LOS ANGELES, Feb 17 (Reuters) - The U.S. Nuclear Regulatory Commission has approved a rule for allowable radiation levels at the proposed nuclear waste site at Yucca Mountain in Nevada for up to 1 million years, the NRC announced on Tuesday.

The NRC is now accepting the radiation standards from Yucca Mountain as determined by the U.S. Environmental Protection Agency.

The NRC kept the EPA's rule of limiting the dose of radiation to 15 millirem for the first 10,000 years after disposal. Now, the NRC has adopted the EPA's limit of 100 millirem from 10,001 years to 1 million years.

In the United States, the average American is exposed to 350 millirem per year, from sources ranging from X-rays to food, according to Princeton University.

Much of the nuclear waste in the United States is now cased in concrete and stored at nuclear power plants. There are 121 storage locations in 39 states.

Yucca Mountain is still a long way from being approved for storage of nuclear waste. The U.S. Department of Energy has said it could open in 2020 at the earliest, about 20 years beyond the initial estimate of its opening.

The idea of a national store for nuclear waste at Yucca Mountain was passed by Congress in 1982.

Last year, the DOE estimated that the cost of Yucca Mountain would be more than $96 billion, up from a 2001 estimate of $57.5 billion.

The DOE last June filed an application with the NRC for Yucca Mountain's operation.