Earlier quoted context omitted.
Do you have a link to the study?
I had to dig around but I think this the one I remember. There are two other reports linked in the comments. https://old.reddit.com/r/preppers/comments/11tblpp/found_it_...
https://irp.fas.org/congress/2008_hr/emp.pdf
It's referring to a fictional story in that quote, but the scientist says that 90% is accurate for the real world if that scenario were to happen. Pretty chilling.