(599e) High Temperature Heat Exchanger and Component Test Laboratory -- a Graded Approach

The Next Generation Nuclear Plant (NGNP) is envisioned as consisting of a high-temperature helium-cooled nuclear reactor, gas-driven or steam-driven electrical generators, and one or more hydrogen production plants. The nuclear plant will be designed to operate with a gas outlet temperature of up to 950°C and would operate at a pressure of up to 9 MPa. The hydrogen production plants would use high-temperature thermal energy from the nuclear reactor and alternative thermochemical, electrochemical, or hybrid processes to increase the efficiency of the hydrogen production process over that of liquid water electrolysis. A necessary component in this plant is the System Interface, the network of heat exchangers and heat transfer loops that would transmit thermal energy from the nuclear plant to the hydrogen plants. The NGNP Project is underway at this time, and an NGNP is expected to be operational in the United States by the 2018-2021 timeframe.

At the present time, there is no readily accessible laboratory in the U.S. for operating at the high temperatures, pressures, and flow conditions needed to test components for the NGNP System Interface. At the lab scale, the capabilities needed to perform high temperature heat exchanger testing are not unique, and a dedicated testing laboratory could be established, with some investment, at almost any university or national laboratory. At the pilot scale, the facility needs are more stringent due to size and power requirements, and the locations where such work could be carried out are more restricted.

Pressure testing and leak testing are needed at high temperature and high pressure to discover the potential for external leaks or cross-contamination between the hot and cold sides of a heat exchanger. Flow testing is needed to determine component friction factors and pressure drop. For heat exchangers, overall heat transfer coefficients are measured under specific fluid flow conditions. Such data are needed in order to advance heat exchanger and component concepts and to scale-up designs to larger sizes and power requirements.

A reduced cost approach to obtaining data at the laboratory-scale is described. Initial pressure testing is performed using water or high pressure air. If leak rates are needed, the component is placed into a kiln or furnace to create a controlled high temperature environment and pressure decay testing is performed in order to isolate and determine external and internal leak rates. A once-through heated flow path is used to create controlled fluid conditions, and inlet and outlet flow conditions are measured to determine pressure drop and friction factors. Air or steam are substituted as the fluid of choice because of their low cost in comparison to helium, and the concept of similitude is used in the selection of fluid conditions in an effort to approach the expected flow conditions in a high-temperature high-pressure helium environment. For heat exchanger testing, two once-through flow paths are used to independently control the flow conditions on each side of the heat exchanger, and fluid flow data at the inlets and outlets of the heat exchanger are used to determine overall heat exchanger coefficients.

At somewhat greater cost, laboratory-scale and larger-scale closed helium loops could be established in order to create the fluid flow conditions that would be experienced in the NGNP that would still allow for the collection of detailed data under controlled fluid flow conditions. Concepts for closed helium loops are presented that could be realized using commercially available components.