Patent Number: 054694809
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT The best solution to the above described problem is to maintain the flow rate of the pump at the normal level, so that the water head should be raised, while avoiding the rumbling of the pump. Thus the air introduction into the suction tube of the residual heat removing system can be prevented during the mid-loop operation. As described before, during the mid-loop operation, the residual decay heat has to be continuously removed, but after 5 days from the stopping of the atomic reactor, the residual decay heat is very low, to such an extent that the actually required flow rate is about 2000 GPM. Therefore, in order to meet the requirement, as shown in FIG. 3, a round-about pipe conduit 4 is installed between a suction pipe conduit 2 and discharge pipe conduit 3 of a residual heat removing pump 1, and a flow rate adjusting valve 5 is installed on the round-about pipe conduit 4. Thus, the flow rate which passes through the pump is maintained at the normal operation level, while the unnecessary flow corresponding to 2000 GPM is made to pass through the round-about pipe conduit 4. Therefore, even if the water head is low at the entrance of the residual heat removing system of a hot leg 6, the air introduction is prevented. For this purpose, the requirement is that a round-about pipe conduit of a proper size is additionally installed between the suction pipe entrance and the discharge pipe conduit of the residual heat removing pump, and a flow rate adjusting valve is installed on the round-about pipe conduit. Thus during the mid-loop operation, as the residual heat is gradually decreased, the round-about flow is gradually increased, so that the suction flow from the hot leg should be maintained at the proper level, thereby preventing the air introduction. Reference code 7 in the drawings indicates a reactor, 8 a cold leg, and 9 a heat exchanger. In the above described manner, the mid-loop operation can be speedily carried out, and therefore, the repair period can be shortened. If the analysis of B & W company is referred, a shortening of about 12 days can be realized. In the case of the nuclear power plant No. 2 of Gori of Korea, if the mid-loop operation is not carried out, the repair period is extended by about 20 days. If this is converted into the economic gain, it is equivalent to an improvement of the efficiency of 4 to 6%. The nuclear power plants on which the present invention can be applied are about 10 plants including the nuclear power plants No. 3 and 4 of Youngkwang, No. 3 and 4 of Ulchin, and No 5 and 6 of Youngkwang, and the 4 nuclear power plants designed by ABB-CE i.e., Palo Verde Unit 1, 2, 3 and 4.