Overall Strategy for theTechnology Development as
the World's Leading Nuclear
Company
KIYOSHI YAMAUCHI* 1
KEIZO OKADA* 1

Mitsubishi Heavy Industries, Ltd. (MHI) has been the sole manufacturer of pressurized water reactors (PWRs) inJapan since the commencement of commercial operations of Mihama Unit 1 of the Kansai Electric Power Company in1970. Over these decades, MHI has endeavored to develop a broad spread of nuclear technology, from design, manufacturing, and construction to plant maintenance services. More recently, with the ever rising need for nuclear power
generation around the world to prevent global warming and to cope with surging oil prices, MHI is striving to expand
its nuclear power business in the world market, such as US-APWR in the U.S., as well as to develop technology foradvanced reactors and nuclear fuel cycles to ensure energy security in the future. This paper introduces these approaches and clarifies the current status and future prospects of MHI as the world's leading nuclear company.
based on earlier experiences (seven plants in the 1980s),
and the recent plants group based on further improvements
and developments to enhance economy, operability, andmaintainability (seven plants in the 1990s), see Fig. 1
1.
At present, Tomari Unit 3 (electric power: 912 MWe) of
Hokkaido Electric Power Company is under construction,
which has up-rated power, and enhanced operability andreliability by integrating all our brand-new technology.
Tsuruga Units 3 and 4 (electric power: each 1,538 MWe) ofJapan Atomic Power Company, the first units of the advanced PWR (APWR) are now being licensed. MHI iscommitted to the completion of these ongoing projects.
MHI has also been developing various inspection andmaintenance techniques for stable operation and enhanced
reliability to support utility companies, and these techniques greatly contribute to the enhancement of plantreliability through service activities.

1. Introduction
MHI has constructed 23 PWR plants in Japan andthrough the operation and maintenance of these plants,
has continued to develop and enhance the technology whichmeets the needs of utilities while ensuring a wide technical base as an all-round plant supplier. During this period,
through the three phases of the Improvement Standardization Program for Light Water Reactors with thecooperation of the government, utilities, and suppliers, MHI
has established domestic PWR technology and further enhanced plant safety, reliability, economy, operability, andmaintainability and accumulated our own technology.
These transitions are described from the initial plant groupconstructed using imported technology (nine plants in the
1970s), the next plant group constructed using MHI's own
technology, designed for enhanced reliability and safety
1970s

Imported
technology andlocalization
9 units
6 793 MWe

1980s

1990s

Reliability
Further improvements
improvements
based on operation of safety, reliability
and economy
experience
7 units
5 805 MWe

2020s

Commercial operation ofTomari Unit 3(2009)

7 units
6 768 MWe

Commercial operation of
Tsuruga Units 3 and 4First Second Third
Phase Phase Phase
Improvement Standardization
Program for Light Water
Reactors of the Ministryof International Trade andIndustry (current Ministry of
Economy, Trade and Industry)

2010s

2000s

APWR
Development andupgrading of APWR

Safety review
and construction

For foreign market

US-APWR
1000 MWe class plants
Fig. 1 Development of Mitsubishi PWR plant technology

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 4 (Dec. 2006)*1 Nuclear Energy Systems Headquarters

1

Number of shutdowns/ unit/ year

2.0

: Japan
: USA

1.8
1.6
1.4
1.2

1.2

1.3

1.6

Commercial operation of the plant is scheduled to commence in December 2009.
The first advanced PWR (APWR) applied in Tsuruga
Units 3 and 4 has been developed to achieve significant
improvements in economy and safety due to its large power
output and innovative technology for safety systems. The
development and validation was carried out mainly under
the Third Phase Improvement Standardization Programfor Light Water Reactors by the government, utilities, andsuppliers from 1981 to 1985, and the subsequent enhancement program by the utilities and MHI, from 1986.
Currently licensing is undergoing as one of the largest
plants in the world, with an electric power of 1,538 MWe.
Core design has been improved to stretch the core thermal power by increasing the number of fuel assemblies from
193, for a conventional 4-loop plant, to 257, thus power is
up-rated combined with the development of high-performance and large-capacity components such as steam
generators, and reactor coolant pumps. A compact and highperformance steam generator adopting 3/4-inch tubes andhigh-performance moisture separators, and a large-capacity, high-performance reactor coolant pump have beendeveloped for the APWR. The design of the reactor internal vessel has been improved by adopting a ring-block
neutron reflector to reduce the neutron dose to the vessel
to approximately one-third that of the baffle-former structure and significantly reducing the number of bolts usedin the core region.
For safety design, a 4-train mechanical system configuration has been adopted to enhance the redundancy of thesafety systems, and the low pressure injection system canbe eliminated by the adoption of advanced accumulatorswith a low pressure injection function using passive technology, enabling automatic switching of the injection flowrate during accidents. The high-pressure injection system
also can be simplified by adopting a direct vessel injection
design to minimize the injection flow rate, which leads tothe optimization of all safety systems. Further enhancement of safety can be attained by eliminating
valve-switching operations during accidents through the
installation of a in-containment refueling water storage pit,
water source of safety components.
2.1.2 Approaches to new plant development
In the United States, the construction of new nuclear
power plants waned for many years, however the U.S.
market is now rising with the prospective demand for dozens of plants to be constructed up to 2030, prompted chiefly
by the need to prevent global warming and cope with surging oil prices. In July 2006 MHI started the procedures tosubmit an application to the U.S. Nuclear Regulatory Commission (NRC) for Design Certification of the US-APWR
Fig. 3(Fig.
3), a 1,700 MWe class advanced plant based on established APWR technology and modified to reflect US utility
requirements by incorporating new and well-validated technology. In conjunction with that, the company has also

1.6

1.3

1.0
0.8
0.6
0.4

0.3

0.2

0.1
0.0
2000 2001 2002
(year)

0

0.2
2003

0.1
2004

(From) (1) Operation Status of Nuclear Facilities in Japan,
Japan Nuclear Energy Safety Organization(2) Power Reactor Status Report/ Monthly Operating Report, NRC

Fig. 2 Unscheduled shutdown rates of PWR plants

By these broad activities from design and construction
to inspection and maintenance services, unscheduled shutdown rate, one of the important indicators of plantreliability, remains at 0 - 0.3 times/unit/year for the Japanese PWR plants, which indicates excellent plantFig. 2
performance compared with that of US plants (Fig.
2).

2. Technology development in light water reactor power
generation plants
2.1 Trend of development of plant design
2.1.1 Approaches to new plant construction
The construction work for Tomari Unit 3 commenced
in November 2003. The latest technology is applied to enhance the economy, reliability, and operability of this latest
3-loop plant. One of the main features of the plant is uprating power to 912 MWe, achieved by the combination ofincreased main steam pressure by raising the reactor coolant temperature and a 54-inch blade turbine system todecrease exhaust loss. Integral shroud blades are also
adopted for the turbine system to enhance reliability, andits vibration characteristics, structural integrity, and performance have been sufficiently validated throughfull-scale rotational vibration tests and approximately 50%
scale actual steam loading tests. An advanced main control board using total digital technology has been adopted
to improve plant operability and economy, reducing theoperator load by means of soft operation using CRTs, andreducing the cable volume through multiplex transmissions. The operability of the advanced main control board
was sufficiently validated in advance using mock-up testing equipment, and the integral combined test wascompleted at shop by October 2006.
For other plant facilities the latest technology has been
applied to enhance reliability and operability, such as ironconcentration reduction countermeasures in the main feedwater (i.e. high pH operation), high-density spent fuel racks
containing boron (10B) effective for the maintenance of subcriticality to stretch storage capacity, and to reduce theconstruction period, such as large block installation of thecontainment vessel upper head before the onset of winter.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 4 (Dec. 2006)2

2.2 Enhancement of technology of light water reactor
power generation plants
2.2.1 Core design method
To improve the core design, MHI is developing methods
which enhance and maintain the prescribed design accuracy in cores loaded with high-burnup fuel. To improve thenuclear design, we have introduced a three-dimensionalcore calculation by enhancing and upgrading the conventional core calculation code previously used by combining
the axial one-dimensional and horizontal two-dimensional
codes. This core calculation code is based on the modern
nodal method and can determine the core nuclear characteristics with three-dimensional calculations. With thesefeatures the code can cope with high accuracy to the advanced cores planned for the future.
An improved statistical thermal design method has been
introduced to enhance the thermal hydraulic design. This
will increase the flexibility of design for the selection offuel patterns, as the thermal margin in the core is now
more clearly understood. MHI has also developed ANCK,a three-dimensional core kinetic characteristics code, andMIDAC, a three-dimensional thermal hydraulic characteristics code. These codes, together with the development of
the thermal hydraulic design and the application of thenuclear-thermal hydraulic coupling method to the merging of the nuclear design are now being prepared for
application to actual plants. This technology, once in place,will maintain the margin of core safety at the current leveland ensure the flexibility of core operation even during
operation in an upgraded power state.
To provide the high accuracy necessary to cope with thecomplexities entailed in future work to upgrade the core,
MHI is developing a three-dimensional core calculation codefor the next generation of nuclear design which treats eachfuel rod as a separate calculation unit. Though the method
will involve immense levels of detail and require tremendous calculations, the latest acceleration calculation
technology and methods such as parallel calculation, areexpected to reduce the calculation time and maintain thecalculation accuracy.
2.2.2 Safety design method
During the licensing of recent high-burnup fuels and
MOX fuels, MHI used conservative safety analysis methods for both analysis conditions and physical models in thesafety evaluations. In order to determine appropriate safetymargins, MHI expects to apply new methods to further
performance improvements such as up-rating power andhigh-burnup fuels in the future. With the recent significant progress in computer performance and numericalanalysis technology, detailed modeling with simulation code
becomes possible and allows the acquisition of more realistic and more accurate simulation results. MHI endeavors
to develop new safety analysis methods, which can evaluate appropriate safety margins, by employing such newtechnology.

Fig. 3 US-APWR (3D-CAD model)

established MHI Nuclear Energy Systems Inc., a wholly
owned subsidiary, in Washington, D.C.
The US-APWR realizes 1,700 MWe of electric power byincorporating high-performance steam generators and turbines with the same core thermal output alreadydemonstrated by the APWR. A design with triangular-pitch
tubes has been adopted for the high-performance steam
generators to prevent increases in component size as muchas possible while increasing the heat transfer area. The
performance of the turbines is also improved by adopting
new techniques such as the 70-inch class blades for low
pressure turbines.
The fuel design enables economical longer cycle operation for 24 months by extending the effective fuel heightfrom 12 ft to 14 ft and by adopting a low power density
core, through the simplification of the lower reactor
internals with the reactor vessel being unchanged. The incore instrumentation is improved for top insertion, basedon the requirements of US utilities, eliminating the bottom-mounted instrumentation nozzles.
The design of the emergency power supply system has
been improved to four trains to realize a complete 4-train
configuration of the safety systems, that enables the online maintenance, and gas turbine generators with simple
utility equipments has been adopted for cost reduction.
The plant building design has been improved throughthe reduction of the volume of buildings by adopting small
separate buildings allowed by lower seismic conditions in
the United States.
In addition to the 1,700 MWe class US-APWR, MHI has
agreed to develop a new 1,000 MWe nuclear power plant
employing the latest technology in collaboration with
AREVA of France, in order to cope with the demands fromutilities overseas.
In Japan, meanwhile, the Framework for Nuclear Energy Policy established in 2005 enshrines the development
requirements for the next generation of light water reactors to meet the demand for rebuilt plants in Japan in 2030
or later. The government is leading a plant development
project in cooperation with industry and MHI is participating as the sole PWR plant supplier in Japan.

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 4 (Dec. 2006)3

To improve the LOCA analysis, MHI has developed
MCOBRA/TRAC, a best estimate code. This code has ability to predict the thermal-hydraulic phenomena inside thereactor vessel and the other components in the primarysystem of a PWR with more accuracy than the conventional
deterministic evaluation method which is combined withconservative analysis conditions and physical models. At
the same time, a statistical evaluation method has beendeveloped to quantify the uncertainty of prediction. Thesedevelopments have led to accurate simulations of the fuelcladding temperature and thermal-hydraulic response during LOCA, and to optimum safety margins.
To improve the non-LOCA analysis, MHI has developed
the SPARKLE code. This code is a plant system transient
analysis code which includes a three-dimensional core kinetics module coupled with a thermal hydraulics module.
SPARKLE is distinct from the conventional evaluation
method, which is done by a set of separate conservativecodes, and is expected to lead to more accurate simulations of plant transients and to optimize safety margins.
MHI is preparing for examination by the regulatory
agency in order to apply these new methods to the licensing
analysis of power up-rating and future high-burnup fuels.
2.2.3 Plant design method
Plant design requires integration and validation activities to achieve the most effective arrangements ensuringfunctional requirements not only for component layouts, butalso for the routes for piping, ducts and trays routings installed in buildings. Three-dimensional CAD has been fully
applied to integrate and validate layouts which deal withhuge amounts of data with high accuracy and effectiveness.
The development and application of NUWINGS, a system
for unified management of all information, from the basic
design to detailed design, fabrication, and installation withthe three-dimensional CAD data as its nucleus, improves
the reliability and efficiency of plant design and site work.
2.2.4 Fuel design
MHI has considerable and excellent operating experience with PWR fuel since it first supplied to Mihama Unit 1
in 1970. More than 17,000 assemblies have been produced.
In particular, as a result of steady root-cause analysis andcountermeasures against problems (including fuel leakages), MHI has realized an excellent operating experience
with no fuel leakages observed for approximately 13 years
from 1991.
In the field of fuel development, MHI has reduced fuelcosts by burnup extension which reduces the number of
reload assemblies step by step. Recently, the utilities haveapplied the 55,000 MWd/t fuels licensed discharge burnup
of 55,000 MWd/t in assembly average to commercial reactors. The economy and reliability of the 55,000 MWd/t fuelhave been improved by a zircaloy grid for neutron economy,a corrosion resistant cladding material MDA (Mitsubishi
Developed Alloy), a debris filter to increase debris trap capability, and other new technology.

To facilitate fuel development in the future, MHI ismaking every effort to develop advanced fuel that can realize longer cycle operation and plant uprating, as well as
higher burnup fuel. To provide a further thermal margin
for the uprated core, MHI has developed a new grid spacer
design with high DNB performance. For higher burnup,
we are developing M-MDA (modified MDA) with a corrosion resistance superior to that of the MDA currently inuse. M-MDA is now under fourth cycle irradiation in a PWR
plant in Spain, and its improved corrosion resistance isconfirmed by third cycle irradiation. As a cladding material with more excellent corrosion resistance, the Japaneseindustry has developed J-AlloyTM, a new material of Zr-Nb
alloy. The out-pile tests are almost completed and an irradiation test commenced in a Spanish commercial PWR in
April, 2006.
For the more effective use of uranium resources, domestic and foreign reprocessed uranium fuels are already being
utilized in commercial reactors. Also for plutonium utilization, utilities have contracted MOX fuel fabrication inforeign countries with MHI, and MHI is preparing to fabricate MOX fuel for commercial reactors.
2.2.5 Main component design
Japanese utilities are renewing the main components
of primary and secondary systems from the viewpoint ofpreventive maintenance, and MHI has responded to theneeds of its customers for improved reliability andperformance by supplying replacement components
incorporating the latest technology. MHI has also received
many orders for reactor vessel closure heads, steam
generators, etc. from overseas mainly from Europe and theUnited States, since 2003, based on our experience in Japan
Fig. 4(Fig.
4). The development technology for reactor vessel
closure heads include the application of high nickel alloy
690 with excellent corrosion resistance for CRDM nozzle
penetrations, the integrated forging of vessel head andflange, and the assembly shipping of a reactor vessel
closure head with CRDMs installed for the first time in
the world. Also regarding steam generators, the applicationof high nickel alloy, TT690, to the steam generator tubes,

Fig. 4 Transportation of reactor vessel closure head

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 4 (Dec. 2006)4the tube support structure at U-bend and the highperformance moisture separator of MHI's own unique design
improve the reliability and performance of the components.
Besides the above, MHI has completed the replacementof reactor internals in Ikata Units 1 and 2 of Shikoku ElecFig. 5
tric Power Company (Fig.
5) and Genkai Unit 1 of Kyushu
Electric Power Company for the first time in the world andreplaced the main control boards of Genkai Units 1 and 2of Kyushu Electric Power Company. MHI also received theworld's first order for a replacement pressurizer adopting
high density heaters together with a reactor vessel closure
head and steam generators and delivered on schedule in
May 2006 to the Fort Calhoun Power Station of Omaha
Public Power District. These activities are highly evaluated by customers through the strict quality control andschedule control conforming to the design and production
standards both inside and outside Japan.
MHI has also improved the performance of secondary
systems by replacing secondary turbines with the latest
technology to domestic and overseas plants, such as replacing with longer integral shroud blades, improving
drain-removal performance, and short period replacement
technique of condensers tubes. MHI delivered low pressure
turbines with 54-inch integral shroud blades to the KRSKOPower Station in Slovenia in April 2006 and completed thereplacement work within a short period.
2.2.6 Manufacturing technologies
MHI possesses a high level of manufacturing technology for welding, machining, and assembling main
components of PWR plants. In welding, MHI has developed and applied practical clad welding technology of highquality, such as electron beam welding and laser beam
welding techniques to minimize the heat load for joint welding, Inconel plasma welding for steam generators, andelectroslag welding for reactor vessels. The reactor vessel
can be worked vertically in the same condition as when it
is installed on site by the super large multi-functional NC
machine Super Miller manufactured by MHI, ensuring highaccuracy by excluding accumulated errors. For the manufacture of steam generators, MHI has improved thereliability of working and assembling by the exclusive useof automatic devices for insertion and expansion of thesteam generator tubes. For the secondary turbines, thecompany possesses the integrated technology and facilities for manufacturing from the formation and working of
blades, working of rotors to assembly.
With this manufacturing technology, MHI can supply
high-quality components and will make continuous efforts
for development and improvement.
2.2.7 Plant construction technologies
MHI has also developed various technology and techniques for plant construction work. In Tomari Unit 3, thecompany applied large block installation for the containment vessel upper head using a large-capacity crane (lifting
capacity 1,200 t) and completed the construction work
Fig. 6
within a short period (Fig.
6). In Tsuruga Units 3 and 4,
MHI aims at the large-scale reduction of the assembly workrequired inside the containment vessel by applying steel
plate concrete structures to eliminate the reinforcing bars
conventionally used in reinforced concrete and plans toachieve quick construction by using large-capacity cranes
whenever possible for large block installation of the main
steam piping room and lifting-in of heavy components,
which are critical in the construction schedule.
2.2.8 Operation and maintenance technologies
After commencing the commercial operation of plants,
MHI has developed and improved operation and maintenance technology in response to the needs of utilities basedon its broad experience as a plant supplier.
To improve operation technology, MHI and the utilities work together on primary chemical control proceduresfor high-burnup fuel, optimization of the concentrationsof dissolved hydrogen, suppression of scale deposition byhigh pH operation to prevent corrosion and degradationof secondary system components, and decontamination of
steam generators.

Fig. 5 World's first replacement ofreactor internals

Fig. 6 Large block installation of containment vessel upper headof Tomari Unit 3

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 4 (Dec. 2006)

5

To reduce occupational radiation exposure, MHI undertakes such measures as environmental improvement,
operational improvement, and design modification. Alongwith its years of work for operational improvement ofinspection and repair to be remote and automated inhigh-dose environments, MHI recently introduced zinc
injection to actual plants. Zinc injection for the primarysystem has recently been confirmed to bring about a dosereduction effect for environmental improvement.
A major target in maintenance technology is to simultaneously improve both the economy and reliability ofmaintenance work. The optimization of maintenancebased on RCM (reliability centered maintenance) has
attracted attention as a means of improving economy,
and MHI also actively endeavors, jointly with the utilities, to optimize the frequency and content of equipment
maintenance work. To improve reliability, MHI makes
selective efforts to develop aging countermeasuresagainst primary water stress corrosion cracks (PWSCC)
of 600 alloy for plants with more than 30 years of operation. The developed technology includes (1) inspection
techniques such as intelligent ECT (eddy current test),
phased array UT (ultrasonic test) for the reactor vessel
nozzle, steam generator tubes, (2) residual stress improvement techniques such as shot peening, water jet
peening, and outer surface irradiated laser stress improvement process, we call L-SIP, for welds, and (3)repair techniques to improve materials by replacing 600
alloy with 690 alloy (an alloy with superior SCC resistance). MHI contributes to the stable and safe plant
operation using these techniques.

reactor was entrusted to FBEC (FBR Engineering Co.,
Ltd., a jointly owned subsidiary) by Japanese power companies, and was carried out collaboratively by its fourowners (MHI, Hitachi, Ltd., Toshiba Corporation, andFuji Electric Holdings Co., Ltd.) from fiscal 1981 to 1983.
Given that the design was based on Monju, the construction cost significantly exceeded that of a light water
reactor at that time, which meant that construction costs
had to be radically reduced. To meet that end, in 1984,
MHI independently developed the "top-entry-method
Fig. 7),
7 a design that significantly
loop-type reactor" (Fig.
reduced construction costs.

Fig. 7 Top-entry-method loop-type reactor

The design can reduce the length of the primary piping system to about half that of Monju through the
installation of an intermediate heat exchanger and a primary pump into vessels, respectively, in addition to thereactor vessel; and the connection of these vessels withinverted U-shaped piping. This design configuration ismade possible by the development of 316 FR steel, with
better strength at high temperatures, and the upgradedassessment method in high-temperature design standards. Both technologies were the result of MHI'sdevelopment efforts. Furthermore, the development ofhigh chromium steel allows for usage of an integrated
one-through type steam generator, and significantly reduces the amount of required materials. The
construction cost of the reactor system, after the incorporation of other rationalization concepts, was found to
be about 1.5 times more than that of a light water reactor (1,000 MWe) at that time.
After 6 years of design research on the loop-type reactor and pool-type reactor, conducted independently, but
in parallel, by MHI, and Hitachi and Toshiba, the topentry method loop-type reactor, which MHI backed, wasselected by power companies in June 1990 as the designbasis to be pursued thereafter. This was decided basedon such results as of development experience, achievements in Japan, earthquake resistance, ease ofmaintenance and repairment.

3. Technology development in advanced reactor plants
3.1 Fast breeder reactor (FBR)
The FBR can breed more fuel than other reactors used
to generate electricity, and the efficient utilization of uranium can be dramatically increased. These advantages
have prompted research and development for the FBR
as a national project. MHI has participated in the design and construction of the Experimental Fast Breeder
Reactor "Joyo," and Prototype Fast Breeder Reactor"Monju," as well as the design and technology development of a demonstration reactor in collaboration withelectric power companies.
Through participation in the design and constructionof Joyo and Monju, MHI has acquired extensive experience in almost all stages of hardware and softwaredevelopment of FBR plants, including core and safety
design, design and fabrication of primary components,
such as reactor vessels, and steam generators. No major problems arose during construction.
From the latter half of the 1970s, MHI began design
and technology development for a demonstration reactor in order to cultivate the required technological skills.
The conceptual design research of the demonstration

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 4 (Dec. 2006)

6

It was determined that the design research, startingfrom 1990, should be undertaken in collaboration withall four companies. MHI has conducted extensive design research, including the engineering of the entire
plant (core design, safety design, system design, layout
design, etc.), as well as component and equipment design for the reactor vessels, heat exchangers, pumps, andso on. In addition, MHI has conducted extensive researchand development of such areas as specific phenomena to
the top-entry method loop-type reactor (such as multiple
coolant level fluctuation, sloshing, gas entrainment in
the coolant, etc.), study of countermeasures, upgrade ofhigh-temperature structural design standards, development of the structural materials, development of an
integrated one-through helical type SG, and so on. The
collaborative design research entrusted to the four companies by the power companies ended in fiscal 1999, witha formulated plant concept. However, further cost reduction for a commercialized reactor was required.
To formulate a strategy for a low-cost and commercially viable reactor, the study "Feasibility Study on
Commercialized Fast Reactor Cycle System" was initiated from fiscal 1999 chiefly under the direction of theJapan Atomic Energy Agency (JAEA). The purpose of
the research was to determine the optimal technologies
for the FBR cycle to flexibly respond to the various needsof society in the future through the evaluation of widerange alternatives. Dozens of concepts in combination
could be adopted for the FBR, with substantial variations in the coolants (sodium, gas, heavy metals, etc.),
fuels (MOX, metals, etc.), and plant sizes. MHI has proposed seven versions of the plant concept, including
large-scale and medium-scale plants, with sodium coolant (1,500 MWe and 750 MWe, respectively), a heliumgas cooled plant, lead and lead-bismuth cooled plants,
and small-scale plants with sodium and lead-bismuth
coolant. MHI independently conducted the design research for two years during the Phase I design stage,
which ended in fiscal 2000. A comparison and assessment have been carried out by JAEA and others. Amongthe seven concepts, six concepts, excluding the leadcooled plant concept, were selected for further investigation.
To finalize the design concept, Phase II design research was carried out for the six plant concepts until
fiscal 2005. In the end, the large-scale sodium-cooled
fast reactor (as shown in Fig. 88, 1,500 MWe, 2 loops) was
selected as the primary concept. The deciding factors
were high-level compliance with safety requirements(avoidance of re-criticality during core damage, etc.), cost
efficiency (the construction cost in the practical application stage: 200,000 yen/kWe, etc.), low environmental
burden (utilization of low decontaminated TRU fuel), etc.,
which are defined in "Feasibility Study on Commercialized Fast Reactor Cycle System."

The concept aims at a larger plant capacity and simultaneously adopts innovative approaches to reduce thenumber of loops, to employ a high chromium steel with a
low thermal expansion coefficient and excellent high-temperature strength, to shorten the piping length by adopting
a top flow-in/out piping system (i.e. by L-shaped pipes), tosimplify the primary coolant system by employing an intermediate heat exchanger integrated with a primary
pump, and so on. Those innovative approaches will cut
the amount of required materials thereby reducing the cost.
In addition, to present the feasibility of the concept, MHI
has executed feasibility confirmation tests for thedownsized reactor vessel, intermediate heat exchanger integrated with a primary pump and L-shaped piping.
There have been two reactor design selections in the
past: the top-entry method loop-type reactor in 1990 by
the power companies, and the large-scale sodium-cooled
fast reactor in 2006 by JAEA, et al. The loop-type reactor designs developed by MHI were selected both times.
In March 2006, the Fast Reactor Cycle System wasnamed as one of the "National Essential Technology" in
the Council for Science and Technology Policy. Researchand development are promoted selectively and accelerated aiming at the realization (the initiation of operation)of the FBR demonstration reactor by about 2025, and thefull-scale introduction on commercial plants before 2050.
Research and development aimed at the demonstration and practical application of the FBR cycle will begin
from fiscal 2007, with funds from the Ministry of
Economy, Trade and Industry in addition to the Ministry of Education, Culture, Sports, Science andTechnology. MHI will be in charge of the main tests on
the above-mentioned innovative technologies under
JAEA.

Fig. 8 Large-scalesodium-cooled fast reactor

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 4 (Dec. 2006)

7

3.2 PBMR
The PBMR (Pebble Bed Modular Reactor) is a heliumgas cooled reactor that uses a type of ceramic-coated fuelparticle. The reactor was developed by PBMR Ltd. capitalized by ESKOM (a state-run power company in South
Africa), the South African government, etc. The output
will be 400 MW of thermal power, with a reactor outlet
temperature of 900oC.
MHI has been awarded the contracts for the basic design of the gas turbine as well as the basic design andmaterial procurement of the core barrel. The fabrication and construction stages will soon follow, with the
installation at site scheduled in 2009 or later.
3.3 Nuclear hydrogen production (for use in a hightemperature gas reactor)
The HTTR (High-Temperature Test Reactor) of JAEA
is a coated fuel particle-graphite moderating helium gascooled reactor that runs at a reactor outlet temperatureof 850 - 950 o C. In April, 2004, it achieved the rated
power of 30 MWt, with the coolant temperature of 950oC
at the reactor outlet. MHI coordinates the design as anadministrative company for four mechanical and electrical manufacturers, while simultaneously participatingin the design and fabrication of containment vessels,
high-temperature components, and so on.
For the development of hydrogen production technology by the thermo-chemical water-splitting cycle (I-S
process; I: iodine and S: sulfur) utilizing high-temperature helium since fiscal 2004, MHI has fabricated aceramics heat exchanger (SO 3 resolver) and now has agood chance of developing a component with excellent
corrosion resistance at high temperature.
3.4 Nuclear fusion
In nuclear fusion, which is expected as the ultimate
source of energy, MHI has actively endeavored to develop
technologies and design, as well as manufacture equipment and components (mainly vacuum vessels, tritium
related equipments, fuel supply and exhaust systems,etc.) for experimental fusion devices, such as the JT-60U,
JFT-2M of JAEA. Such research will be utilized in theInternational Thermonuclear Experimental Reactor(ITER), which pursues this endeavor.

tance, storage, chopping/shearing, dissolution, and analysis of the spent fuel. MHI has developed various
techniques for the components and equipment of thesefacilities. MHI has also developed inspection devices forthe components and piping to enhance plant operability,
introduced analysis techniques for automated components to reduce exposure and labor as well as rationalized
the processes to enhance economy and reduce the environmental load.
MHI contributed to the Feasibility Study on Commercialized Fast Breeder Reactor (FBR) Cycle Systems
conducted as a part of the technology development program for FBR fuel reprocessing executed by JAEA andthe utilities. Specifically, MHI is developing the key technological concept of the study, Advanced Aqueous
Reprocessing. The company is also trying to develop a
new reprocessing technology based on supercritical carbon dioxide to improve economy, as well as preprocessing
processes such as disassembly of fuel assemblies, chopping/shearing, and dissolution.
4.2 Interim storage of spent fuelThe measures to increase the spent fuel to be stored
until now have mainly focused on expanding the storage
pool capacity. Utilities are currently proceeding with aconstruction plan for an interim storage facility in Mutsu
City, Aomori Prefecture, which is the first off-site facility applying metal dry cask technology. The facility is
expected to be in service in fiscal 2010. In Europe, especially in Germany, the interim storage using metal drycasks is advanced as a measure for increasing spent fuel.
MHI is developing the MSF series of metal dry caskswith outstanding safety and economy, for interim storage. The interim storage casks must be able toefficiently store more fuel, meeting the regulations andstandards for both transport and storage. MHI has endeavored to steadily develop the technology of the MSF
casks as well as developing of a boron-added aluminum
Fig.9
alloy. Demonstration tests with a full-scale model (Fig.9
Fig.9)
have already been performed within the licensing procedures for MSF-57B in Germany.

4. Technology development in the nuclear fuel cycle
4.1 Reprocessing of spent fuelSpent fuel is considered to be a useful recyclable resource containing fissile materials such as plutonium.
Japan Nuclear Fuel Limited (JNFL) has constructed a
reprocessing plant applying the PUREX process (solvent
extraction process) in Rokkasho-mura, Aomori Prefecture, to reprocess spent light water reactor fuel. JNFL
is now in the active test stage using spent fuel with atargeted launch of operations set for fiscal 2007.
MHI supplied the key facilities in the construction of
the reprocessing plant, including the facilities for accep-

Fig. 9 Mitsubishi metal dry cask (full scale model)

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 4 (Dec. 2006)8

4.3 Treatment and disposal of radioactive waste
As treatment for low level radioactive waste generated
from the operation of nuclear power plants MHI has completed various radioactive waste treatment techniques inaccordance with the waste properties, including sewage
treatment using activated sludge with a low amount of secondary waste generation, a micro-filtration hollow fiber
treatment to enhance the backwash performance, an evaporation and concentration treatment suitable for both PWR
and BWR liquid wastes, a high-pressure compacting treatment, and other methods. The adoption of these techniques
has already been decided by actual nuclear power plants.
The intermediated disposal depth (50 - 100 m or deeper)for the disposal of radioactive waste with a relatively highradioactive level such as metals, concrete, etc. generated
during decommissioning of power plants, etc. is planned.
MHI is now involved in the basic design of this intermediate depth disposal and is establishing specifications for thewaste packages to be disposed.
On the other hand, the authorities have instituted aclearance level below which waste with extremely low activity levels can be treated in the same manner as generalindustrial waste. Its actual implementation in nuclear facilities is expected. MHI has also developed a device capableof measuring extremely minute amounts of radiation,amounts lower than levels in the natural world, in order toeffectively measure the clearance level. The first of thesedevices has been delivered to the Tokai Power Station ofFig. 10
the Japan Atomic Power Company (Fig.
10).
Furthermore, the plan proceeds to vitrify the high level
radioactive waste generated from the reprocessing facilities and to dispose of it in geological formations 300 m below
ground level, or deeper. The Nuclear Waste Management
Organization of Japan (NUMO) was established as the responsible organization in 2000, and an invitation for public
subscription for the candidate disposal site has been issued. MHI seeks to rationalize the disposal of high-level
radioactive waste by developing disposal containers (overpack), techniques for transferring waste to deep
underground sites and fixing it there, and techniques forsafety evaluation after final disposal.

Fig. 10 Clearance level measurement device

5. Conclusion
An overview of recent technological development activities of MHI has been presented above. Based on thesetechnologies as a base, MHI will continue further development for the new domestic plant constructions such as
Tomari Unit 3, next-generation light water reactors, andplant operating and maintenance services, with the cooperative guidance of the government and utilities. MHI will
also accelerate its development of technology to further
expand its business in the world market, such as the application for Design Certification of the US-APWR to the
NRC, and respond to the needs of all customers as theworld’s leading company in nuclear power generation.

Kiyoshi Yamauchi

Keizo Okada

Mitsubishi Heavy Industries, Ltd.
Technical Review Vol. 43 No. 4 (Dec. 2006)9