Johnson, Joel
THE USE OF A PASSIVE ENDOTHERMIC REACTOR COOLING
SYSTEM FOR LWR EMERGENCY COOLING
Faculty Mentor: Dr. Matthew Memmott, Chemical Engineering Department
Introduction
The purpose of the project was to test the viability and begin design on a passive
endothermic reaction cooling system (PERCS). The idea behind PERCS is to improve
the safety of and to avoid potential disasters resulting from accident conditions in
nuclear reactors. To do this, a PERCS will be designed that can be simply integrated
into current nuclear power plant systems. The PERCS concepts to date are completely
passive; rather than requiring valve or operator actuation, the system initiates due to
natural conditions in the reactor system.
Without a passive cooling system, it is possible that during severe accidents, core
cooling capabilities may be lost. When this happens, fuel temperature increases, to the
point where the fuel may reach a critical temperature where harmful chemical reactions
or even fuel meltdown may occur. To prevent this, a PERCS or essentially a tank filled
with coolant materials will be installed inside the containment of the reactor (figure 1).
The PERCS system provides completely passive cooling capabilities through
exploitation of endothermic chemical reactions. For these reactions, once a physically
defined temperature is reached, the reactions begin to occur. These reactions require
external heat to proceed, and thus the cooling tank will become a heat sink used to cool
the core via natural circulation.
The proposed concept includes multi-phase reactants, phase changes, and a multi-step
endothermic reaction or decomposition. This is done to optimize the heat absorption
capability of the PERCS concept. The passive reactor coolant system should have the
capacity to absorb heat for 31 days, after-which the core can be safely air-cooled.
Methodology
The initial portion this project was to search for possible reactions and study them
further. I began by looking through peer-reviewed papers to find endothermic reactions
and storing each reaction in a database. After finding reactions, the density and melting
point temperatures for each compound were found. With this information, the total
possible amount of heat (heat of reaction/decomposition) which the reaction could
absorb was calculated using:
Where ΔHj is the change in enthalpy given in kJ/mol, ν is stoichiometric coefficient, and
Hj are the heats of formation. With this collected data and the calculated possible
energy absorbed, the necessary volume to store enough reactant to cool a nuclear
reactor for 31 days was calculated. From these values, the energy density was also calculated. A toxicity report was also completed for each reaction chemicals before and after the reaction.
Results
During this part of the project seventy endothermic reactions were explored and studied. Of these, the most promising reactions to date include the decomposition of NiS04, MgCO3, CoSO4, and CuSO4. These reactions have a heat removal capacity of 10.6 GJ/m3, 5.8 GJ/m3, 5.8 GJ/m3, and 5.6 GJ/m3 respectively. For reference passive water boiling cooling systems have a heat removal capacity of 2.5 GJ/m3. Of these four endothermic decompositions, MgCO3 has the safest reactant and products, producing MgO and CO2 after decomposing.
Discussion
Future work will explore the potential for a PERCS concept to remove heat in short-term and long-term cooling applications. If the PERCS proves capable of removing short and long term decay heat, this increasingly passive system will dramatically increase the safety and mitigate the consequences of system blackouts and nuclear power plants will be much safer and have a significantly lower potential for public and environmental exposure.
Conclusion
I presented this research in an oral presentation at the International Congress on Advances in Nuclear Power Plants (ICAPP) April 2016 meeting. At this conference academic researchers and industry leaders meet to discuss and present the future of nuclear power plants safety and technology. This project has great potential and work is currently underway to model and design this system.