Of all of the scenes that pushed the phrase 'poetic license' to breaking point, Indiana Jones and the Kingdom of the Crystal Skull may have nuked the competition.
Check out the scene that really ground the gears of scientists and accuracy-lovers the world over: Indiana surviving a close-range nuclear blast by hiding in a refrigerator.
Sorry, fridge fans, but there are many ways in which science says that Indy would have been obliterated by the atomic incident, despite the lead-lined walls of his flimsy frigidaire. Overthinking It compiled a nice list of potential causes of death for this scenario, including but not limited to:
Being crushed under the shockwave or on reentry, lethal acceleration, fatal whiplash, spontaneous combustion, scorching by molten lead or incendiary air, suffocation or acute lethal dose of ionizing radiation.
The odds, Mr. Jones, are against you:
In conclusion, we estimate the odds of surviving a nuclear blast in the manner depicted here to be roughly 0±0%
Still, maybe there is a reason that Indy survived, hiding within the canon of the Indiana Jones series. Redditor cold_in_the_south posits:
He did drink from the cup of Christ. He might not have been granted eternal life, but I think it helped him survive other things. That's the only way I can rationalize the fridge.
This actually seems kind of reasonable, no? Inasmuch as one could ascribe reasonability to a movie that depicts a human being surviving telepathic aliens, giant ants, and a nuclear blast hidden inside a fridge, of course.
Did Indy really choose more wisely than he could have known?
In terms of questioning the way this 'Grail Magic' works, this explanation from Redditor That_secret_chord is particularly helpful:
Maybe the Grail has "regenerative abilities" and that alone. Think in terms of HP or a power up.
Henry had low HP when he was laying there with the wound. Drinking from the Grail, most of the regeneration goes to heal his wounds and raise his HP back up to 200.
Indie, and the Knights for that matter, didn't have low HP, so the grail could pass their full 200HP and they could gain the Temporary Immortality Powerup. The Knights drank from the cup on multiple occasions so the powerup stacked. That is why Indie's immortality didn't last long. His timer was running out.