FEATURE: Cleanup continues 52 yrs after partial meltdown in Los Angeles+

SIMI VALLEY, California, Aug. 12 Kyodo -
In 1959, a nuclear reactor at a research facility 70 kilometers from Los Angeles experienced a partial meltdown that was largely unknown by the public for 30 years. Now preparation for a final cleanup is under way.
North American Aviation Inc. built the 1,150-hectare Santa Susana Field Laboratory in the dry, rugged hills above Simi Valley, California, in 1947. The company conducted research on nuclear and aerospace technology, some of it for the U.S. government, including 30,000 rocket tests and running 10 experimental reactors.
One reactor was built to test sodium coolant technology. More than a month after the accident that caused part of the reactor's fuel to melt, the company said in a press release, ''No release of radioactive materials to the plant or its environs occurred and operating personnel were not exposed to harmful conditions.''
What actually occurred has been the subject of intense controversy.
According to the U.S. Department of Energy, the reactor overheated and partially melted 13 of the 43 fuel assemblies, releasing radiation into the reactor building. Excess gas from the reactor was pumped into holding tanks and then released into the atmosphere. The DOE maintains that the radioactive material contained in the gas was within legal limits.
Some experts have argued a significant amount of radioactive iodine may have been released. One estimated the released amount at between 200 and 4,000 curies -- or 15 to more than 200 times the official estimate of that released during the Three Mile Island accident.
Though operations at the Simi Valley site were well-known by nuclear researchers, residents were largely unaware until a DOE report was leaked to a local paper in 1989.
''We always knew it was there, but it was just top secret,'' said Holly Huff, who has lived directly below the site for 40 years.
The Santa Susana research reactor was 128 times smaller than Unit 2 at Three Mile Island, a full-scale commercial reactor which experienced a partial core meltdown in 1979. But the California reactor was connected to the grid, making it the first commercially utilized reactor to experience a meltdown accident.
The accident was not the only potential source of pollution. In addition to reactors, the site was home to a ''hot lab'' where nuclear fuel was cut apart and studied, as well as to disposal pits where radioactively contaminated sodium was burned for more than 20 years.
Throughout the 1980s and 1990s, the buildings and soil with the highest radiological contamination were removed. But as pollution kept being detected, residents and lawmakers contested the adequacy of the cleanup. In December 2010, the DOE agreed to restore its part of the site to its natural state.
The U.S. Environmental Protection Agency is now conducting a $4.4 million study of the 100-plus hectare nuclear area. Using gamma scanning equipment mounted on a bulldozer, specially designed all-terrain vehicles and even mules, EPA contractors have scoured the steep and rocky terrain looking for remaining radioactive contamination in the soil and groundwater.
So far, 60 spots show higher-than-usual gamma activity, including several patches with slightly elevated levels of cesium-137 near the site of the 1959 incident. Soil from these areas will be analyzed to determine the exact levels of contamination.
The site is one of the DOE's 17 radioactive cleanup sites in 11 U.S. states. Compared with sites such as Hanford in the state of Washington, where plutonium was created for the Fat Man bomb dropped on Nagasaki and millions of gallons of highly radioactive waste remain, the scope of the contamination here is small.
''I'm more concerned about trace amounts of radioactive material leaving the (California) site over the years,'' says Gregg Dempsey, a senior science adviser at the EPA who has been involved with the site since 1989.
''Unlike most of the other facilities, there are very large communities nearby...most of the other facilities are somewhat remote.''
Dempsey, who is also a national commander of the EPA's Radiological Emergency Response Team, says his work has taught him not to take any increased risks to the public for granted.
''Oftentimes people will compare radiation exposure here on the site to a flight across country in an aircraft...But it's voluntary versus involuntary exposure,'' he explains.
Studies have suggested higher rates of certain cancers among workers and the small population living within 3 km of the mountainous site. While former workers have received more than $40 million in compensation for health problems caused by radiation exposure, the situation is different for residents.
''You can't say that our health issues came from the site, because you'd have to prove it,'' said Huff, who lives with a chronic form of leukemia. But she is glad to see progress on the cleanup she has been waiting for since 1989.
Under the 2010 agreement, the DOE will remove all but naturally occurring radioactivity from the site. Its cleanup is expected to be finished by 2017.
''We want to work ourselves out of a job...so that all our children and grandchildren can play up here one day,'' Stephanie Jennings, DOE deputy federal project director, said.