There are three areas where engineering-based assessments are being conducted. These are (1) evaluating A-SMRs in a load-following hybrid energy system (HES) architecture, (2) collecting fundamental data on sodium to carbon dioxide (CO2) heat

exchangers, and (3) demonstrating the operation of supercritical CO2 (S-CO2) power conversion system (PCS) to match with A-SMRs providing enhanced conversion efficiencies up to 50%.

Initial assessments are being conducted of A-SMR concepts for an SFR, HTGR, and FHR in load-following HES architectures to analyze A-SMR performance characteristics and reactor dynamic operations. The hybrid operation will focus on integration of these A-SMR concepts with wind power. The SFR concept is to be studied in an HES configuration to produce electric power, methanol, and hydrogen. The aforementioned supercritical CO2 PCS is being included as part of some of the HES analyses.

SFR designs will likely have intermediate heat exchangers. To reliably design sodium heat exchangers, fundamental data are needed on the draining of sodium from heat exchanger channels to understand the potential stresses resulting from inadvertent freezing and remelting. Sodium drain and fill test designs shall provide a means to experimentally verify that the heat exchanger sodium channel configuration and orientation provides for efficient draining and subsequent refill of sodium. Inadvertent freezing and thawing of sodium is known to have caused failure of specific sodium components.

DOE-NE’s A-SMR is leveraging work conducted by Sandia National Laboratory over the past several years to further develop and demonstrate its S-CO2 PCS. This is also a program that has been supported by DOE-NE’s ARC program as well. A 1 MW S-CO2 Brayton cycle test assembly has been developed and is undergoing testing [11]. The split-flow recompression loop test assembly as presented in Figure 14.7 is the focus and provides the basis for conducting R&D under the ART R&D program for extrapolating the performance of the 10 MWe system.

The current scope of work under the ART program is to develop the engineering basis for such a system that will lead to a 10 MWe system design, including achieving the pressure and temperature design points. Performance studies are planned to

High temp
Printed circuit heat

exchanger recuperator 2.2 MW Low temp Printed circuit heat exchanger recuperator 1.6 MW

Printed circuit heat
exchanger
gas precooler

0.5 MW

Electrical immersion

heaters 130 kW each,
ASME 810K/1000F
Ш 2600 psia (18 MPa)

Turbo-alternator-compressor
re-compressor, 122 kWe

Turbo-alternator-compressor main compressor, 124 kWe

Figure 14.7 Sandia S-CO2 Brayton test assembly [11].

examine options for pressure ratios, turbine inlet temperature, compressor inlet temperature, and mass loading.

As the technology develops for the S-CO2 Brayton cycle as an advanced PCS technology, issues have been identified with heat exchangers due to cost for compact printed circuit heat exchangers and possible high-temperature corrosion of diffusion bonded stainless steel under stress. A testing program is also being developed to examine the corrosion of stainless steels under stress at 550 °C.