Had to create an account for this. You're looking for "Time for a Hero" (1995) by Brian M. Thomsen. Pretty obscure - looks like it only got printed in one anthology, Superheroes.
Regarding the following part of your description...
two scientists talking to a man with amnesia. They tell him he is superhuman and he needs to save them all from a nuclear plant about to meltdown.
... here's a relevant excerpt from the story itself:
"The bazooka shell," repeated Parker. "Don't you remember?"
"No. I don't remember anything. This all must be some dream. Getting hit in the head would kill an ordinary man… probably blow him to bits. No, I'm just not awake yet. This is all just a dream," he added, the pounding in his head becoming more and more noticeable. "I'm going to just close my eyes, go back to sleep, and wake up later when I'm not so delirious."
"You can't do that," insisted Dr. Kirschenbaum. "We need you. Surely you must remember the crisis… your mission… what you have to do…"
"What do I have to do?" he asked, hoping that this dream would soon be over.
"Save the world, of course," answered Parker.
Googling the phrase "Parker said to Kirschenbaum" leads to an online version of the story, including the mention that it was a suicidal mission.
"Well, it certainly works," said Parker, patting the older doctor on the back. "In less than two hours we can turn an ordinary soldier with human flaws and instincts for self-preservation into a confident and carefree hero with no other concerns except the completion of his mission. One man dies so that many
can be saved. No matter how you look at it, that's a more than acceptable casualty rate. Lt. O'Connor, aka Meteor Man I, will get a hero's funeral, and the day will be saved."
"A hero's funeral," mused the increasingly more depressed Dr. Kirschenbaum. "I remember reading about the Soviet firemen who rushed into Chernobyl to contain the fire to keep the plant from exploding, knowing that in doing so they were signing their own death warrants. I also remember stories of soldiers earning medals that were awarded posthumously by jumping on top of hand grenades..."
Great story in a quality 1990s anthology!