14.6:1

18.5:1

20.4:1

22.6:1

low

very low

high

very high

below 50%

between 50 and 85%

between 85 and 95%

between 95 and 100%

2000 to 4000 volts

4000 to 6000 volts

6000 to 10 000 volts

10 000 to 12 000 volts

absorb excess neutrons

control fuel consumption

control temperature

all of these