These assurances are that the US would ensure that there is a lifetime supply of fuel for India's nuclear reactors and that they help India build its strategic fuel reserve.
If the US is unable to fulfill this commitment, it will convene a group of countries like Russia, France and the UK to ensure supply.
Even if, for some reason, they were to take back nuclear fuel, India retains the right to seek alternate sources of fuel for itself. India will have to build strategic reserve so that it does not go out nuclear fuel.
