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I believe that you can't. Lake must not be frozen.

There are two items in the bunker to build Kerfur omega - the recipie and the manual book.

During the event when omega Kerfur gets abducted and his camera shows that he is in the "bowels" - player has to find him. During my playthrough - when I found him, he had two options available to select: deactivate and unequip (he was wearing a Jacket). When I clicked on "deactivate"  Kerfur disappeared completely and his Jacket dropped to the ground.  There was no glitching sounds or anything to indicate where did he go. When I checked the computer, Kerfur camera was no longer available, radar didn't showed his location either. After some time main menu glitching stopped and saving became available but Kerfur was gone.