HTGR power plant hot reheat steam pressure control system

摘要

A control system for a high temperature gas cooled reactor (HTGR) power plant is disclosed wherein such plant includes a plurality of steam generators, each deriving heat from a respective circulating flow of reactor coolant gas to supply superheated steam to a common main steam header and reheated steam to a common hot reheat header. Dual turbine-generators are connected to the common headers, a high pressure element of each turbine receiving steam from the main steam header, and an intermediate-low pressure element of each turbine receiving steam from the hot reheat header. Associated with each high pressure element is a bypass line connected between the main steam header and a cold reheat header, which is commonly connected to the high pressure element exhausts. Associated with each intermediate-low pressure element is a first bypass line connected between the hot reheat header and a respective condenser, and a second bypass line connected between the hot reheat header and an alternate steam receiving means such as a secondary condenser or atmosphere. The reactor coolant gas is circulated through each steam generator by an associated helium circulator which is rotated by an auxiliary steam turbine connected between the cold reheat header and the reheater section of the respective steam generator. A control system governs the flow of steam through the first and second bypass lines to provide for a desired minimum steam flow through the steam generator reheater sections at times when the total steam flow through the turbines is less than such minimum, and to regulate the hot reheat header steam pressure to improve control of the auxiliary steam turbines and thereby improve control of the reactor coolant gas flow, particularly following a turbine trip. When the desired steam flow through an intermediate-low pressure turbine is less than the predetermined minimum, the control system governs the flow of steam through the first bypass line so that the combined turbine and bypass steam flow is equal to the predetermined minimum. The steam flow through the second bypass line is controlled to regulate the flow of steam through the first bypass line at a predetermined variable limit value. At times when there is a difference between detected and desired values of hot reheat header steam pressure, the control system reduces such difference by varying the steam flow through one of the bypass lines in proportion to such difference. The steam flow through the second bypass line is varied only when the flow of steam through the first bypass line is at the predetermined variable limit.