|Dec3-12, 09:20 PM||#18|
100MW reactor must produce a 110MW
the reactor is not like a gasoline engine, ie limited by a its fuel flow to a relatively fixed output. Its fuel is 100% there,built in, and control systems determine at what rate it burns hence energy conversion progresses.
Designers build in natural thermal feedbacks to make a gross limit on power
but for fine control rods are used.
A typical commercial PWR would have control systems that stop rod withdrawal around 102% or 103% rated poweras measured by neutron detectors , and would drop them all in(trip reactor is the tern we use) at about 108%-110% on presumption something is awry.
There's also systems that infer power from temperature rise across core and trip reactor should it reach the 107%-110% range by thermal measurement.
So most reactors could do 110% if allowed to, but we don't hot-rod them.
|Dec3-12, 10:06 PM||#19|
Let me just point out that a naval nuclear power plant (primarily for propulsion) operates a bit differently than a commercial power plant (for electrical generation and contrained to a 60 Hz grid in the US or 50 Hz in Europe and other countries).
To get more efficiency out of a nuclear power plant one either raises the hot temperature to the high pressure turbine, or reduces the cold temperature in the condenser, after discharge from the LP turbine. When the cooling water is warmer, the turbines are slightly less efficient.
Generally reactors are contrained by cladding surface temperatures on the fuel. The higher the temperature the higher the corrosion (cladding oxidation). There is also a concern about nucleate boiling in PWRs, since that is where crud likes to deposit, and that can (and has in rare cases) lead to fuel failure (water chemistry, e.g., pH and Ni content is usually the other factor). The hot coolant temperature is usually limited because corrosion of steam generator materials (which is usually the main source of crud species). Lower cooling water temperature at the condenser is a preferred way to get more efficiency, but it's usually a fraction of a percent.
Commercial plants must produce electricity at 60 Hz or 50 Hz, to large turbines run at 1800 rpm (60 Hz) or 1500/3000 rpm (50 Hz), and there is little variation.
Reducing core inlet temperature, but reducing feedwater temperature can increase reactivity in the core, and this can be used toward end of cycle to get a little more energy out of the core - but that doesn't so much increase the thermal efficiecy of the plant.
Some plants have replaced their turbines with more efficient turbines, with advanced blade geometry and improved sealing between stages. This can boost efficient 1 to 2%, as has been the case at some German plants. The best PWRs are about 36 to 37% efficient, from a combination of slightly higher hot temperature in conjunction with more efficient turbines.
As far as I know, naval plants aren't as constrained as commercial plants.
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