Boric acid in added cooling water ensures that nuclear fission is shut down . Cement grouting is most likely unsuitable at this stage because a functional cooling system needs to be maintained for as long as possible. Once short lived isotopes have decayed and heat production diminishes, then other options need to be explored. Partial meltdown may rule out dismantling the core. Japan has a highly developed reprocessing industry. Recycling the fuel elements would be the best long term strategy but entombing the whole lot in concrete would be in the mix of options.
