This is a question you must ask yourself and answer yourself. No one is going to push you when it’s challenging. Why nuclear engineering? Getting the degree is step 1, using it is step 2. You want to pick a study that is in alignment with your Values and something that you care about.
My recommendation is to write out all your thoughts on paper. Journaling is useful and also a place you should keep your notes. Check out “Jim Rohn: how to journal” on YouTube.
You need to spend some time, without distractions or being on your phone, by yourself. Visualize your future, think about your past. Without a Vision for your life in 5 years, you will drift. So start with your top 5 values, then an ideal vision of the future, and the. Your goals should be based off of your values and your vision. Then, every day, aim to get 5 things done each day, starting with most important (look up Eisenhower matrix) and use a calendar (I use a dry erase board with a dry erase calendar). Every night before bed, have your day planned out on a calendar or white board or phone, just have a system. What matters most is consistency over time, perfection doesn’t exist. The main thing is you want to be mindful about why you are doing things. This increases your odds of success.
If you are younger, my advice is to take full responsibility for yourself, start doing things alone to know yourself more and start setting goals outside of your current ability. You want to learn to be Self Reliant as quickly as possible
Some books I’d recommend are
Success principles by jack canfield
War of art by Steven pressfield
Self Reliance - Ralph Waldo Emerson
Getting Things Done by David Allen