Coolant Temperature Rise Research Articles

Hydrodynamics of degraded core cooling

The literature on hydrodynamics of forced convection cooling of particle beds is reviewed and used to assess the characteristics of in-situ cooling of a degraded LWR reactor core under conditions representative of severe accidents. It is found that the pressure head required, for a given rate of liquid water flow, through a totally degraded core is one to two orders of magnitude higher than the case of intact core geometry. To remove decay heat of up to 1–2% of the reactor normal power, even with conservative assumptions, the pressure head is within the capability of the main reactor pumps. However, particles with very small diameter (less than 100 μm) will potentially be swept out by the flow. The sensitivity of the hydraulic characteristics to the allowed coolant temperature rise across the fragmented core is also investigated.

Power: Britain's fast breeder: The Dounreay test reactor experience has instilled confidence in its designers to press for commercialization

Discusses the Dounreay test reactor experience which has instilled confidence in its designers to press for commercialization. The test experience is based on the Dounreay test reactor (60 MW) and a prototype fast breeder (600 MW). The safety features designed into the prototype fast-breeder reactor include: Natural circulation to deal with fission product decay heat. It appears to be more than adequate to dissipate such heat. Natural feedback phenomena which would shut down the reactor from full power in the event of a mean coolant temperature rise over 620°C. No significant energetic fuel coolant interaction in the event of fuel meltdown has been found in a wide range by experiments. Acoustic waveguide devices to give indication of boiling in a few milliseconds and a triangulation technique to locate the point of boiling.

Condensation of a vapour with variable coolant temperature

Nusselt type condensation models are employed to evaluate the laminar film condensation of a pure vapour on a vertical or a horizontal tube with significant coolant temperature variation along the condensing surface. It is found that the solutions approach the Nusselt result if both the coolant-to-wall heat transfer resistance is negligible and the coolant flow rate so high that the coolant temperature rise is negligible. Similarly if the condensate film heat transfer resistance is negligible, we recover the usual heat exchanger solutions. New special cases are obtained when the coolant-to-wall heat transfer resistance is negligible but the coolant temperature rise is significant. General solutions in implicit form are also obtained.

Condensation of a vapour with variable coolant temperature

Nusselt type condensation models are employed to evaluate the laminar film condensation of a pure vapour on a vertical or a horizontal tube with significant coolant temperature variation along the condensing surface. It is found that the solutions approach the Nusselt result if both the coolant-to-wall heat transfer resistance is negligible and the coolant flow rate so high that the coolant temperature rise is negligible. Similarly if the condensate film heat transfer resistance is negligible, we recover the usual heat exchanger solutions. New special cases are obtained when the coolant-to-wall heat transfer resistance is negligible but the coolant temperature rise is significant. General solutions in implicit form are also obtained.

Effect of Gas Entrainment on Thermal-Hydraulic Performance of Sodium Cooled Reactor Core

With the view to determining whether or not gas entrained in the sodium coolant could cause overheating of a fast reactor core, the following items were studied: 1. The effect of gas entrainment on the coolant flow rate and on coolant temperature rise. 2. The effect of gas entrainment on the coolant heat transfer coefficient and film temperature drop. Equations were derived to serve in estimating the thermal-hydraulic effect of the gas entrainment, and calculations performed therewith to obtain information on conditions corresponding to the Core A under operation in the Fermi Reactor. The results of the present examination reveal that in the Fermi Reactor an amount of gas almost inconceivable as a practical possibility must be entrained before the coolant or the fuel surface would be heated to the boiling point of sodium.

Simplified Analysis of Coolant Flow and Outlet Temperature in Gas-Cooled Nuclear Reactor Cores

If the coolant mass flow were constant across the core, the coolant temperature rise would be proportional to the channel power. But, without orificing, the coolant mass flow in the hot channel is ...

Thermal performance of ceramic-clad gas-cooled reactor cores

Simple relationships between dimensionless core parameters have been derived for the case where the maximum internal fuel temperature is fixed. The linear rating is found to be nearly proportional to the difference between maximum fuel and coolant temperatures ( T m− t e) and to the effective fuel conductivity. The ratio of core pressure drop to average coolant pressure varies approximately like T m−t e t e−t i 2 L d 5.5 where ( t e− t i) is the coolant temperature rise and ( L/ d) is the coolant channel length to diameter ratio. Numerical results for a typical High Temperature Gas Cooled Reactor design show the lack of sensitivity of thermal power to channel dimensions and the rapid variations of pumping power with channel geometry.

Thermal aspects of changes in the environment of underground cables

The thermal field established by a trench containing three closely spaced single-core cables in horizontal formation, bedding sand, concrete slabs and backfill has been determined by the use of an electrolytic tank, and the effects of variation in the backfill thermal resistivity obtained for bedding-sand and soil resistivities of 150 and 120cmdegC/W, respectively. The effective thermal resistances from the cable outer surface to the ambient surroundings are compared with those obtained by the analytical method of Schmill, which applies to only two different resistivities, backfill and soil. The effect of changes in the bedding-sand resistivity are summarised in a simple equivalent thermal circuit. Using this, the cable-surface-temperature-rise/cable-loss curves are obtained for sand-resistivity/temperature relationships which are assumed to represent the moisture-migration process; this applies for moisture migration in the bedding sand alone. It is seen that the temperature dependence of the resistivity of the material immediately around the cables is decisive when determining thermal runaway. The cable-surface temperatures are determined with artificial cooling using external water pipes, and include the effects of coolant-temperature rise and bedding sand. It is shown that the thermal time constants obtained for a particular environment and cooling scheme may be approximately adjusted to represent others, provided that the burial depth is the same. The changes in conductor temperature with an interruption in coolant supply are shown.

Steady-state thermal analysis of a 400 kV-cable through joint

Temperature distributions in a 400kV through joint and associated cable, as used in directly buried transmission circuits, are obtained for natural cooling and various forms of artificial cooling. The joint, rather than the cable, is seen to limit the current rating for all forms of cooling. With the higher ratings resulting from artificial cooling, the joint limitation becomes more severe. In all the cases considered, including the use of water jackets around the glass-fibre box surrounding the joint, the conductor temperature at the centre of the joint is above 85°C when the rating is decided by the cable alone. A thermal resistivity of the soil of 120degCcm/W, and a maximum coolant-temperature rise of 20degC are assumed. Investigation into joint power factors in the. range 0.004-0.008 shows a large temperature dependence with natural cooling, but small dependence with artificial cooling.

Temperature distribution in cooled turbine disks

The axisymmetric distribution of temperature is calculated for disks in which the thickness varies exponentially with radius, neglecting temperature variation through the thickness. An analytical solution is found for the case of disks of uniform thermal conductivity, constant heat-transfer co-efficient and negligible coolant temperature rise. When the conductivity varies with temperature, or the heat-transfer coefficient varies with radius, or the temperature rise of the coolant is appreciable, a numerical solution is adopted. A few computed results are presented, showing that relatively small flows of coolant produce eflective cooling, and that variation of thermal conductivity with temperature is significant for some materials in current use.

The Thermal Design of Nuclear Power Reactors

Abstract This paper presents the development of relationships between maximum fuel-element surface temperatures, coolant temperature rise, flow, pumping power, and operating steam temperatures for use in the design of a power-producing nuclear reactor. The heat output of a power-producing reactor is generally limited by the maximum metal-surface temperature which can be utilized without incurring excessive corrosion or dangerous conditions of boiling. The design of a reactor on the basis of maximum metal-surface temperature is particularly important in view of the fact that heat is not generated uniformly throughout the reactor and because of the fact that tolerances which must be established for manufacturing purposes may lead to further increases in hot-spot temperatures.