Nuclear power plants (NPPs) typically have four classes of electrical supply systems to provide redundant and resilient power to ensure safe operation, cooling, and shutdown of NPPs. Class III emergency power traditionally uses standby diesel generators to fulfill equipment electrical demands. This requires a reliable source of diesel energy and reliance on one particular kind of fuel source for backup power.

During the North American blackout of 2003, hospitals had to run on backup generators that were mostly diesel fired. A prolonged blackout could have negatively affected hospital infrastructure and patient health. With current diesel generators, capable of supporting critical systems for up to 72 hours (for most NPPs), a prolonged loss of power or transient could similarly also have adverse effects on NPPs.

A Combined Heat and Power (CHP) system is a power generation system that generates electricity, in addition to concurrently having heating and cooling capabilities. Often, gas or steam turbines are used to generate electricity. CHP heating and cooling capabilities can be met via absorption coolers and heat pumps. Low-grade exhaust heat from turbines could be used for the absorption processes. Absorption coolers/heaters produce cold/warm fluid using a heat source via the vapor compression cycle, taking advantage of high affinity fluids. The absorbent allows for the refrigerant to boil at lower operating conditions, which allows for heat transfer.

CHPs’ that are capable of accepting natural gas as a form of fuel will increase resiliency of NPP power supply. This ensures a reduced risk of running out of fuel during prolonged transients due to continual supply via pipelines already in place.

The objective of this work is to generate a conceptual design of a multi-fuel source CHP system that is capable of at least accepting natural gas as an alternative to Class III diesel generators for a NPP. The system will be capable of supplying Class III power to Small Modular Reactor (SMRs), as well as commercial NPPs, such as CANDU, PWR, and BWR types.

Current state of the art Class III backup power systems, CHP systems, CHP thermodynamic cycles, multiple compatible fuels, as well as absorber heaters and coolers have been investigated. Ranking systems were used to determine the top three designs. The parameters included turbine type, efficiency, flow rates, operating temperature/pressure, fuel type, fuel to energy ratio, fuel availability, absorber chiller/heater fluid efficiency, operating temperature and thermal conductivity.

Based on the ranking system parameters, a thermodynamic model including mass, energy and entropy balance of an 8 MWe CHP with heating and cooling capability between the ranges of 15°C to 27°C was conceptually designed.

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