BS IEC 62118:2000 pdf download-Nuclear reactor instrumentation Ð Pressurized water reactor (PWR) ofVVER design Ð Monitoring adequate cooling within the core during cold shutdown.
4.5 Cold shutdown operations Cold shutdown operations are defined as maintenance operations when coolant temperature is below 1 00 °C (21 2 °F), with all RPV head closure bolts fully tensioned, and refueling operations with temperature 70 °C (1 58 °F), with one or more RPV head closure bolts less than fully tensioned. Residual heat is removed by the secondary auxiliary RHRS in the systems shown in figure 1 or by the primary RHRS in the systems shown in figure 2. Redundant components and emergency power availability minimize the possibility that core cooling capability would be lost. A reduced inventory condition will exist in the systems shown in figure 2 for maintenance operations (e.g. reactor coolant pump maintenance) when the water level in the RPV is lower than the top of the RPV outlet piping (either the hot leg or the cold leg, depending on the direction of flow through the RPV) nozzle elevation. In these specific operations, coolant inventory is maintained at or above the water level in the RPV outlet piping required to circulate coolant to the RHRS. Reverse coolant flow through the core is maintained in this mode by primary RHRS operation aligned to take suction from the RPV cold leg piping and discharge to the RPV hot let piping. Throughout this standard, the discussion of the VVER 1 000 RPV outlet pipe in reduced inventory conditions always refers to the RPV cold leg which has the RHRS suction nozzle at the lower elevation. Since loop components can be isolated for maintenance by valves in the VVER 440 design (systems shown in figure 1 ), intentional reduced inventory conditions are less likely to occur. During a reduced inventory condition in the RPV of a VVER 1 000, (systems shown in figure 2), an inadvertent increase in coolant inventory could result in coolant overflow through openings in the RCS pressure boundary, possibly causing personnel contamination.