Safeguards & nuclear physics measurements

aim

measurement of neutron and gamma output of irradiated fuel

typical use

• the fork detector can be used in the reactor pond (for measurement under water) and in any storage location (in dry conditions).

basic mechanism

• the fork detector uses fission chambers and ionisation chambers for neutron counting and gamma current determination; correlations exist that link the neutron count rate to burnup and Pu-content, and gamma current to cooling time; corrections on the measurement data are necessary, and can be performed by using a reactor code for build-up and depletion calculations
• calibrations are established for every particular initial enrichment, and are obtained through the measurement of a series of known irradiated fuel assemblies
• normal sample geometry: a fuel assembly is inserted between the arms of the fork detector, and measurements are made in a fixed position or in an axial scan

type of samples

• fuel assemblies

applicability range

• detection requirements: burnup > 10000 MWd/t
• accuracy:
  • burnup: 2 à 3 %
  • Pu-content: 5 à 7 %
  • Cooling time: 10%

turn-around time

• 1 minute per measurement; a complete scanning of a fuel assembly can contain 15 points
• the installation time of the fork detector, is about 1 to 2 hours

advantages

• non-destructive method, not touching the integrity of the assembly
• simultaneous identification and determination of neutron and gamma signal from an irradiated fuel assembly
• accuracy determined by specific conditions
• good sensitivity
• absence of external interrogation sources
• highly automated

disadvantages

• no direct measurement of the fissile component in the fuel

contact

Dr. van der Meer Klaas
Dr. Bruggeman Michel

aim

measurement of the neutron output of waste barrels and fissile material containers.

typical use

• calibrated measuring chain for neutron measurement on 220 l waste barrels and absolute filters, depending on the radiation level, using high-sensitivity He-3 counters

basic mechanism

• the Neutron Cavity contains 60 He-3 neutron detectors, embedded in polyethylene, forming an hexagone and each detector bank contains 3 tubes, and is mounted on a modular frame
• the system is equipped with a time interval analyser (TIA) and uses computed neutron coincidence counting

type of samples

• small samples up to 400 liter drums

applicability range

• normal range: from mg to kg Pu
• detection limits: for 1000 s measurement time, and 3-sigma confidence level:
  • total counting: 2 mg Pu typical
  • coincidence counting: 2 mg Pu-240 equivalent
  • multiplicity counting: 100 mg Pu-240 equivalent
• accuracy: Under good conditions, 1 to 5 % at the 1-sigma level, depending on the composition

turn-around time

• depends on the typical measuring time, 0.5 to 1 hour per sample

advantages

• non destructive method
• indirect measurement of transuranic elements
• moderate to high sensitivity
• highly automated

disadvantages

• the transuranium element or the isotopes present have to be known in advance, and so the isotopes present
• the measurement needs to be completed by a gamma spectroscopy for isotopics determination
• sensitive to sample geometry and matrix effects

contact

Dr. Bruggeman Michel
De Boeck Wim

aim

gamma spectroscopy on waste barrels and absolute filters

typical use

• calibrated measuring chain for gamma spectroscopy on 220 l waste barrels, with 3 high-efficiency (20%) liquid-nitrogen cooled Ge(rmanium) detectors and electronics in 4pi shielding. The system is used with radiation levels lower than 20µSv/h (measurement for free release)

basic mechanism

• Calibrated system for activity determination using density based correction for gamma attenuation in the sample.
  Normal sample geometry: waste barrels and filter boxes are installed in a reference position on a turn table

type of samples

• waste barrels/absolute filters

applicability range

• normal range: 60 to 1500 keV
• detection limits: some mBq/g, depending on shielding, presence of interfering gamma-emitters, branching ratio of the gamma-ray, measuring geometry, measuring period
• precision: under good conditions, 1 to 5 % at the 1-sigma level

turn-around time

• typical measuring time, 10 min. up to 60 min. per sample
• tthe overall time, including reporting, is less than 1 day

advantages

• non destructive method, not touching the integrity of the container
• simultaneous identification and determination of many radionuclides (specific mono-energetic gamma-rays and high energy resolution of the Ge detectors)
• accuracy determined by matrix and source position
• very high sensitivity
• highly automated

disadvantages

• gamma attenuation in the sample can be considerable, affecting accuracy; no segmentation
• sensitive to sample geometry
• necessity of calibration sources

contact

Dr. Bruggeman Michel
De Boeck Wim

aim

gamma spectroscopy of waste barrels

typical use

• calibrated measuring chain for gamma spectroscopy on 220 l waste barrels in a scanning or non-scanning mode. The system is used with radiation levels higher than 20µSv/h

basic mechanism

• Calibrated system for activity determination using density based correction for gamma attenuation in the sample
  Waste barrels are installed in a reference position on a turn table, combined with axial scanning over different segments

type of samples

• waste barrels up to 400 liter

applicability range

• normal energy range: 60 to 1500 keV
• detection limits: some 100 mBq/g, depending on shielding, presence of interfering gamma-emitters, branching ratio of the gamma-ray, measuring geometry, measuring period
• precision: under good conditions, 1 to 5 % at the 1-sigma level

turn-around time

• depends on the number of segments and of the analysis (typical measuring time, 3600 sec. per sample)
• the overall time, including reporting, is less than 1 day

advantages

• non destructive method, not touching the integrity of the container
• simultaneous identification and determination of many radionuclides (specific mono-energetic gamma-rays and high energy resolution of the Ge detectors)
• isotope vector can be measured per segment
• the segment is defined by the collimator
• accuracy determined by matrix and source distribution
• moderate sensitivity
• highly automated

disadvantages

• gamma attenuation in the sample can be considerable, affecting accuracy, but inherent to waste barrel measurements
• sensitive to sample geometry
• necessity of calibration sources

contact

Dr. Bruggeman Michel
De Boeck Wim