Pellet Expansion Research Articles

Hot air expansion of potato starch pellets with different water contents and salt concentrations

The expansion and puffing kinetics of commercial potato starch pellets were examined using a hot air fan oven in order to determine the puffing kinetics. The time for the onset of expansion showed uni-molecular type kinetic behaviour and was modelled by an Arrhenius plot. A pseudo-activation enthalpy for pellet expansion was also determined. The initial moisture content of the commercial pellets was controlled and the changes in the extent of puffing and the pseudo-activation enthalpy were found. The effect of type and quantity of cation in the formulation was then investigated. Expansion occurred even when no cation was added although the presence of cation did improve pellet expansion. The ratio of the native and pre-gelatinized starch in the pellets was also varied and showed to have limited effect on the extent of expansion. The puffing mechanism is discussed in light of these observations.

Pore formation in in situ processed MgB 2 superconductors

MgB 2 bulks were prepared by an in situ process which utilizes the reaction between boron and magnesium powder. The reaction time was fixed at 0.5 h and the temperature was changed from 600 °C to 1000 °C. The density decrease due to pore formation and mass (mainly magnesium) loss during the formation reaction of MgB 2 was observed in all samples. In addition to the pore formation, a pellet expansion which can be explained by the outgrowth of MgB 2 grains was also observed. Two different mechanisms were adopted to explain the pore formation; Kirkendall pores formed at a temperature below the melting point (m.p.) of magnesium by a difference in the diffusivity between magnesium and boron, and the pores formed at a temperature above the m.p. by melting of magnesium and a capillary movement. The density, T c and J c results suggest that the current carrying capacity can be improved by a careful control of the process parameters regarding a pore evolution.

Behavior of CANDU fuel under power pulse conditions at the TRIGA reactor of INR Pitesti

Abstract Pulse irradiation tests on short fuel elements have been carried out in TRIGA Annular Core Pulse Reactor (TRIGA ACPR) of INR Pitesti to investigate aspects related to the thermal and mechanical behavior of CANDU type fuel elements under short duration and large amplitude power pulse conditions. Short test fuel elements were instrumented with thermocouples for cladding surface temperature measurements and pressure sensors for element internal pressure measurement. Transient histories of reactor power, cooling water pressure, fuel element internal pressure and cladding temperature were recorded during tests. The fuel elements were subjected to total energy deposition from 70 to 280 cal g–1 UO2. Rapid fuel pellet expansion due to a power excursion caused radial and longitudinal deformation of the cladding. Cladding failure mechanism and the failure threshold have been established. This paper presents some recent results obtained from these power pulse tests performed in TRIGA ACPR of INR Pitesti.

Toward an Atomistically Informed Fuel Performance Code: Thermal Properties Using FRAPCON and Molecular Dynamics Simulation

A proof-of-principle study is presented in which the results of atomic-level simulations of the thermal expansion and thermal conductivity of UO2 are integrated into the fuel performance code FRAPCON. The beginning-of-life (BOL) thermal conductivity profile of a fuel pellet and the evolution of the pellet expansion over its lifetime are determined. It is found that (a) modifying FRAPCON to accept input from atomistic simulations (or elsewhere, such as new experiments or other calculations) is relatively straightforward, at least for these two properties, and (b) the properties determined from atomistic simulations yield predictions in FRAPCON that are in good agreement for the BOL thermal conductivity, but much less satisfactory for the pellet expansion.

Effects of dietary cellulose level on pellet quality and nutrient digestibilities in rainbow trout (Oncorhynchus mykiss)

The study was conducted to examine if cellulose affected physical characteristics of extruded feed and nutrient digestibilities in rainbow trout. Five diets with cellulose inclusion levels ranging from 0 to 150 g kg−1 were produced with a target apparent bulk density of 520 g l−1 and fed to triplicate groups of fish (average weight 0.45 kg) twice a day for 31 days. Production parameters during feed production and physical pellet quality were recorded. During the feed production specific mechanical energy (SME) was around 32 watt hour (Wh) kg−1 for all of the five extruded diets. Pellet expansion decreased linearly with cellulose inclusion, while pellet hardness and durability increased in a non-linear manner. There was a non-linear increase in water hydration capacity and a decrease in protein dispersibility index in response to increasing dietary cellulose level. No significant effects of cellulose inclusion were found on digestibility of main nutrients. The faecal excretion of sodium increased significantly with increased cellulose inclusion. In conclusion, digestion of main nutrients in rainbow trout was not affected by cellulose inclusion, but cellulose inclusion increased pellet durability and hardness.

Behavior of 60 to 78MWd/kgU PWR Fuels under Reactivity-Initiated Accident Conditions

To provide a data base for the regulatory guide of light water reactors, behavior of reactor fuels during off-normal and postulated accident conditions such as reactivity-initiated accident (RIA) is being studied in the Nuclear Safety Research Reactor (NSRR) program of the Japan Atomic Energy Agency (JAEA). The paper presents recent results obtained from the NSRR power burst experiments with high burnup fuels, and discusses effects of pellet expansion as PCMI (Pellet-Cladding Mechanical Interaction) loading and cladding embrittlement primarily due to hydrogen absorption. Results from the recent four experiments on high burnup (about 60 to 78 MWd/kgU) PWR UO2 rods with advanced cladding alloys showed that the fuel rods with improved corrosion resistance have larger safety margin against the PCMI failure than conventional Zircaloy-4 rods. The tests also suggested that the smaller inventory of inter-granular gas in the pellets with the large grain could reduce the fission gas release during the RIA transient; and high burnup structure in pellet periphery (so-called rim structure) does not have strong effect on reduction of the failure threshold because the PCMI load is produced primarily by solid thermal expansion.

Technical quality of dog food and salmon feed containing different bacterial protein sources and processed by different extrusion conditions

The effect of basic bacterial protein meal (BPM) and bacterial protein meal homogenate (HOM) on length, expansion, density, sinking rate, fat leakage, durability, and breaking force of extruded dog food and salmon feed exposed to mild and moderate processing conditions was evaluated. The treatment consisted of a control diet and four test diets where high-quality (low temperature dried; LT) fish meal was partly replaced with either 25 or 50 g BPM or HOM kg −1. The differences in processing characteristics were obtained by a combination of conditioner and extruder adjustments. Fat was added to the extruded diets by vacuum coating. In the dog diets, the inclusion of BPM and HOM resulted in shorter pellets with increased diametric expansion, and reduced dust percentage, sinking rate and breaking force, with the effect being in general greatest with the highest concentration. In general, moderate feed processing resulted in increased pellet length and expansion while sinking rate and fat leakage decreased in both the BPM and HOM diets. Neither BPM nor HOM affected fat leakage, but fat leakage decreased by moderate processing. In the salmon diets, dietary BPM and HOM increased density and breaking force, but decreased durability and had no effect on sinking rate or fat leakage of the extruded salmon pellets. A significant interaction between feed processing and bacterial protein source was found for pellet length and diameter. Moderate feed processing increased pellet length in the BPM diets but reduced pellet length and increased pellet expansion in the HOM diet. Moderate processing decreased durability and sinking rate of the pellets. Coefficients of total tract apparent digestibility (CTTAD) of the control, 50 g kg −1 BPM and 50 g kg −1 HOM dog diets exposed to mild and moderate feed processing were determined in mink. There was no significant effects of type of diet or feed processing on CTTAD of major dietary components. The results demonstrate that low amounts of BPM and HOM influenced the technical quality of extruded diets for dogs and salmon. The effect of BPM and HOM was different in dog food with higher starch content compared to the salmon feed with lower starch content, and was dependent on extrusion conditions.

Behavior of 60 to 78 MWd/kgU PWR Fuels under Reactivity-Initiated Accident Conditions

To provide a data base for the regulatory guide of light water reactors, behavior of reactor fuels during off-normal and postulated accident conditions such as reactivity-initiated accident (RIA) is being studied in the Nuclear Safety Research Reactor (NSRR) program of the Japan Atomic Energy Agency (JAEA). The paper presents recent results obtained from the NSRR power burst experiments with high burnup fuels, and discusses effects of pellet expansion as PCMI (Pellet-Cladding Mechanical Interaction) loading and cladding embrittlement primarily due to hydrogen absorption. Results from the recent four experiments on high burnup (about 60 to 78 MWd/kgU) PWR UO2 rods with advanced cladding alloys showed that the fuel rods with improved corrosion resistance have larger safety margin against the PCMI failure than conventional Zircaloy-4 rods. The tests also suggested that the smaller inventory of inter-granular gas in the pellets with the large grain could reduce the fission gas release during the RIA transient; and high burnup structure in pellet periphery (so-called rim structure) does not have strong effect on reduction of the failure threshold because the PCMI load is produced primarily by solid thermal expansion.

Effects of red yeast inclusions in diets for salmonids and extrusion temperature on pellet tensile strength: Weibull analysis

Enhancement of fish feed extrusion-technology and improvements of technical pellet quality requires knowledge about causal connections amongst variables of processing condition and raw materials, and how these connections can be elucidated by measurements. Weibull analysis of feed pellet tensile strengths may represent one possible measurement tool for this purpose; this analysis is evaluated here and compared with the Holmen durability test. Diets added pre-treated red yeast Xanthophyllomyces dendrorhous (Basidiomycetes) that differ in the degree of enzymatic cell wall digestion (45, 70 and 97% CWD) were extruded at two temperatures, 100 and 140 °C. Pellet expansion ratio (32%) was independent of both temperature and yeast CWD. Bulk density and sinking velocity corroborated accordingly, with only marginal difference in density (640 kg m −3) and no effect of the independent variables on sinking velocity (10.7 ms −1). Average Holmen durability was significant higher (P<0.01) for pellets extruded at 100 °C (97.2%) than at 140 °C (96.4%), and the difference increased disproportional for testing times of 90 and 120 s. Tensile stresses at failure were Weibull distributed with values for the modulus m in the range 4.3–6.6, and the scale parameter σ 0 in the range 360–430 kPa. Inclusions of yeast cells with digested cell walls (97% CWD) improved tensile strengths significantly, and the positive effect was evident at both extrusion temperatures. Pellets extruded at the highest temperature showed significant lower strength. Weibull analysis suggests that the effect of temperature is caused by differences in anisotropy in these feeds.

Factors That Influence the Microwave Expansion of Glassy Amylopectin Extrudates

ABSTRACTThe microwave expansion of glassy, unexpanded amylopectin pellets was studied. Amylopectin was extruded at three levels of specific mechanical energy (483, 809, and 846 kJ/kg), and 35–40% moisture content, without expansion at the die. Glassy pellets were obtained by drying and equilibrating the extrudates at five water activities (aw 0, 0.11, 0.33, 0.67, and 0.75). The pellets were characterized by measuring volume, porosity, and moisture content. The pellets were then expanded in a constant power microwave oven to determine the degree of expansion. When subjected to microwave heating, regardless of extrusion condition and initial aw, the pellets expanded from the center where the highest temperature was recorded and then expansion advanced in the whole volume. Maximum expansion was reached after 30 sec of heating, after which samples started to burn from the center. Samples simultaneously expanded and lost moisture, both processes being faster and more intense for pellets of higher initial aw. No expansion was observed for the pellets stored at aw 0, while collapse was observed for pellets stored at aw 0.73. A linear correlation between pellet expansion temperature and glass transition temperature was obtained. A hypothesis for the microwave expansion of glassy extrudates was formulated and represented on a state diagram.

LWR pellet-cladding interactions: Materials solutions to SCC

Zirconium alloys are commonly used as fuel-cladding tubes in water reactors because of their inherent resistance to a variety of environmental conditions. One of the major fuel-reliability issues of the 1970s and early 1980s was pellet cladding interaction (PCI). The mechanism of PCI is one of stress corrosion cracking (SCC) by a combination of aggressive fission products and cladding stress from pellet expansion. The severity of the problem, in particular in boiling water reactors, led to the development of barrier cladding by co-extrusion of Zircaloy-2 with an inner iodide zirconium that essentially eliminated the PCI-related failures. However, the substantially lower corrosion resistance of the zirconium layer led to clad breach and failures by other mechanisms. The difference in corrosion resistance could lead to some dramatic differences in post-failure fuel operations. This article briefly summarizes how PCI-SCC factors led to the development of PCI-resistant fuel cladding and concludes with a note on future research needs.

Effect of Amylose Content on Expansion of Extruded Rice Pellet

ABSTRACTRice pellets were prepared by single‐screw extrusion cooking with an in‐barrel water content of 50 wt%. Three different types of rice, indica glutinous, japonica, and indica, were used as raw materials. Reconstituted rice flour was made to study the effect of amylose content on pellet expansion. The glass transition (Tg) and expansion (Te) temperatures of extruded pellet were determined by differential scanning calorimetry (DSC) and noncontact infrared thermometer, respectively. The amylose content was not significantly affected by extrusion cooking. The reduction in intrinsic viscosity indicated that amylopectin experienced some degradation. The Tg and Te were not functions of amylose content, which affected the expansion ratio of the pellets. The Gordon‐Taylor equation was applied to estimate the Tg of the rice pellets.

Response of granular powders to uniaxial loading and unloading

This study examines the effects of organic binder content and binder plasticity on the stress–strain response of a poly(vinyl alcohol) (PVA)-containing spray dried alumina powder (A16SG) in uniaxial compaction and ejection. Binder content ranged from 2.45 to 7.80 wt.% and the binder glass transition temperatures ( T g) ranged from −32°C to +35°C. As binder content increases, the compaction stress required to attain a specified density increases due to the greater amount of binder, which needs to be deformed and displaced. When pressing a powder, which contains a binder with a T g much lower than the working temperature, the binder is easily deformed and high green densities can be achieved at moderate stresses. As binder T g is increased, it becomes stiffer, requiring higher compaction stresses to achieve a given density. Pellet expansion after ejection occurs mainly in the axial direction and the total dimensional change is dominated by instantaneous springback. Increasing sample size resulted in less instantaneous springback and time-dependent relaxation. This effect may be due to a limited region of expansion in the pellets.

フライアッシュ人工骨材の発泡機構 フライアッシュ人工骨材 （第２報）

To produce an artificial aggregate of stable quality, investigations of the expansion / sinter mechanism of coal fly ash are required. The purpose of this study is to clarify the influence of carbonecious substances on pellet expansion by firing, especially related to the atmospheric conditions. The study revealed two types of expansion. One relates to unburned coal fragments which exist separately from ash particles. In this case, large pores are formed around an oxidization front in the expanded pellet, accompanied by a macroscopic double - core structure in the sintered zone proceeding from outside. The other relates to very small coal fragment trapped in glassy spheres. Because the spheres in the pellet are distributed homogeneously, small pores are also inflated homogeneously with producing CO2 and CO. These gasses are generated by a reaction of the unburned coal fragments and oxygen in the glassy structure.

Transient Elongation of a Fresh Fuel Rod under Reactivity Initiated Accident Conditions

In-pile experiments of fresh fuel rods under reactivity initiated accident (RIA) conditions have been performed in the Nuclear Safety Research Reactor at the Japan Atomic Energy Research Institute in order to understand the basic pellet cladding mechanical interaction (PCMI) behavior. Rapid fuel pellet expansion due to a power excursion would cause radial and longitudinal deformation of the cladding. This PCMI could be one of the possible incipient failure modes of an embrittled cladding of a high burnup fuel under the RIA conditions. Basic PCMI behavior was studied by measuring cladding deformation of a fresh fuel rod without complicated irradiation effects. The transient elongation measurements of the fuel with two kinds of gap width indicated not only PCMI-induced cladding elongation, but also reduction of the pellet stack displacement by the cladding constraint. In the tests under a high-pressure and high-temperature condition simulating an operation condition of BWRs, additional ridge-type cladding deformation was generated due to the axial collapse of the cladding. A preliminary analysis for interpretation of the tests was made using a computer code for the transient analysis of fuel rods, FRAP-T6.

Transient Elongation of a Fresh Fuel Rod under Reactivity Initiated Accident Conditions.

In-pile experiments of fresh fuel rods under reactivity initiated accident (RIA) conditions have been performed in the Nuclear Safety Research Reactor at the Japan Atomic Energy Research Institute in order to understand the basic pellet cladding mechanical interaction (PCMI) behavior. Rapid fuel pellet expansion due to a power excursion would cause radial and longitudinal deformation of the cladding. This PCMI could be one of the possible incipient failure modes of an embrittled cladding of a high burnup fuel under the RIA conditions.Basic PCMI behavior was studied by measuring cladding deformation of a fresh fuel rod without complicated irradiation effects. The transient elongation measurements of the fuel with two kinds of gap width indicated not only PCMI-induced cladding elongation, but also reduction of the pellet stack displacement by the cladding constraint. In the tests under a high-pressure and high-temperature condition simulating an operation condition of BWRs, additional ridge-type cladding deformation was generated due to the axial collapse of the cladding. A preliminary analysis for interpretation of the tests was made using a computer code for the transient analysis of fuel rods, FRAP-T6.

Expansion of BiSrCaCuO pellets

The pellet expansion was found during the sintering of the BiSrCaCuO oxide. The lead doping in BiSrCaCuO oxide accelerates the expansion as well as the promotion of the high T c phase. The apparent density increased at the early stage of sintering of about 20 h, but abruptly decreased until 80 h and then stabilized. The release of gasifying elements such as lead and bismuth from the PbBiSrCaCuO pellet is considered to be responsible for the pellet expansion. We discussed the causes for the expansion in relation to the formation mechanism of the high T c phase and the growth characteristics of the superconducting phases.

Improvements to COMETHE III-J fuel rod modeling code

Current improvements to the COMETHE fuel performance code focus on pellet-clad axial interaction and Zircaloy cladding failure predictions. Slipping and sticking between pellets and clad as well as trapped stack are evaluated. The main conclusions are that slipping with friction concerns only local effects while axial PCMI is primarily dependent on pellet expansion with a strong ‘strain biaxiality’ effect dictated by the dishing. The notion of locking prior to radial PCMI is also introduced, which explains experimental features not previously understood. Benckmarking of the version of COMETHE against ramp tests has been initiated and will enable assessment of the code capability in Zircaloy clad failure predictions.