Yeah radiation isn't an issue, when you dilute it in billions tons of water it doesn't matter. We fired dozens if not hundreds of nukes in underwater tests and no pollution problems arouse because of it.

As for tsunami, one nuke shouldn't be enough but a number properly positioned should. It's pretty pointless though since at this point you're getting nuked back for sure, and your tsunami does nothing in preventing enemy from nuking you back (and nuclear war is all about killing enemy's ability to nuke you, attacking cities is distraction that wastes valuable warheads)

Its supposedly 100 megatons Same size as the Tsar Bomba. That's a lot of energy too.