Nuclear Plant Journal, May-June 2014 NuclearPlantJournal.com
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6.
What are the plans to repair possible
problems within the pressurizer, and
other equipment and instruments within
the RPV?
SC-HTGR does not have a
pressurizer. All major components (core
barrel, core support structure, permanent
graphite reflector, steam generator,
etc.) are designed for the plant lifetime.
Nonetheless, all components within the
primary coolant vessels are replaceable, if
necessary. Steam generator performance
in gas-cooled reactors has historically
been very good. If necessary, individual
tubes can be plugged easily. The entire
steam generator can also be replaced,
although this is not expected to be
necessary. Helium circulators will be
removed and replaced periodically for
routine refurbishment.
7.
How long can the reactor keep
operating without:
Off-site power supply?
Cooling water supply?
Off-site power supply
:
Offsite power supply is not an issue
for normal reactor operation.
For accident response, off-site power
is never required. No electrical power is
required for heat removal or for activation
of any safety systems. Limited on-
site electrical power is needed only for
accident monitoring, in order to inform
regulators and to provide data necessary
to approve plant restart.
Cooling water supply
:
During normal reactor operation,
cooling water is used for normal heat
rejection from the condenser as in any
other thermal power plant.
For accident response, the reactor
can go seven days before replenishment
of cooling water in the Reactor Cavity
Cooling System (RCCS) is needed.
Going beyond seven days without adding
water could result in equipment damage,
making plant restart questionable. But
public safety would still be maintained.
8.
Are there provisions to bring external
portable connections for insuring water
supply and electric connection for
cooling in case of a Beyond Design Basis
Event (BDBE) ?
No electrical connections are needed
for safety (connections will be provided
for monitoring).
No water makeup is required for
safety for Beyond Design Basis Event
(BDBE). Nonetheless, provisions are
available for replenishing the RCCS.
9.
What enhancements have been
made to the NGNP’s HTGR design after
Fukushima?
No enhancements were necessary.
SC-HTGRs can withstand extended
power outages. The passive and intrinsic
safety of the plant will maintained by the
initial design.
The plant will be designed to
withstand the local maximum expected
seismic activity and any other external
effects (tsunami, tornado, etc.).
10.
Provide the capacity for different
applications
including
hydrogen
generation, electricity generation and
district heating for a NGNP’s HTGR
reactor?
The reference 625MWt modular
SC-HTGR selected by the Alliance for
initial commercialization operates at a
conservative reactor outlet temperature of
750°Cproducingsteamat16.7MPa/566°C
comparable to modern fossil boilers and
gas-turbine combined cycle power plants.
Combined with safety characteristics
that allow close-in siting, the HTGR can
serve a range of applications similar to its
fossil counterparts, including electricity
generation, process steam and medium-
range thermal energy for industrial
applications
(e.g.,
petrochemical,
heavy oil and bitumen recovery from
oil sands via steam injection, as well as
lower temperature applications such as
desalination and district heating). With
its higher-temperature capability and
efficiency, the HTGR is particularly
adaptable to site conditions requiring dry
cooling.
In the future, very high temperature
versions of the HTGR with increased out-
let temperatures around 950°C will be ap-
plied to more advanced applications (e.g.,
direct hydrogen production via thermo-
chemical water splitting and direct heat
supply to high temperature chemical pro-
cesses such as ethylene cracking). The
HTGR coated particle fuel system has al-
ready been demonstrated to be viable for
such operating temperatures in test reac-
tors. However, further advances will be
necessary related to available materials
for heat exchangers to transfer the ther-
mal energy from the HTGR to the appli-
cation process. Initial commercialization
of the SC-HTGR will greatly facilitate
the evolution to these future advanced
systems.
11
What is the design life of the plant 60
years or 80 years?
The present design basis for the mod-
ular HTGR is 60 years, which is consis-
tent with both investment guidelines and
the available design basis for materials
that operate above the time-independent
temperature regime. With appropriate
reevaluation and/or replacement of a lim-
ited number of high-temperature internal
components, extended lifetimes beyond
60 years should be possible. Neutron ir-
radiation effects on the primary pressure
boundary components are typically lower
in HTGRs. The plant’s non replaceable
components (RPV) are made from cur-
rent pressurized water reactor (PWR) re-
actor vessel materials. So subsequent life
extension work underway for PWRs will
be used to support 80 year life. All inter-
nal components are replaceable.
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