FAQ: How will San Onofre store its spent nuclear fuel?

Southern California Edison announced it will permanently close the remaining reactors at the San Onofre nuclear power plant. The spent nuclear fuel will be stored on site "for  a very long time," said Edison chief executive Ted Craver during a press conference on Friday.

According to Craver, the company has a $2.7 billion fund to help shut down the site. That will include decommissioning the reactors, disposing of equipment and moving radioactive spent fuel to storage units.

The shutdown raises questions about how the potentially hazardous materials will be stored and what risks are involved. We have some answers below.

Q: What will happen to the spent fuel at San Onofre nuclear plant?

Spent fuel rods are stored in two ways at San Onofre. After they are used in the reactor, they are moved into a pool where they cool down. Since these rods are radioactive and extremely hot, this cooling process can take up to 5 years.

Once they are cool enough to move, they are transferred to a storage device called a dry cask. Dry casks are essentially steel and concrete structures made for long term storage. They are sealed tight, keeping the radioactive materials from entering the environment. They are very common and used for storage at nuclear plants around the world. 

Q: How much spent fuel is there at San Onofre?

The plant has generated around 1,400 metric tons of nuclear waste over its lifetime. The majority of it is still waiting in the spent fuel pools to be moved to dry casks. Right now, San Onofre has around 40 casks full of spent fuel. It will need about 100 more to store the remaining waste. Each dry cask costs roughly $1 million.

Q: What is the spent fuel made of?

The fuel starts off as uranium. After being irradiated in a nuclear reactor, it turns into a "witches brew" of radioactive material, according to Michael Mariotte, executive director of the environmental advocacy group Nuclear Information and Resource Service. That brew includes dangerous material such as plutonium-239, strontium-90 and cesium-137. Some of these materials will take millions of years to reach undetectable levels.

Q: How long will the waste be stored at San Onofre?

Right now there is no end date for how long this nuclear waste will remain at San Onofre. And there is also no long term storage for spent nuclear materials in the U.S. In 2010, President Obama stopped plans to create an underground nuclear storage site at Yucca Mountain in Nevada.

Dry casks are not a long term storage solution since they can start to crack after as little as 30 years, though they may last up to 100 years. The spent fuel needs to remain sealed for hundreds of thousands of years. The U.S. government currently has no serious long term storage plan in the works.

Q: What are the risks involved with storage at San Onofre?

Storing spent fuel in cooling pools, as is currently the case with much of the waste at San Onofre, is "not a very risk-free situation," says Najmedin Meshkati, professor of engineering at USC.

If a natural disaster were to damage the pools, the water could drain out and the exposed fuel rods could catch fire and start a meltdown. This was one of disaster scenarios engineers feared after the Fukushima Daiichi nuclear plant in Japan was damaged by a tsunami in 2011. 

However, Meshkati says while that series of events is possible, he doesn't think residents of Southern California should be alarmed. He says the bigger concern is finding a permanent place to keep the fuel once it is moved to dry cask storage.

"This is a temporary place," says Meshkati. He insists that the United States needs a larger, permanent home for its spent fuel.

What do you think of Edison's plans? What do you believe should be done with the nuclear material? Let us know in the comments.