Sanderson, D.C.W., Cresswell, A.J., Murphy, S., and McLeod, J.J. (2001) An Airborne Gamma-Ray Spectrometry Survey of Nuclear Sites in Belgium. Technical Report. Scottish Universities Research and Reactor Centre, East Kilbride. Copyright © 2001 The Authors. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge The content must not be changed in any way or reproduced in any format or medium without the formal permission of the copyright holder(s) When referring to this work, full bibliographic details must be given http://eprints.gla.ac.uk/39222/ Deposited on: 20 April 2015. Enlighten – Research publications by members of the University of Glasgow http://eprints.gla.ac.uk Scottish Universities Research and Reactor Centre An Airborne Gamma-Ray Spectrometry Survey of Nuclear Sites in Belgium D.C.W. Sanderson, A.J. Cresswell, S. Murphy, J.J. McLeod January 2001 SUMMARY An Airborne Gamma Spectrometry (AGS) survey was conducted to establish the contemporary radiation environment of the Belgian nuclear sites of Mol-Dessel and Fleurus. The project was commissioned jointly by the Belgian Nuclear Research Centre (SCK-CEN) near Mol, and the National Institute for Radioelements (IRE Fleurus) as part of a contract under NIRAS/ONDRAF, the authority responsible for the management of radioactive wastes arising from nuclear sites. The survey was conducted in May 2000 by the SURRC AGS team using a twin-engined AS355 aircraft equipped and tested in the UK and transferred to Belgium for the survey. The site near Mol in northern Belgium incorporates a complex of nuclear facilities operated by the Belgian Nuclear Research Centre (SCK-CEN), Belgoprocess, Belgonucléaire, and FBFC International. The complex also includes a non-nuclear technical research centre, VITO, operated by the Flemish authorities. The European Commission’s Joint Research Centre - Institute for Reference Materials and Measurements (IRMM) is located south-west of SCK-CEN, near Geel.The Institut National des Radioelements (IRE) is located at Fleurus near Charleroi, south of Brussels. The aircraft arrived on the 9th May and completed the survey of the Mol-Dessel area on the 10th-11th May. The IRE site at Fleurus was surveyed on the 12th May and the aircraft returned to the UK the following day. More than 12000 spectra were recorded using a 16 litre NaI(Tl) and approximately 6000 spectra were recorded with a 50% efficiency Ge (GMX) spectrometer during the survey together with positional information from GPS and ground clearance data from radar altimetry. The results were used to prepare radiometric maps of 137Cs,60Co,40K,214Bi and 208Tl activity, along with the total gamma-ray dose rate for each of the survey areas, which together with spectral information can be used to evaluate the radiometric impact of each site.The natural radiation background levels observed in the areas are typical of radiometric surveys, the Mol-Dessel area having generally lower levels than the Fleurus area. The data sets reveal a variety of signals associated with the nuclear sites, representing known sources of radioactivity or radiation from materials contained onsite, varying in response to the type of operation and radioactivity on each site. Small signals observed at IRMM are characteristic of machine sources, with high energy components and annihilation radiation present. Those at FBFC are associated with uranium and MOX fuel materials, which give rise to signals from 234mPa,214Bi and 662keV radiation. The SCK-CEN complex produced a range of signals including 41Ar from the BR1 reactor, and 134Cs from agricultural research plots to the west of the site. The Belgoprocess sites produced a range of signals including 137Cs and 60Co from stored materials on both sites, and 214Bi signals, mainly from 226Ra. At the IRE site small anomalies associated with 99Mo and 131I were observed. The gamma dose rate maps show the relative importance of the anthropogenic radiation fields on the nuclear sites and their surroundings. The spatial distribution and nature of these signals is highly consistent with expectations based on the types of operation taking place within the sites. The data sets serve as a reference against which future changes can be measured. Whether in response to an internal or external event, or simply as part of a regular series of campaigns to document the changing environments of the sites, as new construction and decommissioning of old plant, or development of new waste-management approaches take place, it would be possible to repeat this survey rapidly to document change. i ACKNOWLEDGEMENTS The survey was commissioned jointly by the Belgian Nuclear Research Centre (SCK-CEN) near Mol, and the National Institute for Radioelements (IRE Fleurus) as part of a contract with NIPAS/ONDRAF. We are grateful for the support given by Ir Mark Loos, Dr Frank Hardeman, and Dr Carlos Rojas-Palma of SCK-CEN and by Dr Antoine Debauche of IRE for initiating and coordinating the project, and for their support in general. We are also grateful for the support and cooperation given to the survey by Dr Walter Blommaert of Belgoprocess, Freddy Goens of FBFC, and Dr Luc Peeters of IRMM and Ir Mark Van Reusel of VITO. We appreciate the practical support support given by SCK-CEN and IRE for provision of office accommodation and for facilitating the airborne operations. We are also greateful to PDG Helicopters for their support with aircraft engineering, operations support and especially Dominic Lawlor for making arrangements for transfer of the aircraft and systems to Belgium with appropriate permissions from the Belgian aviation authorities to conduct the low level operations in the survey areas. We are particularly grateful to John Constable for his expert contribution to the project, which resulted in a safe, highly efficient and accurate survey operation. ii CONTENTS 1. Introduction.................................................................................................................................1 1.1 Airborne Gamma Spectrometry..................................................................................................1 1.2 The Survey Areas.........................................................................................................................2 2. Methodology..................................................................................................................................5 2.1 Instrumentation...........................................................................................................................5 2.2 Installation, Testing and Deployment for Survey.................................................................5 2.3 Measurement Procedure...............................................................................................................6 2.4 Data Analysis...............................................................................................................................7 3. Results............................................................................................................................................9 3.1 Mol-Dessel area.........................................................................................................................12 3.2 Fleurus site................................................................................................................................20 4. Discussion and Conclusions.........................................................................................................27 References.................................................................................................................................28 APPENDICES Appendix A. Summary of Detector Calibration and Data Processing Appendix B. Coordinate Transformation Appendix C. Detailed Maps and Spectra iii FIGURES Figure 1.1 Map showing the location of the institutes and facilities surveyed in this work.........4 Figure 3.1 Flight track recorded by the Garmin GPS89 unit for the Mol survey.....................10 Figure 3.2 Flight track recorded by the Garmin GPS89 unit for the Fleurus survey................11 Figure 3.3 The distribution of 137Cs signals (662 keV) in the Mol survey area...........................14 Figure 3.4 The distribution of 60Co signals (1.1-1.3 MeV) in the Mol survey area....................15 Figure 3.5 The distribution of 40K signals (1.46 MeV) in the Mol survey area............................16 Figure 3.6 The distribution of 214Bi signals (1.76 MeV) in the Mol survey area........................17 Figure 3.7 The distribution of 208Tl signals (2.6 MeV) in the Mol survey area...........................18 Figure 3.8 Ground level gamma-ray dose rates (mGy a-1) in the Mol survey area. Net dose rates after subtraction of cosmic ray and detector background...........................................................................19 Figure 3.9 The distribution of 137Cs signals (662 keV) in the vicinity of the IRE site.................21 Figure 3.10 The distribution of 60Co signals (1.1-1.3 MeV) in the vicinity of the IRE site........22 Figure 3.11 The distribution of 40K signals (1.46 MeV) in the vicinity of the IRE site..............23 Figure 3.12 The distribution of 214Bi signals (1.76 MeV) in the vicinity of the IRE site............24 Figure 3.13 The distribution of 208Tl signals (2.6 MeV) in the vicinity of the IRE site..............25 Figure 3.14 Ground level gamma-ray dose rates (mGy a-1) in the vicinity of the IRE site. Net dose rates after subtraction of cosmic ray and detector background...................................................................26 APPENDIX C Figure C.1 Gamma-dose rate map for the area surrounding the SCK-CEN site, C 3 incorporating observations affected by 41Ar released from BR1 Figure C.2 Gamma-ray spectra in the vicinity of SCK-CEN showing (i) 41Ar C 4 from the BR1 reactor, (ii) 134Cs from labelled cultivation plots near the site Figure C.3 Gamma-dose rate map showing interference from the 41Ar plume from BR1. C 5 Note that the dose rate calibration is based on a terrestrial radionuclide distribution, and therefore does not quantify the dose rate due to 41Ar at ground level Figure C.4 Gamma-dose rate map in the location of figure C.3, when BR1 is not C 6 operating, showing the position of the labelled cultivation plots to the west of the SCK-CEN site. Figure C.5 Gamma-ray spectra for three areas within Belgoprocess site 1 C 9 Figure C.6137Cs signal distribution around Belgoprocess site 1, as measured from the C 10 airborne survey. Note that source geometries, shielding and local configurations are relevant to interpretation. Figure C.760Cosignal distribution around Belgoprocess site1, as measured from the C 11 airborne survey. Note that source geometries, shielding and local configurations are relevant to interpretation. Figure C.8 214Bi signal distribution around Belgoprocess site1, as measured from the C 12 airborne survey. Note that source geometries, shielding and local configurations are relevant to interpretation. Figure C.9 Gamma-ray dose ratedistribution around Belgoprocess site 1, as measured C 13 from the airborne survey. Note that source geometries, shielding and local configurations are relevant to interpretation. Figure C.10 Gamma-ray spectra for two areas within Belgoprocess site 2 C 14 iv Figure C.11 137Cs signal distribution around Belgoprocess site 2, as measured from the C 15 airborne survey. Note that source geometries, shielding and local configurations are relevant to interpretation. FigureC.1260Cosignal distribution around Belgoprocess site 2, as measured from the C 16 airborne survey. Note that source geometries, shielding and local configurations are relevant to interpretation. Figure C.13 214Bi signal distribution around Belgoprocess site 2, as measured from the C 17 airborne survey. Note that source geometries, shielding and local configurations are relevant to interpretation. Figure C.14 208Tl signal distribution around Belgoprocess site 2, as measured from the C 18 airborne survey. Note that source geometries, shielding and local configurations are relevant to interpretation. Figure C.15 Gamma-ray dose ratedistribution around Belgoprocess site 2, as measured C 19 from the airborne survey. Note that source geometries, shielding and local configurations are relevant to interpretation. Figure C.16 Gamma-ray spectra from the FBFC site showing evidence of 234mPa and C 22 662 keV radiation in addition to naturally occurring components Figure C.17137Cs equivalent activity distribution around the FBFC site C 23 Figure C.18 234mPasignal distribution aroundthe FBFC site C 24 Figure C.19 214Bi signal distribution aroundthe FBFC site C 25 Figure C.20 Gamma-ray dose ratedistribution aroundthe FBFC site C 26 Figure C.21 Gamma-ray spectra recorded in the vicinity of the IRMM LINAC C 28 Figure C.22137Cs signal distribution around the IRMM site. Note that the low level C 29 anomalies seen at this scale are not due to 137Cs, but arise as a consequence of spectral interference from activation products and scattered radiation generated in the vicinity of the LINAC accelerator Figure C.23 208Tl signal distribution around the IRMM site. Note that the anomaly is C 30 attributed to the presence of high energy scattered radiation in the vicinity of the LINAC accelerator Figure C.24 Gamma-ray dose ratedistribution aroundthe IRMM site C 31 Figure C.25 Gamma-ray spectra from the IRE site C 33 Figure C.26137Cs signal distribution within the IRE site C 34 Figure C.27 60Cosignal distribution withinthe IRE site. Note that the anomaly is not C 35 located above the shielded 60Co irradiator. It may reflect the presence of other nuclides with photon emission in the 1-1.5 MeV energy range associated with the radiochemical laboratories or waste stores. Figure C.28 Gamma-ray dose ratedistribution withinthe IRE site C 36 Figure C.29 Net counts in the GMX detector <300 keV withinthe IRE site C 37 v TABLES Table 2.1 Summary of measurements taken from the field at the IRE site.............................................8 APPENDIX A Table A.1 Spectral windows for NaI(Tl) detector A 3 Table A.2 Background count rates (cps) recorded over water A 3 Table A.3 Stripping ratios measured November 2000 A 4 Table A.4 Calibration Constants A 4 Table A.5 16 litre NaI(Tl) detector daily performance check A 5 Table A.6 Summary of survey data files A 5 vi 1. INTRODUCTION This report documents the results of an airborne gamma-ray survey conducted by the Scottish Universities Research and Reactor Centre (SURRC) on behalf of the Belgian Nuclear Research Centre (SCK-CEN), located near Mol in the north of Belgium and the National Institute for Radioelement (IRE), located further south near Fleurus. The project was financed by NIRAS-ONDRAF. The objective of the study was to establish the contemporary radiation environment of nuclear sites of Mol-Dessel and Fleurus, using airborne gamma ray techniques. In particular the specific activities of naturally occurring isotopes (40K,214Bi,208Tl), anthropogenic137Cs and 60Co, and the dose rate at ground level were to be mapped using AGS techniques, and the results related to established calibration sites. The survey was conducted using a UK helicopter deployed between the 8th and 13th of May 2000. The system was installed, tested and pre-calibrated prior to routing to Belgium on the 8th May, arriving on the 9th May. The survey was conducted between 10th and 12th May, the aircraft returning directly thereafter. This report gives details of the AGS method, the survey areas, deployment, calibration and field work together with a presentation of the radiometric maps produced for the nuclides specified above. Further technical information is provided in appendices, including details of individual sites. 1.1 Airborne Gamma Spectrometry (AGS) The airborne gamma spectrometry (AGS) method is highly appropriate for large scale environmental surveys of areas of potentially contaminated ground. The methodology for aerial surveys is well established (Sandersonet al, 1994a, 1994b), and has been used by the SURRC team for a variety of purposes including environmental assessments of contamination (Sanderson et al, 1990a, 1990b); Chernobyl fallout mapping (Sanderson et al, 1989a, 1989b, 1990c, 1994c); baseline mapping around nuclear establishments (Sanderson et al, 1990d, 1992, 1993b, 1994d); the effects of marine discharges on coastal environments (Sandersonet al, 1994c); epidemiological studies (Sanderson et al, 1993a); and radioactive source searches (Sanderson et al, 1988b, 1991). In addition, the technique has been used by airborne survey teams from Scandinavia, Germany and France and other countries. By operating suitable spectrometers from low flying aircraft, in this case a helicopter, it is possible to map the distribution of gamma-ray emitting radionuclides at ground level. This has a number of advantages when compared with conventional methods. High sensitivity gamma-ray detectors installed in the aircraft are capable of making environmental radioactivity measurements every few seconds, thus providing a sampling rate some 102-103 times greater than other approaches. The radiation detector averages signals over fields of view (Tyler et al, 1996a) of several hundred metre dimensions, resulting in area sampling rates some 106-107 times greater than ground based methods. Sequences of gamma-ray spectra, geographic positioning information and ground clearance data are recorded, and are used to quantify levels of individual radionuclides and the general gamma-dose rate. The high mobility of the aircraft is also advantageous, as is its ability to operate over varied terrain, unimpeded by ground level obstacles or natural boundaries. Moreover, the remote sensing nature of the measurements minimises exposure of survey teams to contamination or radiation hazards. This results in a practical means of conducting surveys with total effective coverage, which can be used for rapid location of point sources or areas of radioactive contamination. This has important implications for environmental radioactivity studies, especially where there are time constraints, and is highly significant in emergency response situations. 1 The SURRC team has also utilised a combined detector system, utilising both a 16 litre NaI(Tl) detector and one or two cryogenically cooled germanium (Ge) semiconductor detectors, for airborne radionuclide monitoring. Whilst the use of NaI(Tl) detectors is well established and used frequently in airborne surveys, the use of Ge detectors is relatively new. Ge detectors have a much higher energy resolution than the NaI(Tl) scintillator detector, and so are better able to identify the nuclides contributing to the gamma ray spectrum, particularly where complex fission product sources are present. However, they are considerably less sensitive than NaI(Tl) requiring the use of longer integration times with a resulting loss of spatial resolution in all but the most active environments. In the current work a single 50% efficiency Ge (GMX) detector mounted inside the aircraft was used. 1.2 The Survey Areas The survey area comprised the nuclear site complex near Mol, and the environment of the IRE site near Fleurus. Figure 1.1 indicates the location of these sites, showing some of the facilities and institutes at each site. The site near Mol, approximately 80km north east of Brussels, is a complex of several nuclear facilities. The site is occupied by a number of institutes: (i) the Belgian Nuclear Research Centre (SCK-CEN) is primarily concerned with research into nuclear safety, waste management and radiation protection, and its facilities include research reactors and laboratories handling radioactive materials; (ii) Belgoprocess specialises in radioactive waste management and decommissioning of nuclear facilities; (iii) Belgonucléaire produces mixed oxide (MOX) fuel material; and (iv) FBFC International is a fuel fabrication plant making uranium fuel elements and assembling MOX fuel elements. The European Commission’s Joint Research Centre - Institute for Reference Materials and Measurements (IRMM) is located approximately 5km south west of the SCK- CEN site, and is a centre of excellence for measurement sciences with a number of nuclear facilities including accelerators. The location of the principal facilities and institutes within the Mol area are included in figure 1.1. Permission was granted to over-fly all areas, with the exception of the Belgonucléaire site, subject to constraints agreed with individual site safety officers. The facilities of SCK-CEN which could be expected to have radiometric signals include three research reactors: BR1, a 700kW air-cooled graphite moderated reactor which discharges gaseous 41Ar while operating; BR2, a high flux materials research reactor, which is licensed to operate at approximately 100 MWt; and BR3, a PWR in process of decommissioning. Other facilities include various laboratories handling radioactive materials, and several small plots of land deliberately contaminated with 137Cs,134Cs and85Sr (which has subsequently decayed to very low levels) to investigate radionuclide uptake by plants. Belgoprocess occupies two sites in the complex, handling and storing a wide variety of radioactive materials including those derived from the nuclear fuel cycle and from decommissioning. There is a considerable quantity of waste material stored on these sites in well shielded buildings, although there is some discharge of222Rn gas from 226Ra and uranium-series wastes through filtration systems. 2