- #1
girts
- 186
- 22
This is more or less a question to which I think I know the answer to but want to make sure I'm right.
So in light water reactors one of the safety features is that the light water coolant also serves as the neutron moderator slowing them down to the "thermal" range so that they can cause fission more efficiently in U 235, so if somehow the water level drops too low or there is too much steam neutron moderation is lost there are fewer thermal neutrons and more fast ones which can't fission U 235 effectively and hence the reaction decreases and so does the power,
Now in Chernobyl's RBMK-1000 due to a sudden increase in power water was boiling off fast and turning into steam while still in the pipes in the active zone of the core, normally this would or should lead to a decreased reactivity but in the RBMK it lead to an even greater increase in reactivity, what is essentially know as the positive void coefficient, now was that because the specific design of the RBMK unit used essentially two moderators, the main one being graphite and also water so even when the water was lost to steam the neutrons still were moderated in the graphite and so there was no decrease in reactivity?
So in light water reactors one of the safety features is that the light water coolant also serves as the neutron moderator slowing them down to the "thermal" range so that they can cause fission more efficiently in U 235, so if somehow the water level drops too low or there is too much steam neutron moderation is lost there are fewer thermal neutrons and more fast ones which can't fission U 235 effectively and hence the reaction decreases and so does the power,
Now in Chernobyl's RBMK-1000 due to a sudden increase in power water was boiling off fast and turning into steam while still in the pipes in the active zone of the core, normally this would or should lead to a decreased reactivity but in the RBMK it lead to an even greater increase in reactivity, what is essentially know as the positive void coefficient, now was that because the specific design of the RBMK unit used essentially two moderators, the main one being graphite and also water so even when the water was lost to steam the neutrons still were moderated in the graphite and so there was no decrease in reactivity?