Selection of a steam generator pressure control program for a 500 MWe pressurized heavy water reactor power plant through transient analysis

Abstract

A personal computer based 500 MWe pressurized heavy water reactor (PHWR) power plant transient analysis code has been developed for analysing plant operational transients, for sorting out design issues and for taking decisions on new operating procedures and safety-related transient events. This code is based on the coupled solution of the conservation equations of mass, momentum and energy and the equation of the fluid state for simulation of process transients/dynamics. It includes mathematical models for all the major equipment/subsystems, i.e. the reactor core heat transfer, steam generators (SGs), surge tank (pressurizer), bleed condenser, etc., of the 500 MWe PHWR power plant. All the associated control systems on the primary and secondary sides are also incorporated. These codes are also validated against the available plant data. This code was also used to resolve the issues related to SG pressure control program selection. Two fundamental types of SG pressure control program are available for nuclear power plants, i.e. the constant boiler pressure program (CBPP) and the variable boiler pressure program (VBPP) for power manoeuvring from zero to 100 per cent of full power (FP), and vice versa. With CBPP the secondary steam cycle design and operation are simplified, at the cost of more load on the primary heat transport (PHT) pressure control system, whereas VBPP reduces the load on the PHT pressure controller. Parametric studies were carried out by taking into account the reactor trip, turbine trip and the IRV sizing design basis transient for comparison of these SG pressure control programs, i.e. (1) the earlier old design VBPP with constant PHT temperature 25 per cent of FP onwards, (2) CBPP and (3) VBPP similar to the 220 MWe PHWR SGPC program. After examining the two extremes in cases 1 and 2, the third scheme similar to the 220 MWe boiler pressure control (BPC) program was found to be most suitable. Schemes 2 and 3 put more load on the PHT pressure control and make use of the capacities enhanced by the pressurizer. The dip in the pressurizer level is acceptable in the CBPP, i.e. in the second case also. All the pros and cons of the selection of a BPC program were clearly quantified and resolved by considering a wide range of transients. All the related transient studies are discussed in this paper.