Per cent mille explained
A per cent mille or pcm is one one-thousandth of a percent.[1] It can be thought of as a "milli-percent". It is commonly used in epidemiology, and in nuclear reactor engineering as a unit of reactivity.
Epidemiology
Statistics of crime rates, mortality and disease prevalence in a population are often given in [2] [3]
Nuclear Reactivity
In nuclear reactor engineering, a per cent mille is equal to one-thousandth of a percent of the reactivity, denoted by Greek lowercase letter rho. Reactivity is a dimensionless unit representing a departure from criticality, calculated by:[4]
where k
eff denotes the
effective multiplication factor for the reaction. Therefore, one pcm is equal to:
[5]
This unit is commonly used in the operation of
light-water reactor sites because reactivity values tend to be small, so measuring in pcm allows reactivity to be expressed using whole numbers.
[6] Related units
See also
Notes and References
- SCALE: A Comprehensive Modelling and Simulation Suite for Nuclear Safety Analysis and Design. Available from Radiation Safety Information Computational Center at Oak Ridge National Laboratory as CCC-785. Oak Ridge, TN: Oak Ridge National Laboratory, June, 2001. Version 6.1. ORNL/TM-2005/39
- Web site: Number of Infections and Incidence* per 100,000 Persons | FoodNet | CDC. 28 September 2018.
- Web site: GHO | by category | Homicide - Estimates by country.
- Web site: Reactivity measurements. Merljak. Vid. University of Ljublj. September 17, 2017. ana
- Web site: Reactivity. nuclear-power.net. September 17, 2017.
- Web site: percent mille – pcm – unit of reactivity. nuclear-power.net. September 17, 2017.