As Duanmu Huai currently hasn't unlocked the Tribunal Library, he can't yet analyze the Antimatter Energy Core. Therefore, he chose to send the Antimatter Energy Core back to the warehouse in the Core Cabin using a teleport beacon. After all, he can't just walk around with such a thing in his hands.
Although the technology of the ancient saints was not problematic, this was an energy core. If it exploded, the consequences would be far more dangerous than a nuclear power plant leakage. There was even an incident where a player's careless actions caused the destruction of an entire galaxy. Even though the danger level of the Antimatter Energy Core was not as high as the Dark Matter Energy Core, if it exploded... Well, considering Duanmu Huai's current 22nd level, he would probably be obliterated in a blink of an eye.