Nuclear Fuel Rods are one of the main collectibles in The Sims 2. Their main purpose is to be used to recharge the furnace in the Reactor Room of Strangetown Hotel, but they can also be sold to the Clerk at the City Hall for 40 simoleons.
Along with Gourds, they can be found around town and in the Desert at various points in the day, but are relatively common. Nuclear Fuel Rods are needed to complete part of the main goals at the start of the game and also during Optimum Alfred's stay in the hotel, when he asks you to bring him 20 of them. Players that cannot find any more of them to the naked eye can go into the desert and use the Metal Detector and dig them up if they have it.
Nuclear Fuel Rods respawn everytime the game is opened after being closed, which has led to many players collecting them, saving, then restarting the game to get more and earn more money. They can, as mentioned above, be dug up from the desert if the player has the Metal Detector.