Thursday, May 12, 2016

Cesium in the Biosphere: Guest Post by Stewart Farber

Stewart Farber
Air Pollution and Dosimetry

Starting in 1972, for about 3 years, as a Public Health scientist and air pollution control specialist, I was responsible for upgrading and reviewing the Radiological Environmental Monitoring Program data from VY (and other Yankee plants) and generating periodic summary reports to the NRC.

In 1975, I was responsible for getting approval for a multi-million dollar centrally located state-of-the-art, greatly enhanced environmental lab. This lab was far more advanced than the labs of any of the then-current commercial contractors.  The lab was established as the Yankee Atomic Electric Co. Environmental Lab in Westboro, MA. Vermont Yankee management were willing to share in the substantial expense of setting up this advanced facility. This lab analyzed radiological environmental samples from VY, as well as Maine Yankee, Yankee-Rowe, and Seabrook (and misc. other plant samples) and performed personnel dosimetry services for these nuclear plants for over 25 years.

Meteorological Monitoring

I proposed upgrading the meteorological monitoring program at all Yankee plants in 1974, including VY. To its credit, VY willingly, despite the cost, supported installation of a 300' meteorological tower (vs. 120'). This met tower had  more advanced met instrumentation, and a computerized data acquisition system to digitize wind speed, wind direction, and temperature at 3 elevations so it could be reviewed from a central facility on a routine basis. This made met parameters available remotely in the event of an emergency, in order to assist in emergency planning. VY recognized the value of having good met and environmental radiological data and willingly shared in the costs this required. The sponsor companies and staff at VY deserve substantial credit.

A comment follows on the variability of environmental radioactivity of nuclear fission isotopes as a cautionary note on jumping to conclusions about environmental radioactivity based on limited sampling, something which VT politicians with an agenda often used against VY to negatively influence public opinion and advance their short-sighted agenda.

Wood Ash and Cs

Wood burning fireplace
In 1990 I took a sample of wood ash from burning hardwoods in my fireplace at a vacation home I had in Warren, VT (which is 130 miles distant from VY in Vernon, VT) and had it analyzed for radioactivity level by sensitive gamma spectroscopy at the Yankee lab. Wood ash is the end product of burning roughly 100 to 300 pounds of wood to yield 1 pound of ash, so ash concentrates what minerals are in the wood to yield a sample that can serve as a very sensitive indicator of natural environmental radioactivity and potential contamination from man-made isotopes . This sample from Warren, VT as would be expected, contained very high levels of the natural isotope K-40 (half life= 1.2 billion years), multiple isotopes of the U-238 (half life 4.5 billion years) decay chain, and multiple isotopes of the Th-232 (half life= 14 billion years) decay series. These are primordial isotopes present in the environment; they are residual from the Big Bang. In addition, this sample contained very high, and quite surprising, levels of the nuclear fission product Cs-137 residual from atmospheric nuclear bomb testing by the US and USSR which ended in 1963.

This initial sample of wood ash from Warren, VT contained 15,000 pCi/kg ash of Cs-137 --the highest level of Cs-137 the Yankee Lab had ever seen in any background environmental sample analysis. I asked VY staff (and other nuclear facilities across the US) to submit a wood ash sample gamma spec analysis after the initial measurement in Warren was so surprisingly high. The wood ash sample from trees grown near VY was analyzed showing a Cs-137 level of about 1,500 pCi/kg ash --10% of the level of fallout Cs-137 seen 130 miles distant!!!! This demonstrated how variable man-made nuclear isotope fallout can be in the environment. This has NOTHING to do with a nuclear plant: a nuclear plant releases essentially zero levels of Cs-137 and Sr-90 in airborne releases.

Cs lower near Vermont Yankee

Many years later after 2011, anti-nuclear politicians like Governor Shumlin in VT, set out with their agenda to make VY look bad because slight differences in Sr-90 (present throughout the environment residual from open air bomb testing) were seen in a few fish near the plant and upriver from VY. A few isolated environmental measurements mean very little. As was seen with the wood ash measurements mentioned above, the Cs-137 level in wood ash near VY in 1990 was 1/10th the level measured 130 miles away in Warren.

This difference was not likely due to major differences in fallout from past bomb testing in Central vs. Southern VT but due to soil chemistry factors between the two locations. Can you imagine what some environmental activist charlatans might do and demand if Cs-137 levels in trees was 10 times higher near VY vs. 130 miles away, rather than the other way around as is actually the case?


Steward Farber holds a degree in chemistry from Brown University, and an MS Public Health from UMass Amherst.  Farber originally submitted this post as a two-comment set on my blog post Cinco de Bye-O at Vermont Yankee. However, I felt this knowledgeable and extensive comment deserved its own post.  You might also want to look back at the original post, where Farber's writing gathered two more comments. One was about the different uptake of Cs by different tree species, and and the second comment was about pulses of radionuclides that are released in forest fires.


Leslie Corrice said...

Good and poignant posting.

Jaro said...

Great article!
Thanks Stewart and Meredith !

Dr.K S Parthasarathy said...

Cs-137 volatilizes very easily. The actual concentration in wood ash is likely to be much higher.This does not contradict the observation that environmental sampling can offer highly variable data.

Stewart Farber said...


Hello Dr. Parthasarathy,

The issue of Cs volatility in ash from burning wood or wood residues is quite a bit more complicated than the general assumption about Cs being extremely volatile.

In 1991, I delivered a paper to the Annual Meeting of the Health Physics Society in Washington, DC presenting a talk titled: "Cesium-137 in Wood Ash --Results of National Survey (or 'Woodburners and Organic Farmers: Is it Time to Kiss Your Ash Goodbye?' )". I mention this because I noted in passing in my presentation that wood ash from the Northeastern US measured as high as 15,000 pCi/kg ash and that if the more than million tons of radioactive wood ash generated each year in the US from industrial wood burning (and hundreds of thousands of tons of wood ash from domestic wood burning) were subject to the same requirements as various low-level radioactive waste from hospitals and nuclear power plants, it would cost over $10 billion/year for disposal at 1991 disposal costs. A reporter, Janet Raloff, for the publication "Science News" happened to spend some time at the DC HPS meeting and include brief notes about 2 talks, including my presentation. Ms. Raloff summarized my presentation under the title: "Woodash-The Unregulated RadWaste." Well, this comment from Science News kicked off a panicked response from the pulp and paper industry which burns millions of tons of "hogged fuel" (which includes bark, trimmings, and waste wood) residual from making paper, and "black liquor" a concentrate of digesting wood with NaOH and other chemicals to turn cellulose from trees into kraft paper and other papers. After various steps, the "Black liquor" is dried in rotary heaters, and then burned in industrial boilers to make electricity while burning the organic soup, and recover various chemical used in digesting pulp. Black liquor contained very elevated concentrations of Cs-137 depending on the source of the wood. I'm telling the story about how wood and wood waste from paper manufacture is burned in industrial boilers in vast quantities because it gives an insight to Cesium-137 volatility in high-temperature Industrial boilers vs. domestic wood burning. From very limited data from my unfunded Cs-137 in (domestic) wood ash it appears there is relatively little Cs-137 volatility in burning wood at the temperatures achieved in domestic wood burning -fireplaces or wood stove. I posit that this may be because as wood burns, any Cs-137 in the wood may be intimately bound in a Potassium matrix and K is not very volatile. I measured Cesium-137 in wood chips from one unburned wood sample in 1990 and based on the Cs-137 in wood ash it seemed that very little Cs-137 was volatilized.


Stewart Farber said...


After the flap with the national lobbying group for the Pulp and Paper Industry (P&PI) of the Science News article and the headline "Wood ash-The Unregulated Radwaste", the P&PI hired a group of academic researchers to measure Cs-137 from an Industrial boiler at a Kraft paper mill burning wood waste. Based on very detailed measurements made of Cs-137 in wood being burned, and Cs-137 in the bottom and fly ash, it was determined from the Cs activity balance, that more than 90% of the Cs-137 was volatilized and exited the boiler up the stack. This is a VERY INTERESTING finding. Based on this study carried out by a group of radiation specialists from a University in the south hired by the P&PI, the amount of Cs-137 being released from this one Kraft Paper Mill as of 1991 exceeded the routine Cs-137 being discharged from the average nuclear plant. There are 100 large Kraft paper mills in the US. There are roughly 100 nuclear plants in the US releasing trivial amounts of airborne Cs-137. The 100 Kraft paper mills as of the 1990s may have volatilized and discharged up the stacks of their industrial boilers more Cs-137 from wood burning which contained residual weapon's test fallout, than the Cs-137 discharged in airborne effluents from nuclear electric generating stations producing 20% of US electric power. I was never able to pursue further measurements of Cs-137 in domestic wood ash or any other wood waste streams. After leaving the nuclear industry in 1993, I submitted a proposal to the EPA to make a large number Cs-137 in wood ash measurements but the EPA rejected my proposal. Despite having gathered data from my 1991 HPS presented study:

Cesium-137 in Wood Ash --Results of National Survey (or 'Woodburners and Organic Farmers: Is it Time to Kiss Your Ash Goodbye?' )"

the EPA reviewers of my 1994 proposal, which I prepared and submitted jointly with the University of RI Nuclear Research Reactor which would have done the gamma spec analyses, refused to fund the small study. The EPA "expert" reviewers (unidentified) amazingly claimed they did not believe that Cs-137 would be present in trees residual from atmospheric nuclear tests, the majority of which were conducted prior to the 1963 Nuclear Test Ban Treaty. Apparently the EPA experts did not believe actual data from measurements made by more than a dozen facilities across the US. Alternatively, the EPA had an agenda not to make any measurements related to radioactivity and wood burning so they let their prejudices and simple dogma trump any balanced decision about what represented a subject deserving of study.