Nuclear waste is not a reason to avoid using nuclear energy, according to Bill Gates, the Microsoft co-founder and philanthropist who more recently founded a next-generation nuclear energy startup, TerraPower.

One common criticism of nuclear power is that nuclear reactors generate waste that stays radioactive for thousands of years.

“The waste problems should not be a reason to not do nuclear,” Gates said in an interview with the German business publication Handelsblatt, published on Thursday. “The amount of waste involved, the ability to do geological sequestration — that’s not a reason not to do nuclear.”

The volume of nuclear waste is very small, especially when compared with the energy generated, Gates said.

“Say the U.S. was completely nuclear-powered — it’s a few rooms worth of total waste. So not, it’s not a gigantic thing,” Gates said. The cost of storing and sequestering nuclear waste underground is “not a huge problem,” as it can be put into deep boreholes underground “where it stays geologically for hundreds of millions of years,” he said.

In contrast, the amount of carbon dioxide emissions generated from burning fossil fuels for energy is “something gigantic” and sequestering that underground is a very hard problem, which Gates said “may not be possible.”

Nuclear power is classified as a “zero-emission clean energy source” by the U.S. Department of Energy, because generating electricity with nuclear fission does not release any greenhouse gas emissions.

Currently, 19% of electricity generated in the United States comes from nuclear power plants, according to the U.S. Energy Information Administration. That represents about half of the carbon-free electricity generation in the U.S., according to the U.S. Department of Energy.

But after a boom of nuclear power reactor construction in the 1970s and 1980s, the construction of new nuclear power generation came to a virtual standstill.

“The best hope for nuclear is if we could get a completely new generation — and I’m biased, because I’m involved in that — where the countries that are committed to nuclear prove it out and show that the economic safety, waste management is handled,” Gates said.

“And then the other countries who are less engaged can look at that and see what they think, give it a fresh evaluation. And, you know, that data on that won’t be in for almost another eight years or so,” Gates said.

After decades of nuclear power generation, there is still no permanent repository for nuclear waste in the United States. The closest the U.S. nuclear industry got to a permanent nuclear waste repository was at Yucca Mountain in Nevada, but that effort has been stalled because of political impasses.

Currently, nuclear waste is stored in dry casks, which are stainless steel canisters surrounded by concrete. The top nuclear watchdog in the U.S., the Nuclear Regulatory Commission, considers these dry casks to be safe. The world’s first permeant underground geological storage site is being constructed in Olkiluoto, Finland.

Also, not all nuclear waste has the same level of radioactivity. Most of the radioactivity is in a very small percentage of the waste generated.

“The vast majority of the volume of nuclear waste there is Low Level Waste,” Jonathan Cobb, spokesperson for the World Nuclear Association, told CNBC. “Around 90% of the volume of nuclear waste produced is LLW, but it contains only 1% of the radioactivity. This can include things like protective clothing, mops, filters, equipment and tools that have become contaminated with radioactive material at a low level. One common category of LLW comes from nuclear medicine use and can include swabs, injection needles and syringes.”

Meanwhile the high-level nuclear waste, which includes used nuclear fuel or higher activity wastes from reprocessing, is “about 3% of the volume of radioactive wastes produced, but contains 95% of the radioactivity,” Cobb told CNBC.