18.08.2015   Passive Safety Systems and Natural Circulation in Water Cooled Nuclear Power Plants

SUMMARY OF REACTOR AND PASSIVE SAFETY SYSTEM CATEGORIES

The characterization of the nuclear reactor designs based on the passive (sub-) systems constitutes the objective of the present section. This can be achieved by combining the reactor descriptions given in Annexes I to XX and the passive systems identified in Sections 2 and 3. Furthermore, the ‘passive’ thermal-hydraulic phenomena characterized in Section 4 can be cross-correlated with the reactor configurations.

Type of Passive Safety System

Passive Safety Systems of Advanced Designs

Related

Phenomena

Pre-pressurized Core Flooding Tanks (Accumulators)[1]

— Section 2.1 —

Accumulators (AP-1000)

ECCS accumulator subsystem (WWER-640/V-407) First stage hydro-accumulators (WWER-1000/V-392) Advanced accumulators (APWR+)

Standby liquid control system (ESBWR)

Accumulator (AHWR)

8,2,5

Emergency core coolant tanks (SMART)

Elevated Tank Natural Circulation Loops (Core Make-up Tanks)

— Section 2.2 —

Core make-up tanks (AP-1000)

Second stage hydro-accumulators (WWER-1000/V-392) Core make-up tanks (ACR-1000)

Core make-up tanks (SCWR-CANDU)

Emergency boration tanks (IRIS)

8,6,9,5,15

Elevated Gravity Drain Tanks — Section 2.3 —

Core flooding system (SWR 1000)

IRWST injection (AP-1000)

ECCS tank subsystem — Elevated hydro-accumulators open to the containment (WWER-640/V-407)

Gravity-driven cooling system (SBWR and ESBWR) Suppression pool injection (SBWR and ESBWR) Gravity-driven core cooling system (LSBWR)

Gravity-driven water pool (GDWP) injection (AHWR) Reserve water system (ACR-1000)

Reserve water system (SCWR-CANDU)

8,5

Containment suppression pool injection (IRIS)

Passively Cooled Steam Generator Natural Circulation (water cooled)

— Section 2.4 —

SG passive heat removal system (WWER-640/V-407)

Passive residual heat removal system (SMART) Emergency decay heat removal system (PSRD) Stand-alone direct heat removal system (IMR)

Passive emergency heat removal system (IRIS)

13,1,6

Passively Cooled Steam Generator Natural Circulation (air cooled)

Passive residual heat removal system via SG (WWER- 1000/V-392)

Passive core cooling system using SG — open loop (APWR+)

6,4

— Section 2.4 —

Stand-alone direct heat removal system — late phase (IMR)

Passive Residual Heat Removal Heat Exchangers

— Section 2.5 —

Passive residual heat removal system (AP-1000)

Passive moderator cooling system — inside insulated PT without CT (SCWR-CANDU)

Residual heat removal system on primary circuit (SCOR)

13,6,2,1

Passively Cooled Core Isolation Condensers

— Section 2.6 —

Emergency condensers (SWR 1000)

Isolation condenser system (SBWR and ESBWR) Passive reactor cooling system (ABWR-II)

Isolation condenser (RMWR)

Isolation condenser (AHWR)

Residual heat removal system (CAREM)

13,6,1

Sump Natural Circulation — Section 2.7 —

Lower containment sump recirculation (AP-1000)

Primary circuit un-tightening subsystem (WWER-640/V — 407)

ADS-steam vent valves and submerged blow-down nozzles (MASLWR)

6,1

Containment Pressure Suppression Pools

— Section 3.1 —

ADS 1-3 steam vent into IRWST (AP-1000)

Automatic depressurization through safety relief valves — vent into suppression pool (SBWR and ESBWR)

Steam vent into suppression pool through SRV and DPV (LSBWR)

Steam vent into suppression pool through safety valves (CAREM)

Steam dump pool (SCOR)

Containment pressure suppression system (SCOR)

Steam vent into suppression pool through ADS (IRIS)

1,7,3

Containment Passive Heat Removal/Pressure Suppression Systems (Steam Condensation on Condenser Tubes)

— Section 3.2 —

Containment cooling condensers (SWR 1000) Passive containment cooling system (AHWR)

4,1,2,3

Containment Passive Heat Removal/Pressure Suppression Systems (External Natural Circulation Loop)

— Section 3.2 —

Containment passive heat removal system (WWER-640/V — 407)

Containment water cooling system (PSRD)

4,1,2,3

Containment Passive Heat Removal/Pressure Suppression Systems (External Steam Condenser Heat Exchanger)

— Section 3.2 —

Passive containment cooling system (SBWR and ESBWR) Passive containment cooling system (ABWR-II)

Passive containment cooling system (RMWR)

4,1,2,3

Passive Containment Spray Systems

— Section 3.3 —

Passive containment cooling system (AP-1000) Passive containment cooling system (LSBWR) Containment cooling spray (ACR-1000) Containment cooling spray (SCWR-CANDU)

3,2,4

All of these is achieved by Tables 3 and 4 that make reference to two reactor categories, respectively:

(a) PWR, BWR and SCWR (Super Critical Water Cooled Reactor) systems, Annexes I to XIII;

(b) Integral Reactor Systems, Annexes XIV to XX.

The main information in Tables 3 and 4 connects the reactor type with the passive safety systems, e. g. column 1 and 4. Thermal-hydraulic phenomena are cross-connected with specific passive safety systems in columns 4 and 5. Finally columns 2 and 3 provide elements, as an example, namely the thermal power and the ‘boiling’ or ‘pressurized’ feature, that characterize the reactor system.

‘Proven’ technology reactors, i. e. with final design already scrutinized in a formal safety review process, or under construction, or with an already built and operated prototype, are listed in Table 3, with a few exceptions constituted by the RMWR, the LSBWR and the SCWR that are at different levels of early design stages.

TABLE 3. PWR, BWR AND SCWR SYSTEMS AND TYPES OF PASSIVE SAFETY SYSTEMS

Reactor System

Reactor

Type

Power

(MW^th)

Passive Safety Systems

Related

Phenomena[2]

SWR 1000 AREVA, France

BWR

2778

Emergency Condenser System

13,6,1

Core Flooding System

8,5

Containment Cooling Condensers

4,1,2,3

Advanced Passive PWR AP 600 and AP 1000 Westinghouse Electric, USA

PWR

1940

3415

Passive Residual Heat Removal System

13,6,2,1

Core Make-up Tanks

8,6,9,5,15

Automatic Depressurization System 1-3 Steam Vent into IRWST

1,7,3

Accumulator Tanks

8,2,5

In-containment Refuelling Water Storage Tank Injection

8,5

Lower Containment Sump Recirculation

6,1

Passive Containment Cooling System

3,2,4

WWER-640/407 Atomenergoproject/Gidropress, Russian Federation

PWR

1800

ECCS Accumulator Subsystem

8,2,5

ECCS Tank Subsystem

8,5

Primary Circuit Un-tightening Subsystem

6,1

Steam Generator Passive Heat Removal System

13,1,6

Containment Passive Heat Removal System

4,1,2,3

WWER-1000/392 Atomenergoproject/Gidropress, Russian Federation

PWR

3000

First Stage Hydro­accumulators

8,2,5

Second Stage Hydro­accumulators

8,6,9,5,15

Passive Residual Heat Removal System via Steam Generator

6,4

Advanced PWR (APWR+) Mitsubishi, Japan

PWR

5000

Passive Core Cooling System using Steam Generator

6,4

Advanced Accumulators

8,2,5

Simplified Boiling Water Reactor (SBWR)

General Electric, USA

BWR

2000

Gravity Driven Cooling System

8,5

Suppression Pool Injection

8,5

Isolation Condenser System

13,6,1

Passive Containment Cooling System

4,1,2,3

ADS-SRV Vent into Suppression Pool

1,7,3

Economic Simplified Boiling Water Reactor (ESBWR)

General Electric, USA

BWR

4500

Gravity Driven Cooling System

8,5

Suppression Pool Injection

8,5

Isolation Condenser System

13,6,1

Standby Liquid Control System

8,2,5

Passive Containment Cooling System

4,1,2,3

ADS-SRV Vent into Suppression Pool

1,7,3

Advanced BWR (ABWR-II)

Tokyo Electric Power Company (TEPCO), General Electric, Hitachi and Toshiba, Japan

BWR

4960

Passive Reactor Cooling System

13,6,1

Passive Containment Cooling System

4,1,2,3

Reduced-Moderation Water Reactor (RMWR)

Japan Atomic Energy Agency (JAEA), Japan

BWR

3926

Isolation Condenser System

13,6,1

Passive Containment Cooling System

4,1,2,3

Advanced Heavy Water Reactor (AHWR)

Bhabha Atomic Research Centre, India

HWR

750

Gravity Driven Water Pool Injection

8,5

Isolation Condenser System

13,6,1

Accumulator

8,2,5

Passive Containment Cooling System

4,1,2,3

Advanced CANDU Reactor (ACR 1000)

Atomic Energy of Canada Ltd, Canada

HWR

3180

Core Make-up Tanks

8,6,9,5,15

Reserve Water System (RWS)

8,5

Containment Cooling Spray

3,2,4

Long operating cycle Simplified Boiling

Water Reactor (LSBWR) Toshiba, Japan

BWR

900

Gravity Driven Core Cooling System

8,5

Passive Containment Cooling System

3,2,4

Steam Vent into Suppression Pool through SRV and DPV

1,7,3

SCWR-CANDU

Atomic Energy of Canada Ltd, Canada

SCWR

2540

Core Make-up Tanks

8,6,9,5,15

Reserve Water System

8,5

Passive Moderator Cooling System

13,6,2,1

Containment Cooling Spray

3,2,4

Integral type reactors are considered in Table 4. All of these are of PWR type, second column, and can be assumed to constitute a special class of Light Water Reactors (LWR). In integral PWR, the major components of the nuclear steam supply system (NSSS) such as the core, steam generators, main coolant pumps, and pressurizer are integrated into a reactor vessel without any pipe connections between those components. This makes integral PWR systems relatively compact.

As a difference from the reactors listed in Table 3, all the integral reactor systems in Table 4 are in a design stage and no-one of such design has undergone a comprehensive safety scrutiny process (i. e. the licensing). However, in some cases, e. g. CAREM and to a lower extent IRIS, the reactor systems are under design since couple of decades, thus testifying the technological difficulties encountered for the exploitation of the integral nuclear reactor configuration idea.

TABLE 4. INTEGRAL REACTOR SYSTEMS AND TYPES OF PASSIVE SAFETY SYSTEMS

Integral Reactor System

Reactor

Type

Power

(MW4h)

Passive Safety Systems

Related

Phenomena[3]

System-Integrated Modular Advanced ReacTor (SMART)

Korea Atomic Energy Research Institute, Republic of Korea

PWR

330

Passive Residual Heat Removal System

13,1,6

Emergency Core Coolant Tank

8,2,5

CAREM

CNEA National Atomic Energy, Argentina

PWR

100

. Residual Heat Removal System — Emergency Condenser

13,6,1

Steam Vent into Suppression Pool through Safety Valves

1,7,3

Multi-Application Small Light Water Reactor (MASLWR)

INL, OSU, Nexant, USA

PWR

150

ADS-Steam Vent Valves and Submerged Blow-down Nozzles

6,1

Passive Safe Small Reactor for Distributed Energy Supply System (PSRD) Japan Atomic Energy Agency (JAEA), Japan

PWR

100

Emergency Decay Heat Removal System

13,1,6

Containment Water-Cooling System

4,1,2,3

Integrated Modular Water Reactor (IMR)

Mitsubishi, Japan

PWR

1000

Stand-alone Direct Heat Removal System

13,1,6

Stand-alone Direct Heat Removal System-Late Phase

6,4

Simple COmpact Reactor (SCOR)

Commissariat a l’Energie Atomique, France

PWR

2000

Residual Heat Removal System on Primary Circuit RRP

13,6,2,1

Steam Dump Pool

1,7,3

Containment Pressure-Suppression System.

1,7,3

IRIS

Westinghouse Electric, USA

PWR

1000

Passive Emergency Heat Removal System (EHRS)

13,1,6

Emergency Boration Tanks (EBT)

8,6,9,5,15

Containment Suppression Pool Injection

8,5

Steam Vent into Suppression Pool through ADS

1,7,3

6. CONCLUSIONS

Passive systems are widely considered in ‘innovative’ or advanced nuclear reactor designs and are adopted for coping with critical safety functions. The spread and the variety of related configurations are outlined in the present document.

Twenty ‘innovative’ nuclear reactors are described, specially giving emphasis to the passive safety systems, in the annexes and distinguished in two groups; (see also Tables 3 and 4):

• Advanced water cooled nuclear power plants,

• Integral reactor systems.

The levels of development, or even the actual deployment of the concerned reactor designs (i. e. equipped with passive systems) for electricity production are very different, and the range of maturity of these extend from reactors already in operation to preliminary reactor designs which are not yet submitted for a formal safety review process.

A dozen different passive system types, having a few tens of reactor specific configurations, suitable to address safety functions in primary loop or in containment have been distinguished, as in Table 2. These include systems like the core make-up tanks, the containment spray cooling and the isolation condenser.

The thermal-hydraulic performance of the passive systems has been characterized by less than a dozen key phenomena at their time characterized through specific descriptions including a few tens of relevant thermal-hydraulic aspects, see Table 1 and the Appendix. Cross correlations between key thermal-hydraulic phenomena, reactor specific safety systems and ‘innovative’ nuclear plants have also been established (See Tables 2, 3, and 4).

There is the need to demonstrate the understanding of the key thermal-hydraulic phenomena that are selected for characterizing the performance of passive systems: this implies the identification of parameter ranges, the availability of proper experimental programs and the demonstration of suitable predictive capabilities for computational tools.

Comprehensive experimental and code development research activities have been conducted, also very intensely at an international level, in the past three to four decades in relation to the understanding of thermal-hydraulic phenomena and for establishing related code predictive capabilities for existing nuclear power reactors. In the same context, research activities also addressed some of the phenomena for passive systems. However, a systematic effort for evaluating the level of understanding of thermal-hydraulic phenomena for passive systems and connected code capabilities appears to be limited and in general lacking.

Appendix