Nitrogen is a big neutron absorber in gas-cooled reactors. It's actually used as a secondary shutdown mechanism in the UK's AGR reactors. So if it was to leak o

Nitrogen is a big neutron absorber in gas-cooled reactors. It's actually used as a secondary shutdown mechanism in the UK's AGR reactors. So if it was to leak out (lose pressure) you'd see an increase in power at the same time as a loss of cooling... Not a great idea!