Three weeks after a radiological release at the Waste Isolation Pilot Plant exposed 13 people, reassuring test results have been received and the organization is gearing up to send people back down into the military-related nuclear waste repository near Carlsbad, New Mexico, as soon as this week.

As of 8 March, 17 people tested positive for contamination at very low levels just above background radiation, indicating no increased risk of health effects from exposure. The 13 employees who initially tested positive had been working above-ground when they were exposed. The radionuclide released was predominantly the alpha-emitter americium-241 (half-life 430 years). Screening analysis of a filter retrieved on 15 February found a contamination of 0.6 Bq; WIPP laboratory analysis has increased the value to 0.87 Bq. Lab work also increased the dose estimate from 2 to 3 mrem. Since then, radiation levels have fallen and are at close to normal levels.

Happily, worker samples were negative for plutonium and americium, both of which were detected in initial sample testing, said Jose Franco, manager of the Carlsbad Field Office of the Department of Energy in a 5 March letter to local residents. The fact that the contamination was found in stool samples and not in urine suggests that it was not breathed into the lungs, WIPP operator Nuclear Waste Partnership said, which is good news because it indicates a lesser degree of internal contamination, particularly hazardous in the case of alpha- and beta-emitters.

On 7-8 March, sensors for radiation and air quality were lowered into two salt handling and air intake shafts. Preliminary readings found no evidence of radioactive contamination, which is good news, but was also expected because neither were in the flow path from the area where the radiation originated, NWP said. These measurements will establish how much protection workers will need.

After surveys are complete, personnel will go back into the site to check the stability of the mine and to try to identify the source of the contamination. First they will check the shafts, then air and surface contamination between the shafts, then they will go where operations were being carried out prior to the leak. Once they will find it, they will isolate it and make a plan to remove it, NWP said.

Operations have stopped at the site since the leak whilst surveying and preparatory work were being carried out. The New Mexico Environmental Department granted WIPP a 30-day extension to store waste above-ground while it plans to restart operations.

"We have not faced this kind of challenge in our 15-year history of waste operations, but I have the utmost confidence in the recovery team," said Jose Franco, manager of the DOE’s Carlsbad field office, in the 5 March note to residents.

The WIPP plant, built in the 1980s, is owned by the US Department of Energy (DOE) and operated by Nuclear Waste Partnership LLC (NWP). The facility disposes of transuranic waste packages from the US military in an underground salt formation.

Preparing instruments to send down WIPP salt handling shaft hoist on 7 March