Recall from the Standard Model Path that protons are positive and that the
nucleus is held together by the
residual strong interaction.
A nucleus would blow
apart from the electrical repulsion between protons if it weren't "glued"
together by the gluon particles which affect every part of the nucleus.
Think of a nucleus as a tightly cocked spring (the electrical repulsion ) held in place by a very big rope (the residual strong force). Even though there is a lot of stored-up energy in the spring, it can't release this energy because the rope is too Strong.