ALBUQUERQUE, N.M. (AP) -- A union representing some 200 workers at the nation's only underground nuclear waste dump said Tuesday its wants to be sure employees are safe when the repository reopens after a radiation leak that exposed at least 13 people. 
The Waste Isolation Pilot Plant near Carlsbad has been off-limits to most workers for nearly three weeks. Only essential workers have been called to duty and others have been using the down time to keep current with regular training requirements at an off-site training center, said officials from United Steelworkers of America.
Union officials said they're waiting for more information from the U.S. Department of Energy and Nuclear Waste Partnership LLC, the contractor that runs the repository.
"What we're trying to understand is what happened, where this contamination came from and then understand how to correct this problem and make certain that something similar is not going to happen again," said Jim Frederick, assistant director of the union's health, safety and environment department.
Some of the 13 workers who were exposed during the Feb. 14 night shift were union members. Another 140 employees showed up for work the following day, and union officials say if there's any doubt about whether they were exposed, more tests should be done.
WIPP officials say they have yet to determine what caused the leak. The results of more air, soil, vegetation and water samples are expected in the coming days.
WIPP is the nation's first underground nuclear repository and the only facility in the country that can store plutonium-contaminated clothing and tools from Los Alamos National Laboratory and other federal nuclear sites.
It remained unclear Tuesday how soon the repository could begin accepting shipments again.
The uncertainty continues to fuel questions about the cornerstone of the Department of Energy's $5-billion-a-year program for cleaning up waste scattered across the country from decades of nuclear-bomb making.
In budget proposals unveiled Tuesday, the DOE requested $5.6 billion for environmental management programs that include the cleanup of millions of gallons of liquid radioactive waste, thousands of tons of nuclear material and large volumes of other low-level waste. That's more than what was spent in 2013 but less than the $5.8 billion authorized this year.
According to the DOE, its request for the next fiscal year makes shipments of transuranic waste from Los Alamos to WIPP a priority. The agency's proposed spending for environmental management projects at WIPP and Los Alamos is slightly less than this year's respective budgets of $221 million and $224 million.
A union representing some 200 workers at the nation's only underground nuclear waste dump said its wants to be sure employees are safe when the repository reopens after a radiation leak.