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Research Papers: Nuclear Power

# Advanced High Temperature Gas-Cooled Reactor Systems

[+] Author and Article Information
Yasuyoshi Kato1

Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 2-12-1-N1-2, O-okayama, Meguro-ku, Tokyo 152-8550, Japan

1

Present address: MCX Institute, 2-5-10-105, O-okayama, Meguro-ku, Tokyo 152-0033, Japan.

J. Eng. Gas Turbines Power 132(1), 012902 (Oct 01, 2009) (7 pages) doi:10.1115/1.3098416 History: Received November 06, 2008; Revised November 06, 2008; Published October 01, 2009

## Abstract

Three systems have been proposed for advanced high-temperature gas-cooled reactors: a supercritical carbon dioxide $(S-CO2)$ gas turbine power conversion system, a new microchannel heat exchanger (MCHE), and a once-through-then-out (OTTO) refueling scheme with burnable poison (BP) loading. A $S-CO2$ gas turbine cycle attains higher cycle efficiency than a He gas turbine cycle because of reduced compression work around the critical point of $CO2$. Considering temperature reduction at the turbine inlet by $30°C$ through intermediate heat exchange, the $S-CO2$ indirect cycle achieves an efficiency of 53.8% at a turbine inlet temperature of $820°C$ and a turbine inlet pressure of 20 MPa. This cycle efficiency value is higher by 4.5% than that (49.3%) of a He direct cycle at a turbine inlet temperature of $850°C$ and 7 MPa. A new MCHE has been proposed as an intermediate heat exchanger between the primary cooling He loop and the secondary $S-CO2$ gas turbine power conversion system and as recuperators of the $S-CO2$ gas turbine power conversion system. This MCHE has discontinuous “S-shaped” fins providing flow channels resembling sine curves. Its pressure drop is one-sixth that of a conventional MCHE with a zigzag flow channel configuration, but it has the same high heat transfer performance. The pressure drop reduction is ascribed to suppression of recirculation flows and eddies that appear around bend corners of the zigzag flow channels in the conventional MCHE. An optimal BP loading in an OTTO refueling scheme eliminates the shortcoming of its excessively high axial power peaking factor, reducing the power peaking factor from 4.44 to about 1.7, and inheriting advantages over the multipass scheme because it obviates reloading in addition to fuel handling and integrity checking systems. Because of the power peaking factor reduction, the maximum fuel temperatures are lower than the maximum permissible values of $1250°C$ for normal operation and $1600°C$ during a depressurization accident.

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## Figures

Figure 1

Partial precooling cycle configuration

Figure 2

Cycle efficiencies of S-CO2 cycle and He cycle in the one-intercooler system

Figure 3

Conventional zigzag model

Figure 4

Zigzag model in three dimensions

Figure 5

Swirl flows, eddies, and recirculation flows in a bent pipe. (From Japan Society of Mechanical Engineers, “JSME Data Book, Hydraulic Losses in Pipes and Ducts,” Maruzen Co. Ltd., Tokyo, Japan, Fig. 4.74, p. 80.)

Figure 6

Velocity distributions

Figure 7

Heat transfer rate versus pressure drop. Pressure drop per unit length, ΔP, heat transfer rate per unit volume, Q/V, are calculated as ΔP=(Pin-Pout)/Lx, Q/V=Q/(Lx×Ly×Lz).

Figure 8

Unit cell lattice model in the MVP code

Figure 9

Contour lines of initial k∞ and reactivity swing

Figure 10

k∞ change with burnup at the optimal radius and number BP particles

Figure 11

Radial x-section of the pebble bed HTGR core

Figure 12

OTTO refueling model

Figure 13

Axial power distribution in the channel where power peaking appears

Figure 14

Maximum fuel temperature in normal operation

Figure 15

Maximum fuel temperature at depressurization accident

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