Contamination of piping from disassembled A-1 nuclear power plant secondary circuit

The method of estimating the average contamination by measuring external gamma radiation in the centre of the pipe was used. Compared with the method of sampling by etching, the method was shown to be considerably more accurate and faster and did not require any processing of pipes supposed to be discarded. The method can be used to determine contamination of pipes of 200 to 500 mm in diameter and 300 to 800 mm in length with an error of max. 25%. The measurement time is about 10 seconds for a pipe of an average 60Co contamination of the order of 100 Bq.cm-2 measured using a NaI(Tl) scintillator 100 mm in diameter and 100 mm in length. For experiments, NaI(Tl) scintillators with a two-channel measuring instrument are sufficient with one channel set to the 137Cs photopeak and the other to the 60Co photopeaks. In deriving the 137Cs and 60Co activities from pulse counts in the individual channels, the coefficients can be used calculated by the Monte Carlo method. (author). 3 figs., 3 tabs., 7 refs