It is well known that turbulent temperature fluctuations penetrate into the heated wall that is being cooled with a turbulent flow. The present work represents a theoretical analysis of the heated slab that is being cooled with turbulent flow from both sides. Results of the direct numerical simulations predict penetration of the turbulent temperature fluctuations into the solid wall. For a sufficiently thick slab, temperature fluctuations from both sides of the slab do not interfere. As the slab gets thinner, fluctuations from both sides interfere and tend to a finite value as the slab thickness limits toward zero. Due to the non-coherent turbulent flows on each side of the slab, thermal fluctuations in the zero-thickness slab are actually lower than in the case of the zero-thickness wall, which is heated by the same turbulent flow from a single side and is isolated on the other side. Spectral numerical scheme was used for Direct Numerical Simulation of fully developed channel flow that is cooling the idealized slab heated with constant volumetric heat source. Implemented boundary conditions for liquid and solid energy equations correspond to the geometry that can be found in some experimental nuclear reactors with fuel in the form of parallel slabs. Periodicity of streamwise and spanwise directions was assumed for velocity and passive scalar temperature field. For temperature, periodicity of the computational domain was assumed also in the wall-normal direction. Most of the simulations were performed at constant friction Reynolds number 180 and Prandtl number 1 with various geometrical and material properties of the heated slab. Some additional analyses were performed also at friction Reynolds number 395 and Prandtl numbers 0.1 and 10. (C) 2013 Elsevier Ltd. All rights reserved.