Abstract: A thermocouple containment chamber for use in conjunction with a high pressure vessel wherein such thermocouples are emplaced within an elongated conduit which receives a plurality of thermocouples for sensing temperatures to determine the temperature or reaction rate within the high pressure vessel in which they are emplaced. The conduit is secured to the vessel by means of a flanged securement that in turn is welded to a concentric reducer with the thermocouples extending therefrom into a containment chamber of this invention. The containment chamber of this invention incorporates at least one access cover in the form of a high pressure flanged cover permitting access to the containment chamber for the thermocouples so that they can be changed and serviced, and incorporates a valve for relieving pressure, as well as a pressure gauge.