The main reason for the prohibition of simultaneous injection of positive reactivity in two or more ways is the requirements of the nuclear safety rules for reactor installations. The introduction of positive reactivity by the means of influence on reactivity, provided for by the technical design of the reactor installation, should be excluded, if the emergency protection working bodies are not brought to the working position. Technical measures should exclude the possibility of introducing positive reactivity simultaneously by two or more provided means of influencing reactivity, as well as introducing positive reactivity by means of influencing reactivity during fuel loading and unloading. The rate of increase in reactivity by means of influencing the reactivity should not exceed 0.07 βef/s. For the working bodies of the control and protection system with an efficiency of more than 0.7 βef, the introduction of positive reactivity should be stepwise, with a step weight of no more than 0.3 βef (provided by technical measures). In the technical design of the RU, the size of the step, the pause between steps and the rate of increase in reactivity should be indicated. The consequence of introducing positive reactivity in two or more ways is a possible violation of the conditions for normal operation of nuclear power plants due to an uncontrolled increase in the neutron flux in operating and emergency modes of the reactor. The installed second-type warning protection, which is supposed to solve this problem, has shortcomings in its operation that lead to a clear violation of the current prohibition on the simultaneous introduction of positive reactivity in two or more ways. On the basis of the conducted research, the existing error in the operation of the PP-2 was identified and analyzed. To avoid the problem with the simultaneous introduction of positive reactivity in two or more ways, it is proposed to modernize the system of PP-2 with its further operation on reactivity indicators.
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