SEDIMENT PROFILE OF NP-237 IN THE IRISH SEA - ESTIMATION OF THE TOTALAMOUNT OF NP-237 DISCHARGED FROM SELLAFIELD

Sediment profiles of Np-237 in cores from the Irt, Mite and Esk Estuar ies in the Irish Sea have been studied together with plutonium isotope s (Pu-238, Pu-239.240 and Pu-241). One of the three sediment cores mea sured, the core from the Irt Estuary, provided a record of the tempora l variations of these radionuclides discharged from Sellafield. The ac tivity concentrations of Np-237 and the activity ratios of Np-237/Pu-2 39,Pu-240 within the depth studied varied widely 0.16 to 13.1 Bq/kg an d 0.02 to 0.71%, respectively. The depth profiles of Np-237 differed m arkedly from those of Pu isotopes. A chronology was established by com paring the Pu isotope activity concentrations and their activity ratio profiles with data from the Sellafield discharges. This allowed an es timate to be made of the total amount (6-8 TBq) of Np-237 discharged u ntil 1989.