[en] The invention provides a calandria tank which can effectively absorb the difference in thermal expansion between the calandria tank barrel and the calandria tubes, and which permits the reduction of the distance between the outermost calandria tubes and the inner peripheral surface of the calandria tank barrel to the minimum required distance. The tank comprises upper and lower barrel sections having cylindrical forms with upper and lower end openings. The upper end opening of the lower barrel section is positioned opposite the lower end opening of the upper barrel section at a suitable distance from and coaxially with the latter. A tube sheet attached to the upper barrel section closes the upper opening of the barrel section, and the calandria tubes are connected at their upper ends to the tube sheet. Similarly, a lower tube sheet attached to the lower barrel section closes the lower opening of the lower barrel section, and the calandria tubes are connected at their lower ends to the lower tube sheet. A connecting mechanism joins the lower end opening of the upper barrel section and the upper end opening of the lower barrel section so as to allow an axial movement of the barrel sections with respect to each other. The connecting mechanism includes an aseismatic ring making a sliding contact with an inner surface of one of the upper and lower barrel sections and having elongated guide bores, and being attached to the other barrel section. Protrusions attached to the barrel section make sliding contact with the aseismatic ring, by engaging with the guide bores to prevent the ring from moving in a circumferential direction but, allowing the ring to move in the axial direction