Nuclear renewable hybrid energy system assessment through the thermal storage system

Abstract

Summary In support of the use of more efficient and low‐carbon nuclear energy along with solar energy in power generation systems, the present paper presents a technical‐economic analysis of a nuclear renewable hybrid energy system (NR‐HES) case study for a given electricity and residential heat demand profiles of a typical remote community in Canada. The studied hybrid energy system is composed of a small modular nuclear reactor (SMR), a concentrated solar tower (CST), and a thermal energy storage (TES) unit. A fossil fuel backup energy source is also considered to generate excess electricity as needed. The CST and nuclear reactor both share the same TES system. Five different thermal storage fluids are examined: Therminol, Dowtherm, solar salt, Hitec salt, and Hitec XL salt. A transient thermodynamic mathematical model is developed in order to determine the overall configuration, performance, and operation strategy for the NR‐HES. The operational strategy of the NR‐HES is based on the steady‐state full‐power operation of the SMR, storing the excess energy in the TES system when the combined nuclear and solar power generation exceeds the power demand of the electrical grid and using the stored thermal energy during the periods of peak demand A detailed economic analysis of the NR‐HES is conducted for each operational scenario, including the annualized cost of the TES system and the NR‐HES plant, as well as annual revenue and profit generated by the TES system. The developed model is used to obtain the most economical thermal storage fluid and to optimize the size of TES system in order to minimize the use of fossil fuels and maximize profit. Parametric studies of reactor thermal power and CST's field area are conducted to determine their effect on the performance and configuration of the NR‐HES. Based on the current case study in terms of demand profiles, the results revealed that Therminol is the most economical thermal storage fluid for the present NR‐HES with a charging capacity and round‐trip storage efficiency of 237 268 MWh/year and 96%, respectively. The optimum Therminol storage tank size is evaluated to be 14 m in height and 10 m in diameter with a yearly average power cycle efficiency of ~36% and economic profit of 1 158 30 CAD/year. The parametric studies indicated that a larger TES size may decrease the usage of fossil fuel energy sources; however, it increases system total capital cost and decreases the power cycle efficiency and TES profit at given load. The results of this study indicate that an NR‐HES is a promising low‐carbon power generation system with the potential to meet the electricity and residential heat demand of remote communities.

Molten salts: Potential candidates for thermal energy storage applications

“…Due to the high operating temperatures of solar salts, they cannot be used with light‐water reactors since they tend to solidify during off‐hours. Hence, there is a requirement for a material that is already a liquid at the reactor coolant temperature—this brings us back to synthetic HTFs like Therminol 122 and a mixture of C 14 and C 30 alkyl benzenes, also known as Dowtherm 123 . For light‐water nuclear reactors, these fluids are preferred over molten salts and alumina, whereas for MHTGR, both molten salts and pebbled alumina can be used.…”

“…Li et al 158 used SiO 2 particles with a binary molten salt mixture (53 wt% KNO 3 + 47 wt% Ca(NO 3 ) 2 ·4H 2 O) and found that doping the salt mixture with 1 wt% of 20 nm SiO 2 brought about an increase of 17.8% in specific heat (from 1.7 to 1.94 J/g K). When LiNaKCa nitrate was doped with 0.5 wt% SiO 2 , an increase of 24.48% was observed in the salt's heat capacity 123 . The majority of the studies done to enhance the specific heat capacity of different molten salts are summarized in Table 9.…”

“…Recently, nuclear energy researchers have claimed success in consolidating a list of operations and functions that can together be called NHES. 123 NHES is defined as an arrangement consisting of a nuclear power generator (the generator), heat appliance that utilizes the heat generated, an energy source, and finally a molten salt energy storage unit (due to the molten salt's low viscosity and high melting point and volumetric heat capacity). 124 The molten salt ESS can further be broken down into two components:…”

“…When LiNaKCa nitrate was doped with 0.5 wt% SiO 2 , an increase of 24.48% was observed in the salt's heat capacity. 123 The majority of the studies done to enhance the specific heat capacity of different molten salts are summarized in Table 9. Moreover, inclusion of nanofluids in molten salts can have an impact on the corrosion of the metallic pipes (as discussed in Section 8), thus, the main challenge in using molten salts is to simultaneously increase their thermophysical properties while keeping the cost of the system low.…”

Small modular reactors for nuclear‐renewable synergies: Prospects and impediments

“…An overview on the opportunities of nuclear‐renewable hybridization was provided by Ruth et al 3 Their paper explored the concept and its value toward achieving higher grid flexibility and reduced greenhouse gas emissions. Bayomy and Moore 4 studied an integrated SMR with a concentrated solar tower and a thermal energy storage as a case study for Canada. Cho and Yim 5 investigated the feasibility of a case study on the use of nuclear in hybridization with high solar penetration in Korea.…”