IF A volcano ever erupted beneath the planned nuclear waste repository at Yucca Mountain in Nevada it could cause a devastating explosion that sent high-level nuclear waste spewing into the atmosphere.
Yucca Mountain lies about 145 kilometres north-west of Las Vegas, within an active volcanic field. An eruption at the site is considered extremely unlikely, but it is possible. There are six craters within 20 kilometres of the site, including Lathrop Wells volcano, which formed by eruptions just 80,000 years ago. A study in 2000 estimated that there was a 1 in 1000 chance of an eruption at the site during the 10,000 years it will take for the radioactivity of the waste stored there to dissipate. And a recent report suggests that a more active cluster of volcanoes 100 kilometres to the north could be an even bigger threat (New Scientist, 20 April, p 11).
Now Andrew Woods of the BP Institute at the University of Cambridge and his colleagues have found that if an eruption occurred beneath the site, a rising sheet of magma could burst into the proposed storage tunnels 200 to 300 metres below the surface. The pressure in the hollow tunnels would be much lower than in the surrounding rock, so once the magma broke through it would gush into the tunnels at tens or hundreds of metres per second. The heat would be enough to deform and rupture the 7-centimetre-thick walls of the waste canisters in just 20 minutes, the researchers say.
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Worse, if the storage tunnels were open to the main access tunnel, this could act as an easy escape route for the magma to reach the surface, sending nuclear waste several miles skyward in an explosive eruption. According to Woods鈥檚 model, even if the tunnels were blocked, the magma could still build up enough pressure to break through to the surface. The study, which was funded by the Nuclear Regulatory Commission, is published in Geophysical Research Letters (DOI: 10.1029/2002GL014665).
The effort to determine whether Yucca Mountain would be a safe place to stash more than 75,000 tonnes of high-level nuclear waste has lasted more than 20 years and cost over $4 billion. The US Congress approved the site earlier this year, and last month President Bush signed a bill giving it the green light. But the state of Nevada is fiercely opposed and has five lawsuits pending against it. And the Department of Energy must still apply for a licence from the Nuclear Regulatory Commission to store waste underground at Yucca Mountain 鈥� a process that could last up to five years.
Volcanoes aren鈥檛 the only threat that has Nevada on edge about the plans for Yucca Mountain. Earthquakes and rising groundwater could also bring radioactive material to the surface.