zirconium clad rods exposed to air generate hydrogen gas. not a good thing.
If the fuel rods are stored indoors, that building will already be on fire before the rods get that hot.
If the rods aren’t in an enclosed volume, any hydrogen would rapidly diffuse. Eventually it would either oxidise (too spread out for “burn” to feel like the right word) or escape into space.
If they’re in a building which is on fire and while it’s on fire someone sprays water on them, then they’ll produce hydrogen.
IDK if that hydrogen would burn away fast enough to not be an explosion hazard or build up enough that it is, but it shouldn’t come up anyway because any firefighters on site ought to know not to use water in that situation.