ISSN:0550-3043    

DOI:10.13182/NT70-A28782

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe thermal effects of different types of void volumes within a fuel pin, such as porosity, central void, and the gas gap between fuel and clad are examined. A new general relation for the dependence of thermal conductivity on the closed porosity is deduced. For given gas contents and specific ranges of pore temperatures and sizes, a simple approximate equation is set up, which is in good agreement with experimentally obtained results. A central void is very effective in reducing the maximum temperature; and its use implies a considerable increase in linear pin power. In-pile migration of the porosity in the hotter regions of oxide fuel pins forms or increases the central void and densifies the hotter region. This effect is calculated in a two-zone porosity model. For a uniform gap between fuel and clad, the temperature drop is calculated as a function of gap width, linear pin power, inner temperature of clad, inside radius of clad, emissivities of surfaces, and types of gas within the gap, such as noble gases and mixtures of He with gaseous fission products.

ISSN:0550-3043    

DOI:10.13182/NT70-A28783

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe SWELL fuel element lifetime code employs the“cumulative damage”approach to estimate when the cladding of an LMFBR mixed-oxide fuel element is likely to fail under normal and off-normal conditions. In the estimating process, properties and behavior of irradiated, as well as of unirradiated, cladding are considered. A unique feature of SWELL is its use of an empirical function, developed by calibration with experimental data, which relates the pressure-exerted-on-cladding-by-fuel-swelling to the pressure-of-fission-gas-retained-in-fuel.SWELL predicts that the lifetimes of some typical fuel elements will have to be reduced significantly if the elements are to be expected to withstand rather modest off-normal conditions near end of life. However, there are reasons why the predictions may be overly pessimistic.Early results from the newer and more-detailed LIFE fuel element behavior code indicate that the accuracy with which a fuel element's operating history is followed may be important for gaining understanding of the element's behavior. To conserve computer time, the best way to simulate actual history, as jar as claddingΔD/D predictions are concerned, appears to be to use time-averaged power (excluding downtime) for a length of time sufficient to produce the actual burnup, which happens to be the SWELL practice.

ISSN:0550-3043    

DOI:10.13182/NT70-A28784

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractA computer program has been developed and used to validate and adjust models for predicting fuel-pin deformations. An existing computer program, DEFORM, was combined with a clad swelling model to be a subroutine for calculating fuel-pin deformations. Predictions of deformations made with this subroutine are compared with measured deformations in a parameter fitting program, SIMPLEX. A comparison of analyses made with this program, using input data collected from experiments on four irradiated fuel pins, indicated that the program version assuming only a clad swelling model predicted the mean deformations of these pins better than the program version assuming both clad swelling and a mechanical interaction between the fuel material and the clad material.

ISSN:0550-3043    

DOI:10.13182/NT70-A28785

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractPreliminary models for fuel and cladding performance are described and their predicted behavior compared with experimental data. These models are then applied in a performance analysis of a typical stainless-steel-clad mixed-oxide fuel pin. The results of the analysis indicate that any problems associated with fuel swelling or fuel-cladding interaction for this pin are swamped out by the cladding-swelling effect. The cladding-swelling relationship used requires extrapolation far beyond the fluence range where experimental data are available, thus emphasizing the difficulty encountered in attempting such analyses on LMFBR fuel pins to burnup levels considered economically necessary, but for which materials data are not available.

ISSN:0550-3043    

DOI:10.13182/NT70-A28786

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe status of fast reactor mixed-oxide fuel performance model development, involving the OLYMPUS and CYGRO-F codes, is reviewed. Input information in several critical areas is examined including: the swelling, irradiation creep, and ductility of stainless-steel cladding; and the swelling and plasticity of mixed-oxide fuel. The predictions from the two codes are illustrated by parametric studies and application to high fluence/burnup ratio fuel rods of interest to the LMFBR program. The analytical studies indicate the major effects of stainless-steel swelling on fuel rod performance and the relationship between fuel density and cladding creep strain.

ISSN:0550-3043    

DOI:10.13182/NT70-A28787

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe steady-state theory of fuel pin swelling in which the majority of fuel pin diametral increase is ascribed to the effects of solid and gaseous fission product swelling of the fuel is in apparent conflict with a body of data relating to oxide fuel pins. The non steady-state or ratchetting theory holds that fuel-cladding mechanical interaction occurs by thermal expansion interaction of the fuel and cladding during reactor temperature or power changes. The primary rate determining mechanism is considered to be something other than the steady-fuel swelling rate. Examples of non-steady-state mechanisms, which experimental evidence suggests may be important, include fuel clad interference occurring during the first startup of the fuel pin, the buildup of porosity in the fuel due to a cracking and healing process, mass transport of fuel from the inside to the outside of the fuel column, and fuel clad interference occurring during reactor shutdown and subsequent removal of the pin from the reactor.

ISSN:0550-3043    

DOI:10.13182/NT70-A28788

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractA model has been developed to describe the kinetics of void growth in metals during irradiation which explicitly includes the presence of both migrating interstitials and vacancies. It is clear that void growth can occur only when an excess flux of vacancies arrives at the void surface and this can be achieved by taking into account the preferred drift of the interstitials to the dislocation sinks as a result of the long-range size effect interaction. Results of numerical calculations of the vacancy and interstitial average concentration in stainless steel and molybdenum irradiated under typical fast reactor conditions are presented, and these are used to calculate void growth rates as a function of temperature. It is shown that the void growth rate goes through a maximum when plotted against temperature and this is consistent with the experimental swelling data. During the early stages of irradiation, when the number of point defects arriving at voids is negligible compared with those being lost at other sinks, the swelling rate is proportional to (t)3(t = time). Cold work has a beneficial effect in the early stages of irradiation by reducing the void growth rates, but it could have a deleterious effect over a long term by prolonging the period over which the swelling follows the rapid (t)3law.

ISSN:0550-3043    

DOI:10.13182/NT70-A28789

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractA method was developed for determining the optimum fuel utilization for the Plum Brook Reactor (PBR). The method used available PBR criticality data to incorporate the effects of neutron leakage and nonuniformity of burnup in a point model of the core. This allowed the model to predict the performance of the core as a function of new element weight and number of uses per element. A graphical model was devised to determine the optimum. The article shows the derivation of the model and its application for a typical PBR configuration.

ISSN:0550-3043    

DOI:10.13182/NT70-A28790

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor

摘要:

AbstractThe amount of fission products remaining in the molten mass of material that could result from core melt-through must be known to evaluate the heat loads on various parts of the structure, and depends on many factors too numerous to mention here. The present work was confined to an approximate evaluation of diffusion and internal convection as mass transfer mechanisms under fairly quiescent conditions. This condition was chosen because it would result in larger amounts of heat-generating fission products remaining in the melt than would be the case with more violent agitation.Internal heat generation in a molten slab of fluid cooled primarily from the upper surface would create a temperature gradient which, at some critical value, would cause internal convection currents due to the greater buoyancy of the hotter material in the lower portions of the melt. These convection currents enhance both the heat and mass transfer from the interior of the molten material to the surface.The heat transfer and rate of release of fission products (using yttrium oxide as an example) from a slab of molten fuel and steel were calculated and the results compared with a diffusion calculation.A sensitivity analysis was performed and the effects of wide variations in the thickness of the melt, viscosity, coefficient of thermal expansion, diffusion coefficient, specific heat, and thermal conductivity are reported. For the base case of yttrium oxide in 200 tons of molten UO2and steel in a slab 17.1 cm thick, the time required to release 80% of the fission product was 9 h, compared with 40 days for the case where a diffusion model was assumed.Although these results are very approximate, being based on estimated thermophysical properties and idealized assumptions, they show that the effect of internal convection on mass transfer is so important that it cannot be ignored in any process where its occurrence may be suspected.

ISSN:0550-3043    

DOI:10.13182/NT70-A28791

出版商:Taylor&Francis    

年代:1970

数据来源: Taylor