First of all, you do not need to know anything about prisons!
Job Simulation Assessment Centres are about putting you in situations that you may find yourself in, such as dealing with conflict, accepting and giving of bo**ockings, gathering information from someone who may have difficulty expressing themselves, etc.
If one of the role players shouts at you, it is not at you personaly, but at what you represent, and once you have fully explained what it is that they are angry at, they will calm down.
Having acted as an assessor in JSACs, the best advice I can give is to tell you that all the clues are there. If something is said, it is for a reason, and if you don't pick up on it, it will be repeated at least once, but then it will be gone, so listen for key phrases being repeated.
Stay calm, don't get involved in an argument, and try to stay neutral and non-judgemental.
And good luck. Let us know how you get on.