Investigation of the Cooling of Water-Cooled and -Moderated Reactors Based on Electricity Generation Via Residual Heat i
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INVESTIGATION OF THE COOLING OF WATER-COOLED AND -MODERATED REACTORS BASED ON ELECTRICITY GENERATION VIA RESIDUAL HEAT IN EMERGENCY SITUATIONS WITH DE-ENERGIZATION R. Z. Aminov,1 V. E. Yurin,1 and D. Yu. Kuznetsov2
UDC 621.039.566.8
Safety enhancement of NPP power units with water-moderated and -cooled reactors on the basis of installation of additional multifunctional low-power steam-turbine generators is studied. It is shown that the parameters of the primary and secondary loops change as the VVER-1000 reactor is cooled via the use of the residual heat in the core to generate steam that serves as the working body for a low-power steam-turbine plant. Uninterrupted power supply for the NPP’s own needs is achieved on account of the fact that in normal and emergency regimes the low-power turbine unit supplies electricity to power consumers during cooldown of a reactor in an emergency situation with a blackout. It is shown for the example of 6 and 12 MW turbine units that the residual heat from one VVER-1000 reactor is sufficient to cool two such reactors for 72 h with de-energization of the NPP and depressurization of the primary loop in one of them.
One of the main agreed-upon safety indicators for a nuclear reactor in NPP is the probability of serious accidents with large accidental emissions outside the containment. It follows from this that the risk of the appearance of such accidents will increase as the number of reactors put into operation. For this reason, as the number of operating reactors increases, their safety requirements must be continually tightened. One of the most important requirements is the need for prolonged removal of residual heat on reactor shutdown with mandatory powering of the cooling systems. In emergency situations with NPP blackout, two to four independent emergency cooling channels are provided in each power-generating unit using their own diesel generators. According to the new version of IAEA requirements, a mandatory feature is the additional use of passive heat-removal systems that do not require intervention by service personnel or external power sources in an emergency with loss-of-power [1]. In the event of loss of emergency power in NPP, the passive heat-removal system must support the autonomy of the stations for 72 h, including in the event of loss-of-coolant in the primary loop. On this basis, the modern designs AES-2006 and VVER-TOI are equipped with additional passive heat-removal systems to prevent the development of a serious accident [2]. These designs are being implemented at the Novovoronezh and Kursk NPP-2, respectively. In the event of emergency situations with loss-of-power and a large leak in the primary loop, these designs provide hydraulic reservoirs with stored water and allow autonomous cooling of the reactor station without damage to the core by flooding. In the absence of loss-of-coolant in the primary loop, a passive heat-removal system removes the residual heat from the reactor via the steam generators. For this, the design provides air heat exchangers-
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