Current status and technical description of Chinese 210 MWe HTR-PM

Feb 2009 status of China’s High Temperature modular pebble bed reactor project ( 8 page pdf) by Zhang

The expected project construction period from pouring the first tank of concrete to generating electricity for the grid is scheduled to be 50 months. Although the workload of building, construction and installation is relatively clear and straight forward, the project schedule, nevertheless, leaves certain time margins allowing for possible uncertainties. The current plan aims for feeding electricity to the national power grid in 2013

Current status and technical description of Chinese 2×250MWth HTR-PM demonstration plant

The HTR-PM plant will consist of two nuclear steam supply system(NSSS), so called modules, each one comprising of a single zone 250MWth pebble-bed modular reactor and a steam generator. The two NSSS modules feed one steam turbine and generate an electric power of 210MW. A pilot fuel production line will be built to fabricate 300,000 pebble fuel elements per year. This line is closely based on the technology of the HTR-10 fuel production line.

The main goals of the project are two-fold. Firstly, the economic competitiveness of commercial HTRPM plants shall be demonstrated. Secondly, it shall be shown that HTR-PM plants do not need accident management procedures and will not require any need for offsite emergency measures. According to the current schedule of the project the completion date of the demonstration plant will be around2013. The reactor site has been evaluatedand approved; the procurementof long-lead components has already been started.

After the successful operation of the demonstration plant, commercial HTR-PM plants are expected to be built at the same site. These plants will comprise many NSSS modules and, correspondingly, a larger turbine.

The spherical fuel element with a diameter of 60mm contains a multitude of ceramic coated particles. The coated fuel particles are uniformly embedded in a graphite matrix of 50mm in diameter; while an outer fuel-free zone of pure graphite surrounds the spherical fuel zone for reasons of mechanical and chemical protection. Each spherical fuel element contains about 12,000 coated fuel particles. A coated fuel particle with a diameter of nearly 1.0mm is composed of a UO2 kernel of 0.5mmdiameter and three PyC layers and one SiC layer (TRISO). The heavy metal contained in each spherical fuel element is chosen to be 7.0 g. The design burn-up will be 90GWd/tU, while the maximum fuel burn-up will not be in excess of 100GWd/tU. In order to reach a fairly uniform distribution of fissile material throughout the whole core a “multi-pass” scheme of fuel circulation had been adopted.

Main technical goals of the HTR-PM project

The HTR-PM should achieve the following technical goals:
(1) Demonstration of inherent safety features: the inherent safety
features of modularHTGRpower plants guarantees and requires that under all conceivable accident scenarios the maximum fuel element temperatures will never surpass its design limit temperature without employing any dedicated and special emergency systems (e.g. core cooling systems or special shutdown systems, etc.). This ensures that accidents (e.g. similar to LWRs coremelting) are not possible so that not acceptable large releases of radioactive fission products into the environment will never occur.

(2) Demonstration of economic competitiveness: the first HTR-PM demonstration power plant will be supported by the Chinese government, so that the owner can always maintain the plant operation and obtain investment recovery. However, this government supported demonstration plant has to prove that a cost overrun during the construction period will be avoided and that the predicted smooth operation and performance will be
kept. Hence, the demonstration plant must clearly demonstrate that follow-on HTR-PM plants will be competitive to LWR plants without any government support.

(3) Confirmation of proven technologies: in order to minimize the technical risks the successful experiences gained fromthe HTR-10 and from other international HTGR plants will be fully utilized in the HTR-PM project. The HTR-PM reactor design is very similar to the HTR-10. The turbine plant design will use the mature technology of super-heated steam turbines which is widely used in other thermal power plants. Besides, the manufacture of fuel elements will be based on the technology verified and proven during the HTR-10 project. In addition, the key systems and equipments of the plant will be rigorously tested in large-scale experimental rigs in order to guarantee the safety and reliability of all components. Furthermore, international mature technologies and successful experiences will be absorbed through international technical consultations.

(4) Standardization and modularization: the HTR-PM demonstration plant, consisting of two pebble-bed module reactors of combined 2×250MWth power, adopts the operation mode of two modules connected to only one steam turbine/generator set. This design allows to demonstrate the advantages and key benefits of employing and implementing a design of standardization and modularization. If the construction and operation of the HTR-PM demonstration plant proves to be successful, larger scale HTR-PM plants – using multiple-modules feeding one steam turbine only – will become a reality.

The economics of the HTR-PM
According to our investigations and regarding specific costs (Zhang and Sun, 2007), there is no significant difference between an HTR-PM plant and a PWR plant when the costs of infrastructure, R&D, project management, etc. are effectively shared in a commercial-scale, multiple-module HTR-PM plant.Compared with PWRs, inherently safe HTR-PM plants exhibit smaller power density, in total heavier PRVs and core internals, and higher specific cost. The other components of a nuclear power plant, however, depend upon the power to be generated, and no significant difference exists between PWRs and an HTR-PM plant. The reactor pressure vessel and the costs of reactor internals of a PWRaccounts for only ∼2% of the total plant costs (including financial cost, from the practical data in Chinese PWR project, Zhang and Sun, 2007), so the cost increase from RPVs and reactor internals in HTR-PM has a limited impact. This limited impact will be compensated by simplification of the reactor auxiliary systems, the I&C and electrical systems, aswell as by the benefit of mass production for the conventional island equipments, RPVs and reactor internals. In addition, it is expected that the costs of an HTR-PM plant will be further decreased through reducing the workload of design and engineering management, shortening construction schedules and lessening financial costs by making use of modularization.

In summing up it is expected that modular HTGR power plants will show to be economically competitive with PWRs due to the following reasons:
(1) simple systems;

(2) high operation temperature and the use of a high-pressure super-heated steam turbine-generator; this is similar to normal fossil power plants. Hence, amuchhigher thermal efficiency can be realized;

(3) multiple-module reactors coupled to one steam turbine generator, sharing common auxiliary systems, and further reducing the costs through modularization and standardization for manufacture and construction;

(4) the operation mode of on-line continuous fueling will improve
the availability of the power plant;
(5) the design burn-up of the fuel is expected to reach at least 100GWd/t or even more; this will reduce the fuel cycle costs. From our current knowledge and for Chinese market conditions we estimate the necessary budget excluding R&D and infrastructure costs for the first HTR-PM demonstration plant to be about 2000USD/kWe.

Of course, all these claims, drawn from our year-long analysis, must clearly be verified in detail. By successfully operating the HTRPM in the very near future we are confident to reach these our claims.

Fourth Generation Reactor Next

The HTR-PM project will establish the technical foundations to be able to realize Generation-IV nuclear energy system goals in the next stage, such as:
(1) Largely enhanced safety features: a successful HTR-PM will have already proven this technical target of Generation-IV nuclear energy systems.

(2) Achieving outlet temperatures beyond 1000 ◦C [very hightemperature gas-cooled reactor (VHTR)]: the reactor of current design and using current fuel element technologies has already the potential of realizing a gas outlet temperature of 950 ◦C. A further improvement of the fuel element performance is already foreseeable which will allow reaching this goal of attaining an outlet-temperature of 1000 ◦C.

(3) Hydrogen production, use of helium turbine or supercritical steam turbine: the current reactor design, verified by the HTR-PM, can readily be applied for the helium turbine or super-critical steam turbine or for the generation of large-scale production of hydrogen by nuclear energy.

HTGR plants can achieve a thermal efficiency of 42% by even employing subcritical superheated steam turbines or reaching ∼45% when supercritical steam turbines are installed. The efficiency could be improved even further when adopting direct helium gas turbines with recuperators or when choosing a combined cycle.

On the basis of the HTR-10, the ongoing Chinese HTR-PM project is considered to be a decisive new step for the development of Chinese HTGR technology. Its main target is to finish building a pebble-bed HTR-PM demonstration plant of 210MWe around 2013. Through the mutual efforts of all relevant scientific research organizations nd industrial enterprises, and having the strong support of the Chinese government, the HTR-PM project will certainly play an important role in the world-wide development of Generation-IV nuclear energy technologies.

A presentation on buying and building six packs of these pebble bed reactors.