Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you'd like to add some nuclear energy stocks to your portfolio, the iShares S&P Global Nuclear Energy Index Fund ETF (NASDAQ: NUCL) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The iShares ETF's expense ratio -- its annual fee -- is a relatively low 0.48 %. The fund is very small, though, so if you're thinking of buying, beware of possibly large spreads between its bid and ask prices. Consider using a limit order if you want to buy in.

This ETF has underperformed  the world market over the past three years, in part due to the low price of natural gas. As with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

Why nuclear?
If you don't like the idea of fossil fuels, or think that their demand and/or supply will run out too soon, you might want to consider nuclear-focused companies. Nuclear power has many detractors, but it also makes sense to a lot of people, and permits are being issued for more plants.

Few nuclear-related companies  had strong performances over the past year, but most could see their fortunes change in the coming years. Shaw Group (NYSE: SHAW), for example, surged 71%, but that's mainly on being acquired by Chicago Bridge & Iron (CBI). The latter provides services to the energy and natural resources sectors, working on projects related to water, hydrocarbon, and nuclear industries. The purchase of Shaw has some worried about additional debt, and others not happy about Shaw's nuclear energy operations. But Shaw does bring a big backlog.

EnergySolutions (ES) and FirstEnergy (FE 0.47%) each gained 4%. EnergySolutions is involved in nuclear waste treatment and disposal, and fell over the past year on news of a management shake-up and reduced guidance. My colleague Tom Jacobs saw that as an overreaction, however, and found the stock a bargain. Others like it, too, especially given the fact that some aging nuclear plants will be decommissioned in the coming years, requiring its services.

FirstEnergy, meanwhile, has suffered from being in the path of Hurricane Sandy. It has also been challenged in balancing its coal and gas operations and in dealing with lower energy prices and shrinking margins. Nonetheless, patient shareholders can collect a 5.2% dividend yield.

Meanwhile, Exelon (EXC 0.56%), which is having a rough year, dropped 22%. It's the nation's largest nuclear-power company, and is also involved in other energy-generation businesses as well. It's trading near a 52-week low and its dividend yield is near 7%. The company has been whacked by the relatively high cost of nuclear energy in an environment of very low gas prices. The current situation won't last forever, though. Exelon carries a lighter debt load than many peers, and is expanding into solar and wind power.

The big picture
Demand for energy isn't going away anytime soon, and nuclear energy is far from well out of favor. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.