Inside Chernobyl Nuclear Power Plant 2011, Part II: Deaerator Corridor and Unit 1 Control Room » P1020048

One of the changes to the RBMK control system that was made after the 1986 accident was the addition of a control room display of the calculated quantity known as the “operational reactivity margin” (оперативный запас реактивности or ОЗР), basically the reactivity of control rods remaining in the core. Having too few there, as happened in the Chernobyl 4 accident, can set the stage for a positive scram, among other deleterious effects. This is a chart recorder (at right) labelled “запас реактивн[ости]”, probably Unit 1’s retrofitted display for this quantity. Above it is a Nixie tube display, also probably for this quantity.

One comment

  1. To be more precisely ORM symbolise not a number rods in active zone but amount of reactivity which will be added into core by rising up all remaining control rods in active zone. Like ORM=10 can be achieved in 8 or 12 or any other number of control rods in active zone of reactor. ORM was calculated as pretty big sum of two integrals of neutron flux (where constant value is a reactivity of one manual control rod calculated for “hot” operating reactor, that is why ORM unit is “control rod”), so ORM highly depends on the thermalhydraulic state of reactor.


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