2
1 Introduction
(INET) at Tsinghua University in China. The HTR-10 is among the few test reactors of high-temperature reactor over the world [15–18]. HTGRs are being deployed
very rapidly and are intended to be commercialized for large-scale applications in
the near future. The High-Temperature Reactor-Pebble bed Modules (HTR-PM) was
approved as one of the national major science-technology projects of China [19]. The
HTR-PM is under construction in Shandong Province of China.
1.1.2 Main Features and Advantages
Helium-cooled pebble bed in the high-temperature gas-cooled reactor (HTGR) has
the structure of packed sphere fuel balls in the reactor core. In contrast to conventional
reactors, there are no structured fuel assemblies in a pebble-bed HTGR. The HTGR
configures the core with a packed pebble bed composed of randomly and densely
packed mono-sized spherical pebbles. The HTGR core is cooled by helium gas
under high pressure, e.g., about 7 MPa for the HTR-PM nuclear reactor [20, 21].
The fuel element of high-temperature gas-cooled reactor is made by dispersing allceramic coated particles in a graphite sphere matrix, which can maintain integrity
up to 1600
◦ C [18]. Pebbles traverse the core under gravity and their positions are
determined by the flow of the pebble bed. Pebble-bed HTGR runs in a recirculating
mode. Pebble elements are drained out from the discharge hole at the base of the core,
whereas new elements are reinserted into the core at the top. When the pebble bed
achieves an equilibrium state, the total number of pebbles in the core is approximately
constant.
The pebble-bed high-temperature gas-cooled reactor meets all kinds of requirements of the generation IV advanced reactor system. One of the most outstanding
advantages of the pebble-bed high-temperature gas-cooled reactor is its inherent
safety. Other advantages, such as modularity, short construction period, non-stop
reloading [8, 9], market flexibility, and broad applications such as high-temperature
process heat, are also significant compared with current operating Generation II and
Generation III reactors. Hence, the pebble-bed HTGR has drawn great public attention and it is generally recognized as the most promising reactor type in the USA,
and even in the world in this century. The pebble-bed reactor is becoming the mainstream technical solution for HTGRs. In 2006, China included the high-temperature
gas-cooled reactor project in the Outline of the National Medium- and Long-term
Science and Technology Development Plan (2006–2020).
1.2 Pebble Bed Type HTGR in Tsinghua University
The HTGR has been studied for decades at the INET of Tsinghua University in
China, for exploring and developing modular HTGR technology. For pebble-bed
HTGR reactor, the core is filled with large quantities of mono-sized large pebbles
1 Introduction
(INET) at Tsinghua University in China. The HTR-10 is among the few test reactors of high-temperature reactor over the world [15–18]. HTGRs are being deployed
very rapidly and are intended to be commercialized for large-scale applications in
the near future. The High-Temperature Reactor-Pebble bed Modules (HTR-PM) was
approved as one of the national major science-technology projects of China [19]. The
HTR-PM is under construction in Shandong Province of China.
1.1.2 Main Features and Advantages
Helium-cooled pebble bed in the high-temperature gas-cooled reactor (HTGR) has
the structure of packed sphere fuel balls in the reactor core. In contrast to conventional
reactors, there are no structured fuel assemblies in a pebble-bed HTGR. The HTGR
configures the core with a packed pebble bed composed of randomly and densely
packed mono-sized spherical pebbles. The HTGR core is cooled by helium gas
under high pressure, e.g., about 7 MPa for the HTR-PM nuclear reactor [20, 21].
The fuel element of high-temperature gas-cooled reactor is made by dispersing allceramic coated particles in a graphite sphere matrix, which can maintain integrity
up to 1600
◦ C [18]. Pebbles traverse the core under gravity and their positions are
determined by the flow of the pebble bed. Pebble-bed HTGR runs in a recirculating
mode. Pebble elements are drained out from the discharge hole at the base of the core,
whereas new elements are reinserted into the core at the top. When the pebble bed
achieves an equilibrium state, the total number of pebbles in the core is approximately
constant.
The pebble-bed high-temperature gas-cooled reactor meets all kinds of requirements of the generation IV advanced reactor system. One of the most outstanding
advantages of the pebble-bed high-temperature gas-cooled reactor is its inherent
safety. Other advantages, such as modularity, short construction period, non-stop
reloading [8, 9], market flexibility, and broad applications such as high-temperature
process heat, are also significant compared with current operating Generation II and
Generation III reactors. Hence, the pebble-bed HTGR has drawn great public attention and it is generally recognized as the most promising reactor type in the USA,
and even in the world in this century. The pebble-bed reactor is becoming the mainstream technical solution for HTGRs. In 2006, China included the high-temperature
gas-cooled reactor project in the Outline of the National Medium- and Long-term
Science and Technology Development Plan (2006–2020).
1.2 Pebble Bed Type HTGR in Tsinghua University
The HTGR has been studied for decades at the INET of Tsinghua University in
China, for exploring and developing modular HTGR technology. For pebble-bed
HTGR reactor, the core is filled with large quantities of mono-sized large pebbles