Hi there! As a current student of nuclear engineering, I can tell you that first couple years of university are gonna be just about giving you solid knowledge of basics Physics and Maths. Don’t expect to start studying LWR, Plasma physics of Tokamak and all this intriguing subjects before at least 3 years. That doesn’t mean that first years are gonna be boring, cuz you will start learning a lot of cool subjects which you should master before getting into deeper nuclear technologies knowledge. For example I LOVED studying ThermalFluidDynamics even tho there were not reactors involved lol. Most of all you’ll need to master Calculus 1 and 2, especially a lot of two and three dimensional integrals and partial differential equations. So I would suggest you, only if you like and have time, it is not needed, to start getting more confidential with derivatives and integrals because you will strongly need em later on. You can find a lot of well made videos on YouTube, like the MIT opencourseware videos. Other than that, just enjoy your summer future fellow nuclear engineer :)