One may cross the street all one's life without being run over and without looking both ways, but one's luck does not mean that it is right or all right not to look both ways. Requirements are there to make sure that one do what needs to be done to prevent accidents. It does not follow that if one has not had any accidents, that one need not do what is required. One may not have had any accidents because one has done what is required. But the thrust of the objection Louks and Carpello make is that since the heat exchangers are an extra safety device in any event, not required, it makes no sense to follow the Criteria and see what happens if one of them fails.
Many plants have neither, and they have had no problems.
It is not unusual to have a situation where one has something extra and then is required, because one has something extra, to make sure it works properly. If car seats for babies were not required by law, but one had one, it would not be inappropriate for a legislature to require that one check to be sure that it works properly. The baby might be no worse off in a car seat that did not stay in place in an accident than if he or she were in an accident without a car seat at all, but since the parent has provided one, the legislature may require that it work properly. Reduced insurance premiums might depend upon the seat working properly, or the legislature might want to be sure that the person who bought it has peace of mind appropriately, and not because of the mistaken assumption that the car seat will protect the child. Just so, NRC may not require heat exchangers, but may require, if a plant has them, that they do the job even if one is down.