Nuclear Structural Engineering最新文献

This paper summarizes some of the significant research and development efforts in nondestructive testing of nuclear reactor components done by various U.S. Atomic Energy Commission agencies and contractors since 1958. The methods of nondestructive testing discussed here include fuel assay, thermal testing, penetrating radiation (X-rays, gamma-rays, beta-rays, and neutrons), ultrasonics, and eddy currents. A nondestructive testing system for evaluating fuel element cores is described.

A major problem in space flight has been leakage of fluids and gases and is particularly serious at launching. Comparatively small leaks of propellant and/or oxidizer can cause disasterous explosions. The emphasis on the initial studies reported in this article has been the development of an improved method for leak detection during factory test and checkout prior to launching and space flight. However, the long-range objective of a versatile leak detection system that could be used in space, during launching, as well as during static testing, was kept in view. A leak detection technique was developed based on the use of Kr⁸⁵ as a radiotracer. This technique is described and is believed to be more versatile than any other. Krypton has sufficient solubility to be used as a tracer in all liquids tested, except hydrogen. Leakage rates can be determined with greater precision in the order of 0.005 SCIM (Standard Cubic Inches per Minute) than by any other methods. Because of safety and ease of use, radiokrypton shows great promise for many applications.

End closure design for reactor fuel elements must account for the transition in materials, geometry, and thermal conditions. In this paper, a method of analysis and numerical results are presented which apply to the designing of closures of cylindrical fuel elements. The significance and application to end cap design of the results of a series of parametric studies for bending and shear stresses in transitions having various heights, lengths, shapes, and thickness-to-radius ratios are discussed.

Present design philosophy for the advanced concept of the high temperature gas cooled reactor recommends easily removable and replaceable heat exchanger units which are enclosed within the prestressed concrete pressure vessel. This results in relatively large penetrations in the vessel wall becoming a prime requirement, because the openings required for heat exchanger withdrawal are of necessity much larger than those for the insertion of refuelling machines or control mechanisms.

The present paper deals with the simplest case likely to occur in practice, namely an individual circular opening in an infinitely wide slab of uniform thickness subjected to unidirectional stress in the plane of the slab. The theory presented assumes that the reinforcement to the penetration (i.e., the shutter tube) is bonded to the slab material and that both materials behave in a perfectly elastic manner. A further simplifying assumption made in the development of the theory is that the reinforcement material is concentrated along the edge of the opening in the slab. This to all intents and purposes is true for most practical values of reinforcement thickness. Allowance is made for the difference in elasticity between the materials of the slab and its reinforcement at the penetration.

The equations developed will apply equally well to a similar plane stress problem where there exists the combination of any two elastic materials bonded together at a circular opening. A part of the theory developed may be applied directly to the case of hydrostatic plane stress conditions in the slab in the region adjacent to such a circular reinforced penetration.

Equations describing the behaviour of shallow anisotropic plastic shells are derived. The treatment includes the problem of load carrying capacity and optimum (minimum volume) design. The material of the shell is assumed to be rigid-plastic and to obey Hill's yield condition and the associated flow rule.

This paper is concerned with the analysis of problems in thermoviscoelasticity. The displacement equations of equilibrium governing the behavior of stressed, isotropic, thermorheologically simple materials subjected to thermal variations are formulated with respect to integral constitutive equations. This leads to a system of three, second order, variable coefficient, partial differential equations in the spatial coordinates and integral equations in the time. The general problem is formulated within the framework of classical, uncoupled thermoviscoelastic theory. A solution to the general displacement equations of equilibrium is presented for a point symmetric temperature field and point symmetric boundary conditions.

The general theory is also formulated from the principle of virtual displacements. From the principle of virtual displacements, it is shown how exact, as well as approximate, solutions may be obtained. An example is included for the solution to an incompressible hollow cylinder subjected to an axisymmetric temperature field.

The temperature distributions in bonded end closures of annular fuel elements, such as those often used in nuclear superheating power reactors, are determined analytically. The solution for the temperature distributions is represented by products of the Bessel functions with hyperbolic functions. An illustrative example is that for enriched uranium oxide and plutonium oxide (UO₂.PuO₂) fuel with zircaloy-4 cladding and end closures in an inner (or central) superheating fast-reactor core. The assumed lengths of the end closure are 0.1, 0.5, 1.0 and 1.5 times the outer radius of the fuel element. The calculated results of the example indicate that

• 1.

  1. the temperature distributions in the end closures approach constants as the lengths of the end closures increase;

• 2.

  2. there is an optimum length of end closure for each fuel element design; further increase in its length will waste the end-closure material;

• 3.

  3. the temperature distribution in the thin end closures is approximately linear.

• 4.

  4. to maintain the integrity of fuel elements, surface temperatures of cladding and end closures of the fuel elements must be kept appreciably below the known corrosion temperature limit of the coolant.

Experimental study has been carried out on the burst strength of fuel cladding tubes of stainless steel and zircaloy under simulated loss-of-coolant accidents in water-cooled power reactors. The results of high-temperature tensile tests and high-temperature burst tests conducted under static and dynamic loading conditions are analysed. The effect of absorbed hydrogen on the mechanical properties of the tubes is investigated.