Water like that will absorb neutrons, not heat. It is the neutrons that you want to stop anyway.
There are two water systems. One to absorb the heat of reaction, and carry that to steam turbans to turn a generator shaft. Control rods work by absorbing neutrons. Water can do the same thing, so an emergency shutdown can occur by simply flooding the reactor.
This is why you can store spent fuel in pools.
Radiation accidents:
Chernobyl, a graphite moderated reactor, exploded due poor maintenance and combined operator error. There was no containment.
Daichi plant in Japan, the Ni plant suffered sudden catastrophic damage from a tidal wave. All control to the reactor was lost, including the damping rods. No way to SCRAM it. The core melted and became a twisted mass of metal and nuclear fuel until it solidified underwater. Radiation was limited to the plant, although few high speed neutrons were detected elsewhere. Even fishing wasn't affected much. Japan is big on fishing.
Three Mile Island. A reactor became dangerously low on coolant due to combined indicator failure and operator failure to cross check. Steam was released from the primary cooling system and a pressure relief valve opened in the containment. No radioactive material or other damage to the reactor occured, and it SCRAMed automatically. It was listed as an accident by the Nuclear commission, due to the damage to primary cooling system. Effectively a plant accident, and radiation was limited to the plant site itself. Expensive to repair and re-certify. A movie dramatization was later made, placing the event in California, with obvious intent to scare people about nuclear power plants. To the uneducated (most of the public) about nuclear power, it worked. After that, it became next to impossible to successfully construct a nuclear power plant and get it certified for operation.
The reactor bottles are really pretty tough. To blow it up would take a seriously powerful bomb. Oh, you could bounce it around, but to break it or shatter it would require a lot more and a direct hit. Even then, once the material scatters, all nuclear reactions will stop.