Measurement of decay heat in neutron irradiated 197 Au foil using whole energy absorption spectrometer
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Measurement of decay heat in neutron irradiated 197Au foil using whole energy absorption spectrometer D. V. Subramanian1 · G. Pandikumar1 · Adish Haridas1 · John Arul1 Received: 28 February 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract In a nuclear reactor, heat generated by the decay of fission products and radioactive materials is called decay heat or decay power. For measuring decay heat from radioactive samples, bismuth germanate scintillators based whole energy absorption spectrometer was commissioned recently. To standardize it, decay heat from neutron irradiated 197Au foil was measured from 7 min to 480 h. In this cooling period the decay heat reduced from 1668 ± 12.5 to 10 ± 1.8 pW. The measurements were compared with the predictions and the C/E ratios were found to be 95%. This makes the decay power measurement for long cooling periods. Hence it is selected for the measurements. The sample is cleaned using acetone to remove dust or dirt, if any, and wrapped in a sheet of paper. Before irradiation,it is introduced into a rabbit and transferred to irradiation location through PFTS. The sample is irradiated for 10 min at 10 W reactor power. After the irradiation for the required time, in few seconds (5–6 s), the rabbit (with the sample) is pushed out from the irradiation spot to the location where it is initially loaded. The total contact dose rate measured by using a tele detector is found to be 160 μSv/h and gamma alone is 2 μSv/h. It
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Journal of Radioanalytical and Nuclear Chemistry
used. The standard gamma reference sources such as 133Ba, Cs and 60Co are used and the calibration factors are found for individual detectors and for the sum. With quadratic calibration, the channels are assigned with energy values (E) in keV using the following formula (1)
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Fig. 5 Sample holder
is observed that the dose rate of the sample is low enough to start counting and hence is transferred to WEAS within few minutes.
Sample holder
E = A + (B(Channel no)) + (C(Channel no)2 )
(1)
where A, B and C are calibration factors. When the assigned energy values for channels are compared with the reference source energy values, their deviation from reference energy values is within ± 4%.
Gamma and beta absorption efficiency of detector
The irradiated sample is transferred to WEAS through sample holder. Figure 5 shows the sample holder made for decay power measurement. The holder is made of copper sheet of thickness 0.4 mm, 122 mm length and 40 mm breadth. It has an opening of 30 mm by 30 mm to match with the window area in the detectors. In the sample holder, opening is covered with thin cellophane tape from the bottom side. The irradiated sample is placed on this cellophane tape. Then, the top surface (with sample) is also covered with cellophane tape. This is done to ensure that the sample will not move or fall-out from the sample holder.
The ratio of absorbed energy by the BGO scintillators to total decay energy is defined as the energy absorption efficiency and is obtained by using Monte Carlo
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