Fuel assembly

Purpose: To improve the safety of a BWR type reactor by increasing the shutdown margin of the reactor regardless of maintaining the same performance as a conventional reactor during its operation. Constitution: The infinite amplification factor (concentration degree) of a fuel rod is increased from the channel box of a fuel assembly toward the center, and the infinite amplifacation factor of the fuel rod adjacent to the water rod existing at the center is reduced. When the infinite amplification factor of the center is increased in this manner, the power of the periphery having low concentration degree becomes higher than that at the center having high concentration degree. Consequently, the infinite amplification factor at the time of low temperature for stopping the reactor can be decreased, and accordingly the shutdown margin can be improved. (Kamimura, M.)