A Question About "Critical Mass"-Nuclear Reactors

I understand that “critical mass” is the amount of uranium you need to have a chain reaction-power generation. Suppose the following were to happen:
-a reactor gets so hot that the core and fuel rods melt.
-you now have a puddle of molter uranium on the floor-will this mass become critical? If it does, wold it naturally spread out (and end the chain reaction)?

Mass is important but so is geometry. If it’s spread out on the floor, the mean path of the neutrons will tend to be small – in other words, they will tend to shoot out the top or bottom of the mass. If they don’t go through a lot of uranium on average, too few of them will run into other atoms to sustain a chain reaction.

The amount of uranium which is required to generate a chain reaction is partially determined by the presence of other materials around the core which influence the neutron flow. Most reactors contain moderating materials, water or graphite, which slow down neutrons. Slowing down the neutrons actually makes them more likely to be captured by uranium atoms, which means that the amount of uranium needed to generate a chain reaction is less. Remove the moderator, or remove the uranium from the presence of the moderator, and the same amount of uranium is no longer a critical mass. Some reactors also have material around the core that reflect neutrons back into the core - again, this reduces the amount of uranium that you need for a critical mass. If the core melts into a puddle, it will no longer be a critical mass due to lacking moderation and not having the right geometry anymore to support a chain reaction.

There is also the issue of neutron moderators. Any meltdown that results in the uranium being puddled on the floor of the reactor vessel or containment building will likely result in the moderators either boiling away (if water is the moderator), burning away (if graphite), or being distributed on the floor in a non-optimal configuration highly unlikely to support criticality.

ETA: too slow by three minutes…

The enrichment level (amount of U-235 vs U-238) of the fuel used in reactors is too low for criticality without a moderator. Bombs work without a moderator, but this requires highly enriched uranium. U-235 and U-238 will not separate when melted. Separating them takes an elaborate process using specialized machinery, and is the main thing keeping evil people from making nuclear bombs.