“Neutron activation analysis on slurry resulted from waste water conditioning” INSTITUTE FOR NUCLEAR RESEARCH PITESTI – ROMANIA INSTITUTE FOR NUCLEAR RESEARCH PITESTI – ROMANIA Authors: Dumitru Bărbos, Constantin Păunoiu Constantin Păunoiu Affiliation: Institute for Nuclear Research (INR) Piteşti, Romania

Abstract The present paper presents the method for determining the elemental concentration in the slurry resulted from waste water conditioning at the INR site. In achieving of this goal, we used the ACPR TRIGA reactor as neutron source, operated in stationary mode. The TRIGA Annular-Core Pulsing Reactor (ACPR) is a pool type pulsed reactor. The samples were irradiated in the pneumatic rabbit of this reactor. There are presented the results of the measurements for neutron flux-spectrum characterization in the pneumatic rabbit irradiation location, and the results obtained for multi-elemental analysis using the Zr method.

NEUTRON FLUX-SPECTRUM MEASUREMENTS Neutron flux spectrum measurements in the ACPR pneumatic rabbit dry channel were performed using multi-foil activation techniques. Activation reaction rates were obtained by absolute measurement of the induced activity using gamma-ray spectroscopy techniques. Neutron flux spectrum measurements in the ACPR pneumatic rabbit dry channel were performed using multi-foil activation techniques. Activation reaction rates were obtained by absolute measurement of the induced activity using gamma-ray spectroscopy techniques. The foil detectors were placed into an polyethylene cartridge and introduced in the dry hole using pneumatic rabbit. During the foil detectors irradiation the reactor was operated in steady-state mode at a power level of about 100 kW. The foil detectors were placed into an polyethylene cartridge and introduced in the dry hole using pneumatic rabbit. During the foil detectors irradiation the reactor was operated in steady-state mode at a power level of about 100 kW.

For flux spectrum measurements, the multifoil activation method was applied. The neutron spectra and flux are obtained by unfolding from measured reaction rates. Nine thermal, epithermal and threshold foil reaction rates were measured. For gamma spectrum counting a 20% efficiency and 128cm 3 high purity Germanium detector connected to a spectrometer with multichannel analyzer installed on PC with ADC interface were used. The spectrometer is absolute-efficiency calibrated for the usual counting distances. Self-shielding corrections for the activation foils are also applied. The self- shielding corrections are computed using Monte-Carlo simulation methods. The solution spectrum obtained by the SAND-II code runs, and the response functions are presented in Figure 1. The solution is obtained after 2 iterations with a standard deviation of measured activities equal to 2.51 %. The guess spectrum used for unfolding was generated using SAND II energy mesh according to the formula: and matched to fission spectrum at 0.5 MeV

The thermal to epithermal ratio is estimated from measured cadmium ratio of 197 Au (n,  ) reaction. The integral flux measured value is 3.01* n/cm 2 s.. The sub cadmium neutron flux value is 1.4*10 12 n/cm 2 s and cadmium ratio Rcd=1,94.

Elemental concentration determination in the analyzed samples using the Zr standardization method. To determine the elemental concentration in the analyzed samples, the multi-isotope foil standardization method ( Zr method) was used. To determine the elemental concentration in the analyzed samples, the multi-isotope foil standardization method ( Zr method) was used. Zr monitor has a double utilization : From the specific reaction rates of 95 Zr and 97 Nb, the thermal to epithermal neutron flux ratio is determined, using the relation :

In the following, the isotope 94 Zr is used as a comparator also. In the following, the isotope 94 Zr is used as a comparator also. The elemental concentration is computed with the relation : The elemental concentration is computed with the relation :

Samples were collected from calming basins no 1 ad 2 at the waste water conditioning plant at the INR site. Together with each sample, a Zr monitor was irradiated in order to measure the thermal ( E < 0.5 eV) to epi-thermal flux ratio. During irradiation, the reactor was operated in stationary mode at a constant power level of 100 kW. Irradiation time was of two hours. Samples were collected from calming basins no 1 ad 2 at the waste water conditioning plant at the INR site. Together with each sample, a Zr monitor was irradiated in order to measure the thermal ( E < 0.5 eV) to epi-thermal flux ratio. During irradiation, the reactor was operated in stationary mode at a constant power level of 100 kW. Irradiation time was of two hours. The induced reaction rates in the samples and the monitors were measured by the means of the gamma-ray spectrometry chain already described here. The thermal to epi-thermal flux ratio is f= The induced reaction rates in the samples and the monitors were measured by the means of the gamma-ray spectrometry chain already described here. The thermal to epi-thermal flux ratio is f= The gamma-ray spectrometry measurements showed the presence of important Uranium quantities. It is important to emphasize that its concentration is so large ( percent levels) so that for this (rather small) irradiation time, fission reaction were already observed. The gamma-ray spectrometry measurements showed the presence of important Uranium quantities. It is important to emphasize that its concentration is so large ( percent levels) so that for this (rather small) irradiation time, fission reaction were already observed. The analyzed samples showed the presence of Na, K, Sc; Cr, Fe, Zn, Br, W, As, Co, as well as traces of Au and La. Concentration values are given in Table 2. The analyzed samples showed the presence of Na, K, Sc; Cr, Fe, Zn, Br, W, As, Co, as well as traces of Au and La. Concentration values are given in Table 2.

Table 2 Loc de prelevare Tir (h) Concentration(ppm) LaNaKAsBrScCrFeWZnCoUAu Bazin 1 SCN 2,0160, ,0317,876,446104,58%13, ,050,18%0,11 Bazin 2 SCN 2,0125, ,0134,734,52673,08%5, ,080,09% 0,08 4 +/- Overall uncertainty Sample Sample