On the one hand, she needs to second the observation Mark Reynolds makes. So, Alison can and should say, she is not asking for much and is asking only for what is required. But, on the other hand, she needs to respond to the points Louks and Carpello bring up. It is not to the point to argue, as they do, that so far the plant has been accident-free. 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.