Power startup of the IBR-2M reactor. Fast power reactivity feedback parameters

The paper presents the study results on the fast power coefficients of feedback reactivity at the modernized IBR-2 (IBR-2M) reactor. The study was conducted based on the 2011 power reactor startup program at up to 140 MW day power production.The paper illustrates that the reactivity coefficient of fast power reactivity feedback is negative at all levels of capacity and sodium flow rate throughout the active zone. At 2 MW capacity and sodium flow rate of 80-100 m3/h the power feedback coefficient is -0.043 ± 0.0066, 10-2 βeff / kW. At 0.5 to 2 MW capacity the fuel and sodium parts of the power feedback coefficient were separated. It was shown that the sodium part of the power feedback coefficient at nominal capacity of 2 MW is negligible. The fuel part of the power feedback coefficient is constant at all levels of power and equal to 0.047 ± 0.0066, 10-2 βeff / kW. Changes in the power feedback coefficient from sodium heating in the active power zone can be characterized as threshold. Above the threshold temperature level of 40 °C, the power feedback coefficient decreases sharply (1.7 times). Power feedback coefficient is sufficient for consistent reactor performance at capacity of up to nominal of 2 MW