I don't know that much about the physics of neutrino radiation, or the fine details of bomb design. I do have a hard time believing that such a beam can dump enough neutron radiation into a subcritical bomb core to trigger a meltdown or fizzle detonation without also giving a dangerous exposure to any human who is in the way of that beam.

I'm also suspicious of the difficult of aiming a beam that's a meter wide at the target distance to hit a nuclear warhead core reliably halfway across the world. If you miss, how do you tell what direction you missed in and correct?