I understand that in nuclear reactions such as fusion or fission, it is known that energy released due to the mass defect to obey the conservation of energy.
However, researching online; I fount that the conservation of momentum is also conserved! What is the reason, even though total mass is not conserved?
My reasoning, is that since there are no external forces, conservation of momentum is always true. But since there is a mass defect, then mv inital ≠ mv final.
How do I reconcile these two contradictions?