> why did a crew of people wade into highly radioactive water -- a probable suicide mission

This is a common myth (probably recently propagated by the scare-mongering TV series), but that mission was perfectly safe. Three men, equipped with dos meters, waded into the water and opened a valve, that was it. One died of a heart attack at 65 and the other 2 are still alive.

Furthermore, the operation was in the end unnecessary: there was no risk of such an explosion.