P. Chellapandi

LESSONS LEARNED FROM SODIUM-COOLED FAST REACTOR OPERATION AND THEIR RAMIFICATIONS FOR FUTURE REACTORS WITH RESPECT TO ENHANCED SAFETY AND RELIABILITY

Abstract Eighteen sodium-cooled fast reactors (SFRs), a number that includes reactors in operation or shut down, have provided 388 reactor-years of operating experience to date. This paper summarizes the important incidents related to fast reactor sodium components and systems. The solutions incorporated, based on experience, analysis, experimental tests, and research and development for past and current SFRs, are described. The paper also describes lessons learned for future SFRs.

Influence of mis-match of weld and base material creep properties on elevated temperature design of pressure vessels and piping

The stress and strain concentrations developed at the weldments during the long time operation of pressure vessels and piping at high temperature due to the mis-match in the creep properties of weldment constituents (weld, heat affected zone and base metal) are estimated using detailed finite element analysis. Three materials, viz. 2.25Cr 1Mo, SS 316 LN and modified 9Cr 1 Mo which are the most commonly used materials in the nuclear and thermal power plants are considered. A longitudinal seam weld with single and double V (X) configurations are analysed. Parametric studies have been done on weld angle and stresses. Based on the analysis, critical locations and the maximum stress concentration factors in the weldments for the above materials are identified. The weld design procedures of the currently used pressure vessel and piping codes are commented. The importance of ductility based failure criteria is emphasised.

Design, Development, Testing and Qualification of Diverse Safety Rod and Its Drive Mechanism for a Prototype Fast Breeder Reactor

Prototype fast breeder reactor is U-PuO 2 fueled sodium cooled pool type fast reactor and it is currently under construction at Kalpakkam, India. Prototype fast breeder reactor is equipped with two independent fast acting and diverse shutdown systems. A shutdown system comprises of sensors, logic circuits, drive mechanisms, and neutron absorbing rods. The two shutdown systems of prototype fast breeder reactor are capable of bringing down the reactor to cold shutdown state independent of the other. The absorber rods of the second shutdown system of prototype fast breeder reactor are called as diverse safety rods (DSRs) and their drive mechanisms are called as diverse safety rod drive mechanisms (DSRDMs). DSRs are normally parked above active core by DSRDMs. On receiving scram signal, the electromagnet of DSRDM is de-energized and it facilitates fast shutdown of the reactor by dropping the DSR into the active core. For the development of prototypes of DSR and DSRDM, three phases of testing, namely, individual component testing, integrated functional testing in room temperature, and endurance testing at high temperature sodium, were done. The electromagnet of DSRDM has been separately tested at room temperature, in furnace, and in sodium. Specimens simulating the contact conditions between electromagnet and armature of DSR have been tested to rule out self-welding possibility. The prototype of DSR has been tested in flowing water to determine the pressure drop and drop time. The functional testing of the integrated prototype DSRDM and DSR in aligned and misaligned conditions in air/water has been completed. The performance testing of the integrated system in sodium has been done in three campaigns. During the third campaign of sodium testing, the performance of the system has been verified with 30 mm misalignment at various temperatures. The third campaign has qualified the system for 10 years of operation in reactor. This paper presents design, development, testing, and qualification of the prototype DSR and DSRDM. Salient design specifications for both DSRDM and DSR are listed initially. The conceptual and detailed design features are explained with the help of figures. Details on material of construction are given at appropriate places. Test plans and criteria for endurance testing in sodium for qualification of DSRDM and DSR for operation in reactor are briefed. Brief explanation of test setups and typical test results are also given.

Progressive deformation behaviour of thin cylindrical shell under cyclic temperature variation using Combined Hardening Chaboche Model

This study intends to evaluate thermal ratchetting deformation due to cyclic thermal loading along the axis of a smooth cylindrical shell. Two cases of progressive deformation behaviour are discussed for different loading methods. The aim of the first case is to recognize the shakedown behaviour of the cylinder under applied loading cycles. Alternatively, second case is highlighting the ratchetting behaviour of the cylinder. Based on the loading method in second case, a smooth thin hollow cylinder is considered to simulate the progressive deformation. This condition simulates the 1/25th scale down model of the Prototype Fast Breeder Reactor (PFBR) main vessel.

Effect of manufacturing errors on load distribution in large diameter slewing bearings of fast breeder reactor rotatable plugs

Fuel and other subassemblies in fast breeder reactor are handled through a combination of small rotatable plug, large rotatable plug and transfer arm. Rotation of the plugs is facilitated through large slewing bearings. These bearings are subjected to heavy loads and moments. Manufacturing errors on the rolling elements and races influence the load sharing among the elements. As a result, higher load acting on a rolling element causes excessive local deformation and unacceptable indentation. The higher load can also cause excessive sub-surface shear stress and fatigue failure of rolling races. Too stringent tolerances demand sophisticated machines, whereas liberal tolerances mean compromise on the performance and life of the bearing. There are no established methods for design of slewing bearings that include the influence of manufacturing errors. Hence, an attempt has been made to find the influence of manufacturing errors on load distribution among the rolling elements using finite element method. It is observed that size error on the ball and waviness error (waviness spacing and height) on the raceway are the two influencing factors on load distribution. To study the influence of waviness error on the raceway, three sectors of bearing simulating waviness spacing of 10.8°, 18° and 36° with different waviness (peak-to-valley) height of 30 µm, 50 µm and 75 µm are analysed. It is observed that waviness height has larger influence on the load distribution among bearing balls when compared to waviness spacing.

Sodium Fast Reactors with Closed Fuel Cycle

Sodium Fast Reactors with Closed Fuel Cycle delivers a detailed discussion of an important technology that is being harnessed for commercial energy production in many parts of the world. Presenting the state of the art of sodium-cooled fast reactors with closed fuel cycles, this book: Offers in-depth coverage of reactor physics, materials, design, safety analysis, validations, engineering, construction, and commissioning aspects Features a special chapter on allied sciences to highlight advanced reactor core materials, specialized manufacturing technologies, chemical sensors, in-service inspection, and simulators Addresses design essentials with a focus on reactor assembly including core and coolant circuits, fuel handling, instrumentation and control, energy conversion, and containment systems Provides design codes and standards with sufficient background information to ensure a solid understanding of the underlying mechanics Supplies guidelines for concept selection, design, analysis, and validation Sodium Fast Reactors with Closed Fuel Cycle is a valuable reference for industry professionals involved in the construction of fast-reactor power plants, as well as graduate-level engineering students of the design and development of sodium-cooled fast-reactor systems and components.

Nonlinear Finite Element Analysis of Sloshing

The disturbance on the free surface of the liquid when the liquid-filled tanks are excited is called sloshing. This paper examines the nonlinear sloshing response of the liquid free surface in partially filled two-dimensional rectangular tanks using finite element method. The liquid is assumed to be inviscid, irrotational, and incompressible; fully nonlinear potential wave theory is considered and mixed Eulerian-Lagrangian scheme is adopted. The velocities are obtained from potential using least square method for accurate evaluation. The fourth-order Runge-Kutta method is employed to advance the solution in time. A regridding technique based on cubic spline is employed to avoid numerical instabilities. Regular harmonic excitations and random excitations are used as the external disturbance to the container. The results obtained are compared with published results to validate the numerical method developed.

Structural integrity assessment of reactor assembly components of a pool-type sodium fast reactor in a core disruptive accident - II: Analysis for a 500-MW(electric) prototype fast breeder reactor

Abstract A core disruptive accident, considered a beyond-design-basis accident, for the 500-MW(electric) capacity Prototype Fast Breeder Reactor (PFBR) is analyzed using the FUSTIN in-house computer code. In order to have a good understanding of the complicated loading mechanisms and sequences, the analysis studies the effects of introducing internals in the main vessel. Further, the structural integrity of heat exchangers—which are important for decay heat removal during postaccident conditions - was demonstrated with tests that were conducted on a 1/13th scaled-down mock-up; a suitable low-density explosive was developed and characterized to simulate nuclear energy release characteristics. The tests have indicated relatively smaller displacements and strains in the vessel, compared to numerical predictions, and the structural integrity of the decay heat exchangers including tubes was demonstrated. Thus, the reactor assembly components meet the safety criteria specified for PFBR with comfortable margins for the specified mechanical energy release of 100 MJ.

Aerosol characterization and measurement techniques towards SFR safety studies

An Aerosol Test Facility (ATF) has been designed, fabricated and commissioned at Radiological Safety Division, Safety Group, Indira Gandhi Centre for Atomic Research, INDIA, to carry out safety studies related to aerosols in Sodium cooled Fast Reactor (SFR). The sources of aerosol generation during normal operation of SFR and accidental scenario have been discussed. Aerosol sampling issues to get the representative samples and how they are implemented in ATF are presented. Aerosol measurement techniques and the instruments deployed for the measurement of various aerosol properties have been described briefly. The sodium and fission product aerosols are generated and the sample data analysis is presented. The analysis of data for aerosol characterization include: (i) Initial size distribution of sodium and fission product aerosols, (ii) Chemical speciation of sodium aerosols (iii) Co agglomeration and co deposition of sodium and fission product aerosols and (iv) Enhanced Brownian coagulation of sodium aerosols in the presence of gamma radiation field. Besides, the on going aerosols studies are also presented.

A nonlinear analysis of the effect of heat transfer on capillary jet instability

Breakup of slender liquid jets under isothermal conditions has been studied extensively. In this work, we investigate the breakup of a viscous jet emanating from an orifice in the presence of convective heat transfer. We study the case where heat is transferred from the jet to the ambient fluid. The temperature varies axially and both viscosity and surface tension are taken to be temperature dependent. Marangoni stresses caused by a thermally induced surface tension gradient are included here. A numerical model based on a one-dimensional slender jet approximation of the equations of motion and heat transfer is used. This results in three coupled nonlinear partial differential equations, which are solved using the method of lines. The advantages of using this approximation lie in (i) its computational elegance and (ii) the physical insight that it provides. We compare the model predictions of both spatial and temporal stability analysis with experiments of a jet of molten Woods metal in water. Molten Woods...