An exemplary heat exchanger includes a heat exchanger core having a core side fluid space and a cover plate and a substantially U-shaped wall fitted at one end with an inlet header and, at an opposing end, with an outlet header, which in combination with the cover plate, define a shell side fluid space. In this example, the cover plate forms two seals with two opposing sides of the U-shaped wall, forms a seal with the inlet header and forms a seal with the outlet header. Such a heat exchange may be suitable for use as an EGR cooler. Other exemplary devices, methods and systems are disclosed.