Nuclear Hydrogen and Heat Application Research

9-1

Small Nuclear Reactor for Multiple Heat Applications with Attractive Safety Features－ Conceptual Design of Small High-Temperature Gas Cooled Reactor for Developing Countries －Design targets and results
Design items

Design target

Criteria

Reduce the number of uranium
enrichments①Core②Component

Other design results
Results

Feasibility3○< 6 (HTTR: 12)

Design items

Results

Thermal power

50 MW

Reactor inlet
temperature

325 ℃

Reactor outlet
temperature

750 ℃,
900 ℃※

Increase core power density

3.5 MW/m 3 (HTTR: 2.5 MW/m3)

3.5 MW/ m3○

Increase refueling interval

730 d (HTTR: 660 d)

730 d

○

Increase thermal duty of IHX

20 MW (HTTR: 10 MW)

20 MW

○

0 MW〜25 MW○

Demonstration test canbe performed using IHX○Primary pressure

4 MPa

Biological shielding concrete temp. at normal operation: <65 ℃

64.8 ℃○

Satisfy the acceptance criteria for accidents in safety analysis

Mn-Mosteel

All criteria are satisfied○

Reactor pressure
vessel material③SystemSatisfy the user requirements formultiple heat applications④Safety

Design of the engineered safety
features of the residual heat removal
system (i.e., VCS) as passive methods

Heat supply for district heating network: 0 MW〜25 MW(50% partial load operation of steam turbine)
Demonstration test of gas turbine electricity generation andhydrogen production can be performed※ demonstration of the gas turbine andhydrogen production

Example of system configuration①Core design
The core performance is enhanced by
the optimization of the fuel temperature
distribution, which is obtained by
optimizing the layout of the different
enrichment fuels and burnable poisonsin the core.
④Safety design
The engineered safety feature of theresidual heat removal system (i.e., VCS)
is designed as passive methods. The
heat removal performance is ensured bynatural circulation of the cooling waterowing to the decrease in the pressure
loss, a component layout that increases
the water head, etc.

Vessel cooling system (VCS)

ReactorIntermediate heat exchanger (IHX)

Steam turbine

Steamgenerator(SG)

Hydrogen production,
Gas turbine

Electricity
generation

Districtheating②Component design
In the IHX design, the thermal duty isincreased to twice (i.e., 20 MW) that ofHTTR, ensuring the strength of the heattransfer tube for its own weight.

③System design
The various system configurations aredesigned by applying heat utilization incascade (i.e., installation of IHX and SG inserial, steam extraction from steam turbine,etc.) to satisfy the user requirements.

Fig.9-2 Design targets and results of small HTGR system design
The conceptual design of a 50 MWt small HTGR system was completed. It can satisfy the user requirements for multiple heatapplications, and its performance is superior to that of the HTTR. The technical feasibility was confirmed by the results of the core,component, and system design, and a safety analysis in the event of representative accidents.

We tested the High-Temperature engineering Test Reactor(HTTR) to establish the high-temperature gas cooled reactor(HTGR) fundamental technologies and to obtain the datarequired for commercial HTGR design. Since 2010, we also
developed the conceptual design for a 50 MWt small HTGR
system that can satisfy the user requirements, aiming atconstruction of a demonstration plant in a developing country
in the 2020s. Its performance was improved over that of theHTTR without significant research and development, using theknowledge obtained from HTTR design and operation (Fig.9-2).
In the core design, the number of uranium enrichments wasreduced to three (i.e., one-quarter that of the HTTR), and theaverage core power density was increased to 3.5 MW/m3 (i.e.,
1.4 times that of the HTTR), satisfying the maximum fueltemperature criterion throughout the burnup period of 730 d.
In the component design, the thermal duty of the intermediate
heat exchanger (IHX) was increased to twice (i.e., 20 MW)

that of the HTTR; the strength of the heat transfer tube for its
own weight was ensured by increasing the tube diameter todecrease the stress and by increasing the flow rate to increase
the heat transfer performance. The system configurations weredetermined so as to use the nuclear heat for district heating
and process heat based on a steam turbine system, and todemonstrate a helium gas turbine and hydrogen production tosatisfy the user requirements. In the safety design, the residual
heat removal system (the vessel cooling system) was designed
as a passive system. The safety was confirmed by a safety
analysis of representative accidents.
The Republic of Kazakhstan initiated a development
program for the nuclear industry in that country in June 2011,
which includes a construction plan for the Kazakhstan hightemperature gas-cooled reactor (KHTR) based on this small
HTGR system.

Reference
Ohashi, H. et al., Conceptual Design of Small-Sized HTGR System (IV) −Plant Design and Technical Feasibility−, JAEA-Technology 2013-016, 2013, 176p.
(in Japanese).

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JAEA R&D Review 2013