| 1. |
- Eriksson, Marcus, et al.
(författare)
-
Inherent Safety of Fuels for Accelerator-driven Systems
- 2005
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 151:3, s. 314-333
-
Tidskriftsartikel (refereegranskat)abstract
- Transient safety characteristics of accelerator-driven systems using advanced minor actinide fuels have been investigated. Results for a molybdenum-based Ceramic-Metal (CerMet) fuel, a magnesia-based Ceramic-Ceramic fuel, and a zirconium-nitride-based fuel are reported. The focus is on the inherent safety aspects of core design. Accident analyses are carried out for the response to unprotected loss-of-flow and accelerator beam-overpower transients and coolant voiding scenarios. An attempt is made to establish basic design limits for the fuel and cladding. Maximum temperatures during transients are determined and compared with design limits. Reactivity effects associated with coolant void, fuel and structural expansion, and cladding relocation are investigated. Design studies encompass variations in lattice pitch and pin diameter. Critical mass studies are performed. The studies indicate favorable inherent safety features of the CerMet fuel. Major consideration is given to the potential threat of coolant voiding in accelerator-driven design proposals. Results for a transient test case study of a postulated steam generator tube rupture event leading to extensive coolant voiding are presented. The study underlines the importance of having a low coolant void reactivity value in a lead-bismuth system despite the high boiling temperature of the coolant. It was found that the power rise following a voiding transient increases dramatically near the critical state. The studies suggest that a reactivity margin of a few dollars in the voided state is sufficient to permit significant reactivity insertions.
|
|
| 2. |
- Gottlieb, C., et al.
(författare)
-
Feasibility study on transient identification in nuclear power plants using support vector machines
- 2006
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 155:1, s. 67-77
-
Tidskriftsartikel (refereegranskat)abstract
- Support vector machines (SVMs), a relatively new paradigm in statistical learning theory, are studied for their potential to recognize transient behavior of detector signals corresponding to various accident events at nuclear power plants (NPPs). Transient classification is a major task for any computer-aided system for recognition of various malfunctions. The ability to identify the state of operation or events occurring at an NPP is crucial so that personnel can select adequate response actions. The Modular Accident Analysis Program, version 4 (MAAP4) is a program that can be used to model various normal and abnormal events in an NPP. This study uses MAAP signals describing various loss-of-coolant accidents in boiling water reactors. The simulated sensor readings corresponding to these events have been used to train and test SVM classifiers. SVM calculations have demonstrated that they can produce classifiers with good generalization ability for our data. This in, turn indicates that SVMs show promise as classifiers for the learning problem of identifying transients.
|
|
| 3. |
- Hansson, Roberta Concilio, et al.
(författare)
-
Dynamics and preconditioning in a single-droplet vapor explosion
- 2009
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 167:1, s. 223-234
-
Tidskriftsartikel (refereegranskat)abstract
- The present study aims to develop a mechanistic understanding of the thermal-hydraulic processes in a vapor explosion, which may occur in nuclear power plants during a hypothetical severe accident, involving interactions of high-temperature corium melt and volatile coolant. Dynamics of the hot liquid (melt) droplet and the volatile liquid (coolant) were investigated in the Micro-Interactions in Steam Explosion Experiments (MISTEE) facility by performing well-controlled, externally triggered, single-droplet experiments, using a high-speed visualization system with synchronized digital cinematography and continuous X-ray radiography, called Simultaneous High-speed Acquisition of X-ray Radiography and Photography (SHARP). After an elaborate image processing, the SHARP images depict the evolution of both melt material (dispersal) and coolant (bubble dynamics) and their microscale interactions. The analysis of the data shows a deficiency in using the bubble dynamics alone to provide a consistent explanation of the energetic behavior. In contrast, the SHARP data reveal a correlation between the droplet's dynamics in the bubble's first cycle and the energetics of the subsequent explosive evaporation in the bubble's second cycle. The finding provides a basis to suggest that a so-called melt-droplet preconditioning, i.e., deformation/prefragmentation of a hot melt droplet immediately following the pressure trigger, is instrumental to the subsequent coolant entrainment, evaporation, and energetics of the resulting vapor explosion.
|
|
| 4. |
- Hultqvist, Martha, 1983-, et al.
(författare)
-
Secondary doses in anthropomorphic phantoms irradiated with light ion beams
- 2009
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 168:1, s. 123-127
-
Tidskriftsartikel (refereegranskat)abstract
- The mathematical anthropomorphic phantoms EVA-HIT and ADAM-HIT have been used in the Monte Carlo code SHIELD-HIT07 for simulations of lung tumor and prostate irradiation with light ions. Calculations were performed for 1H, 7Li, and 12C beams of energies in the range of 80 to 330 MeV/u. The secondary doses to organs, due to scattered primary ions and secondary particles produced in the phantoms, were studied taking into account the contribution from secondary neutrons, secondary protons, pions, and heavier fragments from helium to calcium. The doses to organs per dose to target (tumor) are of the order of 10-6 to 10-1 mGy Gy-1 and decrease with increasing distance from the target. In general the organ dose per target dose increases with increasing Z of the primary particle; however, for lighter primary ions (Z 3) and for organs close to the target, scattered primary particles show a nonnegligible dose contribution.
|
|
| 5. |
- Kienzler, Bernhard, et al.
(författare)
-
ACTINIDE MIGRATION IN FRACTURES OF GRANITE HOST ROCK : LABORATORY AND IN SITU INVESTIGATIONS
- 2009
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 165:2, s. 223-240
-
Tidskriftsartikel (refereegranskat)abstract
- Within the scope of a cooperation between Svensk Karnbranslehantering AB and Forschungszentrum Karlsruhe, Institut fur Nukleare Entsorgung, a series of actinide migration experiments were performed both in the laboratory and at the Aspo Hard Rock Laboratory in Sweden. The objectives of these experiments were to quantify, the sorption of different actinide elements in single fractures of a granite host rock and to investigate the sorption mechanisms. To guarantee the most realistic conditions-as close to nature as possible-in situ experiments were performed in the Chemlab 2 borehole probe. These migration experiments were complemented by laboratory sorption and migration studies. The latter included batch experiments with flat chips of natural material extracted from fracture surfaces to identify the mineral phases relevant to radionuclide sorption by means of autoradiography. Scanning electron microscopy analyses provided information on the composition of sorption-relevant phases and X-ray photoelectron spectroscopy of Np, Tc, and Fe distribution revealed the redox states of these elements. Important mineral phases retaining all actinides and Tc were Fe-bearing phases. From the migration experiments, elution curves of the inert tracer (HTO), Np(V), U(VI), and to a small extent of Tc(VII) were obtained. Americium (III) and plutonium(IV) were not eluted. The mechanisms influencing the migration of the elements Np, U, and Tc depended on redox reactions. It was shown by various independent methods that Np(V) was reduced to the tetravalent state on the fracture surfaces, thus resulting in a pronounced dependence of the recovery on the residence time. Technetium was also retained in the tetravalent state. Elution of natural uranium from the granite drill cores was significant and is discussed in detail.
|
|
| 6. |
- Liu, Longcheng, et al.
(författare)
-
Analysis of fluid flow and solute transport in a fracture intersecting a canister with variable aperture fractures and arbitrary intersection angles
- 2005
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 150:2, s. 132-144
-
Tidskriftsartikel (refereegranskat)abstract
- A multitude of simulations have been made for different types of rough-walled fractures, by using FEM-LAB((R)), to evaluate the mass transfer to and from water flowing through a fracture with spatially variable apertures and with an arbitrary angle of intersection to a canister that contains spent nuclear fuel. This paper presents and discusses only the results obtained for the Gaussian fractures. The simulations suggest that the intersection angle has only a minor influence on both the volumetric and the equivalent flow rates. The standard deviation of the distribution of the volumetric flow rates of the many realizations increases with increasing roughness and spatial correlation length of the aperture field, and so does that of the equivalent flow rates. The mean of the distribution of the volumetric flow rates is determined, however, solely by the hydraulic aperture, while that of the equivalent flow rates is determined by the mechanical aperture. Based upon the analytical solutions for the parallel plate model, it has been found that the distributions of both the volumetric and the equivalent flow rates are close to the Normal. Thus, two simple expressions can be devised to quantify the stochastic properties of fluid flow and solute transport through spatially variable fractures without making detailed calculations in every fracture intersecting a deposition hole or a tunnel.
|
|
| 7. |
- Marklund, Lars, et al.
(författare)
-
Impact of landscape topography and quaternary overburden on the performance of a geological repository of nuclear waste
- 2008
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 163, s. 165-179
-
Tidskriftsartikel (refereegranskat)abstract
- The topographical driving forces for groundwater on different spatial scales in several ways influence the performance of a repository for nuclear waste located at large depth in crystalline bedrock. We show that the relation between local topographical characteristics (topographical steepness and wavelengths) in the area of a repository (kilometer scale) and the large-scale (hundreds of kilometers) surroundings, together with repository depth, are the primary controls of residence time distributions and the discharge pattern of radionuclides released from an underground repository. In addition, the topography affects the groundwater flow at repository depth and, therefore, influences the long-time degradation of the repository. In the areas studied, all located in Sweden, the local topography mainly controls the groundwater flow down to a depth of ∼500 m, which is the suggested depth of the Swedish repository. The importance of the large-scale topography increases with depth but even at depth where local-scale topography is dominant, the continental-scale topography affects length and depth of flow paths as well as groundwater velocities. The impact of large-scale topography is particularly clear in areas where the steepness of local-scale landforms is relatively small. The study also shows that quaternary deposits (bedrock overburden) may have a significant impact on the overall residence times in the underground because of their hydraulic and sorption properties. This effect is fiirther enhanced by the fact that flow paths originating from repository depth generally emerge in topographical lows with relatively deep layers of quaternary deposits. The findings of this study underscore the need to consider multiscale topographical characteristics as well as bedrock overburden in assessments of radiological consequences of underground repositories.
|
|
| 8. |
- Nilsson, Karl-Fredrik, et al.
(författare)
-
A probabilistic methodology to determine failure probabilities and acceptance criteria for the KBS-3 inserts under ice-age load conditions
- 2008
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 163:1, s. 3-14
-
Tidskriftsartikel (refereegranskat)abstract
- The Swedish KBS-3 copper-cast iron canister for geological disposal of spent nuclear fuel is in an advanced stage. This paper deals with the cast iron insert that provides the mechanical strength of the canister and outlines an approach to assess the failure probabilities for manufactured canisters at large isostatic pressure (44 MPa) that could occur during future glaciations and first steps to derive acceptance criteria to ensure that failure probabilities are extremely small. The work includes a statistical test program using three inserts to determine the tensile, compression, and fracture properties. Specimens used for material characterization were also investigated by microstructural analysis to determine the microstructure and to classify and size defects. It was found that the material scatter and low ductility were caused by many defect types, but slag defects in the form of oxidation films were the most important ones. These data were then used to compute defect distributions for the probabilistic failure analysis of the KBS-3 canisters. A large number of finite element-analyses of canisters were performed at the maximum design load (44 MPa) covering distributions of material parameters and geometrical features of the canisters. The computed probabilities for fracture and plastic collapse were very low even for material data with low ductility. Two large-scale isostatic compression tests of KBS-3 mock-ups to verify safety margins are also described. The failure occurred at loads above 130 MPa in both cases, indicating a safety margin of at least a factor 3 against the maximum design load. As a result of the project, new acceptance criteria are being proposed for insert geometry and material properties, and the manufacturing process for inserts has been modified to ensure that these criteria are always fulfilled.
|
|
| 9. |
- Painter, Scott L., et al.
(författare)
-
Time-domain random-walk algorithms for simulating radionuclide transport in fractured porous rock
- 2008
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 163:1, s. 129-136
-
Tidskriftsartikel (refereegranskat)abstract
- Time-domain random-walk (TDRW) algorithms are efficient methods for simulating solute transport along one-dimensional pathways. New extensions of the TDRW algorithm accommodate decay and ingrowth of radionuclides in a decay chain and time-dependent transport velocities. Tests using equilibrium sorption and matrix diffusion retention models demonstrate that the extended TDRW algorithm is accurate and computationally efficient. When combined with stochastic simulation of transport properties, the resulting algorithm, Particle on Random Streamline Segment (PORSS), also captures the effects of random spatial variations in transport velocities, including the effects of very broad velocity distributions. When used in combination with discrete fracture network simulations, the PORSS algorithm provides an accurate and practical method for simulating radionuclide transport at the geosphere scale without invoking the advection-dispersion equation.
|
|
| 10. |
- Titarenko, Y., et al.
(författare)
-
Beam dump and local shielding layout around the itep radiation test facility
- 2009
-
Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471. ; 168:2, s. 472-476
-
Tidskriftsartikel (refereegranskat)abstract
- The Radiation Test Facility (RTF) is under construction at the Institute for Theoretical and Experimental Physics to control the electronics under irradiation of particles that imitate cosmic rays (protons, carbon, aluminum, iron, tin, bismuth, and uranium). For the norms of radiation safety of personnel and users of the RTF to be observed, a local shielding and beam dump must be designed. Simulations of the dose rates around the designed shielding and beam dump are carried out in the present work.
|
|
