We (USN) only use pumps at certain power levels, as may be required to meet some steam plant demands. Otherwise, the systems operate on natural circulation. Haven't seen a Jane's for quite a while, but the "NC" feature was mentioned in the ship class data in those tomes, as well as many other documents
in the public domain. S5G (Narwhal)and S8G (Ohio)plants were discussed a lot.
We (Battlestar Narwhalica) discovered by happy accident (forgot to start the pumps!)after the 1974 overhaul, that even the small auxiliary seawater systems up forward worked just fine, without scoops, under moderately heavy heat loads, without problems to the serviced components. We just got even more quiet! We ran that way a good part of my time onboard 'til I left in early '78.
Scoops themselves make noise! Never had a Russian we couldn't track in my 22 yrs. service!! :^)
"If you ignore the problem long enough, it will go away. Even flooding stops eventually!"