Radiation Exposure from Gorleben Castor 2006

Two different kinds of radiation penetrate the walls of Castor casks: Gamma-rays and neutron beams. The gamma rays originiate from radioactive atoms, which evolve during the power production in the atomic power plant from the fission of uranium. Neutron rays are generated inside the Castor cask by various reactions, like the fission of very heavy atoms such as uranium and plutonium (fission neutrons). A study of the "Gesellschaft für Anlagen- und Reaktorsicherheit" (GRS) [GRS2000] published in November 2000, had stated that the potential radiation exposure of the population and the police accompanying the transport is very low for Castor casks. The study was based on the assumption that three transportations each consisting of six Castor casks are delivered to Gorleben every year. The study claimed that the residents who live close to the transport route and the residents close to the Dannenberg loading station are not endangered by radioactive radiation from the transport.

Since the end of the temporary transportation prohibition in spring 2001, Castor transports are send to Gorleben regularly every year. The direct radiation emitted by the Castor casks under field conditions is not well known and it was my intention to measure it. This direct, whole-body irradiation potentially endangers humans and animals in the close environment of the transportation. During my visit in Wendland November 2006, I carried a mobile Geiger-Mueller instrument with me to find out what radioactive exposure we have to face.


The radiation measurement

In the early morning on 13 November 2006, I performed radiation measurements during the transport of Castor casks from the loading station at Dannenberg to the temporary storage facilities at Gorleben. The measurements took place at the road crossing close to the loading station. I have participated in the sit-in on the transport road that had been organized by the initiatives "X-tausendmal quer" and "Widersetzen". The measurements took place within the encirclement of the blockade at the loading station, after it had been ended by the police and people had been forced to move into a small square surrounded by fences close to the road.

The radiation measurement was accomplished with a Gamma Scout ( http://www.gamma scout.com). This instrument is an End-Window alpha-beta-gamma detector counting tube according to the Geiger Müller principle. The distance to Castor casks was about 6-7 meters. Police forces and police cars were in front of the casks. The possible shielding by these obstacles is not considered in the calculation of radiation intensities. The measurement is thus likely an underestimation of the radiation that was actually present. The measuring height was approximately 2 meters and thus somewhat above the heads of the policemen. It was measured during the entire time in which Castor containers (altogether 12) drove past the above mentioned place. The maximum measured gamma dose rate was 1.54 µSv/h (see picture). Even higher values were measured, but unfortunately not photographed.


Calculation of the total dose rates

The measurement of the local background radiation in the period of some hours before the arrival of the transport was determined to be 0.11 µSv/h with the portable instrument. This value is somewhat higher than the background radiation of about 0.08 µSv/h, usually measured using professional devices in Dannenberg. The reason for the discrepancy is the specific cut-off energy of the Gamma Scout counting tube, which is about 20 keV. The sensitivity of the Gamma Scout counting tube is about four times lower than that of more expensive Geiger Müller instruments.

After subtraction of the background gamma radiation from the measured maximum value the corrected gamma radiation of 1.43 µSv/h results. The radiation emitted by Castor transports consists usually of 70% neutron radiation and 30% gamma radiation. The assumption that the portion of the neutron radiation (not measured with the device) constitutes 70% of the total raditaion, is based on earlier measurements of Castor containers of the type HAW 20/28 [SSK98]. For the computation of the effective total dose rate for the neutron radiation in accordance with the German radiation protection regulation (StrlSchV), a quality factor of 10 is applied. The quality factor of 10 for the neutron radiation is given in the StrlSchV for the energy range between 2 MeV and 20 MeV. The quality factor indicates how much the (measured) physical dose has to be scaled in order to translate it into a biological dose expressing the adverse effects of the radiation. For the gamma radiation the quality factor is 1. The measured total dose rate amounts thus to 1.43*100/30 = 4.8 µSv/h.

The radiation values measured in 2 m distance of the transport vehicle are of special importance, since in the regulations for transport of dangereous goods the radiation threshold is defined at this distance. According to international transportation regulations for dangereous goods of type B (Castor transports belong to this category) a radiation dose rate of 100 µSv/h must not be exceeded in a distance of 2 meters to the container at any time. With increasing distance from the Castor container the radiation intensity decreases. This decline occurs with the square of the distance (1/r^2 dependence) in the vicinity of the transport. Since the actual distance between the detection instrument and the Castor cask varied somewhat, the total dose rate was calculated using a distance of 6.5 meters. The measured value of 4.8 µSv/h calculated above therefore translates into an effective total dose rate of approximately 101.4 µSv/h in the distance of 2 meters, when extrapolating between the location of measurement to the 2m distance of the casks. The international transportation threshold given for containers with high-radioactive wastes is settled to 100 Mikrosievert per hour in two meters distance of the container. This threshold value is 1400 times above the natural radiation background of the Wendland region.


Possible errors and Comparison with other measurements

Possible errors of the radiation measurement result from the measuring accuracy for gamma rays, which is estimated to be 10% due to the relatively short measurement period, and from the distance correction of approximately 16%. These possible errors combine to a total error of 19% for the total dose rate. The measured total dose rate in 2 m distance is thus determined to be 101 ± 19 µSv/h. Even the lower limit of 82 µSv/h is still very close to the radiation threshold of the international transportation regulation. The error related to the quality factor for neutrons is not considered here. According to estimates of an independent scientist a value of 75 would represent the biological effects of radioactive radiation from transport casks in a more realistic way [KUN2000].

In the literature a total dose rate in 2 m distance of 55 µSv/h is mentioned for Castor containers [GRS2000]. The value of 101 µSv/h determined in this measurement exceeds past measurements by a factor of almost 2. The total dose rate measured during the transport in November 2006 is higher than that of Robin Wood e.V. in March 2001. This group had determined a maximum value of 60 µSv/h in 2 m distance from Castor casks [RWM2001]. Their measurement was performed in a distance of 24.5 meters. A further measurement of Robin Wood e.V. in November 2001 gave a smaller value of 38 µSv/h [RWN2001]. Castor containers carry different amounts of radioactive loads which determines the radiation intensity, and therefore cause fluctuations between individual measurements at different Castor containers. The value measured here is the maximum value, which was reached at one of the 12 containers driving past the measurement location. The maximum measured total dose rate reaches the threshold value of 100 µSv/h in 2 m distance from the container surface. The measurement presented here was performed much closer to the Castor transport than previous radiation measurements of Robin Wood e.V.. In contrast to the Castor transports of the year 2001, twelve containers are transported instead of six containers, very likely resulting in an increase of the total dose rate measured at a certain point in the proximity of the Castor transport.

Apart from the mobile measurements shown here, radiation measurments in the Gorleben area were performed by a specialized working group on radioactivity of the BI Luechow Dannenberg at the same time. According to the analysis of this group, measured radiation data during the Castor transport in the year 2006 did not differ significantly from those of the preceding years ( http://www.castor.de/technik/messung/2006/2006.html). With a gamma ray detector they monitored the radiation at the roadside in Gorleben during the transportation time. The exact distance of the detector to driving Castor casks was not well determined. However, it was clearly within the range where the radiation intensity decline can be described with the square of the distance. The working group on radioactivity states that due to the related uncertainties their derived radiation intensities should only be regarded as a first orientation. Assuming that both measurements during the Castor transport in November 2006 are correct, extremely high radiation intensities were encountered also during the transports of the previous years.


Conclusions

The German radiation protection regulation still relies on the out-dated quality factor of 10 to describe the biological effectiveness of neutrons, although the International Comission on Radiological Protection (ICRP) has recommended to use a weighting factor of 20 for fission neutrons back in 1991 [ICRP60]. The question remains if these quality factors correspond to recent research results on radiative effects on live. The assumption of a linear relationship between the physical absorption of energy and the biological effect does not apply in all investigated cases. Dependent on the neutron energy and biological system differences of more than factor 100 result. In fact low dose rates can result in relatively more radicals (through the radiolysis of cell water) that are available to cause mutations than at higher dose rates, since the process of radical self extinction is less effective at low dose rates. This can lead to a non linear relationship between dose and effect.

According to these measurements, workers and policemen who excort the transport, protesters, and residents living at the route of the Castor transport, are exposed to an increased health risk. The next Castor transport should be supervised at many locations along the transport route with radiation measuring instruments. Anti-nuclear groups should purchase or borrow mobile gamma-ray instruments and probably also devices for the measurement of the neutron radiation (but these are very expensive).

In total three transportations are planned for the years 2008, 2009 and 2010 from France to Gorleben, each bringing eleven containers with radiative wastes from the reprocessing plant at La Hague. For the next transport in autumn 2008 obviously French containers of the type TN85 will be used. Accompanied by protest of local anti-nuclear activists, the "cold" handling of this French container type has been tested in Gorleben already in May this year.

In the last years, the degree in burn-up of the fuel elements that have been delivered from German nuclear reactors to La Hague was much higher than for the former fuels. Therefore the containers must resist the increased thermal output of these elements. The thermal output increases from 45 KW by about 20% to 56 KW. In addition the transport container has to shield effectively the resulting increase of gamma and neutron radiation. Staying about one minute in 1 m distance of a non-shielded Castor container would be enough to cause a deadly dose for humans. The total inventory of a container corresponds to about 20% of the radiation that was released during the Chernobyl nuclear catastrophy. The BI Lüchow Dannenberg criticizes that despite their repeated inquiries, the exact status of the container configuration is not revealed by the authorizing agencies. For more see  http://www.castor.de/presse/biprmtlg/2007/quartal3/0905.html


This article is a translation of the german article "Nachtrag zum Castor 2006 nach Gorleben" posted here:  http://de.indymedia.org/2007/10/197616.shtml


References

SSK98
Strahlenschutzkommission; Strahlenschutz und Strahlenbelastung im Zusammenhang mit Polizeieinsätzen anläßlich von CASTOR-Transporten; Bonn 1998

GRS2000
G.Schwarz, H.-J.Fett, Y.Francois, F.Lange; Sicherheitsanalyse zur bestimmungsgemäßen Beförderung von radioaktiven Abfällen und bestrahlten Brennelementen in der Region Gorleben; GRS-A-2814, GRS 2000

RWM2001
Stefan Hild; Gammadosisleistungsmessungen an CASTOR-Behältern (März 2001); Robin Wood e.V.

RWN2001
Dr. Helmut Hirsch, Stefan Hild; Messungen von Neutronen- und Gammastrahlung an Behältern vom Typ CASTOR HAW 20/28 CG; Robin Wood e.V.; 16.11.2001

KUN2000
Kuni, H.; Wichtungsfaktoren; in: Strahlengefahr für Mensch und Umwelt, Berichte des Otto Hug Strahleninstitutes Nr. 21-22, April 2000

ICRP60
International Comission on Radiological Protection, Publication 60,
Recommendations of the International Comission on Radiological Protections, Annals of the ICRP, Vol. 21, No.1-3, Pergamon Press, Oxford, New York, Seoul, Tokyo, 1991