Assessment of Major Systems Containment S. Michael Modro Joint - - PowerPoint PPT Presentation

1

S.M. Modro, October 2017

Joint IAEA-ICTP Essential Knowledge Workshop on Nuclear Power Plant Design Safety- Updated IAEA safety Standards 9-20 October 2017 Trieste, Italy

• S. Michael Modro

Assessment of Major Systems Containment

2

S.M. Modro, October 2017

Overview

§ Design Requirements § Typical current generation LWR Containment Designs

• Several Examples of BWRs
• Several Examples of PWRs
• Several Examples of VVERs
• Caution: This is NOT a comprehensive survey (several designs are not discussed)

3

S.M. Modro, October 2017

Defense in depth concept

Defense in depth in the term of five protection barriers: – Fuel – Fuel Cladding – Primary Circuit Pressure Boundary – Containment – Emergency Measures

4

S.M. Modro, October 2017

Defense in depth concept

• 1.2m concrete containment

building

• 0.9m concrete shield
• 0.2m steel reactor vessel
• solid nuclear fuel inside metal

tubes

5

S.M. Modro, October 2017

IAEA SSR-2/1 Containment Design Requirements

§ A containment system shall be provided in order to ensure that any

release of radioactive materials to the environment in a design basis accident would be below prescribed limits.

§ This system may include, depending on design requirements:

• leaktight structures;
• associated systems for the control of pressures and temperatures;
• features for the isolation, management and removal of fission products,

hydrogen, oxygen and other substances that could be released into the containment atmosphere.

§ All identified design basis accidents shall be taken into account in the

design of the containment system.

• In addition, consideration shall be given to the provision of features for the

mitigation of the consequences of selected severe accidents in order to limit the release of radioactive material to the environment.

6

S.M. Modro, October 2017

IAEA SSR-2/1 Containment Design Requirements

§ The strength of the containment structure, including

access openings and penetrations and isolation valves, shall be calculated with sufficient margins of safety on the basis of the potential internal overpressures, underpressures and temperatures, dynamic effects such as missile impacts, and reaction forces anticipated to arise as a result of design basis accidents.

§ The effects of other potential energy sources, including,

for example, possible chemical and radiolysis reactions, shall also be considered.

7

S.M. Modro, October 2017

IAEA SSR-2/1 Containment Design Requirements

§ In calculating the necessary strength of the containment

structure, natural phenomena and human induced events shall be taken into consideration, and provision shall be made to monitor the condition of the containment and its associated features.

§ Provision for maintaining the integrity of the containment

in the event of a severe accident shall be considered. In particular, the effects of any predicted combustion of flammable gases shall be taken into account.

8

S.M. Modro, October 2017

IAEA SSR-2/1 Containment Design Requirements

Capability for containment pressure tests

§ The containment structure shall be designed and constructed so that it is

possible to perform a pressure test at a specified pressure to demonstrate its structural integrity before operation of the plant and over the plant’s lifetime.

Containment leakage

§ The containment system shall be designed so that the prescribed

maximum leakage rate is not exceeded in design basis accidents. The primary pressure withstanding containment may be partially or totally surrounded by a secondary confinement for the collection and controlled release or storage of materials that may leak from the primary containment in design basis accidents.

9

S.M. Modro, October 2017

IAEA SSR-2/1 Containment Design Requirements

Containment Penetrations

§ The number of penetrations through the containment shall be kept to a

practical minimum.

§ All penetrations through the containment shall meet the same design

requirements as the containment structure itself. They shall be protected against reaction forces stemming from pipe movement or accidental loads such as those due to missiles, jet forces and pipe whip.

§ If resilient seals (such as elastomeric seals or electrical cable penetrations)

• r expansion bellows are used with penetrations, they shall be designed to

have the capability for leak testing at the containment design pressure, independent of the determination of the leak rate of the containment as a whole, to demonstrate their continued integrity over the lifetime of the plant.

10

S.M. Modro, October 2017

IAEA SSR-2/1 Containment Design Requirements

Containment Isolation

§ Each line that penetrates the containment as part of the reactor coolant

pressure boundary or that is connected directly to the containment atmosphere shall be automatically and reliably sealable in the event of a design basis accident in which the leaktightness of the containment is essential to preventing radioactive releases to the environment that exceed prescribed limits.

§ These lines shall be fitted with at least two adequate containment

isolation valves arranged in series (normally with one outside and the

• ther inside the containment, but other arrangements may be acceptable

depending on the design), and each valve shall be capable of being reliably and independently actuated.

11

S.M. Modro, October 2017

IAEA SSR-2/1 Containment Design Requirements

Containment Isolation

§ Isolation valves shall be located as close to the containment as is

• practicable. Containment isolation shall be achievable on the assumption
• f a single failure. If the application of this requirement reduces the

reliability of a safety system that penetrates the containment, other isolation methods may be used.

§ Each line that penetrates the primary reactor containment and is neither

part of the reactor coolant pressure boundary nor connected directly to the containment atmosphere shall have at least one adequate containment isolation valve. This valve shall be outside the containment and located as close to the containment as practicable.

§ Adequate consideration shall be given to the capability of isolation devices

to maintain their function in the event of a severe accident.

12

S.M. Modro, October 2017

IAEA SSR-2/1 Containment Design Requirements

Internal structures of the containment

§ The design shall provide for ample flow routes between separate

compartments inside the containment.

§ The cross-sections of openings between compartments shall be of such

dimensions as to ensure that the pressure differentials occurring during pressure equalization in design basis accidents do not result in damage to the pressure bearing structure or to other systems of importance in limiting the effects of design basis accidents.

§ Adequate consideration shall be given to the capability of internal

structures to withstand the effects of a severe accident.

13

S.M. Modro, October 2017

IAEA SSR-2/1 Containment Design Requirements

Residual Heat Removal from the Containment

§ The capability to remove heat from the reactor containment shall be

ensured.

§ The safety function shall be fulfilled of reducing the pressure and

temperature in the containment, and maintaining them at acceptably low levels, after any accidental release of high energy fluids in a design basis accident.

§ The system performing the function of removing heat from the

containment shall have adequate reliability and redundancy to ensure that this can be fulfilled, on the assumption of a single failure.

§ Adequate consideration shall be given to the capability to remove heat

from the reactor containment in the event of a severe accident.

14

S.M. Modro, October 2017

IAEA SSR-2/1 Containment Design Requirements

Control and cleanup of the containment atmosphere

§ Systems to control fission products, hydrogen, oxygen and other substances

that may be released into the reactor containment shall be provided as necessary:

• to reduce the amount of fission products that might be released to the

environment in design basis accidents; and

• to control the concentration of hydrogen, oxygen and other substances in the

containment atmosphere in design basis accidents in order to prevent deflagration

• r detonation which could jeopardize the integrity of the containment.

§ Systems for cleaning up the containment atmosphere shall have suitable

redundancy in components and features to ensure that the safety group can fulfil the necessary safety function, on the assumption of a single failure.

§ Adequate consideration shall be given to the control of fission products,

hydrogen and other substances that may be generated or released in the event

• f a severe accident.

15

S.M. Modro, October 2017

Major Types of LWR Containment Designs

§ Boiling Water Reactors (BWRs)

• GE Mark I -- Peach Bottom (USA), Mühleberg (CH)
• GE Mark II -- Limerick (USA), Laguna Verde (Mexico)
• GE Mark III -- Grand Gulf (USA), Cofrentes (ES), Leibstadt (CH)
• KWU Type-69 – Krümmel (D), Type-72 Gundremmingen (D)

§ Pressurized Water Reactors (PWRs)

• Large Dry Cylindrical –

ü (Westinghouse): Indian Point (USA), Vandellos (ES) ü (Framatome N4):

• Large Dry Spherical (Siemens/KWU)– Borssele (NL),Isar-2 (D)
• Ice Condensers – Sequoyah (W-USA), Loviisa (WWER-FI)

16

S.M. Modro, October 2017

Containment Free Volumes and Design Pressures Differences

10 20 30 40 50 60 70 80 90 100 110 BWR Mark I BWR Mark II PWR Ice Condenser BWR Mark III PWR Sub-Atmospheric PWR Large Dry Containment design pressure (psig) 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 Containment net free volume (x106 ft3) Pressure Volume

Design pressure = 62 psig Design pressure = 45 psig Design pressure = 12 psig Design pressure = 15 psig Design pressure = 45 psig Design pressure = 60 psig

17

S.M. Modro, October 2017

Categories of Current (GE) BWR Containments

Mark I Mark III Mark II

Vacuum relief from building vent purge

• utlet

Drywell head Drywell sprays Reactor building Vent from D.W.

Reactor vessel Pedestal

Vent from D.W. Downcomers Drywell vacuum breaker Suppression chamber sprays Reactor building Drywell sprays

Reactor

Drywell Drywell purge exhaust line Vacuum breaker Downcomer Wetwell sprays Suppression pool purge exhaust line

Reactor

Drywell

Upper pool

Suppression pool Weir wall Horizontal vents Reactor shield wall

Containment Containment sprays

Hydrogen igniter

18

S.M. Modro, October 2017

Most Common & Oldest Design is Mark I

l

Containment atmosphere inerted to prevent hydrogen (H2) combustion

EL.92'-6" EL.110'-0" EL.134'-6" EL.165'-0" 195'-0" EL.234'-0" EL.265'-4" EL.290'-0" EL.106'-6" EL.116'-0" EL.165'-0" EL.200'-10" EL.218'-10" EL.84'-0" GRADE LEVEL

Drywell Wetwell (Torus) Reactor Bldg Turbine Bldg

19

S.M. Modro, October 2017

Mark II Design More Unified than Mark I Design

§

Single structure divided into two volumes by concrete floor

• Drywell is directly above wetwell
• Drywell and wetwell connected by vertical pipes

§

Reinforced or post-tensioned concrete structures with steel liner

§

Containment atmosphere inerted to prevent H2 combustion

LaSalle Units 1 & 2 Columbia (WNP-2) Limerick 1 & 2

20

S.M. Modro, October 2017

Mark III Differs in Many Significant ways

§ Two volumes (drywell and ‘containment’) connected by horizontal

vents through suppression pool

§ Significantly larger volume than Mark I and Mark II designs

• but lower design pressure

§ Containment atmosphere NOT inerted

• relies on hydrogen igniters

§ Two types of primary containment designs

• free-standing steel structure
• reinforced concrete with steel liner

21

S.M. Modro, October 2017

Two Types of Mark III Primary Containments

Free standing steel structure

Reactor

Drywell

Upper pool

Supression pool Weir wall Horizontal vents Reactor shield wall

Containment Containment sprays

Hydrogen igniter

Reinforced concrete

22

S.M. Modro, October 2017

Siemens/KWU Designs

Type 69 Type 72

23

S.M. Modro, October 2017

BWR Residual Heat Removal System typically has Multiple Configurations & Functions

Heat sink

Drywell spray Low pressure Coolant Injection Wetwell spray Suppression Pool Cooling

24

S.M. Modro, October 2017

CANDU Systems

ACR 700 CANDU 6

25

S.M. Modro, October 2017

VVER1000 Containments

26

S.M. Modro, October 2017

VVER1000 Containments

27

S.M. Modro, October 2017

PFS filters module Inner containment Outer containment

2nd stage hydro accumulators system 3rd stage hydro accumulators system 1st stage hydro accumulators system

Passive Annulus Filtration System PHRS Heat Exchanger Annulus Corium catcher

VVER-ТОI

Primary circuit

28

S.M. Modro, October 2017

28 Examples of containment design

PWR full pressure dry containment

① Containment ② Containment spray ③ Filtered air discharge

system

④ Liner

29

S.M. Modro, October 2017

29 Examples of containment design

PWR full pressure double wall containment

① Full pressure containment ② Secondary confinement ③ Annulus ④ Annulus evacuation

system

⑤ Filtered air discharged

system

30

S.M. Modro, October 2017

30 Examples of containment design

PWR ice condenser containment

① Containment ② Upper containment volume ③ Ice condenser ④ Lower containment volume ⑤ Lower containment spray system ⑥ Filtered air discharged system ⑦ Liner

31

S.M. Modro, October 2017

31 Examples of containment design

PWR full pressure double wall containment for mitigation of severe accidents ① In-containment ECCS water storage ② ECCS ③ Primary depressurization device ④ Core catcher ⑤ Containment heat removal

system

⑥ Annulus filtered air extraction

system

32

S.M. Modro, October 2017

32 Examples of containment design

PWR passive containment ① In-containment refueling water storage tank ② Primary circuit depressurization system ③ Air baffle ④ Passive containment cooling system: gravity

drain water tank

⑤ Containment vessel gravity spray ⑥ Natural convection air discharge ⑦ Natural convection air intake

33

S.M. Modro, October 2017

International Atomic Energy Agency

…Thank you for your attention

34

S.M. Modro, October 2017

Data Required to Perform Realistic Failure Analysis

§ Geometric data

• General configuration
• Details of structural discontinuities
• Penetration details
• Weld locations

35

S.M. Modro, October 2017

Data Requirements

§ Construction materials

• Rebar, stiffeners, aggregate for concrete
• Steel type(s) and tension
• Results of component testing (if any)
• Seal design/composition

35

36

S.M. Modro, October 2017

Data requirements

§ Definition of loads

• Pressure & temperature history

(quasi-static load)

• Impulse (dynamic load)

37

S.M. Modro, October 2017

Load calculation uncertainties

§ Models and nodalization scheme

• Free volumes (junctions)
• Heat structures
• Initiating and boundary conditions
• Heat transfer condition

§ Verification and validation of codes DBA and SA (MAAP, MELCOR,

GOTHIC,..)

• Containment heat removal
• Steam explosion
• Direct containment heating
• Molten core concrete interaction (MCCI)
• Hydrogen behaviour (other combustible material)
• Containment melt through

§ User effects

38

S.M. Modro, October 2017

Deterministic Safety Analysis Assessment

Example for using 2 DSA codes for containment evaluation

RELAP 5 mod 3.2 SCOPE Inputs: Primary circuit initial conditions Secondary circuit initial conditions Core Initial Conditions Break location, size and model Actuation of:

• Reactor Protection System
• Engineering Safety Features

Results: Plant response Sequence Timing Break Massflow Break Flow Enthalpy MELCOR Inputs: Break Massflow Break Flow Enthalpy Initial conditions for: –Modeled volumes –Modeled heat sinks (walls) Confinement Spray Actuation Results: Confinement response

• Pressure, Temperature,
• Humidity,etc.

RELAP 5 mod 3.2 SCOPE Inputs: Primary circuit initial conditions Secondary circuit initial conditions Core Initial Conditions Break location, size and model Actuation of:

• Reactor Protection System
• Engineering Safety Features

Results: Plant response Sequence Timing Break Massflow Break Flow Enthalpy MELCOR Inputs: Break Massflow Break Flow Enthalpy Initial conditions for: –Modeled volumes –Modeled heat sinks (walls) Confinement Spray Actuation Results: Confinement response

• Pressure, Temperature,
• Humidity,etc.

GOTHIC RELAP 5 mod 3.3

39

S.M. Modro, October 2017

Deterministic Safety Analysis Assessment

Containment Model Plant Analyses

40

S.M. Modro, October 2017

MAAP 4.0.5 Analysis

Enviroment 11

• el. 159.38

Sferical portion of upper compartment 8211 M**3 7

• el. 143.33
• el. 143.33

Upper cylinder compartment 20593 M**3 3

• el. 107.62
• el. 160.79

Contain. Annulus 8 10863 M**3

• el. 100.30
• el. 115.55

Annular Compartmen 4 7330 M**3 recircu.l sump LT6101

• el. 92.08

el.129.05 SG1 Compartment 5 525 M**3

• el. 108.56
• el. 115.55

Lower Compartment 2 1709 M**3

• el. 96.04

el.129.05 SG2 Compartment 6 520 M**3

• el. 108.56
• el. 119.35

PZR Compartment 10 287 M**3

• el. 108.63
• el. 107.62

Rx Cavity 1 250 M**3

• el. 94.46
• el. 96.04

Sump 24 M**3 9

• el. 93.41

Nodalization scheme

# 11

• pen

# 12 failure # 13

• pen

# 5

• pen

# 14

• pen

# 10

• pen

# 8

• pen

# 1 failure # 15

• pen

# 17

• pen

# 2

• pen

# 7

• pen

# 16

• pen

# 4

• pen

# 9

• pen

# 6 4" pipe Connection to FD system via MAAP variable WDCS Recirculation flow CI and RHR (via MAAP variable WCS) For ECCS reverse flow (via MAAP variable WSPTB) Interface for VA 181 system via MAAP variable WVCH0 and event 210 (as long as HC is not turned on) Hydrogen recombiners controlled via SIM IOS REM Interface for HC system via MAAP variable WVCH0 and event 210 - at least one fun is running (flow provided to MAAP based on pressure in node 7 Containment spray via MAAP variable WSPTA CNT failure to AB implemented via malfunction SC01 (variableVA03SC_01AUXLE AKTVVLEAK and to ENV via SC02 (VA17MALF_SC03TVLEAK) TS leakage implemented via REMOTE funct. REM_SC00N001TVTE applied for junctions #13 and #14 # 18

• pen

MAAP 4.0.5 Model

41

S.M. Modro, October 2017

Summary

§ Containment design features vary considerably among

world’s population of nuclear plants

§ Details of design features are important to understanding

containment response during design basis accidents (DBA) and severe (beyond design basis BDBA) accidents

42

S.M. Modro, October 2017

Containment Heat Removal for Large Dry Containment Uses Sprays and Fans Coolers

42

Heat sink Heat sink

Early phase – injection from RWST Late phase - recirculation