Teachers apply for other jobs. Applying for other jobs doesn't necessarily mean you're leaving. Your admin knows this. Just be honest. Tell your principal/supervisor that you're applying for other jobs. Ask to use them as a reference (because your principal should probably be on your reference list). They may ask why but more than likely they'll just say they'd "hate to see you go" but otherwise not make a big deal about it because, again, it happens all the time. There shouldn't be any animosity there.

I applied for other jobs almost every year when I started out and was never non-renewed and I don't personally know anyone who was non-renewed for that reason either.