After some time, you may feel pretty confident in maintaining the demanded power production. However, you will have to face another threat, which is possible malfunctions in the systems. The power plant won't warn you about them. You have to detect and deal with them yourself.
For the moment, the following systems may malfunction: Feedwater pumps, Circulation pumps, Condenser pumps, pre-heaters, Condenser Circulation pumps, and both SJAE. A malfunctioning system will operate at lower efficiency, and you may not notice it at first, but once it's faulty, it will only deteriorate. As a hint, you can use the engineer's panel, which will provide you with the average system condition. If it's below 100%, something is faulty, and you need to start looking for the issue.
How to identify faults? Typically, by comparing them to other systems. Balance your flows and slightly open a feed valve to observe how the flow changes. Return to the previous setting and try the same with the second one. Is there a difference? You might have found what you were looking for. Turn off each preheater one by one and check if the temperature drops to the same level. If it's higher, that's the faulty one. The condenser can be checked when the flow is above 50%. Just turn off one pump and note the flow, then repeat with the other one. Circulation can be assessed directly by observing the flow. Diagnosing condenser circulation pumps can be done in the same way as with condenser pumps. When it comes to SJAE, you will need to experiment, as you do with feedwater pumps (SJAE have a minimal impact on condenser vacuum, making them the most challenging to diagnose, especially at high reactor powers). Remember that in any system, both pumps might be broken, and then you may not be able to see the difference.
Now, you have the option to either temporarily ignore the malfunction, perhaps to meet the demand for a few minutes, but sooner or later, you will need to repair it. To do so, you must shut off the faulty device and then tag it with a yellow tag, which is available from holders at the central desks. You can only tag devices that are prone to breaking down. Just remember that at higher reactor powers, shutting down a feedwater or condenser pump might not be possible. You'll need to lower your power output first. Once that's done, you can call a technician to investigate, and if you're correct, he will affix his red tag to the device. Now, all that's left is to wait patiently for the device to be repaired, and you're done. You will also earn points for every faulty device you detect and repair. However, please be advised that if you tag a device that is working perfectly, you won't gain any points at all.
Leakage is another problem you might encounter. If you suspect that your main cooling circuit might be losing water due to a leak, the best course of action would be to shut down the reactor into a cold state and then a technician to request leak checks. If any leaks are discovered, they will be repaired, and you will earn points. Some leaks can also be visually identified in the condenser hall or detected by measuring radioactivity there.
Sometimes your reactor will go down for maintenance. This is the best time to repair everything that needs attention. If you allow the system to deteriorate below 80% of its condition, it will definitely go for maintenance. So, it might be wise to remember which devices are faulty and continue working until that maintenance period arrives or until you are unable to meet the demand.
Offsite power loss might also happen. This will either be announced or not. If announced reactor can be prepared for islanding mode (refer to Islanding in the manual), otherwise reactor has to be shut down and cooled initially with RCIC and later with RHR powered by EDG (Emergency Diesel Generator).