Pass

BWR

1

27 IAEA PC-Based Simulators Workshop

Politecnico di Milano, 3-14 October 2011

The ESBWR an advanced Passive LWR

Prof. George Yadigaroglu, em.

ETH-Zurich and

ASCOMP yadi@ethz.ch

Pass

BWR

2

27 Removal of decay heat from evolutionary

LWRs with active systems

• Assured by redundant and diverse active ECCS and containment cooling systems

• High degrees of reliability and safety can be achieved by increasing system redundancy, separation, diversity, etc.

• Such improvements may bring, however, added complexity and costs to the systems

Pass

BWR

3

27 Advanced passive ALWR designs - 1

• Replacement of active emergency core and containment cooling systems with passive ones: no active components such as pumps, fans, diesels, water chillers, etc.

• Simple re-alignment of valves allowed

• Use only “natural” devices or forces such as gravity, natural circulation, passive heat sink, stored energy (e.g. compressed gas) to operate

• Passive heat sinks: Containment structures, water pools or the atmosphere

Pass

BWR

4

27 Advanced passive LWR designs - 2

• Require no operator actions to mitigate DBAs • Typical unattended operation period: 72 h

• No redundant, safety-grade, active ECCS and containment cooling systems → no redundant emergency power supplies

• The ambient air is most often the ultimate heat sink → no safety-grade service water system

Pass

BWR

5

27 Passive LWRs for “near-term deployment”

• Replacement of highly redundant safety-grade ECCS systems by passive systems does not necessarily improve safety but has the potential of significantly reducing capital and operating costs: reducing “upstream complexity”:

ECCS

coolant delivery Electricity Diesel Fuel, air, …

Startup and control

Pass

BWR

6

27 Avoid the sophisticated, redundant, etc. safety grade ECCS

and its “upstream complexity”

DC Pwr

Emergency Bus Loading

Program

Plant Service Water Pump Motor

Reactor Component

Cooling Water Pump Motor

Emergency Core Cooling System Pump Motor

Initiation Signal

Aux. Water Source

ECCS Logic

Initiation Signal

HVAC

HVAC

HVAC

ADS Logic

DG Room Ventilation

System

Crankcase Ventilation

Engine Governing Control

DG Lubrication Oil System

Diesel

DG Cooling Water System

Generator

DG Fuel Oil System

DG Fuel Oil Storage and

Transfer System

Generator Control and Protection

Air Intake & Exhaust

Starting Air

DC Pwr

A A

Breaker

Breaker

Breaker

Water Source

Q

Q

Diesel Generator Room 1 of 3

Plant Service Water

M

M

RCCW

Typical of HPCS,

LPCS, & RHR

ADS

S/P

Core

RPV

Emer

genc

y Bu

s

Breaker Closes < 10 s

Plant Service Water

Loads

Loads

Passive Plant

Conventional Active Plant

Courtesy of B. Shiralkar,

GE Nuclear Energy

Pass

BWR

7

27

• Design Objectives • Improve safety and simplify with passive systems • Better plant economics • Continued technical advancements

• Product Outcomes Auto safety response, no AC power or operator action

required for at least 72 hrs No core uncovery in Design Basis Accidents Lower Core Damage Frequency (1 ⋅ 10-8) Significant simplification … lowers costs Evolutionary development

• Key Improvements: simplification

• Reduction in systems and equipment • Reduction in operator challenges • Reduction in core damage frequency (10x) • Reduction in cost/MWe

• Tall chimney above core

• Flattened core

Key ESBWR features

Pass

BWR

8

27

Parameter BWR/4-Mk I (Browns Ferry 3)

BWR/6-Mk III (Grand Gulf)

ABWR ESBWR

Power (MWt/MWe) 3293/1098 3900/1360 3926/1350 4500/1550

Vessel height/dia. (m) 21.9/6.4 21.8/6.4 21.1/7.1 27.7/7.1

Fuel Bundles (number) 764 800 872 1132

Active Fuel Height (m) 3.7 3.7 3.7 3.0

Power density (kw/l) 50 54.2 51 54

Recirculation pumps 2(large) 2(large) 10 zero

Number of CRDs/type 185/LP 193/LP 205/FM 269/FM

Safety system pumps 9 9 18 zero

Safety diesel generator 2 3 3 zero

Core damage freq./yr 1E-5 1E-6 1E-7 3E-8

Safety Bldg Vol (m3/MWe) 115 150 160 <130

Optimized parameters for ESBWR

Pass

BWR

9

27 Cooling of the core under all conditions

Heat removal by the turbine

Heat generation in the core

1

Primary intact: heat removal from the RPV 2

Primary breached: heat removal from the containment

Pass

BWR

10

27 Passive systems for decay heat removal

The classical ECCS and containment cooling systems replaced by: − Natural-circulation cooling of the core

(when the primary system is intact) − Gravity Driven Cooling Systems (GDCS)

(with the primary system breached) – Passive Containment Cooling Systems

(PCCS)

Pass

BWR

11

27

Courtesy of B. Shiralkar,

GE Nuclear Energy

Primary system intact: ESBWR isolation condenser

Isolation Condenser (IC) directly connected to the RPV, immersed in pool outside the containment condenses steam from the core

Pass

BWR

12

27 Decay heat removal: Breached primary system at high

or medium pressure

• AP600, AP1000: Core Make-up Tank (CMT) • SWR-1000: Emergency condenser immersed in core-flooding pool and

permanently connected to the RPV

• For intermediate pressure levels in PWRs: injection of water from accumulators (~50 bar) or core reflood tanks (CRT ~15 bar)

• ESBWR solution: automatic depressurization of the primary system and actuation of the Gravity-Driven Cooling System

Pass

BWR

13

27 ESBWR Gravity Driven Cooling System (GDCS)

Following depressurization of the primary system by the ADS gravity driven flow keeps core covered

Courtesy of B. Shiralkar,

GE Nuclear Energy

Pass

BWR

14

27 Main Steam Line break

Pass

BWR

15

27 Small pipe break at bottom of RPV

Pass

BWR

16

27 The alternative SWR-1000: Primary system breached:

passive core cooling system

Collapse of the voids in and above the core region leads to automatic activation of the Emergency Condenser connected to the RPV without valves and immersed in the Core Flooding Pool.

2-step cooling

Needs some p in primary system Loop seal: hot water does

not rise and start boiling

Pass

BWR

17

27 Decay heat removal from the Containment

• All containment systems profit from the passive heat sink provided by

the containment structures and walls. These are needed to absorb the higher level of initial decay heat generation and the blowdown heat load. When the containment heat sink gets “saturated,” the decay heat level is lower…

• Important timing considerations: heat capacity of system vs time at which cooling function is taken over

• Water pools used as heat sinks can boil off either to the atmosphere (1-step process) or to the containment (2-step process)

Pass

BWR

18

27 PCCS – Passive Containment Cooling System

Long term operation • The DW pressure acts on the

water level in the WW weir and opens the horizontal vents: the steam condenses in the pressure suppression pool

• The DW pressure also pushes the steam into the PCCS condensers and the non-condensables to be vented to the suppression pool: the preferred path for long-term decay heat evacuation

• A delicate pressure balance to ensure that decay heat goes to the PCCS pools

Pass

BWR

19

27 PCC Behavior in presence of steam/air mixtures

The PANDA tests showed:

• PCC heat removal capacity is adjusted to actual requirements

• Decrease in decay heat and PCC-pool level are compensated by changing air content in PCC lower region

Behavior of passive condensers in presence of steam/air mixtures is well understood

Active condenser area is automatically adjusted to match requirements by adjustment of the air content in the lower part of the tubes

0 4 8 12 16 20 24 28 Time (hours)

5

4

3

2

1

0

Water level at test start

Condenser

Water level

Pool

Hei

ght (

m)

active tube lengthInactive secundary side (Water level low)

inactive primary side (air)

Pass

BWR

20

27 Summary: Passive core and containment

cooling of the ESBWR

• The Isolation Condensers (IC) condense steam from the RPV.

• The Gravity Driven Cooling System (GDCS) pool floods the core after depressurization of the primary system.

• The Passive Containment Cooling System (PCCS) condenses containment steam and vents the non-condensibles to the Suppression Pool.

• The PCCS system is modular and can be scaled to any power level

Pass

BWR

21

27 Passive containment cooling: PCCS

The ESBWR and the SWR-1000

Pass

BWR

22

27

ESBWR Passive safety systems within Containment envelope

All Pipes/Valves Inside Containment

High Elevation Gravity Drain Pools

Raised Suppression Pool

Decay Heat HX’s Above Drywell

Courtesy of B. Shiralkar, GE Nuclear Energy

Pass

BWR

23

27 ESBWR passive safety systems

• The ICS condenses steam from the RPV

• The GDCS floods the core after depressurization of the primary system

• The PCCS condenses containment steam and vents the non-condensibles to the Suppression Pool

• The PCCS system is modular and can be scaled to any power level; pools easy to refill

• ADS system

• Passive boron injection

• Non-safety-grade Diesels and closed Cooling Water and Service Water Systems

Pass

BWR

24

27 Natural Circulation

The Dodewaard natural-circulation BWR

• Natural circulation is not new…

• Small BWR, 183 MWth

Pass

BWR

25

27

• Higher driving head • Chimney/taller vessel

• Reduced flow resistance • Shorter core • Increased downcomer flow area

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

Average Flow per Bundle (kg/s)

Ave

rage

Pow

er p

er B

undl

e (M

Wt)

ABWR LUNGMEN

CLINTON

ESBWR 1132 - a

N Power Flow - 1132-4500.XLS Chart1 (5)

ABWR

BWR6

ESBWR

Enhanced natural circulation in the ESBWR

Courtesy of B. Shiralkar, GE Nuclear Energy

Pass

BWR

26

27 Natural circulation in the ESBWR

• Reduction in components – pumps, controls, power supplies – vessel internals

• Passive safety/natural circulation

– more water in the vessel – no external piping, no canned motor penetrations

• Very good performance and reliability

– power/flow ratio similar to pumped plant – large margin to combined t/h – neutronic stability

• Load following with Control Rods

Pass

BWR

27

27 Much more water above the core

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