Evaluation of computational techniques for LMFBR safety analyses

Analysis of Primary Containment Transients (APRICOT) is an ERDA sponsored project in which a variety of reactor safety analysis groups around the world have been invited to participate by performing calculations to verify capabilities of large computer codes used to analyze postulated core disputive accidents of liquid metal fast breeder reactors. Nine groups have performed calculations of the first three problems which were set, using ten computer codes. Two problems were simple test problems for which analytical solutions exist, namely an ideal gas shock tube, and a suddenly pressurized spherical cavity in an infinite elastic medium. The third problem concerns an explosion in a partially water-filled overstrong cylindrical containment vessel for which experimental data exist. A critique of the results of these calculations is given in this paper.     

钠冷快堆失流事故分析

本文介绍了钠冷快堆失流计算的数学模型、FRLOF程序的编制和用本程序对EBR-Ⅱ两个失流工况进行的理论计算。该计算结果与试验测量值吻合较好。     

Tests in support of LMFBR

Tests in support of LMFBR projects for potential incidents involving a hypothetical core disruptive accident or sodium-water interactions in steam generators have two possible goals: (1) to evaluate the integrity of the primary containment after the design is frozen or (2) to investigate design options in support of primary containment design. The test planning approach differs depending on the goal. The Fast Flux Test Facility tests had the first goal, the current Clinch River Breeder Reactor tests have the second goal. This paper discusses test planning, sources for simulating loads, modeling, and instrumentation. The main source described involves controlled venting of explosive gases. The source avoids generation of undesirable shock waves and facilitates calibration because the reaction rate of the explosive is independent of the response. It is indicated that the test program requiring the least time and cost involves a mixture of three types of models: small simple models, small complex models, and large complex models. Instrumentation is discussed that is required for validation of loading, response measurements for comparison with calculations, and response measurements on critical members where predictions are not possible.     

钠冷快堆氢探测技术

本文介绍了钠冷快堆蒸汽发生器钠-水反应的氢探测技术。扩散型氢计和电化学氢计是目前使用的两种主要装置.     

Crack propagation in a LMFBR elbow

This paper provides results from a large scale elbow fracture mechanics fatigue test at LMFBR operating temperature and with sodium as fluid. The material, a Type 304 stainless steel, is one of the selected stainless steels used in breeder reactor design. Crack initiation, crack shape development, ligament instability and safety margins against gross plastic instability were predicted. Initial cracks were located at the crown of the elbow where the highest stresses occur under in-plane bending, which was the loading condition for the test. The nearly pure bending stress across the wall is regarded as a typical loading in LMFBR structures. Cracks under such unfavourable stress distribution extend preferably lengthwise before wall penetration, as compared with cracks under membrane stresses.The experiment, conducted at stress levels approaching the maximum design values, demonstrates low crack growth rates under plant conditions, showing that crack extension during service would be quite small. In fact, more than 28 times the expected transients would be required to advance a crack of 3 mm depth and 30 mm length to penetrate the wall in the region of highest stress.     

A comprehensive approach of reactor safety research aiming at elimination of recriticality in CDA for commercialization of LMFBR

This paper discusses requirement and necessity for elimination of recriticality issue in hypothetical core disruptive accident in future fast reactors, and also necessity of a new comprehensive approach of safety research to achieve this objective. A theoretical investigation of the initiating phase consequences in an unprotected loss-of-flow accidents is shown as an example. A generalized model for core behavior is developed in order to clarify a requirement for mechanism to introduce a negative reactivity (controlled material relocation concept) aiming at elimination of recriticality.     

The role of reliability and risk assessment in LMFBR design: Implementation of reliability in LMFBR design

This paper concerns future developments in LMFBR licensing technology.Federal Regulations (10 CFR 50.34) require that the preliminary safety analysis provide analysis and evaluation “with the objective of assessing the risk to public health and safety” to determine margins of safety and the adequacy of the plant. Hitherto the assessment of risk has been qualitative but it has become increasingly apparent that quantitative assessments would provide a better basis for judgement. Potential future roles of reliability and risk assessment are discussed in the context of providing additional confirmation of the safety of LMFBR designs. Potential acceptability criteria for risk evaluations are outlined.The reliability implications of designing components to the ASME Code Section III requirements are discussed. General judgements are provided as well as the preliminary results of probabilistic studies of selected specific limits. There is a different reliability significance for the mandatory rules for normal, upset, and emergency conditions versus the non-mandatory rules for normal, upset, and emergency conditions versus the non-mandatory guidance for faulted conditions.     

Utilization Factor of Nuclear Material in LMFBR

The effects of γ-irradiation on a simulated nuclear waste glass were studied by electron spin resonance spectroscopy (ESR), and were compared with the results on silica glass and Pyrex glass. Three kinds of glasses were γ-irradiated up to the dose of 1.22 MGy and the ESR spectra were obtained. The intensity of ESR spectra were obtained as a function of irradiation dose and annealing temperature.

The spectrum of the waste glass was characteristic of two typical peaks, Peak 1 was the strong resonance at g=4.3 showing the existence of four coordinated Fe³⁺ and Peak 2 was the weak and broad resonance at g= 2.0 showing the existence of six coordinated Fe³⁺. The ESR spectra of the waste glass before and after γ-irradiation were almost overlapped and a little difference only in the intensity was observed. While in silaca glass and Pyrex glass, the peaks from E'γ center and boron-oxygen hole center (BOHC) were observed to arise after irradiation. The absolute intensity of. Peaks 1 and 2 described above changed in complicated way depending on the dose. The result suggests oxidation or reduction of iron takes place in the waste glass depending on the dose. The isochronal annealing of irradiated glasses shows most of γ-ray- induced damages in the waste glass are restored even at room temperature, although most of the damages in silica glass and Pyrex glass are disappeared at the temperature from 550 to 600 K. The results show that the waste glass with a few weight percent of iron is resistent to radiation than other commercial glasses.     

Role and demonstration of structural integrity of LMFBR structures within the frame of the safety assessment process

The Structural Integrity DEmonstration Strategy (SIDES) has to satisfy two basic needs, namely to assure that the necessary safety precautions are fulfilled and to prove a well based safety and reliability argument for passive structures within the frame of the safety assessment process. The elements of this approach are related to five principles. The intention is to systematically compile all these elements for LMFBRs in order to assess the completeness, consistency and adequacy of the measures provided and to assure that their contribution to the plant's safety and reliability is adequate.The application of SIDES orientates itself on the three safety design levels, which could possibly result in a reclassification of events initiated by failures in passive structures such as leaks and breaks determined by the “Lines of Defense” method.     

Thermo-mechanical analysis of concrete in LMFBR programs

The R&D program described in this paper represents the structural mechanics effort underway and planned at ANL as an attempt to better understand the behavior of concrete structures in LMFBR plants where such structures are subjected to high temperature levels. This paper describes the analytical tools formulated and incorporated into the thermo-mechanical computer code called TEMP-STRESS.Emphasis in this paper is placed on describing the short-time and long-time constitutive formulation for concrete. The primary constitutive relation uses an elasto-plastic technique to simulate concrete nonlinearities, utilizes the von Mises ellipsoid as the loading surface, and assumes a four-parameter failure surface. Post-failure treatment is different when considering surface elements as opposed to internal elements. Creep of the concrete at temperatures up to about 400°C is approximated by a rate-type creep law using Maxwell chain technique. The creep model accounts for moisture and pore pressure disposition of the concrete.     

快堆用钠的除钙技术

本文叙述了商业级钠在充入钠净化回路Ｍｕｌｔｉｐｕｒｐｏｓｅ Ｓｏｄｉｕｍ Ｐｕｒｉｆｉｃａｔｉｏｎ Ｌｏｏｐ之前的除钙技术。处理后的钠中钙杂质含量由的约０．０４％－０．０５％降 ０．０００５％以下，达到堆级钠纯度标准。     

Sodium thermal-hydraulics in the pool LMFBR primary vessel

The three-dimensional flow of the primary sodium in the LMFBR main vessel, circulating by natural and forced convection, results in an uneven temperature distribution in the large mass of sodium itself (stratification, thermal fluctuations, thermal dissymmetry ... ) and on the components walls. In France, extensive interdependent theoretical, numerical and experimental studies have been performed on this subject. They aim at determining the thermal conditions during all operating conditions with a view to assessing the resulting thermal stresses and evaluating structure behaviour.The results of the commissionning tests of the Super-Phenix's plant show the validity of the method used; the thermalhydraulic knowledge leads to an improvement of the tools. They will be used as a design capability, from the viewpoint of compact and economical design for the next European Fast Breeder Reactor.     

Assessment of accident energetics in LMFBR core-disruptive accidents

An assessment of accident energetics in LMFBR core-disruptive accidents is given with emphasis on the generic issues of energetic recriticality and energetic fuel-coolant interaction events. Application of a few general behavior principles to the oxide-fueled system suggest that such events are highly unlikely following a postulated core meltdown event.     

Accommodation of potential hydrogen formation in LMFBR accidents

Results of design verification tests for the FFTF reactor cavity liner system are presented which suggest that steel liners would retain their integrity even under certain hypothetical accident conditions, thus, avoiding the formation of hydrogen. When liner failures are postulated in hypothetical reactor vessel melttrough accidents, hydrogen levels can be controlled by an air purging system. The design of a containment purging and effluent scrubbing system is discussed.     

Irradiation enhanced creep in LMFBR fuel element cladding

Rate changes observed in irradiation enhanced creep and swelling in stainless steel cladding are ascribed to the precipitation of carbide. Empirical equations modified according to precipitation kinetics are consistent with results from fuel element irradiation and in particular describe the “second peak” phenomenon.     

Elevated-temperature structural design evaluation issues in LMFBR licensing

This paper describes elevated-temperature structural design issues and concerns identified by the NRC licensing review of the Clinch River Breeder Reactor Plant for a construction permit. Major issues concern weldment evaluation, notch weakening, steam generator tubesheet evaluation, and the use of “average” rather than “minimum” material properties in inelastic analysis. Other questions concern seismic effects, elastic follow-up, creep fatigue evaluation, plastic strain concentration, and transition welds. All of the issues were resolved but several required CRBRP Project commitment to perform additional confirmatory programs.     

Advances in two-phase flow modeling for LMFBR applications

This paper summarizes the development of numerical models for analysis of sodium boiling phenomena in LMFBR which has been carried out at M.I.T. over the last five years.With regard to the degree of spatial averaging, our models use the porous body approach, in two and three-dimensional configurations. One important advantage of this model is the ability to accommodate homogenization of arbitrary-sized regions of interest.From a numerical point of view our basic approach is a semi-implicit method in which pressure pulse propagation and local effects characterized by short time constraints are treated implicitly, while convective transport and diffusion heat transfer phenomena, associated with longer time constants, are handled explicitly. This method remains tractable and efficient in multi-dimensional applications.Both a six-equation (“two-fluid”) model and a four-equation (“mixture”) model have been pursued. A considerable effort has been devoted to the development of constitutive relations. Our current package provides an adequate simulation capability for a wide range of applications.This paper will present the general physical formulation of the codes, the constitutive relations, the general numerical approach, applications, and finally some concluding remarks based on our experience with these codes.     

Design and analysis of LMFBR structures

In view of the imperatives concerning the LMFBR structure behaviour, the choice of operating conditions is quite limited. In this sense, some considerations regarding materials and manufacturing, stress analysis and design by test will be given. Much has been realized, but efforts are still necessary in order to attain the final goal.