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INSTITUTE FOR NUCLEAR RESEARCHPITESTI ROMANIA 

• Neutron activation analysis on slurry resulted
  from waste water conditioning

Authors Dumitru Barbos, barbos_at_scn.ro
Constantin Paunoiu Affiliation Institute for
Nuclear Research (INR) Pitesti, Romania
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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.

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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.
• 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.

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• 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
  128cm3 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
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• The thermal to epithermal ratio is estimated
  from measured cadmium ratio of 197Au (n,?)
  reaction.
• The integral flux measured value is 3.01 1012
  n/cm2s.. The sub cadmium neutron flux value is
  1.41012 n/cm2s and cadmium ratio Rcd1,94.

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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.
• Zr monitor has a double utilization From the
  specific reaction rates of 95Zr and 97Nb, the
  thermal to epithermal neutron flux ratio is
  determined, using the relation

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• In the following, the isotope 94Zr is used as a
  comparator also.

• The elemental concentration is computed with the
  relation

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• 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 lt 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
  f10.56.
• 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.

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• Table 2

Loc de prelevare Tir (h) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm) Concentration(ppm)
Loc de prelevare Tir (h) La La Na Na K K As As Br Br Sc Sc Cr Cr Fe Fe W W Zn Zn Co Co U U Au
Bazin 1 SCN 2,01 60,79 60,79 2823 2823 6571 6571 4,03 4,03 17,87 17,87 6,44 6,44 610 610 4,58 4,58 13,56 13,56 1719 1719 17,05 17,05 0,18 0,18 0,11
Bazin 2 SCN 2,01 25,22 25,22 2398 2398 5021 5021 1,013 1,013 4,73 4,73 4,5 4,5 267 267 3,08 3,08 5,53 5,53 1581 1581 23,08 23,08 0,09 0,09 0,084
/- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty /- Overall uncertainty
Sample1 2.74 127 127 262.8 262.8 0.20 0.20 0.89 0.89 0.19 0.19 18.3 18.3 0.09 0.09 0.68 0.68 68.76 68.76 0.68 0.68 0.008 0.008 0.006 0.006
Sample2 1.13 107 107 201 201 0.05 0.05 0.24 0.24 0.14 0.14 8 8 0.06 0.06 0.28 0.28 63.24 63.24 0.92 0.92 0.004 0.004 0.004 0.004