There are a few problems that would prevent that.
One problem is that fusion and fission work differently. For fission you have neutron bullets flying around. When one causes fission, it pops off other bullets that can cause fission in other atoms. That's why you get chain reactions. Fusion is different, which is why it is so difficult to create fusion reactors that produce more energy than they require. You need high temperatures and pressures to force nuclei together. The sun gets that for free just by being so large. Even in the core of the sun with all that temperature and pressure, every cubic meter of the core only produces about 100w of energy. 15 cubic meters, like a small room that is 2.5 meters by 3 meters and 2 meters tall, only produces as much heat as a plug-in space heater. If the sun is fusing too much, the temperature goes up, the density decreases, and the reaction slows down. This is a self-regulating reaction that can last billions of years before the hydrogen fuel is used up.
If the moon were made of uranium, it would be about 6 times as dense if it were a solid. 435
In order to provide light like the sun, the outside would have to be the same temperature as the sun, that is what produces the light. Daylight is about 6500k. Uranium's boiling point at atmospheric pressure is 4091k. Tungsten, the element with the highest boiling point, is about 6000k. So to get light like the sun, the surface will have to be gaseous or plasma. Better to have a large surface that is non-reactive to dissipate the heat anyway, you don't want the gamma rays from the reactions directly raining down on the Earth. But for the heat to work it's way to the surface, the core that produces the heat would have to be even hotter. The pressure inside may be enough to keep the uranium liquid, but the outer layers would boil away and be lost to space, eventually exposing the core which would boil away as well without the pressure to keep it from doing so.
The sun is 385 times as far away from the Earth as the moon, so for the moon to provide the earth with the same energy, it must only produce 1/148225th as much energy as the sun. The sun produces about 3.8e26 joules each second, so the moon would only need to produce about 2.5e21 joules each second. That's about 30 million kg or 15,000 tons of U-235 each second. The good news is that if you had a moon's volume of U-235 and could control the reaction, that could last a billion years. 473