In a system for effecting pressure control in a thermal power plant operated at low load connected fluidly in series, a relief conduit is disclosed herein. The relief conduit selectively transfers steam from a cold reheat conduit to the second extraction conduit. The plant further includes a boiler, a high-pressure turbine, an intermediate pressure turbine, a low pressure turbine, a main steam conduit for feeding steam from the boiler to an inlet of the high pressure turbine, a cold reheat conduit for feeding steam from an outlet of the high-pressure turbine through a reheat flow path in the boiler, and a first and second high pressure heaters. A first extraction conduit connects the cold reheat conduit to a first high pressure heater to transfer heat, and a second extraction conduit connects the intermediate pressure turbine to the second high pressure heater, to transfer heat.

Provided in the present disclosure is a control system for a heat supply apparatus of a nuclear power plant, comprising: a first-stage pressure measurement means configured for measuring a first-stage pressure of a turbine to obtain a first-stage pressure signal; a high-exhaust pressure measurement means configured for measuring an exhaust pressure of a turbine high-pressure cylinder to obtain an exhaust pressure signal; a steam extraction heating flow rate measurement means configured for measuring a steam extraction heating flow rate to obtain a steam extraction heating flow rate signal; a data acquisition module configured for acquiring and transmitting the measured first-stage pressure signal, the measured exhaust pressure signal and the measured steam extraction heating flow rate signal to a core operation processing module; the core operation processing module; and a the signal output module.

A balanced grid valve for steam extraction from a multi-stage steam turbine comprising a first balancing chamber and a second balancing chamber which are configured to receive steam at high pressure through at least one duct. The balancing chambers are preferably in the form of annular grooves and are arranged at two different radial distances from the axis of the valve in order to reduce mechanical distortion of the valve.