[en] A proposed method of insulating hot coolant tubes from the moderator in an organic cooled reactor is to use a thin organic insulating annulus. The experiment reported here was a preliminary in-reactor experiment in which a water cooled thimble was insulated from the hot organic in the test section of the X-7 loop in NRX, Approximate measurements of the heat-transfer coefficient across the annulus were made during the test and the annulus was sectioned and examined following the irradiation. The total integrated flux seen by the annulus during the two months irradiation was approximately 1.37 x 10²⁰ n/ cm² (nV _ot). The average bulk organic temperature was approximately 550^oF. This resulted in little or no fouling in the annulus and no significant rise in the overall heat transfer coefficient across the annulus. The report contains details of the operating conditions of the experiment and of the post-irradiation examination, including photographs taken in the cell. (author)