If you no longer need the nucleus, do not execute it. Instead, release it from containment and have drafted pawns attack it until it is destroyed. It will drop 2 shards and more twisted meat upon death.

The Heart of the Horror: Mastering the Fleshmass Nucleus in RimWorld

Whether you've just encountered your first "Fleshmass Heart" event or you’re looking to exploit this biological anomaly for colony gains, here is everything you need to know. What is the Fleshmass Nucleus?

If you are currently staring at a growing blob of meat on your map, follow these steps:

Once a pawn performs this action directly on the Heart, it explodes, leaving behind the Fleshmass Nucleus . Management and Containment

Build a dedicated containment cell with Plasteel Autodoors and Bioferrite Walls . Ensure you have redundant power for your holding platform.

Fleshmass is highly flammable. Use Molotovs or Incendiary Launchers to clear paths quickly.

This is why you fight the Fleshmass rather than just avoiding it.