| 1. |
- Jacobsson, Staffan, et al.
(författare)
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A Tomographic Method for Verification of the Integrity of Spent Nuclear Fuel Assemblies - I: Simulation Studies
- 2001
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Ingår i: Nuclear Technology. - 0029-5450. ; 135:2, s. 131-145
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Tidskriftsartikel (refereegranskat)abstract
- A tomographic method for experimental investigation of the integrity of used light water reactor fuel assemblies has been developed. It is based on spectroscopic measurements of the gamma radiation from fission products in fuel rods. The method utilizes beforehand information about the nominal geometry of both the measured fuel assembly and the measurement equipment. A reconstruction code of the algebraic type has been written. The potential of the technique has been examined in extensive simulations, assuming a gamma-ray energy of either 662 keV (137Cs) or 1274 keV (154Eu). The ability of detecting various configurations of manipulated rods, both single and in groups, has been investigated. Two main types of manipulations have been simulated. First, there is the removal of rods without replacement. The results indicate that all investigated configurations of removed rods in boiling water reactor (BWR) fuel can be reliably detected using 137Cs radiation. For pressurized water reactor (PWR) fuel, the same result is obtained, with the exception of the most central positions. Here, the more penetrating radiation from 154Eu may have to be used. Second, there is the replacement of rods with fresh fuel or fuel-like material. The results clearly indicate that all simulated cases of such manipulation can be most confidently detected. The simulations include various configurations of replaced rods in both BWR and PWR fuel, using both gamma-ray energies.
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| 2. |
- Jacobsson, Staffan, et al.
(författare)
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A Tomographic Method for Verification of the Integrity of Spent Nuclear Fuel Assemblies - II: Experimental Investigation
- 2001
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 135:2, s. 146-153
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Tidskriftsartikel (refereegranskat)abstract
- A tomographic method for verification of the integrity of used light water reactor fuel has been experimentally investigated. The method utilizes emitted gamma rays from fission products in the fuel rods. The radiation field is recorded in a large number of positions relative to the assembly, whereby the source distribution is reconstructed using a special-purpose reconstruction code.An 8 × 8 boiling water reactor fuel assembly has been measured at the Swedish interim storage (CLAB), using installed gamma-scanning equipment modified for the purpose of tomography. The equipment allows the mapping of the radiation field around a fuel assembly with the aid of a germanium detector fitted with a collimator with a vertical slit. Two gamma-ray energies were recorded: 662 keV (137Cs) and 1274 keV (154Eu). The intensities measured in 2520 detector positions were used as input for the tomographic reconstruction code. The results agreed very well with simulations and significantly revealed a position containing a water channel in the central part of the assembly.
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| 3. |
- Jacobsson Svärd, Staffan, 1970-
(författare)
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A Tomographic Measurement Technique for Irradiated Nuclear Fuel Assemblies
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The fuel assemblies used at the Swedish nuclear power plants contain typically between 100 and 300 fuel rods. An experimental technique has been demanded for determining the relative activities of specific isotopes in individual fuel rods without dismantling the assemblies. The purpose is to validate production codes, which requires an experimental relative accuracy of <2 % (1 σ).Therefore, a new, non-destructive tomographic measurement technique for irradiated nuclear fuel assemblies has been developed. The technique includes two main steps: (1) the gamma-ray flux distribution around the assembly is recorded, and (2) the interior gamma-ray source distribution in the assembly is reconstructed. The use of detailed gamma-ray transport calculations in the reconstruction procedure enables accurate determination of the relative rod-by-rod source distribution.To investigate the accuracy achievable, laboratory equipment has been constructed, including a fuel model with a well-known distribution of 137Cs. Furthermore, an instrument has been constructed and built for in-pool measurements on irradiated fuel assemblies at nuclear power plants.Using the laboratory equipment, a relative accuracy of 1.2 % was obtained (1 σ). The measurements on irradiated fuel resulted in a repeatability of 0.8 %, showing the accuracy that can be achieved using this instrument. The agreement between rod-by-rod data obtained in calculations using the POLCA–7 production code and measured data was 3.1 % (1 σ).Additionally, there is a safeguards interest in the tomographic technique for verifying that no fissile material has been diverted from fuel assemblies, i.e. that no fuel rods have been removed or replaced. The applicability has been demonstrated in a measurement on a spent fuel assembly. Furthermore, detection of both the removal of a rod as well as the replacement with a non-active rod has been investigated in detail and quantitatively established using the laboratory equipment.
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| 4. |
- Jacobsson Svärd, Staffan, et al.
(författare)
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Non-destructive experimental determination of the pin-power distribution in nuclear fuel
- 2003
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A need for validation of modern core-analysis codes with respect to the calculated pin-power distribution has been recognized. A non-destructive experimental method for such validation has been developed, based on a tomographic technique. Each axial node of the fuel assembly is measured separately and the relative pin-by-pin content of the direct fission product Ba-140 is determined. Investigations performed so far indicate that 1-2% (1 σ) accuracy can be obtained.A measuring device has been constructed which, when fully equipped, is designed to measure a complete BWR assembly in 25 axial nodes within an eight-hour work shift. The applicability of the constructed device has been demonstrated in measurements at the Swedish BWR Forsmark 2 on irradiated fuel with a cooling time of 4-5 weeks. Data from the core-analysis code POLCA-7 have been compared to measured pin-by-pin contents of Ba-140. An agreement of 3.1% (1 σ) has been demonstrated.As compared to the conventional method, involving gamma scanning of individual fuel pins, this method does not require the fuel to be disassembled. Neither does the fuel channel have to be removed. The cost per measured fuel pin is in the order of 20 times lower than the conventional method.
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| 5. |
- Jacobsson Svärd, Staffan, et al.
(författare)
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Tomographic measurements for partial defect verification – experience with different devices of the stationary type
- 2003
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Ingår i: 25th Annual Meeting - Symposium on Safeguards and Nuclear Materials Management. - 928945654X
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Tomographic measurements have been performed for the purpose of partial-defect verification on the single-rod level. The measurement procedure involves recording of the gamma radiation field emanating from emitted radiation from within an irradiated assembly and consecutive reconstruction of the internal source distribution. Different devices of the stationary type have been utilised, ranging from a laboratory device used in measurements on a fuel model to an in-pool device used in measurements on irradiated fuel in a fuel-handling pool.The tomographic technique has proven to be robust and reliable. Its applicability for partial-defect verification on the single-rod level has been satisfying. Some required properties of a stationary device are discussed.
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| 6. |
- Jansson, Peter, 1971-, et al.
(författare)
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A Feasibility Study of BGO Scintillation Detectors for Tomographic Measurements on Nuclear Fuel
- 2000
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A study of BGO detectors has been performed. The purpose of the study was to determine geometrical shape of the scintillator crystals in order to be suited for use in tomographic measurements on nuclear fuel. Computer calculations using Monte Carlo techniques were used. High count-rate experiments were performed on three nuclear fuel assemblies with the shapes of the crystals determined by the calculations. The resulting characteristics of the detectors show that they are suitable in a tomographic measurement.
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| 7. |
- Jansson, Peter, 1971-, et al.
(författare)
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A Method of Measuring Decay Heat in Spent Nuclear Fuel using Gamma-ray Spectroscopy
- 2001
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Ingår i: Waste Management Symposium 2001 (WM'01).
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Konferensbidrag (refereegranskat)abstract
- In this paper, a method is presented for determining the decay heat in spent nuclear fuel by using gamma-ray spectroscopy. Using this method, the decay heat may be determined within ten minutes per assembly i.e. it is well suited for industrial applications in, for example, an encapsulation facility. The method has been tested and evaluated in the wet Swedish Central Storage for Spent Fuel, CLAB. Although only tested in a wet storage, the method should also be applicable for dry storage.The objective of developing the method was primarily to investigate possibilities to achieve a fast, robust and reasonable accurate determination of decay heat by gamma-ray measurements on fuel assemblies. Such a method could also be for verification of burnup and cooling time, for safeguard purposes prior to encapsulation, (1).So far, measurements and calculations on 35 BWR- and 34 PWR-assemblies, with various nuclear data, have been performed. The test measurements, using preliminary measuring equipment, have shown that the decay heat may be determined within an uncertainty of 3%.
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| 8. |
- Jansson, Peter, 1971-, et al.
(författare)
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Calculations of the Neutron Flux Outside BWR 8×8 Spent-Fuel Assemblies and the Sensitivity to Fuel Pin Diversion
- 2004
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 146:1, s. 58-64
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of detecting replaced fuel rods in a spent-fuel assembly by means of measurement of the emitted neutron- and gamma-ray radiation has been investigated by computer simulations. The radiation field outside a boiling water reactor 8 × 8 fuel assembly with varying patterns of fuel rods replaced with lead dummies was calculated using a simple model for the source distribution and the Monte Carlo code MCNP-4C for the radiation field. In particular, the sensitivity of the thermal neutron field as measured in a Fork detector to various replacement patterns was investigated. The results suggest a detection limit of 5% of the fuel mass replaced, i.e., 3 out of 63 rods, independently of the pattern of the replaced rods.
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| 9. |
- Jansson, Peter, 1971-, et al.
(författare)
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Gamma-Ray Spectroscopy Measurements of Decay Heat in Spent Nuclear Fuel
- 2002
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Ingår i: Nuclear Science and Engineering. - 0029-5639. ; 141:2, s. 129-139
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Tidskriftsartikel (refereegranskat)abstract
- A method for determining the residual thermal power in spent nuclear fuel using gamma-ray spectroscopy is suggested. It is based on the correlation between the residual power and the 137Cs activity, which is nearly linear for fuel with cooling times between 10 and 50 yr. Using available data of calorimetrically measured values of the decay heat in 69 boiling water reactor and pressurized water reactor spent-fuel assemblies resulted in agreement with a standard deviation of 3%.
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| 10. |
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