Neutron bomb won't fix Fukushima. LENR might.

The idea of using a neutron bomb in the first place is to expose the uranium and its radioactive break down elements to a neutron beam to convert them to inert materials.

Problem with a neutron bomb is that the neutrons would not penetrate far into the 'elephant's foot,' and it would destroy all nearby life (down to bacteria), produce radioactive elements in the environment and cover the area in the non-reacted payload.

Details: [link to pesn.com]

Instead, low-energy nuclear reaction technology could be used to transmute fuel rods into stable elements by grinding them up into nano-particles and exposing them to ultra low momentum neutrons.

source: [link to www.i-sis.org.uk]

I'm not sure how they could capture the melted material, but it could be used to decommission any unwanted fuel rods (like those in building 4).

Peace.