I wanted to ask , do you have to be a really smart person , as I would love to get into engineering, I am a hard worker , but I'm afaird that I can't do it as I don't believe that I'm smart enough .

No, you don’t have to be a really smart person to become a nuclear engineer.  You just need to be willing to work hard and not give up.  Remember that life is about learning and realizing that anything is possible when you put your mind to it. Once you realize that, everything will come easier to you. Your fears will disappear and you can take steady steps towards your dreams.  At the same time, mistakes and failures will happen, that is just part of being human, but you need to learn from your mistakes and correct your path along the way to align yourself with your goals.  As the saying goes, sometimes the wind is against you – but remember, although you cannot change the wind, you can adjust your sail and as long as you persist you will succeed. I hope you have not given up on your dream.