It is possible to kill the trapped Atomics with any beam upgrade besides charge. Kill the atomics while waiting for the Coverns to respawn.

Requires:

{
  "not": "f_DefeatedPhantoon"
}
"canRiskPermanentLossOfAccess"
{
  "or": [
    "Ice",
    "Wave",
    "Spazer",
    "Plasma"
  ]
}
{
  "resetRoom": {
    "nodes": [
      1
    ],
    "mustStayPut": false
  }
}
{
  "refill": [
    "Energy",
    "Missile",
    "Super"
  ]
}