Mitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)16Safe, Reliable, Economical Advanced Pressurized WaterReactor for European Market

SHIGEMITSU SUZUKI

MAKOTO KANDASHUNSUKE SHIMIZU

KAZUMASA TANAKASEIJI TERADAHIROTO KAWAHARA|1. Introduction
The design concept of the European Advanced Pressurized Water Reactor (EU-APWR) islargely based on the US-APWR developed for use in the United States, which in turn comes fromthe original APWR designed for operation in Japan. It has a large electric output capacity of 1700
MW, an important feature of the US-APWR. It also includes all the economic, safety, andreliability features that result from using four-train safety systems, advanced accumulator tanks,and digital instrumentation and control equipment. Mitsubishi Heavy Industries (MHI) iscontinuing the development of the EU-APWR for the European market to integrate the European
Utility Requirements (EUR), the additional safety requirements of the electric power companies ineach European country, the regulations specific to each country, and international electricalstandards (IEC), as well tailoring the reactor for 50 Hz applications. Table 1 compares the main
specifications of the APWR and EU-APWR.
Table 1 Comparison of main specifications
Core thermal output(MWt)Electric output(MWe)Core
Safety systems
Electric system
Mechanical system
Accumulator tank
Refueling water storage pit
Emergency power supply for safety system
Final stage blades of the low pressure turbine

APWR
EU-APWR
4,451
4,451
1,538
1,700 class
12-ft fuel  257
14-ft fuel  257
2-train configuration
4-train configuration
4-train configuration
4-train configuration
Advanced accumulator tank  4
Installed in the containment vessel
Diesel generator
Gas turbine generator
54 in
74 in - class|2. Plant overview
The primary component of the EU-APWR is a four-loop pressurized water reactor (PWR)
with a thermal output of 4,451 MWt and an electric output on the order of 1,700 MW. The core isloaded with 257 fuel assemblies, each with an effective fuel height of 14 ft. A stainless steel
neutron reflector is installed around the fuel assemblies to improve reliability by simplifying thestructure and to reduce the fuel cycle cost by using neutrons and the irradiation of the reactor vessel
efficiently. Figure 1 compares the core sizes of the existing PWR, APWR, and EU-APWR. TheEU-APWR and APWR have very large thermal outputs compared to the existing PWR. TheEU-APWR uses 14-ft fuel assemblies to increase the uranium inventory and reduce the power
density without changing the size of the reactor vessel. It also enables a 24-month operation cyclewith the present U-235 enrichment limit of 5 wt% and a fuel rod burnup limit of 62 GWd/t toreduce the generation cost and provide a large design margin for improving safety.
The low-pressure turbines of the secondary system use 74-inch class super-long blades toimprove efficiency. Both the safety and non-safety instrumentation and control systems are fully
digital and provide redundancy, defense in depth, diversity, self-diagnostic ability, and online
maintainability. Figure 2 shows a photo of the main control room.

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)
17
SIP

SIP
CS/RHRP

CS/RHRP

RWSP
C/L

C/L

H/L

H/L

SG

SG

ACC

ACC

SPRAY
HEADER
ACC

SG

Figure 1 Reactor design improvement(Increased core thermal output and low power density)

SPRAY
HEADER
ACC

RV
SG

H/L

H/L

C/L

C/L

CS/RHRP

CS/RHRPSIP

SIP

RV: Reactor vessel SG: Steam generator
ACC: Advanced accumulator tank
SIP: Safety injection pump
CS/RHRP: Containment spray/
residual heat removal pump
CL: Cold leg HL: Hot leg

Figure 2 Main control board

Figure 3 Emergency core coolant
system of EU-APWR(4-loop configuration)|3. Safety system features
3.1

Four-train safety injection system

Figure 3 shows the features of the EU-APWR emergency core coolant systems. Whereas theconventional plant uses a two-train configuration where each of the two trains can handle 100% of
the capacity, the engineered safety features of the EU-APWR are based on a four-train system
wherein each train can handle 50% of the capacity. There is thus no impact on safety in case of an
accident even if there is a failure of one train and a second is out of service for maintenance. The
reduced size of each train requires smaller equipment.

3.2

Elimination of the low-pressure injection system

The accumulator injection system used for injecting cooling water into the core in case of an
accident has the same structure as that in the US-APWR where an advanced accumulator tank(Figure 4) is installed in each primary loop. The accumulator injection system has the function of
injecting boric acid water when the primary pressure drops. The new accumulator tank developedfor use in the APWR injects a large flow of boric acid water in the initial stage of a loss-of -coolant
accident (LOCA), initiated by a passive flow damper that requires no outside power for activation.
The system also injects a small flow required to continue cooling the core in the subsequent stages.
In combination with the high-pressure injection system, this new accumulator injection system hasenabled the elimination of the low-pressure injection system installed in the current reactor.

Figure 4 Advanced accumulator tank

Mitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)18

3.3

Safety system emergency power supply and gas turbine generator

The safety-related emergency power comes from a 4-train system similar to the safety
injection system wherein each train can handle 50% of the load. Online maintenance is possible
because only two of the four trains are required for safe shutdown of the plant. The emergency
power supply system is based on gas turbine generators. Even though the start-up time of a gas
turbine generator is longer than that of a conventional diesel generator, the delay is acceptablebecause of the time margin for the startup of the high-pressure injection system provided by theadvanced accumulator tanks. The simple structure and auxiliary systems of the gas turbine
generators mean easy maintenance and reduced cost.

3.4

Refueling water storage pit (RWSP)

Four recirculation sumps are installed at the bottom of the RWSP, which serves as a water
source for the emergency core cooling system and is located at the lowest part of the containment.
This configuration provides a continuous supply of borated water to the safety injection pumps andthe residual heat removal pumps without switching operation to the recirculation sumps, as isrequired in the conventional design where the RWSP is installed outside the reactor containment
vessel. This eliminates the risks from operator error and equipment failure during an accident andprovides an even higher level of safety.

|4. Building design features
The equipment layout in the EU-APWR buildings is designed to facilitate plant operationand maintenance while minimizing the radiation exposure of personnel. Four-train separation andsegregation barriers are included to ensure that the safety-related systems function correctly in theevent of possible accidents such as fires, floods, and high-energy pipe failures.
The prestressed concrete containment vessel (PCCV) containing the major equipment of theprimary system is designed to provide an efficient leak-proof barrier and radiation protection under
all projected conditions including LOCA. The PCCV is also designed to withstand the peakpressure under LOCA conditions. Figure 5 shows a view of the EU-APWR plant buildings. The
EU-APWR safety-related structures, systems, and components are designed to withstand aircraft
collisions as well as the effects of natural phenomena such as earthquakes without jeopardizing
plant safety.
Furthermore, the safety-critical seismic design is based on the Safe Shutdown Earthquake(SSE) and Operating Basis Earthquake (OBE) concepts. The seismic design response spectra(SDRS) for SSE in the seismic design of the EU-APWR standard plant is based on the spectra
defined by the modified US RG1.60. As shown in Figure 6, the SDRS for the EU-APWR exceeds
the EUR Design Basis Earthquake spectra, which are valid for the potential nuclear sites in Europe.

Figure 5 EU-APWR buildings

Figure 6 Seismic design response spectra (SDRS)|5. Future directions for the EU-APWR
5.1

Severe accident mitigation

The EU-APWR is designed to prevent any impact on the surrounding area should the reactorvessel be damaged in an accident exceeding the severity of the design scenarios. The severeMitsubishi Heavy Industries Technical Review Vol. 46 No. 1 (Mar. 2009)19accident mitigation posture of the EU-APWR is the same as that of the US-APWR. The
fundamental concept is to flood the reactor cavity with coolant water and to keep the molten fuelwithin the reactor cavity. Figure 7 shows the basic system of the standard design with theequipment to process low-concentration hydrogen gas, equipment for injection cooling of thedamaged core, and equipment to remove decay heat.

Figure 7 Severe accident mitigation system of the EU-APWR standard design

In addition, because Europe has also directly experienced the impact of the Chernobylaccident, even stricter safety requirements and countermeasures for severe accidents outside thedesign scenarios are included in the EUR regulations as well as those in each country. Mitigating
the results of severe accidents even further requires a cooling water supply system to provide
reactor cavity cooling with diversity and independence, allowing the design to meet themore-stringent requirements. The core damage frequency of the EU-APWR based on these design
requirements meets the EUR requirement of less than 1  105 per reactor year).

5.2

Future initiatives

The EU-APWR has been developed to meet the European market requirements. This is inaddition to the high level of safety, economy, and reliability inherent in the standard Mitsubishi
APWR design. MHI will continue the evolution of the EU-APWR design and may makemodifications for specific site or country requirements. This ongoing evaluation and the continuous
exchange of technical comments with the electric power companies in each country may lead tomore improvements in the standard design. MHI will continue to market the EU-APWR as a plantsuitable for the European market.

Authors
Shigemitsu Suzuki
General Manager,
Nuclear Systems Department,
Nuclear Energy Systems
Engineering Center,
Nuclear Energy Systems
Headquarters

Makoto Kanda
Deputy General Manager,
Nuclear Systems Department,
Nuclear Energy Systems
Engineering Center,
Nuclear Energy Systems
Headquarters

Shunsuke Shimizu
Manager,
Nuclear Systems Department,
Nuclear Energy Systems
Engineering Center,
Nuclear Energy Systems
Headquarters

Kazumasa TanakaManager,
Nuclear Systems Department,
Nuclear Energy Systems
Engineering Center,
Nuclear Energy Systems
Headquarters

Seiji TeradaManager,
Nuclear Systems Department,
Nuclear Energy Systems
Engineering Center,
Nuclear Energy Systems
Headquarters

Hiroto KawaharaManager,
Nuclear Systems Department,
Nuclear Energy Systems
Engineering Center,
Nuclear Energy Systems
Headquarters