Federal researchers there are seeking to fuse some of the lightest atoms in the universe to study — and hopefully harness — the type of energy produced by hydrogen bombs and the sun.

The tests were delayed six months while safety devices were installed to protect workers from radiation at the National Ignition Facility, a stadium-sized laboratory that contains 192 lasers trained on a target the size of a BB. The goal is to generate temperatures of more than 100 million degrees to fuse hydrogen atoms and release nuclear energy. 

Scientists describe this process, which they hope to achieve next year, as the creation of a miniature star on earth.

But the $3.5 billion ignition facility, derided by some critics as taxpayer-financed science fiction, is running into new challenges that may further delay and perhaps scuttle its goal.

Among those challenges is the unanticipated presence of particles that clog filters designed to prevent the escape of radioactive material. Officials have proposed bypassing the filters for some experiments and venting radioactive particles directly into the air.

Officials say the radiation risks to people living in the surrounding area and to Lawrence Livermore researchers not involved with the experiments will be negligible. But according to a worst-case scenario outlined in a draft environmental report, an average of one worker involved in the experiments could die every 18 years from cancer caused by radiation exposure.

“There is no safe level of exposure,” said Marylia Kelley, the group’s executive director.

The ignition facility was designed to help the United States government monitor the safety of nuclear weapons without having to test them. One of its primary missions is to help improve the United States’ weapons arsenal, but officials also describe the facility as an effort to revolutionize nuclear power.

If researchers can fuse atoms and control the energy that is released, an era of abundant carbon-free power could dawn. The technology would minimize the waste and storage issues faced by fission-based nuclear power plants, which split heavy atoms into smaller ones.

The tipping point for nuclear fusion is “ignition,” the moment when the lasers release the same amount of energy that is required to power them.

But that goal has remained elusive.

“If it was easy, we would have done it 50 years ago,” said Doug Eddy, a senior nuclear security agency operations manager working on the project.

Mr. Eddy said the ignition facility was engaged in a “tuning campaign,” raising the amount of fuel used and the amount of energy generated by the lasers.

“You keep bringing it up a bit more and more and more,” he said. “You don’t want to go big-time straight off the bat.”

Researchers have discovered that more power will be needed for some tests than first thought, Mr. Eddy said. They propose nearly tripling the amount of laser power to 120 megajoules, roughly the equivalent amount of energy produced by 50 pounds of TNT, which will increase radiation levels.

The types of hydrogen that will be fused are called deuterium and tritium. Tritium is radioactive, and fine molecular filters are installed at the facility to prevent it from escaping.

But the tritium is proving difficult to manage. The molecules are so small that other tiny atoms are also captured in the filters. Workers frequently enter the experiment chamber to change the clogged filters.

To solve that problem, officials propose allowing more tritium to accumulate before the filters are removed and sent to Nevada as low-level radioactive waste.

More controversially, the officials have proposed bypassing the filters during some experiments and venting tritium through an exhaust system into the air.

Tritium dissolves in water, persists for decades in the environment and can cause cancer.

“It will bind to DNA, so it gets pretty much everywhere in the body once it’s been absorbed,” said Mark Little, a senior scientist at the National Cancer Institute who has published papers dealing with tritium’s hazards. “With large quantities, damage can be done. As long as the releases are kept within mandatory limits, I would imagine the risks are small.”

Officials at the Department of Energy say the tritium releases at Lawrence Livermore would remain below safety limits set by the Environmental Protection Agency. But Tri-Valley CAREs points to a long list of tritium accidents and airborne releases from Livermore facilities, which have caused radioactive material to accumulate in Livermore’s water, food, honey and wine.

“When tritium gets into the environment and it’s on top of radiation being released from other parts of the laboratory, it potentially increases the dose and potentially increases the risk,” Ms. Kelley said.

And tritium is not her organization’s only concern, she added.

When tritium and deuterium fuse to create helium, a neutron is squeezed out and radiation is released. The neutrons can seep out of the building and rise into the atmosphere, where they cause additional radiation called skyshine to rain back down.

“If it’s high-enough energy, it can scatter and go up to the atmosphere, scatter in the atmosphere and bounce back down,” Mr. Eddy said. “Where it will scatter down is mostly around the site, but there’s no guarantee.”

Officials said that they would determine an area around the Livermore building where radiation might exceed federal safety standards and that Livermore personnel not involved with the research would be evacuated from those areas.

Employees will be warned not to enter the area until after the experiment.

Despite several delays, Mr. Eddy said he was confident that ignition would occur next year. But some scientists question whether ignition will ever be possible.

“It’s a tough job, and some of the peer review questioned whether it would work,” said Frank von Hippel, a Princeton University physics professor and former science adviser to President Bill Clinton. “I think there are still skeptics out there.”