Community Research and Development Information Service - CORDIS


SIGMA is a device designed for the Safeguards verification measurements of the 235U content of THTR (or AVR) pebble fuel elements. It has been in operation for more than 12 years at the HOBEG fuel fabrication plant in Hanau (FRG). The THTR fuel element is a 60 mm diameter sphere composed of particles of a U-Th mixture in a graphite matrix. The device is schematically composed of an irradiation facility, where the pebble is irradiated by 252Cf, and a counting facility, where the delayed fission neutrons are monitored. The system has been updated, the modified instrument being called SIGMA-R. SIGMA-R automatically governs the whole charge-discharge, irradiation and counting sequence, collects the measured counts in the microprocessor memory and performs the relevant calculations, including the statistical evaluation. The instructions are given interactively to the inspector through an IRIS terminal. SIGMA-R provides extensive self diagnosis features. The inspector is also informed explicitly of malfunctions during routine operation. The instrument is equipped with a permanent memory which facilitates the inspector's work considerably. With SIGMA-R it is now possible to measure the 235U content of THTR pebbles in routine operation, with a random error down to 0.15% and a systematic uncertainty estimated at 0.25%, the latter coming from calibration and normalisation procedures.

Additional information

Authors: AGOSTINI P, JRC Ispra, I-21020 Ispra (VA) (IT);BECKER L, JRC Ispra, I-21020 Ispra (VA) (IT);BERNEDE M, JRC Ispra, I-21020 Ispra (VA) (IT);CALDON L, JRC Ispra, I-21020 Ispra (VA) (IT);CORDANI G, JRC Ispra, I-21020 Ispra (VA) (IT);GUARDINI S, JRC Ispra, I-21020 Ispra (VA) (IT);GALANTUCCI R, CEC Luxembourg, L-2920 (LU);HAAS R, CEC Luxembourg, L-2920 (LU);JANSSENS A, CEC Luxembourg, L-2920 (LU)
Bibliographic Reference: EUR 12059 EN (1989) MF, 54 pp., ECU 4, blow-up copy ECU 7.50
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