This came from a colleague here at work. Its an interesting (and hopeful) statement and investigation.
>It's interesting what this high school student found with somewhat
>limited resources. Is this a problem? JTT
>
>http://134.121.112.29/Fair_95/gym/hs013.html
Zack Clayton
zclayton@epa.state.oh.us
Ohio EPA
Voice 614-644-3066
FAX 614-460-8249
Title: A Comparison of the Activities of Alpha Emitting Nuclides in Coal and
Coal Combustion Products
Click to see award.
Everywhere you go on Earth, you will find radiation. Much of this radiation comes from natural sources and is in very small doses. This natural radiation is called background radiation. Background radiation is not harmful and is found even in food products. Normally, however, the only way radiation is portrayed is as being bad for the environment and for the human health.
This is not always true because a major use for radiation has been found in the medical field. It is used in both diagnosis and treatment of many major illnesses. Radiation is present when X-rays are taken and can be used to detect such medical problems as blood clots, stomach reflux, and brain tumors. It also is a major weapon used in fighting cancer.
The main concern about nuclear power is the amount of radiation released into the air and into residential areas. It is felt that the radiation would harm the people around the plant, the overall the risk is too great, and that in the end it is more trouble than it is
worth. Again, this is not the case. Nuclear power plants do release small amounts of radiation, but so do other forms of power production. An example of this would be the coal combustion plants which burn coal to produce energy.
Hypothesis:
In this study, the relative amounts of alpha radioactivity found in coal and it's by products in coal fired plants were examined. It was hypothesized that the levels of alpha radioactivity in the combustion products would be noticeably higher than those in the coal.
Methods and Procedures:
The initial ideas for this experiment came from the September 17, 1994, issue of Discover magazine. This issue contained an article entitled Radon: Some concrete issues, which dealt not only with radon released from coal combustion by-products, but about alpha radiation released in general. It also spoke of testing which took place in the Netherlands that dealt with the amounts of radon contained in concrete combined with fly ash. According to this study, the addition of fly ash into concrete increased the release of radon into homes. This article sparked the curiosity to research radiation levels in coal, fly ash, and bottom ash and posed the question: Is there a reason to worry about this radiation?
Procedure
The first step involved acquisition of materials and designing the experiment. Samples of fly ash, bottom ash, and pulverized coal were obtained from the Centralia Steam Plant and Centralia Mining Co. These samples were then forced through a sifting device so their relative consistencies would be approximately the same. The sifting device was a piece of wire mesh woven at ten wires per inch. Approximately 200 grams of each sample were placed into individual beakers.
Pieces of CR-39 plastic, a type of solid state nuclear track detecting material which is only sensitive to alpha radiation, were then prepared for exposure. CR-39 is a plastic which is scored or marked when alpha radiation passes through it. The radiation leaves a path of destruction in the form of a hole or a gouge. When placed in heated sodium hydroxide (see below for details), the path of destruction is enlarged to the point where they are visible under a microscope. The path is now called a track. Each piece has a protective polyethylene cover on both sides. After removing the polyethylene from one side, a recognizable marking, in this case a letter standing for which sample it went into and a number to signify which piece it was, were placed on the exposed face. This was to aid in identification and to specify which side was to be examined after the etching process Four pieces of CR-39 plastic were completely buried into each of the three samples of fly ash, bottom ash, and coal.
In addition to testing for general alpha emission, separate detectors were constructed to test for radon exhalation from the fly ash, bottom ash, and coal. This involved the preparation of three more pieces of CR-39. After the polyethylene was removed from one side and the appropriate markings made, a small piece of plastic tape was attached to the back of the CR-39. The pieces were then placed into a small paper cup with the tape to hold the CR-39 onto the bottom of the cup. The cup was then covered with a piece of fine facial tissue, which was secured with tape. The cups were placed upside-down on top of the samples of fly ash, bottom ash, and coal. The tissue cover was to block the entrance of any other alpha emitting nuclides besides the radon. All of the detectors were then left to expose for sixteen days.
The pieces were then removed from the samples after the sixteen days and prepared for etching. A 6.25M solution of sodium hydroxide (NaOH) was prepared from solid sodium hydroxide and water. The sodium hydroxide was heated to a temperature of 95C before the CR-39 could be placed into it to etch. The pieces of polyethylene which covered the back side of the CR-39 were then removed. All of the pieces of CR-39 were then hooked together using metal rings similar to those used to hold keys. Since these rings were able to be placed on both the top and bottom of the pieces, the pieces were able to be connected together to form a strip of CR-39 pieces. With three pieces to a ring strip, the pieces were lowered into the sodium hydroxide solution. They were left to etch for 50 minutes. Upon removal, the pieces were rinsed with water and placed on paper towels to dry and then readied for examination.
Three other samples of the fly ash, bottom ash, and coal were taken as well. These samples were used to test the moisture content in each sample material. Fourteen grams (14 g.) of each material were measured out and placed in an individual beaker. They were then set up in a drying oven set at 35C for three days. The mass was recorded both before and after drying.
The fly ash, bottom ash, and coal were also tested with a computer driven Geiger counter. Each sample was placed into an individual tray. The Geiger counter was then placed about eight inches above the samples (one at a time) to test for total radioactivity. The computer recorded the readings every minute and tabulated the readings in terms of microRoentgens (R/h). Each sample was tested fifteen times (see table #).
Evaluation
To observe the alpha tracks, the pieces of CR-39 were examined under a microscope at a total magnification of 200 X. Ten randomly chosen fields of view were examined on each of the pieces. The number of alpha tracks in each field was counted and recorded. These numbers were then averaged to get the average number of tracks per sample. The radon testing pieces were counted in the same manner, but were not part of the average. The averages were then used to figure out the relative activity of each sample in Becquerels per kilogram. The original equation was:
12 x track count cm-1
activity in Bq kg-1 = exposure in days
The field width was measured using a stage micrometer and was found to be .0263 cm2. Then, using this measured number, the equation was altered to read:
activity in Bq kg-1 =
Sample Calculation
12 x 41.4 tracks 31.05 tracks / day
activity in Bq kg-1 = 16 days = 31.05 tracks/ day .0263 cm2 = 1180.6 tracks/day/cm2 =
1180.6 Bq kg-1
After using the equation on each of the piece averages, the average of these numbers were taken (see tables in results section). In addition to this, the average of the piece averages was taken and called the trial average. These averages were also evaluated using the above equation ( see tables in results section).
Results:
The results indicate there is a significant difference in the relative activities of the fly ash, the bottom ash, and the pulverized coal. The average activity for the pulverized coal was found to be 238 Bq kg-1 , while the bottom ash was 578.3 Bq kg-1 , and the fly ash 1022.4 Bq kg-1. This is comparable to a study performed in 1988 by Geoffrey Camplin, Denis L. Henshaw, Sarah lock, and Zoe Simmons. In their research, they tested the soil around coal combustion plants and arrived at a relative range between 200-1000 Bq kg-1. As is seen, the fly ash is slightly above this average.
Table 1: Pulverized Coal Track Count
piece number 1 piece number 2 piece number 3 piece number 4
field number number of number of number of number of
tracks tracks tracks tracks
1 7 6 15 5
2 12 11 11 9
3 15 10 10 6
4 9 8 8 6
5 4 9 9 10
6 8 8 9 9
7 13 7 7 5
8 6 7 12 2
9 9 13 5 4
10 7 6 10 8
Table 2: Fly Ash Track Count
piece number 1 piece number 2 piece number 3 piece number 4
field number number of number of number of number of
tracks tracks tracks tracks
1 34 39 36 36
2 45 34 32 51
3 49 37 19 45
4 28 40 18 39
5 54 43 29 56
6 40 38 18 32
7 46 52 29 26
8 37 25 21 27
9 24 56 13 31
10 40 50 33 32
Table 3: Bottom Ash Track Count
piece number 1 piece number 2 piece number 3 piece number 4
field number number of number of number of number of
tracks tracks tracks tracks
1 25 16 20 20
2 17 10 14 10
3 27 20 17 19
4 30 21 17 34
5 33 24 21 20
6 23 14 24 34
7 28 27 20 19
8 28 15 29 8
9 29 15 32 19
10 31 16 21 18
Table 4: Calculated Activity per Piece
pulverized coal fly ash bottom ash
piece number activity in Bq activity in Bq activity in Bq
kg-1 kg-1 kg-1
1 256.6 1132.3 619.0
2 242.4 1180.6 507.6
3 273.8 707.2 613.3
4 182.5 1069.6 573.4
Table 5: Average Activity per Sample
Sample Type average activity in Bq
kg-1
pulverized coal 238
fly ash 1022.4
bottom ash 578.3
Table 6: Radon Track Count per Piece
pulverized coal fly ash bottom ash
piece number number of tracks number of tracks number of tracks
1 11 8 3
2 21 6 5
3 13 6 11
4 17 5 13
5 15 5 7
6 18 9 4
7 12 8 8
8 19 5 8
9 17 7 11
10 11 7 12
Table 7: Radon Activity per Piece
sample type activity in pCi/L
pulverized coal 5.71
fly ash 2.44
bottom ash 3.07
Conclusion:
The main purpose of this study was to measure the alpha radiation activity in samples of fly ash, bottom ash, and pulverized unburned coal. This was done via two methods. CR-39 detection plastic was used in correlation with a computer driven Geiger counter.
Discussion:
The first fact that must be realized about the results listed in this paper is that it is only listed in terms of activity. This activity is also only for alpha radiation. This does not represent the actual dose received by humans. To find that, a complete analysis of the materials must be done to reduce the samples to their elemental forms. Once in their elemental states, an analysis must be done to determine which isotopes of which elements are producing the radiation. Once this has been determined, the actual dosage could be calculated. Unfortunately, this was not possible with the resources at the school. However, an elemental analysis was obtained from the same plant that the samples came from.
This analysis was examined thoroughly to help determine which elements were decaying. Again unfortunately, the analysis proved to be no help. It showed no record of any actinide series elements. Since many sources listed these elements as being crucial parts of coal's chemical make-up, a question arose. Why did the analysis show no actinide series elements? After much research, the answer was found at the Washington State Department of Health (Radiation Protection Division). The coal plants are not required to break their coal down far enough to show these elements. Furthermore, they are not required to measure for alpha radiation, or any other forms of radiation. Further study may include testing for other forms of radiation, such as beta or gamma, around the coal plant.
Even more surprising is the fact that they do not test for alpha radiation anyway. This is a surprise because they resell the fly ash and bottom ash. It seems reasonable that they would at least test for radon emissions, since, as this study showed, the levels of alpha activity in the fly ash and bottom ash is are larger than that of the unburned coal. Despite the increase in activity, these materials go on seemingly being sold without so much as a question.
The bottom ash is sold mainly to the Centralia Mining Company immediately adjacent to the power plant. It is used there to aid in construction sites and to reinforce foundations. It is also sold to the general public. It is then used for such purposes as reinforcing house foundations and fertilization of gardens. It is also used to build roads.
The fly ash has a somewhat more startling destination. It goes to concrete production companies. It is mixed with the concrete to give it a better hold. A study done in the Netherlands found that radon emissions continued for at least eight years after the concrete was poured. Since fly ash tends to possess more radium than plain concrete, is the use of concrete with fly ash a wise practice in home construction? Is it possible that we are actually creating a bigger problem by solving a small one?
Future Study:
Future study could include testing the fly ash for other forms of radiation, doing a complete elemental analysis of the fly ash, and doing extensive radiation of concrete mixed with fly ash.
References:
1. Barber, D. E., and Giorgio, H. R., Gamma-Ray Activity In Bituminous, Subbituminous, and Lignite Coals, Northern Ireland: Health Physics, Pergamon Press, vol. 32, 1977.
2. Battaglia, A., Capra, D., Queirazza, G., and Sampaolo, A., Radon Exhalation Rate from Coal Ashes and Building Materials in Italy, Sergrate, Milano, and Brindisi Italy.
3. Camplin, Geoffrey, Henshaw, Denis L., Lock, Sarah, and Simmons, Zoe, A National Survey of Background -Particle Radioactivity, IOP Publishing Ltd., 1988.
4. Karamdoost, N. A., Dorrani, S. A., and Fremlin, J. H., An Investigation of Radon Exhalation from Fly Ash Produced in the Combustion of Coal, Nuclear Track Radiation Meas., Pergmamon Press plc, vol. 15, 1988.
5. Ray, Dixy Lee, and Gusso, Lou, Trashing the Planet, National Book Network, Lanham, MD, 1990.
6. Roeck, Douglas R., Reavey, Thomas C., and Hardin, James M., Partitioning of Natural Radionuclides in the Waste Streams of Coal Fired Utilities, Health Physics Society, Pergamon Journals Ltd., 1987.
7. Unknown Author, Evaluation of Radiation Dose from a Coal-fired Power Plant, Health Physics vol. 48 (February), 1985.
8. Unknown Author, Radon: Some Concrete Issues, Discover, September 17, 1994.
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