Hans K. Fauske

External cooling of a reactor vessel under severe accident conditions

Abstract The TMI-2 accident demonstrated that a significant quantity of molten core debris could drain into the lower plenum during a severe accident. For such conditions, the Individual Plant Examinations (IPEs) and severe accident management evaluations, consider the possibility that water could not be injected to the RCS. However, depending on the plant specific configuration and the accident sequence, water may be accumulated within the containment sufficient to submerge the lower head and part of the reactor vessel cylinder. This could provide external cooling of the RPV to prevent failure of the lower head and discharge of core debris into the containment. This paper evaluates the heat removal capabilities for external cooling of an insulated RPV in terms of (a) the water inflow through the insulation, (b) the two-phase heat removal in the gap between the insulation and the vessel and (c) the flow of steam through the insulation. These results show no significant limitation to heat removal from the bottom of the reactor vessel other than thermal conduction through the reactor vessel wall. Hence, external cooling is a possible means of preventing core debris from failing the reactor, which if successful, would eliminate the considerations of ex-vessel steam explosions, debris coolability, etc. and their uncertainties. Therefore, external cooling should be a major consideration in accident management evaluations and decision-making for current plants, as well as a possible design consideration for future plants.

Source term considerations in connection with chemical accidents and vapour cloud modelling

Abstract Source term considerations involving flashing two-phase high momentum releases are presented in terms of simple models. These include methods for assessing discharge rates for subcooled, saturated and two-phase stagnation conditions, expanded jet behaviour including aspects of entrainment, vapourization and cooling as well as the extent of the two-phase jet regime. The models are compared with applicable experimental data including the large scale ammonia and hydrofluoric acid jet releases performed on the Frenchman Flat area of the Department of Energys Nevada Test Site.

Estimation of peak pressure for sonic-vented hydrocarbon explosions in spherical vessels

Two closed-form approximate solutions are presented for the final pressure produced by a hydrocarbon explosion in a spherical vessel with sonic venting. A constant factor which multiplies the ideal spherical flame velocity is used to describe the effect of flame acceleration. One of the solutions is a simple, easy-to-use equation which may appeal to vent designers; it agrees well with reported results from a comprehensive computer model and correlates available experimental data as well as previous models involving several variable turbulence factors.

Assessment of the FBR Core Disruptive Accident(CDA) : The Role and Application of General Behavior Principles(GBPs)

General behavior principles (GBPs) first introduced in 1976 (H. K. Fauske, the Role of Core-Disruptive Accidents in Design and Licensing of LMFBRs, Nuclear Safety, Vol. 17, No. 5, 550–567, 1976) are applied to assess the core disruptive accident (CDA) outcome for a large (3,500MWt) high power density oxide-fueled sodium-cooled fast breeder reactor (FBR). Non-energetic termination in the so-called Initiating Phase is emphasized and is made possible by considering departures from the traditional core design including the Subassembly Inner Duct and Limited Blanket Removal concepts. This early accident scenario termination eliminates potential concerns raised related to recriticality events and also facilitates the potential for in-vessel fuel debris coolability for the large FBR with a compact reactor vessel.

Liquid entrainment by an expanding core disruptive accident bubble—a Kelvin/Helmholtz phenomenon

Abstract The final stage of a postulated energetic core disruptive accident (CDA) in a liquid metal fast breeder reactor is believed to involve the expansion of a high-pressure core-material bubble against the overlying pool of sodium. Some of the sodium will be entrained by the CDA bubble which may influence the mechanical energy available for damage to the reactor vessel. The following considerations of liquid surface instability indicate that the Kelvin–Helmholtz (K–H) mechanism is primarily responsible for liquid entrainment by the expanding CDA bubble. First, an instability analysis is presented which shows that the K–H mechanism is faster than the Taylor acceleration mechanism of entrainment at the high fluid velocities expected within the interior of the expanding CDA bubble. Secondly, a new model of liquid entrainment by the CDA bubble is introduced which is based on spherical-core-vortex motion and entrainment via the K–H instability along the bubble surface. The model is in agreement with new experimental results presented here on the reduction of nitrogen-gas-simulant CDA bubble work potential. Finally, a one-dimensional air-over-water parallel flow experiment was undertaken which demonstrates that the K–H instability results in sufficiently rapid and fine liquid atomization to account for observed CDA gas-bubble work reductions. An important byproduct of the theoretical and experimental work is that the liquid entrainment rate is well described by the Ricou–Spalding entrainment law.

Kinetic and heat transfer-controlled solidification of highly supercooled droplets

Abstract An efficient integral profile computational method is used to solve the problem of the solidification of highly subcooled droplets. The effects of surface cooling by radiation and convection, interface crystallization kinetics and fully time-dependent heat conduction are included in the method. Particular attention is focused on the predicted drop surface temperature-time histories as these, together with available experimental luminosity-time traces for solidifying microspheres of Al2O3 and ZrO2, are used to infer the coefficient of the kinetic law for Al2O3 crystallization—one of the crucial parameters in a recently proposed theory of underwater aluminum ignition.

A model of the dilution of a forced two-phase chemical plume in a horizontal wind

Abstract Accidendtal releases of volatile liquid chemicals from pressurized storage vessels result in the formation of high-momentum flashed jets with liquid phases comprised of extremely fine droplets (aerosol). These jets are typically heavier than air. The subject of this paper is the description of a turbulent entrainment model that predicts the trajectory and dilution of such releases when the release point is elevated above ground-level in a horizontal wind. The model is compared with available field test data for pressurized liquid releases and is found to describe the observations to a degree of accuracy adequate for most hazard assessment purposes. The comparisons include the field measurements made during the liquid ammonia (NH 3 ) and liquid hydrofluoric acid (HF) release test series, namely Desert Tortoise and Goldfish respectively, at the US Department of Energy Fuels Test Facility. The model indicates that over the 3000 m distance in which measurements were made, there is no need to invoke atmospheric turbulence to explain the dilution of the ammonia jet. However, atmospheric turbulence is predicted to dominate the mixing in the far field of the weaker HF jet.

Managing chemical reactivity—Minimum best practice

A minimum best practice (MBP) is proposed to provide enough information to process, store, and transport chemicals safely. The primary objective of the MBP is to reduce the frequency and consequences of runaway reaction‐generated accidents, particularly those occurring within companies with limited technical and financial resources.

Analytical Model for Peak Temperature within a Sodium-Water Reaction Jet

A model for predicting the peak temperature within an oxidizer-steam jet submerged in molten sodium is described. Previous experimental and theoretical work by the present authors has shown that a single, representative droplet size may be used to model droplet-to-gas heat and mass exchange within a submerged jet and that the appropriate droplet size is suggested by assuming that the submerged jet behaves like a plane jet airblast atomizer. These findings are exploited here to develop a rational, integral two-fluid model of the centerline temperature within the submerged steam jet carrying entrained sodium drops and products of combustion. Reasonable agreement with available measurements of the peak centerline temperature within steam-in-sodium jets is obtained.

Establishment of Analytical Model for Peak Temperature Within a Sodium-Water Reaction Jet, (II) Mean Droplet Size in a Submerged Gas Jet

This is a second paper that describes work carried out to aid in the development of an analytical model to predict the peak temperature in a sodium-water reaction jet. Specifically, an experimental investigation was performed to determine the effective droplet size (Sauter mean diameter: SMD) in the near field of a submerged jet. A sufficient number of experiments involving jet-airblast atomization of a shallow liquid water layer were carried out to evaluate the effects of injector diameter, injection pressure, orifice submergence and sampling location on the SMD. Despite the scatter in the data believed to be the result of jet unsteadiness, a reasonable correlation for the SMD was achieved by assuming that the submerged jet behaves much like a plain-jet airblast atomizer.