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A positive void coefficient means that the reactivity increases as the void content inside the reactor increases due to increased boiling or loss of coolant; for example, if the coolant acts predominantly as neutron absorber. This positive void coefficient causes a positive feedback loop, starting with the first occurrence of steam bubbles ...
Certain aspects of the original RBMK reactor design had several shortcomings, [3] such as the large positive void coefficient, the 'positive scram effect' of the control rods [4] and instability at low power levels—which contributed to the 1986 Chernobyl disaster, in which an RBMK experienced an uncontrolled nuclear chain reaction, leading to ...
The reactor had a dangerously large positive void coefficient of reactivity. The void coefficient is a measurement of how a reactor responds to increased steam formation in the water coolant. Most other reactor designs have a negative coefficient, i.e. the nuclear reaction rate slows when steam bubbles form in the coolant, since as the steam ...
This is measured by the coolant void coefficient. Most modern nuclear power plants have a negative void coefficient, indicating that as water turns to steam, power instantly decreases. Two exceptions are the Soviet RBMK and the Canadian CANDU. Boiling water reactors, on the other hand, are designed to have steam voids inside the reactor vessel.
reactors (net): 925 MWe (Units 1–4) plant (net): 4546 MWe (6 reactors) reactors (net): 439 MWe (Unit 1), 760 MWe (Units 2–5), 1067 MWe (Unit 6) Type of reactor: RBMK-1000 graphite moderated, 2nd generation reactor without containment: BWR-3 and BWR-4 reactors with Mark I containment vessels Number of reactors: 4 on site; 1 involved in accident
Control rods used to be tipped with graphite, a material that slows neutrons and thus speeds up the chain reaction. Water is used as a coolant, but not a moderator. If the water boils away, cooling is lost, but moderation continues. This is termed a positive void coefficient of reactivity. The RBMK tends towards dangerous power fluctuations.
Po would already be formed in the LBE exposed to a high neutron flux of the order of 10 15 neutrons・cm –2 ・s –1, typical for a materials testing reactor (MTR). [29] This would correspond to an activity of 5.5 × 10 16 becquerels, [29] or 1.49 × 10 6 curies of 210 Po, just for the first operation cycle.
These so-called delayed neutrons increase the effective average lifetime of neutrons in the core, to nearly 0.1 seconds, so that a core with of 0.01 would increase in one second by only a factor of (1 + 0.01) 10, or about 1.1: a 10% increase. This is a controllable rate of change.