1.2 Pebble Bed Type HTGR in Tsinghua University
5
1.2.1 Competative Technical Routes
The main technical goals of the HTR-PM project are as follows: demonstration of
inherent safety; demonstration of economic competitiveness; confirmation of proven
technologies; standardization and modularization [23]. In severe accidents, e.g., a
loss-of-coolant and depressurized accident under full-power operation, the core temperature will increase above its normal operation core temperature transiently. The
inherent safety requires that the maximum fuel element temperatures should always
be lower than the limiting temperature of 1600
◦ C. If this criterion is met, no core
melting occurs, and no dedicated emergency systems are necessary when all conceivable accidents occur [19, 23].
There are two critical measures to improve the economy of HTR-PM by increasing the outlet temperature to 1000
◦ C and configuring a 458 MWth reactor with
a two-zone annular core as an optimization design [19, 24]. The inherent safety
depends on the robust thermal-hydraulic design of reactor at normal operation and
extreme emergencies. The robust design validates the desirable characteristics of the
generation IV nuclear power system such as inherent safety features and capability
to provide a high-temperature.
In the present design, the helium temperatures at reactor core inlet/outlet are
250
◦ C/750
◦ C, and the produced steam state in the steam generator outlet is 13.25
MPa/567
◦ C. The most crucial issue from a commercial perspective is the economic
competitiveness, compared with the light water reactors (LWRs), which are the primary reactors in the world. According to the cost comparison, the present HTR-PM
is 10–20% more expensive than PWR at the same electric power if the current HTRPM parameters are employed [25]. The current HTR-PM reactor and fuel element
technologies have the potential of achieving 950
◦ C to even 1000
◦ C in helium outlet
temperature. This a typical temperature produced by Very High-Temperature gascooled Reactor (VHTR). The improved temperature will enhance the efficiency and
power of electricity generating and make HTR-PM more competitive in economy
cost. Moreover, a single reactor with a significant thermal power can also be designed
to enhance its economic competitiveness while the inherent safety can be reserved.
1.2.2 Heat Transfer Investigations
As stated above, the inherent safety of HTGR at a higher power level, meaning
better economic competitiveness compared with other reactors, requires a distinct
knowledge on effective thermal diffusivity and conductivity of pebble bed at hightemperature range. Especially, the effectivity thermal diffusivity will determine the
maximum transient temperature after the accident, and the effectivity thermal conductivity will determine the maximum steady-state temperature inside the reactor
core during the decay heat removal period. The pebble bed is represented as a porous
structure, and its heat transfer is a combination of solid heat conduction inside or
5
1.2.1 Competative Technical Routes
The main technical goals of the HTR-PM project are as follows: demonstration of
inherent safety; demonstration of economic competitiveness; confirmation of proven
technologies; standardization and modularization [23]. In severe accidents, e.g., a
loss-of-coolant and depressurized accident under full-power operation, the core temperature will increase above its normal operation core temperature transiently. The
inherent safety requires that the maximum fuel element temperatures should always
be lower than the limiting temperature of 1600
◦ C. If this criterion is met, no core
melting occurs, and no dedicated emergency systems are necessary when all conceivable accidents occur [19, 23].
There are two critical measures to improve the economy of HTR-PM by increasing the outlet temperature to 1000
◦ C and configuring a 458 MWth reactor with
a two-zone annular core as an optimization design [19, 24]. The inherent safety
depends on the robust thermal-hydraulic design of reactor at normal operation and
extreme emergencies. The robust design validates the desirable characteristics of the
generation IV nuclear power system such as inherent safety features and capability
to provide a high-temperature.
In the present design, the helium temperatures at reactor core inlet/outlet are
250
◦ C/750
◦ C, and the produced steam state in the steam generator outlet is 13.25
MPa/567
◦ C. The most crucial issue from a commercial perspective is the economic
competitiveness, compared with the light water reactors (LWRs), which are the primary reactors in the world. According to the cost comparison, the present HTR-PM
is 10–20% more expensive than PWR at the same electric power if the current HTRPM parameters are employed [25]. The current HTR-PM reactor and fuel element
technologies have the potential of achieving 950
◦ C to even 1000
◦ C in helium outlet
temperature. This a typical temperature produced by Very High-Temperature gascooled Reactor (VHTR). The improved temperature will enhance the efficiency and
power of electricity generating and make HTR-PM more competitive in economy
cost. Moreover, a single reactor with a significant thermal power can also be designed
to enhance its economic competitiveness while the inherent safety can be reserved.
1.2.2 Heat Transfer Investigations
As stated above, the inherent safety of HTGR at a higher power level, meaning
better economic competitiveness compared with other reactors, requires a distinct
knowledge on effective thermal diffusivity and conductivity of pebble bed at hightemperature range. Especially, the effectivity thermal diffusivity will determine the
maximum transient temperature after the accident, and the effectivity thermal conductivity will determine the maximum steady-state temperature inside the reactor
core during the decay heat removal period. The pebble bed is represented as a porous
structure, and its heat transfer is a combination of solid heat conduction inside or