Reactor Power Variation Due to Tripping of All Three Level Control Pumps

Dhruva is a 100 MW heavy water moderated and cooled vertical tank-type research reactor. Reactor power is controlled through controlled addition or removal of heavy water in the calandria tank. There are three level control pumps which facilitate pumping of heavy water from dump tank to the calandria. To control the reactor power, the moderator level in the reactor vessel is regulated automatically as demanded by the reactor control system. During the steady state operation of the reactor when the moderator level variation is zero, all the three level control pumps operate at a constant speed and feed the moderator at the corresponding rate and the control valves in the equilibrium position will bleed the moderator at the same rate as the feed rate. Hence, the net inflow/outflow from the dump tank or calandria will be zero, and the system operates at steady equilibrium condition. When there is a demand for the moderator level variation, the opening of the control valves is automatically adjusted and accordingly there will be variation of outflow from the reactor vessel to dump tank. The automatic control of the control valve opening is carried out in proportion to the error signal generated from the reactor power regulating system. The transient introduced due to tripping of any one of the operating LCPs does not affect reactor operation. The regulating system generates the signal to close the control valves suitable to offset reduction in flow due to LCP trip. Similarly, the regulating system copes up by a slight reduction in reactor power even in case of tripping of two LCPs. However, in case of tripping of all the LCPs, the reactor power reduces gradually due to the continuous drop in moderator level and eventually the reactor reaches in shutdown state. The experiment was conducted on Dhruva simulator to establish the above statement. The paper describes the experiment details and discusses the results of the experiment.