{"id":13997,"date":"2017-03-10T17:36:45","date_gmt":"2017-03-10T17:36:45","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=13997"},"modified":"2022-10-21T16:57:17","modified_gmt":"2022-10-21T16:57:17","slug":"reactivity-coefficients-reactivity-feedbacks","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-fission-chain-reaction\/reactivity-coefficients-reactivity-feedbacks\/","title":{"rendered":"Reactivity Coefficients – Reactivity Feedbacks"},"content":{"rendered":"
According to 10 CFR Part 50<\/a>; Criterion 11:<\/p>\n “The reactor core and associated coolant systems shall be designed so that in power operating range, the net effect of the prompt inherent nuclear feedback characteristics tends to compensate for a rapid increase in reactivity.<\/p>\n<\/div><\/div>\n Up to this point, we have discussed the response of the neutron<\/strong><\/a> population<\/strong><\/a> in a nuclear reactor<\/strong> <\/a>to an external reactivity input<\/strong>. There was applied an assumption that the level of the neutron population does not affect<\/strong> the properties of the system, especially that the neutron power (power generated by chain reaction) is sufficiently low<\/strong> that the reactor core does not change its temperature<\/strong> (i.e.,, reactivity feedbacks may be neglected<\/strong>). For this reason, such treatments are frequently referred to as zero-power kinetics<\/strong>.<\/p>\n However, in an operating power reactor,<\/strong> the neutron population is always large enough to generate heat. It is the main purpose of power reactors to generate a large amount of heat<\/strong>. This causes the system’s temperature to change and material densities to change as well (due to the thermal expansion<\/strong>).<\/p><\/div><\/div> Source: Youtube<\/a><\/p>\n See also: General Atomics\u00a0– TRIGA<\/a><\/p><\/div><\/div> Negative feedback<\/strong> as the moderator temperature effect influences the neutron population in the following way. If the temperature of the moderator is increased, negative reactivity is added to the core. This negative reactivity causes reactor power to decrease. As the thermal power decreases, the power coefficient acts against this decrease, and the reactor returns to the critical condition. The reactor power stabilizes itself. In terms of multiplication factor, this effect is caused by significant changes in the resonance escape probability<\/a> and total neutron leakage<\/a>\u00a0(or in the thermal utilization factor<\/a> when the chemical shim<\/a> is used).<\/p>\nExample:\u00a0Change in the moderator temperature.<\/h2>\n