摘要:

AbstractThe178Hf(16+) isomeric state has a 31-yr half-life and could pose serious radioactive activation problems in nuclear fusion reactors if its production in 14-MeV neutron-induced reactions is significant. The relatively high excitation energy (2.447 MeV) of this state causes it to lie in the continuum region. If rotational band members above this state were populated in a reaction, they would gamma cascade into it. While the existence of such levels can be justified theoretically, they have not been experimentally resolved; therefore, it is necessary to reconstruct the rotational levels built on the isomeric state. Using preequilibrium and compound nucleus theories, the cross sections for this and other hafnium isomeric states are calculated and compared with experimental measurements where available.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23812

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractEstimates are made of the positive reactivity introduced through the growth of the coolant void fraction in the Chernobyl reactor at both the average burnup value given by the Soviets and the maximum value.Using Monte Carlo models, various possible axial burnup distributions, displacer models, conditions in the control channels, and control rod positions are considered in calculating the insertion of positive reactivity by the manual and emergency control rods, that is, the“positive scram.”Two possible scenarios are examined for a second reactivity peak: (a) creation of a mixture of fuel, water, and cladding in a number of central fuel channels, resulting in the explosion of these channels, and (b) uniform vaporization throughout the entire reactor, resulting in reactor depressurization.From the data presented in this study, it can be concluded that vaporization of the cooling water in the fuel channel gave the highest reactivity contribution to the Chernobyl accident. The positive reactivity due to insertion of the manual and emergency control rods played only a minor role in the reactivity balance of the accident.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23813

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractPerturbation theory has been used to obtain expressions for the reactivity associated with deformation of a thin plate in a critical reactor. The methodology uses reactivity worth coefficients computed for a homogeneous system to assess the effect of changes in the shape and composition of heterogeneous components such as structural and fuel elements. The resulting expressions are applied to two heuristic sample problems consisting of a uniform plate displacement and a sinusoidal plate bowing deformation. In the former case, the perturbation results agree well with exact analytical calculations. The second case provides useful analytical approximations that illustrate how the deformation reactivity is expected to vary with the fractional plate elongation, the location of the plate in the core, and other parameters.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23814

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractDuring hypothetical severe nuclear reactor accidents, structural materials in the reactor vessel can relocate downward and form debris regions above the lower head. A one-dimensional model is presented that considers melt progression in the debris as well as the thermal and mechanical response of the head. Only creep rupture of the lower head is considered; however, other modes of vessel failure can be considered with the methodology developed, and the model can easily be extended to higher dimensions. Numerical solutions are compared with an analytical model developed by T. G. Theofanous. The goal of the work is to identify the parameters that most affect the state of the debris at the time of lower head creep rupture. Results of sensitivity analyses presented indicate that melt relocation phenomena, the initial composition profile of the debris, and the pressure inside the vessel are all important. On the other hand, changing the porosity or the particle diameter produces less significant effects because several competing phenomena cancel each other.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23815

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractThe problem of reactor vessel-wall cooldown due to high-pressure safety injection in a stagnated primary system is considered. The approach is based on the Regional Mixing Model, which has been previously documented and applied to various tests. This work is devoted to reactor predictions and experimental simulations made for use in the U.S. Nuclear Regulatory Commission’s Integrated Pressurized Thermal Shock study. A brief summary of the model and some refinements to it are also presented.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23816

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractStratification in the cold leg due to high-pressure injection in a stagnated loop of a pressurized water reactor is considered. The working hypothesis is that at high injection Froude numbers, the extent of mixing approaches a limit controlled only by the flooding condition at the cold-leg exit. Experimental data available support this hypothesis. Predictions for reactor conditions indicate a stratification of∼40°C. As a consequence, the downcomer plume would be rather weak (with a low Froude number) and would be expected to decay quickly.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23817

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor

摘要:

AbstractA computer routine was written to enable an efficient, yet accurate, interpolation of the basic probabilities required in integral transport calculations of single lattice, as well as multicell, structures. These are The tables within which the routine interpolates contain remainders between accurate probabilities to respective analytical approximations. There are∼4000 entries for a cylindrical or spherical geometry and 50 for slab geometry. The accuracy is generally within a few tenths of a percent relative error for all the probabilities and can be much lower. The range of optical thicknesses covered is 0 to 20. All the probabilities required for a given layer can be generated on a CRA Y-XMP in a 5×10-6s. A single Dancoff probability can be generated in∼2.7×10-6s.

ISSN:0029-5639    

DOI:10.13182/NSE91-A23818

出版商:Taylor&Francis    

年代:1991

数据来源: Taylor