Effects of core excess reactivity and coolant average temperature on maximum operable time of NIRR-1 miniature neutron source reactor

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“…The control rod position shows a gradual rise with time. This is an in-build future to compensate for high negative temperature coefficient of reactivity in order to keep the reactor at the preset power level [7]. This result is in agreement with the safety requirement of the reactor, which does not permit power excursion and occurrence of boiling.…”

“…(Tables 1-4) reveals that NIRR-1 could be operated at half power (flux of 5×10^1 1n cm -2 s -1 for about seven to eight continuous hours before the control rod attains it maximum value of 232mm which by implication will trigger the reactor to automatically shut down [1]. This, in combination with the limited MNSR excess reactivity that is less than 0.5$ is another safety feature guaranteed by in-build negative temperature coefficient of reactivity, [7] just in case the reactor is left unattended to for so long [16,17].…”

“…These values gave an average temperature difference of 12.1 oC. These temperature values did not give rise to a sharp increase in predicted flux but rather fluctuate due to the inherent features of the reactor and according to the rules governing insertion of excess reactivity into the reactor by the withdrawal of the control rod during the startup [7]. As the inlet and outlet temperature values increase, the effect of coolant temperature and control rod withdrawal on the predicted flux which shows an oscillatory behavior have an approximate values of4.92×10^1 1n cm -2 s -1 and 5.11×10^1 1n cm -2 s -1 respectively [14,15].…”

“…These parameters are to be monitored for every reactor from time to time to establish the stability of the reactor's flux. It has been shown that reactor flux stability is a requirement for Neutron Activation Analysis (a major utilization of the reactor) and precious stone irradiation [2][3][4][5][6][7]. The description of Nigeria Research Reactor-1 (NIRR-1), a tank-in-pool reactor with under-moderation achieved by using a fuel material of highly enriched uranium and light water as moderator and coolant was given in our publications [3,6,8].…”