Arak is one of the largest heavy-water nuclear reactors in the world, and the fact that Iran agreed to (and has) filled the reactor with cement to render it useless is a substantial sign that they are sincerely interested in working towards a peaceful existence. Iran could have easily refused to give up one of their largest nuclear weapons, but in contrast they agreed to disarm and surrender it.
Yes, I agree that Iran's agreement to fill Arak shows their willingness to acheive peace with the rest of the world. This shows that they are willing to minimize their nuclear program so that they will not use it in the future. It also shows that they can be cooperative and peaceful instead of harboring threatening nuclear weapons.
Iran is a Shiite Islamic theocracy. The Shiites believe that it is their mission to bathe the world in blood so ther "messiah" the Mahdi can come back. They will practice taqiyya and lie about intending to fill the facility with concrete, however, they will never do it. They have already broken the treaty when they test-fired a missile within less than a mile of one of our warships. They will lie, and I don't believe they are serious about following the agreement.
It is a strategic temporary truce, or "hudna" which allows Iran to take an economic "breezer". It will take a decade for Iran to economically recover, and after that -- it will not matter because they by agreement will restart the nuclear processing over again. Arak can be rebuilt quite easily.
Iran is definitely not interested in achieving peace with the rest of the world. I think the move to fill its heavy-water nuclear reactor with cement was strictly a tactic to decieve the rest of the world. Iran has proven time and time again that they cannot be trusted. Why would this be any different?