Software Developer Co-Op applicants have rated the interview process at TRIUMF with 3 out of 5 (where 5 is the highest level of difficulty) and assessed their interview experience as 100% positive. To compare, the company-average is 60% positive. This is according to Glassdoor user ratings.
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I applied through university. I interviewed at TRIUMF
Interview
Interviewers asked fairly standard interview questions, no technical questions, and were very easy to get along with. I'd suggest researching the experiment you are applying to work on, and read up on some of the publications of your interviewers. From that, you'll get a good idea of whether or not the project interests you.