X-energy, a startup operating in stealth since 2009, was the recipient of a $40 million grant from the Department of Energy last month.

The firm will use the funding to continue development of its Xe-100 pebble bed High Temperature Gas-cooled reactor (HTGR), according to their official announcement.  HTGR is intended to be a safe, portable reactor capable of generating an estimated 50 megawatts of electricity and 125 megawatts of heat.

Fortune adds that a key component of HTGR “[pebbles that are]…tennis-ball-sized spheres of graphite, which house tiny pellets of uranium that are coated in ceramic,” power the reactor by piling on top of each other to create this energy.

An important distinction between X-energy’s construct and traditional reactors is that HTGR uses helium as a coolant to control the pebbles’ temperature as well as incorporate a form of helium to start cooling down the reactor upon reaching a certain threshold. Normal nuclear reactors rely on water to keep their uranium rods cool, but the removal of H20 can lead to a potential meltdown.

X-Energy CEO Kam Ghaffarian told Fortune the remainder of the grant will be used for doubling its staff, refining the fuel creation process, and advancing development of the company’s reactor designs.

There is a partnership stipulation built into this funding so the enterprise is working with a variety of labs at Oregon State University, Oak Ridge National Laboratory and similar locations to improve their technology.

X-energy is looking to begin operations at demonstration reactor by 2035.