Six decades of environmental radioactivity measurements. Sven P. Nielsen

Transcription

1 Six decades of environmental radioactivity measurements Sven P. Nielsen

2 Research Establishment Risø Established by Government in 1950 s to keep Denmark in line with development of nuclear technology including nuclear power plants. Official inauguration in May 2017

3 Nuclear technologies at Risø Peaceful utilization of nuclear power (atoms for peace) 3 research reactors Bohr Atomic Model,

4 Development since Nuclear power and other energy technologies 1985 No nuclear power in Denmark 1986 R&D with energy as main subject 2000 Shut down of last research reactor 2007 Risø part of DTU, Technical University of Denmark Energy crisis Car free Sundays 2012 DTU Nutech established Nuclear Power- No Thanks, 1977 Visit by ZERMC

5 Investigations of environmental radioactivity from 1956 Work started in 1956 by Heydorn, Lippert and Theodorsson, first in Copenhagen and later at Risø on task: You will map radioactivity in air, water and soil at Risø and Risø surroundings and present a report within one year so it is ready before Risø s first reactor goes critical Five zones established out to 16 km from Risø Sample types Fjord water, sediments, fish, seaweed Soil, aerosols, precipitation Fresh water, milk 5

6 Early beta counters End-window GM counter (Frieseke und Höpfner) tested, low efficiency Cylindrical GM counter (20th Century Ltd.) with thin glass wall, used in the UK End-window GM counter (Anton Electronic Laboratories, USA) with larger window and use of two counters simultaneously, selected due to high efficiency and simple operation. Anton GM counter with sample changer Anton GM counter photo 20th Century GM counter schematic 6 Anton GM counter schematic

7 Fission products in Risø grass 1957 Global radioactive pollution from atmospheric nuclear weapons tests Chemical analyses combined with beta counting provided nuclidespecific data on fission products, e.g. Sr-90 Beta decay of fission products in Risø grass samples

8 Ionisation chamber for alpha spectrometry 8 Alpha spectrometry measurement of air filter sample collected at Risø on 14 Oct 1957 a few days after Windscale accident, showing Pu-239 and Po-210

9 Low-level beta counters Low-level beta counters with anticoincidence guard elements developed in 1960 Need for increased counting capacity prompted development of beta counter with automatic sample changer for up to 30 samples, in operation 1962 Perspex beta counter Beta counter with automatic sample changer 9

10 Risø low-level GM multi-counter Further development of beta counters resulted in low-level GM beta counters with background count rates of cpm Low-level gas flow beta multi-counter system for the measurement of 5 samples simultaneously Used since 1978 for analyses of Sr-90/Y-90 and Tc-99 in environmental samples Low-level beta GM multicounter system 10

11 NaI detectors used since

12 Ge(Li) detector production Compton-rejection setup

13 Radioecological sensitivity, Sr-90 and Cs-137 Aarkrog s studies covering Air, water, soil Grain, bread Grass Vegetables and fruit Sea plants Milk, meat, fish Total diet Human body, bone Radioecological sensitivities are time integrals of quantities of sample types from unit amounts of radionuclide deposition Example for Cs-137 in Danish cow s milk 2.0 Bq/L d per Bq/m 2 13 Aarkrog s Doctoral Thesis, 1979

14 Alpha spectrometry using Si detectors Use of alpha spectrometry with Si detectors was prompted by accident in 1968 at Thule in Northwest Greenland involving US B-52 airplane crash and local Pu pollution Risø took part in initial mapping operations and risk evaluation Measurements of Pu-238, Pu and Am-241 in environmental samples Laboratory measurement capacity increased from 4 Si detectors in 1968 to 10 detectors in 1977 and 32 detectors in 1999 Numerous follow-up studies of Pu in the marine and terrestrial environments at Thule have been carried out since

15 Alpha spectrometry systems at Nutech Si detectors in vacuum chambers for alphaspectrometric analyses of U, Th, Ra, Po, Pu and Am isotopes 15

16 Gamma spectrometry Since 1975 based on Ge detectors commercially available Gamma spectrometry used for analyses of radionuclides in environment, food, export products, decommissioning samples, etc. Gamma laboratory using 12 Ge detectors for routine analyses, 6 Ge detectors for special applications and 2 NaI detectors for analyses of chemical yields Development on new technologies including list-mode data acquisition in combination with multiple detectors 1.E+04 1.E+03 CONCENTRATION (µbq/m 3 ) 1.E+02 1.E+01 1.E+00 Sr-90 Cs E-01 1.E YEAR 16 Sr-90 and Cs-137 in air at Risø

17 Chernobyl accident, 1986

18 Tritium analysis by LSC Since 1977 monitoring of tritium in Risø environment and urine samples from staff at heavy-water cooled research reactor using TriCarb 2425 Now Quantulus and TriCarb 3170 are used for analyses of hard-tomeasure radionuclides including Rn-222 and Ra Tritium in precipitation at Risø

19 Analysis of long-lived radionuclides using mass spectrometry In 1995 Risø acquired a highresolution mass spectrometer (ICPMS) which was occasionally used for analysis of Pu in samples from Thule Analysis of sediments sampled in 1997 at Thule showed significant variation of Pu-240/Pu-239 ratios ICPMS is used on a rutine basis for analysis of stable elements and long-lived radioactive isotopes of U, Th, Pu, Np, Tc Accelerator mass spectrometry used for analysis of U-236 and I- 129 in environmental samples in collaboration with AMS laboratories

20 AMS-measured radionuclides used as environmental tracers Iodine-129 in the North Sea 2005 Uranium-236 in Danish waters

21 Conclusion Through six decades chemical analyses combined with radiometric techniques have been successful in providing detailed information on man-made and naturally occurring radionuclides in the environment Studies on transfer of radionuclides in the environment and through food chains have provided know-how of importance for making reliable assessments of the radiological impact from radioactivity in the environment Studies on environmental radioactivity give important information by using radionuclides as tracers for environmental processes DTU Nutech uses advanced radiochemical techniques and equipment continuing the tradition from Risø s start by providing reliable data on environmental radioactivity 21