Design Report for the ½ Scale Air-Cooled RCCS Tests in the Natural convection Shutdown heat removal Test Facility (NSTF)

Abstract

Facility (NSTF)one of the world's largest facilities for ex-vessel passive decay heat removal testing-confirms the performance of reactor cavity cooling systems (RCCS) and similar passive confinement or containment decay heat removal systems in modern Small Modular Reactors. Originally built to aid in the development of General Electric's Power Reactor Innovative Small Module (PRISM) Reactor Vessel Auxiliary Cooling System (RVACS), the NSTF has a long history of providing confirmatory data for the airside of the RVACS. Argonne National Laboratory's NSTF is a state-of-the-art, large-scale facility for evaluating performance capabilities of containment cooling systems, providing reactor designers with data to validate computer simulations. Many of these simulations employ advanced computational tools running on supercomputers at Argonne's Leadership Computing Facility, home to a world-class computing capability dedicated to breakthrough science and engineering.

An Overview of Non-LWR Vessel Cooling Systems for Passive Decay Heat Removal (Technical Letter Final Report)

“…The mesh convergence sensitivity study showed that the simulation results are highly dependent on the mesh refinement at the fluid-solid boundary, calling for very fine meshes near the reactor vessel surface due to the large temperature gradients at the wall. To examine the feasibility of an air-cooled RCCS option for advanced gas-cooled reactors, an experimental program was established at Argonne National Laboratory [58] in the early 2000s which revitalized the Natural convection Shutdown heat removal Test Facility (NSTF) built previously for RVACS testing in the 1980s. Compared to the legacy NSTF, the modern NSTF stood 26-m in total height and was designed to represent a 1:2 scale model of the primary features of the General Atomic (GA) RCCS design for the MHTGR [59].…”

“…To examine the feasibility of an air-cooled RCCS option for advanced gas-cooled reactors, an experimental program was established at Argonne National Laboratory [58] in the early 2000s which revitalized the Natural convection Shutdown heat removal Test Facility (NSTF) built previously for RVACS testing in the 1980s. Compared to the legacy NSTF, the modern NSTF stood 26-m in total height and was designed to represent a 1:2 scale model of the primary features of the General Atomic (GA) RCCS design for the MHTGR [59]. The test section contained twelve riser ducts and served as the primary flow area for cooling within the heated cavity, Figure 48.…”

“…Testing performed on the modern, air-based RCCS of the NSTF at Argonne examined system response and heat removal performance with blocked riser channels [58]. Their test began by establishing steady-state operating conditions at the normal operating heat load, which defined a full-scale load of 700 kWt, or 26.16 kWt in the test facility, scaled ½ axially from the full-scale RCCS design for the GA-MHTGR.…”

“…Studies performed with the modern air-based NSTF at Argonne also examined the effect of a chimney "short-circuit". In this scenario, a break occurs between adjacent ductwork that allows incoming cold air to by-pass the heated section and instead flows directly back into the exhaust stream [58]. For this test case, a variable damper valve was installed between adjacent ductwork, where one duct serves as the primary fresh air intake and the other as the exhaust discharge.…”

Experimental observations of natural circulation flow in the NSTF

“…Measurements of system mass flow rates, differential pressure drop, surface and gas temperatures, among others, are included in this suite. A summary is provided in Table 1, with additional details such as the heater configuration and insulation properties provided in earlier works by the authors [6,7]. While it is expected that thermal radiation will be the primary mode of heat transfer, the heated cavity (essentially an internal enclosed environment) allows natural circulation cells to develop and grow.…”