[en] The nature of seismic motions and the implications are briefly described and the development of seismic design criteria for nuclear power plants in various countries is described including possible future developments. The seismicity of the United Kingdom is briefly reviewed leading to the present position on seismic design criteria for nuclear power plants within the United Kingdom. Damage from past destructive earthquakes is reviewed and the existing codes of practice and standards are described. Finally the effect of earthquakes on major hazard plant is discussed in general terms including the seismic analysis of a typical plant item. (author)

[en] An equatuion of state has been produced which covers the entire P.V.T. diagram. Thermodynamic consistency has been maintained at all times. The thermodynamic data are presented in the forms of tables and a temperature-entropy chart. A computer program has been written to produce the tables and can also be built into other computer programs. (author)

[en] The available information on seismicity within the United Kingdom has been combined with building damage data from the United States to produce a method of estimating the probability of damage to structures due to the occurrence of earthquakes. The analysis has been based on the use of site intensity as the major damage producing parameter. Data for structural, pipework and equipment items have been assumed and the overall probability of damage calculated as a function of the design level. Due account is taken of the uncertainties of the seismic data. (author)

[en] A probabilistic method for the determination of the chance of structural damage to plants due to the occurrence of earthquakes is described. A Poisson distribution for the occurrence of earthquakes has been assumed and the sensitivity of using either a truncated linear magnitude frequency law or one based on extreme values over finite time intervals has been investigated. The analysis has been carried out in terms of site intensity, this being considered to be the parameter of interest related to damage levels, and suitable attenuation relationships have been employed to construct an annual probability distribution of the exceedence of a particular site intensity in terms of the intensity at the site. The sensitivity of the results to several analytical approximations to this distribution has also been investigated. (orig.)

[en] The paper describes an exercise which has been carried out to test the sensitivity of various assumptions. Previously determined site hazard distributions representing low, average and high seismicity for the United Kingdom have been chosen for this study. Combining these with various assumed fragility distributions leads to an estimate of the risk of failure due to the occurrence of earthquakes at the particular site. (orig./HP)

[en] The implications of the effect of earthquakes on and the potential consequences of failure within hazardous industrial plant have been discussed in relation to the acceptability of the risk involved. A methodology has been described which enables the risk due to structural failure as a result of earthquakes occurring at a rate typical of the United Kingdom to be quantified and thus usefully leading to a comparison with the risk due to other initiating events. The method is still developing but provides a useful way of selecting suitable levels for design. (author)

[en] This paper presents a preliminary discussion of the potential influence of external hazards on the design of secondary containment structures for commercial fast breeder reactors. The discussion is developed with the consideration of two styles of secondary containment, termed low pressure and medium pressure, which are representative of some current design approaches. These two styles have a capability to withstand internal pressure loads arising from some of the major accident sequences in an economic and practicable manner. The two styles have a differing capability with regard to external hazards loads. The implications of the use of seismic isolators are explored, with particular regard to the possible effects of extreme loadings which are beyond the design basis. (author)

[en] The assessment of the safety of nuclear reactors has necessitated the study of the effect of missiles on reinforced concrete containment structures. Two simple theoretical calculational methods have been developed to provide basic information. The first is based on a crude energy balance approach in which that part of the kinetic energy of the missile which is transferred into the containment structure, is absorbed only as bending strain energy. To determine the energy transferred into the structure it is assumed that during the loading the target does not respond. The energy input to the structure is thus equal to the kinetic energy it will possess immediately the impulse has been removed. The boundary of the responding zone is defined by the distance travelled by the shear stress wave during the time in which the impact force increases to the load at which the shear capacity reaches the ultimate shear resistance. The second method is based on the equation of motion for an equivalent one-degree-of-freedom system assuming that only the peak value of deflection is important and that damping can be ignored. The spring stiffness of the equivalent system has been based upon the stiffness of the actual disc configuration responding in the flexural mode only. The boundaries of the disc have been defined by using the elastic plate formulae and equating those positive and negative moments which will produce a specified yield line pattern which may be inferred from plastic plate formulae. The equation of motion is solved to indicate how the quantity of reinforcement included in the structure may modify the peak deflection. By limiting the ductility ratio of the reinforcement to some prescribed level it is possible to indicate the quantity of reinforcement w

[en] The assessment of the safety of nuclear reactors has necessitated the study of the effect of missiles on reinforced concrete structures. A programme of experimental work has been initiated within the United Kingdom to resolve the problem of design for the shear stresses produced by the impact loading. The basic scale of the experiments has been chosen to be 1/25th and both hard and soft missiles have been employed. The missiles are launched by a compressed air gun towards a vertical, circular, reinforced concrete target, high speed cine photography and deflection gauges being employed to record the missile behaviour and response of the target. Hard missiles have initially been plane circular discs and soft missiles have been developed to simulate the scaled load/time characteristic of a MRCA impacting at a velocity of 215 m/s. Targets of different overall thickness and varying amounts of reinforcement have been tested. A theoretical analysis of the impact phenomena has also been carried out using computer programs based on finite difference methods (Dynamic Relaxation and PISCES 2DL). The paper outlines the experimental work performed and discusses the analytical assessment by comparison with the test results. (Auth.)