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…in the nuclear industry is reactivity, which is a measure of the state of a reactor in relation to where it would be if it were in a critical state. Reactivity is positive when a reactor is supercritical, zero at criticality, and negative when the reactor is subcritical.

## What is reactivity unit?

percent mille (pcm)

The reactivity unit is one-thousandth of a percent %ΔK/K (equal to 10^{–}^{2}x10^{–}^{3} = 10^{–}^{5} of k_{eff}). The unit of pcm is used at many LWRs because reactivity insertion values are generally quite small, and units of pcm allow reactivity to be written in whole numbers.

## How do you calculate the reactivity of a reactor?

Reactivity is an expression of the departure from criticality. δk = (k − 1)/k. When the reactor is critical, δk = 0. When the reactor is subcritical, δk < 0.

## Why does graphite increase reactivity in a nuclear reactor?

Graphite facilitates the fission chain reaction in a graphite reactor by slowing neutrons. … With more neutrons becoming available and few control rods inserted to absorb them, the chain reaction accelerated. The power level in the reactor began to rise.

## Why is dollar reactivity measured?

Dollar ($)

The unit of reactivity has been normalized to the delayed neutron fraction. Reactivity in dollars = ρ / βeff. The cent is 1/100 of a dollar. This is a very useful unit because the reactivity in dollars (rather in cents) determines exactly the response of the reactor on the reactivity insertion.

## What is PCM in reactor?

A per cent mille or pcm is one one-thousandth of a percent. It can be thought of as a “milli-percent”. It is commonly used in epidemiology, and nuclear reactor engineering as a unit of reactivity.

## What is multiplication factor in nuclear reactor?

The multiplication factor is a measure of the change in the fission neutron population from one neutron generation to the subsequent generation. If the multiplication factor for a reactor core is less than 1.0, then the system is decaying or dying out and not self- sustaining.

## What is four factor formula in nuclear physics?

Four factor formula. h = the average number of neutrons produced per thermal neutron absorbed in the fuel. e = the number of fission neutrons produced by fast neutrons before they are moderated. … f = the fraction of thermal neutrons absorbed in the reactor that are absorbed in the fuel.

## What is reactor period?

The reactor period, T, is defined as that length of time required to change reactor power (or neutron density) by a factor of e. T is sometimes called the “e folding time”, meaning that every T seconds of operation, n/n_{} increases by a factor e = 2.718.

## What is the principle of nuclear reactor?

Nuclear reactors operate on the principle of nuclear fission, the process in which a heavy atomic nucleus splits into two smaller fragments. The nuclear fragments are in very excited states and emit neutrons, other subatomic particles, and photons.

## Why was iodine given after Chernobyl?

Chernobyl, the miniseries, insinuates that if people in the areas surrounding the catastrophic explosion had kept a supply of potassium iodide tablets on hand and taken them as soon as the disaster occurred, those tablets would have blocked radioactive iodine from flooding the thyroids of people in proximity to the …

## Why boron is used in nuclear reactor?

Boron is widely used in nuclear power as a neutron absorber material, thereby creating the possibility of controlling a nuclear reactor by changing the neutron multiplication factor.

## Why is graphite bad in Chernobyl?

Although the Chernobyl reactor was also cooled by water, the water was essentially only used for cooling, but not slowing down the neutrons. Instead, enormous blocks of graphite surrounded the fuel and were used to slow down the neutrons. … The graphite blocks caught fire causing more heat and damage.