Integrity of the blowdown piping systems in a nuclear power plane—findings and consequences Original Research Article

In a pressurized-water reactor (PWR) the blowdown pipes from the four steam generators (material 1.5415) were examined. All the quality reports of the piping materials and the welding seams as strength and toughness and all non-destructive test findings of the welding seams were listed. According to pipe design drawings, a static calculation of the system under operational loads was conducted. In some cross sections adjacent to elbows an overload was estimated. Selective non-destructive testing of affected sections and inspection of the existing pipe-support conditions were recommended. Non-destructive tests during the inspection in 1994 revealed some longitudinally oriented findings in the base material in the inside walls of two elbows; the two elbows were replaced. The causes of findings were `in-plane bending overloadingʹ, corrosion processes in the two elbows with findings and, most probably, condensation hammers during the startup period of the plane (possibly the opening of the shutoff valves was too fast) which yielded a large displacement of the piping system. Based on findings, the following should be implemented on the 1996 inspection: (1) the two supports U 27 and U 28 are to be changed; (2) the six highly loaded elbows are to be replaced (wall-thickness is to be increased from 5.6 to 6.3 mm); (3) the whole pipework from the four steam generators to the protection barrier is to be replaced.