Abstract: A nuclear reactor primary circuit with a branch equipped with a thermal sleeve is provided. The nuclear reactor primary circuit includes a primary tubing, having an inner surface delimiting an inner volume in which a primary fluid circulates for cooling the nuclear reactor; a branch fastened to the primary tubing and delimiting an inner passage communicating with the inner volume of the primary tubing; a sleeve, having a first end connected to the branch and a second free end engaged in the inner volume of the primary tubing, the second end protruding in the inner volume relative to the inner surface over a non-zero length, an annular space being delimited between the sleeve and the branch.