Power Maneuvering Thermalhydraulics, Control and Reactivity Feedbacks for Connected Parallel Loops Boiling Channel Type Power Plants


Avinash J. Gaikwad1, P. K. Vijayan2, Kannan N. Iyer3, Sharad Bharteya3, Rajesh Kumar1, H. G. Lele1,
S. F. Vhora4, A. K. Maurya4, Philip Fernando4, A. K. Ghosh1 and H. S. Khushwaha5

1Reactor Safety Division, BARC, Trombay, Mumbai 400 094, India.

2Reactor Engineering Division, BARC, Trombay, Mumbai 400 094, India.

3Mechanical Engineering Department, IIT Bombay, Mumbai, India.

4Nuclear Power Coropration of India, NUB, Anushaktinagar, Mumbai 400 094, India.

5Health Safety & Environment Group, BARC, Trombay, Mumbai 400 094, India.

ABSTRACT

Advanced Heavy Water Reactor (AHWR) currently under advanced stages of design is a pressure tube and parallel inter-connected loops type Boiling Water Reactor (BWR). Here the thermalhydraulics and the reactivity feedbacks are closely coupled. Any safety and transient analysis has to include the neutronic feedback as far as possible. The most important reactivity feedback arises due to voids in the primary coolant. Also the coolant reactivity feedbacks contribute positive reactivity following an increase in the coolant temperature. The Doppler fuel temperature reactivity feedback is always negative and has a stabilizing effect. It is also desired that the power coefficient which is sum of all the feedback coefficients must be sufficiently negative for a stable reactor operation. The reactor physics design ensures all the safety requirements, which are being verified by carrying out the power maneuvering transient analysis.

Some of the aspects related to reactivity i.e. Reactor Regulating System (RRS) and various process controls also need to be addressed. A thermalhydraulics simulation model for these reactors has been developed using RELAP5/MOD3.2. All the associated control system models are also included in the simulation. Various issues related to the control system, the safety margins and the operation margins were resolved using the designer feedbacks generated through transient and safety related analysis using the simulation model.

Another case study related to 700 MWe PHWR is also presented in this paper. A limited boiling towards the channel exit is allowed at the power levels beyond 80% full power (FP). Though the reactivity impact is minimal, but the load on the Primary Heat Transport (PHT) system pressure control increases enormously due to appearance and disappearance of coolant voids. The reactivity feedbacks, the PHT pressure controller and the Steam Generator Pressure controller (SGPC) decide upon the sustainable power maneuvering rates. All the modeling and the analysis aspects are discussed in this paper.


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