Not unless the small reactor is designed to produce low energy. HIFR operates at up to 85 MW, but it is about the size of a large washing machine.In small Fission reactors it can be hard to get enough heat in order to boil the water inside the boiler,
Why would it be inefficient?
What temperature differential would one propose? What size generator does one propose? 5 kW, or 10 kW? Slightly above room temperature would have very low Carnot efficiency.low pressure boiler systems, where we can boil water at slightly above room temperature, use it to turn the steam turbine as it flows to the similarly low pressure condenser chamber,
Carnot efficiency is the theoretical thermodynamic efficiency of a process. In a thermodynamic (Rankine) system driving a turbine, heat is put into a liquid (water) which is turned to steam. Steam passes through a turbine and loses energy (enthalpy). The work out of the turbine is equivalent to the energy decrease in the working fluid and other losses. That energy change is slightly more than the energy increase in the boiler.Could you explain it a bit more and help me understand how it is relevant to this situation?
What does one understand about thermodynamic cycles and the production of energy?I am still not sure I understand. If you have chamber A, where steam is produced, and it flows through a turbine into chamber B, which has a lower pressure than chamber A, how does equally increasing or decreasing the pressure in the chambers effect the amount of energy that is produced by the turbine?
Steam by itself is not a very complete description. The amount of energy in the steam depends on the temperature and pressure involved.
The Carnot cycle gives a clear understanding of how much of that energy can be extracted to do useful work.
If the steam is at low temperature and low pressure, very little energy can be extracted. This hold true for any low power and low pressure steam source , whether nuclear or conventional.
BES-5 produces about 100 kW thermal, and converts just 3 kW of that into electricity.A small core still need shielding of the radiation (primarily gamma), and then there is the matter of control of the special nuclear material. So, it's uneconomical to have a small reactor in the kW range.
And the cost is? I seriously doubt that it would economical for a typical household, and the fact that it requires "30 kg of uranium more than 90% enriched U235" raises security/proliferation concerns. Ref: https://en.wikipedia.org/wiki/BES-5BES-5 produces about 100 kW thermal, and converts just 3 kW of that into electricity.
BES-5 also has mass of under 400 kg including shielding.
Note that BES-5 does not have steam: it uses NaK as coolant, and produces energy by thermoelectric means.
... issues not inquired about by OP.And the cost is? I seriously doubt that it would economical for a typical household, and the fact that it requires "30 kg of uranium more than 90% enriched U235" raises security/proliferation concerns.
Yes. And my point is that for low temperature heat engines, steam is not an efficient option even for the Carnot efficiency.The OP was asking about systems using water cooling and steam generation.
Not explicitly. Economy is a consideration in the design and deployment of any engineered system. The OP inquires " so why don't we create low pressure boiler system . . . ," The answer involves the physics/thermodynamics and economics.... issues not inquired about by OP.
Odd example, since little in the natural environment is at or below 0 C, except during winter, and in the polar regions, but the BES-5 example given is a high temperature system.Yes. And my point is that for low temperature heat engines, steam is not an efficient option even for the Carnot efficiency.
For example, if you have a heat source at 37 Celsius and no more, and a heat sink at 0 Celsius, you could run a heat engine at a theoretical Carnot efficiency of (37-0)/(37+273)=37/310=12% efficiency. Yet I doubt that a water steam boiler is an efficient way to use a heat source at 37 Celsius. Something else may have a better efficiency, though of course still under 12 %.
And a part of the answer is that while low temperature heat engines are inherently low efficiency, low pressure water steam is low efficiency even among them. There are more efficient ways to skim the small amount of energy from low temperature difference.Not explicitly. Economy is a consideration in the design and deployment of any engineered system. The OP inquires " so why don't we create low pressure boiler system . . . ," The answer involves the physics/thermodynamics and economics.
Like what? A Thermoelectric generator?There are more efficient ways to skim the small amount of energy from low temperature difference.
Yes.Like what? A Thermoelectric generator?
Yes - given same volume of steam.In pressure systems, isn't the work done by the pressure difference? Like I said, if you have a 18 psi boiler and a 14 psi condenser, isn't the amount of energy you can get out of it equal to the amount you can get out of a 8 psi boiler and a 4 psi condenser? Regardless of temperature difference?
In small Fission reactors it can be hard to get enough heat in order to boil the water inside the boiler, so why don't we create low pressure boiler systems, where we can boil water at slightly above room temperature, use it to turn the steam turbine as it flows to the similarly low pressure condenser chamber, is cooled back down into its liquid form, and pumped back into the boiler?