22 août 2013
Une fuite radioactive sur un système de transfert de cuves à Hanford a entrainé l’évacuation de travailleurs.
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En janvier 2013, a été remise dans l’actualité, la détection de fuites sur de vieux réservoirs contenant des millions de litres de boue radioactive provenant des décennies de production de plutonium destiné aux armes nucléaires. Lors de transferts de ces boues vers de nouveaux réservoirs à double enveloppe, une fuite radioactive est survenue.
UPDATED : Hanford radioactive leak may have been transfer system
Published : August 22, 2013
By Annette Cary — Tri-City Herald
Richland — Work has stopped to empty radioactive waste from old tanks at the Hanford nuclear reservation after an emergency Wednesday night.
An unusual radiation reading at 9:35 p.m. indicated radioactive waste had leaked, possibly from a transfer system being used to empty high level radioactive and hazardous chemical waste from Tank C-101. However, no waste was visible on the ground, indicating the leak may be small.
Four workers immediately stopped using the retrieval system and evacuated the C Tank Farm, an area with 16 underground tanks. No contamination was found on the workers, but they were sent to Kadlec Regional Medical Center in Richland as a precaution.
Others in central Hanford and near the K Reactors along the Columbia River were ordered to take cover and access to Hanford was restricted.
The Department of Energy issued an "alert," the lowest level emergency DOE declares, from 9:35 p.m. Wednesday until about 5:05 a.m. Thursday, and it activated its emergency operations center.
The suspected leak could be another setback for DOE as it struggles to meet a court-enforced consent decree to have all tanks in the C Tank Farm emptied before October 2014.
"Due to this incident, the transfer of waste from C-101 to a double-shell tank has been halted until crews are able to investigate further and ensure that it is safe to resume work," said the Washington State Department of Ecology in a statement Thursday. "It is unknown how long this will take or how any delays may affect U.S. DOE’s ability to meet the 2014 waste retrieval deadline."
DOE had no information available Thursday on how long waste retrieval will be stopped at Tank C-101 or Tank C-110, the only other tank now being emptied at Hanford.
DOE already had notified DOE that two other of the C Farm tanks are at risk of not being emptied by the consent decree deadline. Seven C Farm Tanks still contain waste above regulatory limits.
The Wednesday night incident began when unexpected radiation was detected near a sluicer shield box, which holds equipment for the system used to spray liquid to help remove waste within Tank C-101, a 530,000-gallon capacity underground tank. Liquid already contaminated with radioactive waste is used rather than water to prevent the creation of more waste.
The reading was for beta radiation, which is relatively easy to block, indicating that waste may have escaped containment within the sluice box or a hose within a larger hose used to transfer the waste. Waste from Hanford’s single-shell tanks, some of them built during World War II, is being transferred to newer double-shell tanks until the waste can be treated for disposal.
Initially, a survey was done around the perimeter of the C Tank Farm and found no abnormal radiation readings or hazardous chemicals, according to DOE.
Shortly before it was completed, DOE was confident enough that workers were not in danger to lift the "take cover" order for most Hanford workers at 12:35 a.m. However, workers in the 200 East Area of central Hanford, which includes the C Tank Farm, and the nearby vitrification plant under construction remained under the take-cover order.
At 3:52 a.m., a team of five entered the C Tank Farm to do more monitoring near the Tank C-101 sluicer shield box, according to DOE. The team included two firefighters, a nuclear chemical operator, an industrial hygiene technician and a health physics technician.
The team found no visible spill of waste. But it again found an abnormal radiation reading at the sluicer shield box, although at lower levels than the night before, according to DOE.
Team members applied a fixative to a 3-square-foot area to prevent the spread of any potential contamination.
About 4 a.m. barriers were installed around C Tank Farm and the take-cover order was lifted for the remainder of the 200 East Area and the vit plant. Workers were told to report to work as usual for the Thursday day shift.
About an hour later, DOE lifted the alert. DOE protocol calls for an alert to be issued if there is a liquid waste leak from a transfer system that is visible on the ground or is indicated by abnormal beta radiation readings.
The four workers sent to Kadlec have been cleared to return to work. However, blood and urine samples were collected and laboratory results will not be available for about a week.
The Washington State Department of Health has confirmed that the suspected leak presents no threat to public health or the environment.
"We are pleased with the response from both the U.S. Department of Energy and the contractor, Washington River Protection Solutions, to address the incident quickly and provide prompt notification to the state," said the Department of Ecology statement.
Work had been going well to empty Tank C-101 of radioactive waste until Wednesday. Since December, 87 percent of the estimated 88,000 gallons of solid waste in the tank had been removed.
That included not just the sludge, with a consistency of peanut butter, but also the hard layer beneath it.
That layer was being sprayed with high pressure water from a skid originally set up for the Mobile Arm Retrieval System, or MARS, a robust new robotic arm, which was being used to empty Tank C-107 until a pump failed in that tank this summer.
Engineers installed a splitter on the outlet of the skid to allow high-pressure water to flow to either tank. That allowed the hard waste at the bottom of Tank C-101 to be sprayed with 4,700 pounds per square inch of pressure, breaking up some of the larger pieces of waste.
Work began Monday on the other tank being emptied this month, Tank C-110. Technology called the Foldtrack was being used to remove empty 17,200 gallons of waste remaining at the bottom of the tank after another waste retrieval technology was used to remove most of the waste in the tank.
What remains is waste the consistency of sand that sits in drifts that may hide larger chunks of waste underneath.
The 800-pound Foldtrack extends to 12 feet long to fit through the narrow riser that provides access into the tank. Before it’s lowered completely onto the floor of the tank, it folds in half, placing its two crawling tracks in parallel with a plow blade for pushing the waste in front.
The blade will be used as a backstop to prevent waste from scattering as it is sprayed with a previously installed sluicing system toward a pump in the center of the tank.
The Foldtrack technology has been used once in the past, but it broke down after nine hours of use. Its design has been improved since then.
DOE had been working toward having both Tanks C-101 and C-110 emptied to regulatory standards by the end of September, the end of the federal fiscal year.
Work to empty Tank C-110 had been started earlier than expected after DOE revised its plan to empty tanks after the pump failed in the tank being emptied with the MARS system.
w Annette Cary : 582-1533 ; acary@tricityherald.com ; Twitter : @HanfordNews
Read more here :
https://www.tri-cityherald.com/2013/08/22/2534379/hanford-tank-farm-evacuated-for.html#storylink=cpy
Source : Tri City Herald
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