The possibility to increase the power capacity of an integral supercritical-pressure water-cooled reactor

Abstract

Construction of a supercritical-pressure water-cooled reactor is one of the six main lines for further development of nuclear power engineering envisioned by the international program «Generation IV». Works on developing such reactor installation with an integral layout of the primary coolant circuit main equipment with the steam generator placed inside the reactor vessel (known as VVER-SKDI) are currently underway in Russia. The main advantage of this design is an enhanced level of safety as compared with single-circuit and double-circuit loop-type process arrangements, which is achieved owing to a shorter length of the radioactive circuit, natural circulation of coolant, maintaining the criticality during the campaign by adjusting the neutron spectrum, and by using a less dense lattice of fuel rods. The most essential drawback of this reactor plant is believed to be its rather moderate power capacity (670 MWe against 1300—1800 MWe in the single-loop reactor designs), which is limited by the maximal size of the vessel (as constrained by the conditions of its manufacture) required for accommodating the natural circulation loop inside of it. The present study addresses the problem of increasing the VVER-SKDI reactor plant's power capacity. A higher heat release density in the core while keeping the same maximal temperature of fuel rod claddings and the same geometric parameters of the core can only be achieved by increasing the coolant flow rate and enhancing heat transfer. In view of this, it was decided to adopt the previously used casingtype design of fuel assemblies (FAs). Concurrently, increasing the heating in peripheral FAs by throttling the coolant flow rate makes it possible to increase the average coolant temperature at the core outlet and the temperature difference in the steam generator. However, increasing the coolant flow rate and steam generator height, and decreasing the core hydraulic diameter entail a growth of the loop flow friction. With the adopted natural circulation of coolant, this generates the need to increase the loop height required to create the sufficient hydraulic head, whereas the limit has already been reached at the power level equal to 670 MWe. The solution to the problem is seen in making a shift to forced circulation of the coolant. In this case, with increasing the power output to 1000 MWe, the reactor pressure vessel height with installing the reactor coolant pumps will be by 1.7 m smaller than that at the power capacity equal to 670 MWe with natural circulation. In case the pump motors are disconnected, the hydraulic head will be sufficient for the operation in the natural circulation mode with the power output reduced to 50%.