Determination of Sr90 and the Transuranium Elements in the Event of a Nuclear Accident

Doktorsavhandling, 1999

To reduce the health effects of a nuclear accident, it is essential that suitable analytical methods are available for determinations of radionuclides released to the environment. Sr90 and the transuranium (TRU) elements are of great radiological importance, and they are more difficult to measure than many other radionuclides. The methods are generally time-consuming and labour-intensive, and there is a need for improvement. This work provides information that is useful in the development of more simple and rapid methods and proposes radioanalytical methods for the determination of Sr90 and the TRU elements at an early stage after a nuclear accident. The relative activity levels that can be expected in a fresh fallout from a nuclear reactor (BWR, PWR, RBMK) accident have been estimated. The results show that 238Pu, 239Pu, 2400Pu, 242Cm and 244Cm can be expected to contribute more than 99% of the total .alfa.-activity. These findings can be used to simplify and speed up the analytical procedures since certain chemical or radiometrical separations may be omitted. Information is also gained on which separations are required in the analysis of Sr90. Moreover, .gamma.-spectrometry is shown to be useful for an early indication ( 239Np) and a quick estimation of the amounts (the 141Ce/ 144Ce activity ratio) of Sr90 and TRU elements present. The required detection limits in the analysis of foodstuffs, grass and soil shortly after a nuclear accident have been estimated. Since these limits are orders of magnitude higher than those reported for many existing methods, smaller samples can be used in the development of simpler analytical procedures. The method proposed for the analysis of Sr90 is based on solvent extraction (HDEHP) and Cherenkov counting. The information given on the treatment of the counting data, the Cherenkov radiation and the counting efficiency is also useful for other methods. The method for the TRU elements uses solvent extraction (HDEHP, DMDBTDMA) and LSC.