{"id":13719,"date":"2017-02-05T14:43:44","date_gmt":"2017-02-05T14:43:44","guid":{"rendered":"http:\/\/sitepourvtc.com\/?page_id=13719"},"modified":"2022-10-21T05:37:35","modified_gmt":"2022-10-21T05:37:35","slug":"thermal-non-leakage-probability","status":"publish","type":"page","link":"https:\/\/sitepourvtc.com\/nuclear-power\/reactor-physics\/nuclear-fission-chain-reaction\/thermal-non-leakage-probability\/","title":{"rendered":"Thermal Non-leakage Probability"},"content":{"rendered":"
In an infinite multiplication system, the neutron leakage<\/strong> of the system is logically neglected. But all multiplying systems, all realistic reactor cores<\/a> are finite multiplying systems, and this process may not be neglected. During neutron diffusion<\/strong>, some of the neutrons<\/a> leak out of the boundaries of the reactor core before they are absorbed. This process and its impact on the effective multiplying factor is characterized by the thermal non-leakage factor, Pt<\/strong>, defined as the ratio of the number of thermal neutrons<\/a> that do not leak from the reactor core during the neutron diffusion process to the number of neutrons that reach thermal energies.<\/p><\/div><\/div> 734<\/span><\/strong><\/p>\n \u2193<\/span><\/strong><\/p>\n Pt<\/sub> ~\u00a00.96<\/span><\/strong><\/p>\n \u2193<\/span><\/strong><\/p>\n 705<\/span><\/strong><\/p>\n <\/a> <\/a><\/p>\n Ld<\/sub> is the diffusion length<\/strong>, B <\/strong>is the geometrical buckling<\/strong> (in case of critical state Bg<\/sub> = Bm<\/sub><\/strong>), which depends only on the shape and size of the core. The value of B for small cores is higher than the value for large cores. So that, it is obvious, the thermal neutrons leakage is higher for small cores <\/strong>and depends on the macroscopic slowing down power<\/a> of neutron moderator<\/a> (leakage is higher for poor moderators). The following equation gives the diffusion length<\/b>:<\/p>\n
\nThe thermal non-leakage probability<\/strong> is for large reactor cores about 0.95 – 0.98<\/strong><\/span><\/strong>. This<\/span> value is minimally affected (in comparison with the other factors) by operational changes except for changes in the moderator temperature<\/strong>. The only parameter that influences the thermal non-leakage probability<\/strong> is the moderator temperature. It can be derived from the neutron diffusion theory. The following equation also represents the probability that a thermal neutron will remain in the core:<\/span><\/strong><\/p>\n