THE OBJECTIVE OF THE RESEARCH PROJECT DESCRIBED BELOW IS TO PROVIDE BETTER UNDERSTANDING OF THE TRANSFER BEHAVIOUR OF THE RADIONUCLIDES CS-137 AND CO-60 AFTER DEPOSITION CONSEQUENT UPON AN ACCIDENT. THE EXPERIMENTAL PROGRAMME IN QUESTION IS A FOLLOW-UP TO THE RESEARCH PROJECT ON THE DETERMINATION OF SOIL/PLANT/FOOD-CHAIN TRANSFER AFTER THE DEPOSITION OF GREAT QUANTITIES OF RADIONUCLIDES FOLLOWING AN ACCIDENT WHICH WAS BEGUN IN 1984 AND SUPPORTED BY THE COMMISSION OF THE EUROPEAN COMMUNITIES FOR THAT YEAR. THE WORK BEGUN IN 1984 COVERED THE SIMULATION OF LONG-TERM CONTAMINATION OF THE SOIL BY SMALL QUANTITIES OF RADIONUCLIDES SUCH AS OCCURS NORMALLY DURING THE ROUTINE OPERATION OF A NUCLEAR INSTALLATION AND THE DETERMINATION OF REALISTIC TRANSFER FACTORS FOR THE RADIONUCLIDES CS-137 AND CO-60 IN LYSIMETERS UNDER FIELD CONDITIONS. THE STUDY WAS UNDERTAKEN IN VIEW OF THE FACT THAT THERE IS ALREADY A CERTAIN RADIONUCLIDE INVENTORY IN THE SOIL IN THE VICINITY OF A NUCLEAR INSTALLATION WHEN AN ACCIDENT OCCURS.
DURING THE NEW 1985-89 RADIATION PROTECTION PROGRAMME OF THE COMMISSION OF THE EUROPEAN COMMUNITIES, THE FOLLOWING QUESTIONS WILL BE STUDIED IN THE INSTITUTE FOR RADIOAGRONONMY OF THE JUELICH NUCLEAR RESEARCH CENTRE IN COOPERATION WITH THE INSTITUT DE PROTECTION ET DE SECURITE NUCLEAIRE (IPSN), DEPARTEMENT D'ETUDE ET DE RECHERCHES EN SECURITE (DERS) AND SERVICE D'ETUDES ET DE RECHERCHES SUR L'ENVIRONNEMENT (SERE), CEN, CADARACHE, FRANCE:
- THE DETERMINATION OF SOIL/PLANT TRANSFER FACTORS FOR THE RADIONUCLIDES CS-137 AND CO-60 AND CS-134 AND CO-57 AFTER LONG-TERM CONTAMINATION OF THE SOIL BY SMALL QUANTITIES OF RADIONUCLIDES AND A DEPOSITION OF LARGE QUANTITIES OF RADIONUCLIDES CONSEQUENT UPON AN ACCIDENT AT VARIOUS STAGES OF A VEGETATION PERIOD
- A STUDY OF THE EFFECT OF ELEMENT CONCENTRATION ON SOIL/PLANT RADIONUCLIDE TRANSFER
- APPLICATION OF VARIOUS SOIL WORKING METHODS (NORMAL/DEEP PLOUGHING) WITH A VIEW TO REDUCING THE SOIL/PLANT TRANSFER OF RADIONUCLIDES
Transfer factors were determined describing the uptake of the radionuclides caesium-134, caesium-137, cobalt-57 and cobalt-60 from soil into plants and food chains after simulation of a long term contamination of the soil and of a high depositionof these radionuclides on soil and plants subsequent to an accidental release. For all crops grown during the experimental period, on increase of the caesium and cobalt concentration in the soil resulted in a higher availability of radiocaesium and radiocobalt for root uptake. After the application of caesium-134 and cobalt-57 and of additional stable caesium and cobalt to the soil surface considerable root uptake was observed, although these radionuclides were fixed in the upper 2 to 3 cm layer and the root uptake of nutrients in general takes place in the 5 to 25 cm soil zone. Thorough mining of the contaminated top 6 cm layer into the 0 to 30 cm plough layer produced only a small reduction. It was concluded that the transfer of radiocaesium and radiocobalt from soil into plants would increase in the first and second year after a high deposition, due to incomplete sorption and equilibration in the soil.
The results showed that deep ploughing with thorough mining into the plough layer and deep placement of the radionuclides could be a useful counter measure to reduce the radionuclides could be a useful counter measure to reduce the contamination of the food chain via plant root uptake. As compared to root uptake or transfer into storage organs or seeds, the uptake and translocation of radiocaesium from contaminated plant leaves into plant organs not yet formed at the time of contamination could be higher by several orders of magnitude.
THE SCHEDULED EXPERIMENT PROGRAMME WILL BE IMPLEMENTED AS FOLLOWS:
FOLLOWING THE MIXING OF CS-137 AND CO-60 INTO THE 0-30 CM SOIL LAYER OF 16 LYSIMETERS IN 1984 FOR THE SIMULATION OF LONG-TERM DEPOSITION OF SMALL QUANTITIES OF RADIONUCLIDES, SUMMER BARLEY AND LETTUCE WILL BE PLANTED DURING THE 1985 VEGETATION PERIOD.
IN 1986, THE RADIONUCLIDES CS-134 AND CO-57 (ABOUT 0.5 MCI/NUCLIDE/LYSIMETER), EITHER WITHOUT A CARRIER OR WITH THE NON-RADIOACTIVE CARRIER SALT - I.E., IN LOW AND HIGH ELEMENT CONCENTRATIONS, WILL BE SPRAYED ONTO THE PLANT OR SOIL SURFACES IN ONE OR FOUR APPLICATION OPERATIONS DURING THE VEGETATION PERIOD THUS SIMULATING AN ACCIDENT RELATED DEPOSITION OF THE RADIONUCLIDES CAESIUM AND COBALT IN VARYING CONCENTRATIONS AND FREQUENCIES OF THE ELEMENTS. IN 1986, SUMMER BARLEY WILL BE PLANTED AS THE MAIN CORP AND LETTUCE AS THE ROTATION CROP.
IN 1987, THE SOIL WILL BE TREATED NORMALLY - I.E., TO A DEPTH OF 30 CM - IN EIGHT LYSIMETERS. IN THE CASE OF THE REMAINING EIGHT LYSIMETERS, THE UPPER 10-15 CM OF SOIL WILL BE REMOVED AND, AFTER THE NEXT 35-40 CM HAVE BEEN TAKEN OUT, REPLACED AT A DEPTH OF 50 CM. THIS IS INTENDED TO SIMULATE THE REMOVAL OF THE RADIONUCLIDES DEPOSITED ON THE SOIL SURFACE BY MEANS OF DEEP PLOUGHING. THE ONLY CROP TO BE PLANTED IN ALL LYSIMETERS WILL BE CARROTS.
IN 1988, POTATOES AND, AS THE ROTATION CROP, KIDNEY BEANS WILL BE PLANTED. IN THE NEXT PERIOD (1989), WINTER WHEAT WILL BE USED, WITH ALFALFA AS THE ROTATION CROP.
BY IMPLEMENTING THIS EXPERIMENTAL PLAN AND USING VARIOUS CAESIUM AND COBALT ISOTOPES, IT IS INTENDED TO STUDY ON A COMPARATIVE BASIS THE SOIL/PLANT/FOOD-CHAIN TRANSFER OF THESE RADIONUCLIDES BOTH AFTER LONG-TERM DEPOSITION CAUSED BY ROUTINELY OCCURRING LOW EMISSIONS AND AFTER THE DEPOSITION OF A LARGE QUANTITY OF RADIONUCLIDES CONSEQUENT UPON AN ACCIDENT. THE CHOICE OF PLANTS AND SOIL WORKING METHODS ALSO MAKES IT POSSIBLE TO STUDY THE EFFECT OF THE VARIOUS PARAMETERS ON SOIL/PLANT TRANSFER: E.G. THE KINETICS OF ROOT ADSORPTION, THE EFFECT OF FREQUENCY AND HEIGHT OF RADIONUCLIDE DEPOSITION, CONTAMINATION OF THE SOIL OR THE PLANTS. COOPERATION WITH THE DEPARTEMENT D'ETUDES ET DE RECHERCHES EN SECURITE (DERS) AND THE SERVICE D'ETUDES ET DE RECHERCHES SUR L'ENVIRONNEMENT (SERE), CEN, CADARACHE, WILL ALSO ENABLE A COMPARISON TO BE MADE OF THE BEHAVIOUR OF THE RADIONUCLIDES UNDER VARIOUS CLIMATIC CONDITIONS (DRY MEDITERRANEAN CLIMATE AND WET WESTERN-EUROPEAN CLIMATE).