[en] Plane strain stress intensity factors for cracks along the inside corners of internally pressurized hexagonal subassembly ducts have been calculated by various methods and compared

[en] Explosion experiments have been performed with a pyrotechnic compound in overstrong vessels, without internals or with a perforated plate, and in yielding vessels. Thanks to these tests the charge characteristics have been determined, the pressure-flow characteristics of a perforated plate attached to the roof have been established and the validity of the SURBOUM-II code has been checked for various geometries of yielding vessels

[en] The SAS4A LMFBR accident analysis code system, which is currently under development at Argonne National Laboratory as the successor to the SAS3A code system, is discussed. Significant experience gained in the application of SAS3A to the study of hypothetical core disruptive accidents in a variety of LMFBR designs which has motivated the overall approach taken in SAS4A is cited. The structure and organization of SAS4A is presented, followed by a description of the new general code modules and phenomenological modules that are being developed for SAS4A

[en] A time-independent plasticity model is proposed. The model is incorporated into the LIFE code to predict the high strain-rate cladding deformation. A benchmark problem was solved using the modified code. The results are in good agreement with an analytical solution and a finite-element solution for the same problem. The modified code is also used to predict cladding deformation in simulated over-power transient experiments. In this case, adequate agreement can only be obtained using a strain-rate-dependent yield stress

[en] A new fuel-sodium interaction model programmed as the MURTI code is presented. Owing to a more rigorous treatment of the heat fluxes within fuel and sodium in connection with a space and time-dependent description of the coolant state, it is more generally applicable than the models used so far. Furthermore in this model the region of interaction may be subdivided which enables a very flexaible description of thermal interactions. It is demonstrated that most of the presently used models adequately describe only interactions with strong intermixing of fuel and sodium. In a case with only poor intermixing MURTI predicts early vaporization and the formation of a vaporous layer at the fuel surface while the remaining coolant acts as a heat sink only. Furthermore the MURTI code is applied to study thermal detonations as hypothesized by Board and Hall. It is found that an interaction with pressures far below the level of stable propagation can escalate by itself, if appropriate conditions are encountered

[en] The safety issues for LMFBRs fueled with the candidate advanced-fuels, particularly for commercial size reactors, are reviewed and comparisons drawn with oxide-fueled fast reactors. The extent to which the difinition and resolution of safety issues for advanced-fueled reactors draws on the current level of understanding for oxide-fueled reactors is highlighted. Areas of technology in which work is required and underway to resolve the safety issues are also highlighted

[en] The analysis of unprotected TOP accidents for an irradiated LMFBR core with the codes HOPE and KADIS was improved in two different ways: First, an existing fission gas behavior model was further developed to include a simulation of transient gas release. This model was used to check, and to improve the analysis of the gas behavior during steady state, and also in the predisassembly and disassembly phase of the accident. The effect of transient gas release before melting, which is predicted for a mild TOP, has been simulated in HOPE by adjusting the corresponding gas release parameters. In KADIS, a new equation of state, including fission gas effects, was introduced. Case studies were carried out for the EOL core of the SNR300. For accidents with different ramp rates, pin failure was assumed to occur in the axial peak node, at the onset of unrestructured fuel melting. These cases all lead to energetic core disassemblies and demonstrate the shutdown potential of the fission gas pressure under rather pessimistic conditions. In addition, the influence of transient gas release below the solidus was studied, in connection with a mechanical failure criterion. With this more realistic criterion, the accident is much milder. Gas release below the solidus did not greatly change the overall accident sequence; especially, it did not lead to more coherent failure of the channels, which would be associated with higher energy release

[en] A two-dimensional Implicit Continuous-Fluid Eulerian Code designed for the safety analysis of the primary heat transport systems of LMFBRs is described. The code includes a separate model for all the components of the system, except the primary pump. These models are coupled together hydrodynamically to form a loop that can be subjected to two simultaneous pressure pulses. The structural response of the external walls of all the pipes and components is coupled with the hydrodynamics so that the fluid transients and the structural response of the system can be analyzed. Only the elbow walls are limited to be rigid

[en] Aspects of depressurization accidents have been analyzed for the 300 MWe Gas-Cooled Fast Breeder Reactor (GCFR) demonstration plant which employs 1300 psia (9 MPa) helium as the primary coolant. The coolant loops and major reactor internal components are housed in the prestressed concrete reactor vessel (PCRV). Although extremely improbable, the current GCFR design basis depressurization accident is caused by the seal failure of a large penetration closure which results in a 75 square inch free flow leak area open to the reactor containment building. The depressurization accident was analyzed with two models: (1) the best estimate model which is defined by the use of expected system performance characteristics, and (2) the conservative model which is defined by incorporating uncertainty margins in the performance parameters for the cooling system components. The results of the analyses indicate that the maximum hot spot cladding temperature developed in the core is 1520⁰F (827⁰C) using the best estimate model with three cooling loops operating. The maximum hot spot cladding temperatures calculated with the conservative model with three or two auxiliary loops operating are 1930⁰F (1054⁰C) and 2290⁰F (1254⁰C), respectively. With pressure equalized fuel rods, the cladding temperature safety limit is expected to be near the 2500⁰F (1371⁰C) melting temperature for stainless steel. The thermal response of the GCFR core after the depressurization accident has also been examined with respect to the specific effects of containment back pressure, air ingress and the size of the depressurization leak area

[en] A general procedure is presented for obtaining the probability distributions of selected consequences of an LMFBR hypothetical core disruptive accident. The uncertainties of the consequences are considered as a variability of the system and model input parameters used in the accident analysis. Probability distributions are assigned to these input parameters and parameter values are systematically chosen from these distributions. These input are then used in deterministic consequence analyses which are performed by fast-running analogues of the comprehensive mechanistic accident analysis codes. The results of these deterministic consequence analysis are used to generate the coefficients for multivariate polynomials which approximate the consequences in terms of the selected input parameters. These approximating polynomials are then used to generate the probability distributions of the consequences with random sampling being used to obtain the accident parameters from their distributions. The use of the procedure is illustrated by an application to a postulated loss of flow transient with failure to scram in the CRBR