I have no direct experience with WashUStL. I know several students who attended WUSTL and loved their experience. All were / are top students and are social, but not “partiers”.
With over 7,100 academically motivated & focused students, I think that you will be able to find many like-minded students at WUSTL.
The social scene is what you make of it. There are kids who go out several nights a week and there are kids who study 24/7. All is accepted and it is what you make of it. There is no judgment if you want an active social life or a quieter one. Kids are very friendly and supportive of each other.
Underclassmen tend to party in the dorms and some go out to clubs off campus. Upperclassmen tend to have parties off campus, go to bars and clubs off campus.