Update: A reader pointed out that the headline is inaccurate. The issue at WIPP is airborne contamination (by radioactive material), not airborne radiation. In order to be gentle with search engines and existing links, the headline will remain as is. End Update.
On Friday, February 14 at 11:30 pm, a continuous air monitoring alarm went off at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, NM. The alarm indicated the presence of radioactive isotopes in the air inside the facility downstream of where waste is being stored. On Thursday, February 20, the Carlsbad Environmental Monitoring and Research Center reported that it had found trace levels of americium and plutonium at a monitoring station approximately 0.6 miles from the facility.
WIPP is an operating underground waste repository that is designated as a permanent storage location for transuranic — isotopes of elements heavier than uranium — waste generated by defense-related activities. WIPP’s storage caverns are located more than 2,000 feet below ground in an ancient salt deposit.
There was no one inside the facility when the air monitors alarmed. There have been no injuries or exposures reported. WIPP’s ventilation system immediately shifted to an air recycling mode that prevents air from inside the facility from reaching outside.
This is the first time that the air monitors have alarmed inside WIPP during its 15-year operating history, though there have been four past instances when environmental airborne radiation measurements taken near the site have exceeded the usual background level. In each of the previous cases, the source was eventually traced to fallout from the nuclear weapons tests that were performed during the 1940s through the early 1960s.
According to a February 18 story in the Current Argus News titled WIPP awaits analysis of radiation, the facility operators have not been able to report the cause of the facility’s elevated airborne radiation levels. The underground portions of WIPP have been inaccessible since Friday, with workers being assigned to different tasks while waiting for the airborne radiation level to fall low enough to allow workers to enter the facility. Some people wondered if the temporary suspension of operations would lead to layoffs or furloughs, but that is apparently not the case.
Despite the suspension, rumors about temporary layoffs were unfounded, said WIPP officials.
“No Nuclear Waste Partnership personnel are being laid off due to the halt in operations,” said Donavan Mager, NWP communications manager in an email. “As a precaution, some site personnel are working at the Skeen-Whitlock Building on National Parks Highway.”
Today, the Carlsbad Environmental Monitoring and Research Center (CEMRC) reported that it had detected trace quantities of americium and plutonium on filters that collect air approximately 0.6 miles away from the facility. Here is a quote from their press release:
Following the announcement of the underground radiation detection event by DOE, the air sampling station filter was removed for analysis on Sunday, February 16th at approximately 9:40 am by CEMRC personnel. The filter underwent destructive analysis and radiochemical separation at the CEMRC laboratory and was measured for alpha and gamma radiation activity. Analyses of this filter show that 0.64 Becquerels (Bq) of 241Am and 0.046 Bq of 239+240Pu were found to be deposited on the filter media. The Becquerel is an international unit of measure of radioactivity and is defined as one disintegration per second.
The press release continues with additional details. The filter with the measurable amount of radioactive material had been installed in the air monitoring station at 12:40 pm on Tuesday, February 11th. The previously installed filter was clean; there were no radioactive materials detected. The filter showing detectable levels was removed on Sunday, February 16 at 9:40; it had filtered air for a little more than 33 hours after the initial alarm inside the facility.
According to CEMRC, the measured levels were more than 50 times less than the EPA action level of 37 Bq (0.001 microcurie). However, those levels were higher than previously measured. Since they appeared in close sequence with the facility air monitoring alarm it seems logical to assume that the isotopes detected came from inside the facility.
It is worthwhile to understand the sensitivity of the measurement.
Dr. Russell Hardy, the Director of CEMRC, provided some additional details over the telephone.
The fixed airborne monitoring stations filter 20 standard cubic feet of air per minute (SCFM). With an airflow of 20 SCFM, and a duration of approximately 33 hours between the initial alarm and collecting the filter, the 0.65 Bq of radioactive material reported from the station located 0.6 miles from the facility was distributed in almost 40,000 cubic feet of air.
Analytical processes that can measure 0.046 Bq of plutonium isotopes or 0.64 Bq of Am-241 in that volume of air are designed to almost count atoms.
There are good reasons why it took the CEMRC five days to perform and then announce the results of their radiochemical separation / counting processes. That kind of sensitivity requires a integration process that collects data over a long period of time. Before she can begin the counting process, the analyst must dissolve the filters and then separate the resulting material into its possible chemical components.
The separated samples are counted for gamma emissions for 48 hours. Under normal circumstances, the process uses five days for counting alpha particles, but since there was a known release, the procedure has been shortened to a 24 hour count.
The CEMRC has two other monitoring locations. One located 11.8 miles away from WIPP showed no detectable levels. One that is about 100 yards away from the WIPP exhaust stack was inaccessible until 9:00 am Tuesday, February 18 because the site was closed to all non essential personnel. Dr. Hardy informed me that his team is considered to be “nonessential,” but he persisted in his efforts to obtain access until that permission was granted.
Since the air monitoring equipment was running throughout the time that there was no access, no information will be lost. The access delay merely affected the time when the results will be available.
Soon after Dr. Hardy’s team had collected the filter from the site air monitoring station, CEMRC took delivery of additional air filters from inside the facility. Ten of those filters were in equipment that samples the exhaust stack before air passes through the high efficiency (HEPA) filters that filter air from the operational portion of the facility before it is exhausted to the environment.
Update: (Posted 02/21/2014 at 0324) The underground facility has a ventilation system that draws in 425,000 SCFM of outside air, distributes it through the occupied areas, then past areas containing waste and then back to the environment. There are continuous air monitors that sample the air, both in the spaces where people work and after it passes through areas containing waste.
When the air monitors sense any contamination, that ventilation is immediately redirected through high efficiency particulate absorption (HEPA) filters before being put back into the environment. The flow rate is also reduced by a factor of four to 100,000 SCFM.
Source – Comment from Jim Conca, former Director of CEMRC (2004-2010)
The basis for the design of not always filtering the air is that HEPA filters absorb all particulates. They would get saturated frequently if they were continuously being used to filter 425,000 SCFM even if it was not contaminated. Not only is that an operational and cost issue, but it would not improve safety because the filters would be unlikely to be fully available if they were needed to filter out radioactive contamination.
One of many mistakes made at TMI was that exhaust air was improperly being directed through filters all of the time. Those filters were then not as effective in removing radioactive iodine (I-131) as the designers expected at the time they were actually needed. End Update.
Another set of filters came from sampling equipment located on the other side of the HEPA filter, but still inside of the exhaust stack.
There is only one radiochemist on Dr. Hardy’s staff. That limits the amount of parallel processing that can be done while still maintaining good quality control and producing reliable results.
Because there is a strong desire to understand the exact conditions inside of WIPP, the task of measuring the exhaust stack filters has been prioritized before the third ambient air sample. Dr. Hardy indicated that results from the station located about 100 yards from the exhaust stack will be reported sometime next week.
I want to emphasize one more time that 0.64 Bq of Am-241 is a very small amount of radioactive material; there is no public hazard. The people assigned to monitor WIPP and its effects on the public are taking this event seriously. They are providing the best information they can within the resource constraints available.
Note: CEMRC is a division of the College of Engineering at the University of New Mexico that operates a 26,000 square foot radiochemistry facility. It is under contract with the Department of Energy to provide independent monitoring services in the area around WIPP.