Can you explain why this would be the case? I suppose you might need less manpower to run the reactor, which might mean fewer total man hours. But does that necessarily mean it gets less attention and care?
I think, in other words, the cost to guard and physically secure a reactor doesn't depend on the size of the reactor, just the existence of the reactor [1]. A large reactor would require the same defense as a small one.
Note that the majority of the cost of nuclear is the people [2].
[1] https://www.nrc.gov/security/faq-force-on-force.html
[2] https://energy.mit.edu/news/building-nuclear-power-plants/