Officials: Thorium use at Rocky Flats very limited

Ann Imse and Laura Frank, Rocky Mountain News

Monday, June 11, 2007

Government officials provided detailed testimony today hoping to persuade a federal compensation board that there is little chance workers at the former Rocky Flats site were contaminated by thorium.

The Advisory Board on Radiation and Worker Health is meeting in Denver today to consider whether certain workers from the now-demolished nuclear weapons plant should be grandfathered into a federal compensation program. The board is deciding whether three groups of workers should be automatically approved for aid because records of their contamination are too inaccurate to prove radiation caused their cancers.

Workers are still fighting for automatic approval for all former workers at Rocky Flats who come down with 22 radiogenic cancers. But the board has signaled that is unlikely.

Brant Ulsh, chief scientist for determining radiation doses at Rocky Flats, testified that very few workers at Rocky Flats used thorium, and none were contaminated by it. Ulsh, who works for the National Institute for Occupational Safety and Health, said his team tracked down the names of the small number of workers who used it. He then described the chemical and industrial processes they used, and insisted none had been exposed.

Thorium’s use in the manufacture of nuclear weapons was once so top-secret that it went by the code-name Penbarnite. The reason? Thorium-232 could be converted to weapons-grade uranium 233 in a nuclear reactor, and it was much easier to find than uranium, said John Mauro, a radiation expert who consults for the radiation advisory board.

"The secret was, we can make a weapon from it, and there’s so much of it," Mauro said.

As a result, the use of thorium at many nuclear weapons plants was kept secret. So officials have been surprised to discover records of it being used at many sites — and therefore a potential source of unrecorded contamination. Officials did not look for thorium at Rocky Flats until recently, six years after the compensation program began.

The weapons-grade uranium-233 produced from thorium turned out to contain some U-232, which emits extremely dangerous gamma rays. It would be very dangerous to workers, according to the Nuclear Threat Initiative.

It appears that officials stopped using thorium, but there’s no way to be certain.

"There is still classified information about thorium," Mauro said.

A Department of Energy report on nuclear clean-up from 1996 says the government purchased 13.8 million pounds of thorium from 1946 to 1963, including at least 11.7 million pounds for the Atomic Energy Commission. However, officials said no more than 240 kilos or 528 pounds per year were used at Rocky Flats, basically in experiments.

The board was still meeting this afternoon.