Safety of Nuclear Power Plants - ETH Zurich: Herzlich Willkommen

1

Safety of Nuclear Power Plants

EPR, GIF, HTR, ,

Generation I to Generation IV

Spring 2011 / Prof. W. Kröger Safety of Nuclear Power Plants 2

2

EPR Overall Safety Philosophy

These objectives, motivated by the continuous search for a hi h f t l l i l i f d li ti f thhigher safety level, involve reinforced application of the defense in depth concept: by improving the preventive measures in order to further reduce the

probability of core melt, and by simultaneously incorporating, right from the design stage,

measures for limiting the consequences of a severe accident.


EPR Plant Parameter

Thermal power 4250/4500 MW

Electrical power 1600 MW

Efficiency 36%

No. of primary loops 4

No of fuel assemblies 241

Burnup > 60 GWd/t

Secondary pressure 78 bar

Seismic level 0.25 g

Service live 60 years


3

Risk Reduction – EPR Approach

Reinforced protection in the unlikely event of core meltdown Preventive features include safety devices which further reduce the probability y p y

of a severe accident enlarged water inventory of the main primary system and of the steam

generators; increased reliability of safety systems through 4-fold 100% redundancy (4-train concept); use of diversified technologies for each train of these systems.

Features to mitigate the consequences of such an event: the extremely robust, leaktight containment around the reactor is designed

to prevent radioactivity from spreading outside; the arrangement of the blockhouses inside the containment and hydrogen the arrangement of the blockhouses inside the containment and hydrogen

catalytic recombiners (passive devices) prevent the accumulation of hydrogen and the risk of deflagration;

molten core escaping from the reactor vessel would be passively collected and retained, then cooled in a specific area inside the reactor containment building (“core catcher”)

Enhanced protection against external hazards


EPR – Safety Systems


4

EPR Safety Injection / Residual Heat Removal (SIS/RHRS)


Risk Reduction - EPR Containment

The unique building housing the reactor is extremely robust. It rests on a 6 m thick concrete base mat and is enclosed by a double shell: the inner is made of leaktight, prestressed concrete and the outer one of reinforced concrete, each 1.30 m thick. This total to 2.60 m concrete thickness, capable of withstanding external hazards such as an aircraft crash.Spring 2011 / Prof. W. Kröger Safety of Nuclear Power Plants 8

5

EPR Core Catcher

Even in the event of the core melting, and piercing then escaping from the steel reactor vessel in which it is housed, it would be contained in a dedicated spreading compartment. This compartment is then cooled to remove the residual heat.


EPR Containment Heat Removal System


6

Generation IV International Forum (GIF)

To meet future energy needs, ten countries have agreed f k f i t ti l ti i h fon a framework for international cooperation in research for

an advanced generation of nuclear energy systems, known as Generation IV.

Euratome joined as 11th full member;Switzerland joined in February of 2002


Generation IV – Overall Goals

Development of one or more nuclear energy systems

Deployable by 2030

With significant advances in: Sustainability Safety and reliability Proliferation and physical protection Economics

Competitive in various markets Competitive in various markets

Designed for different applications:Electricity, Hydrogen, Clean water, Heat


7

Generation IV Initiative – Aims (1/2)

Nuclear energy-systems including fuel cycles of the 4th ti h ldgeneration should ...

SR-1 ... be excellent regarding safety and reliability while in operation.

SR-2 ... have very low core damage frequency and little consequences.

SR-3 ... eliminate the need for emergency planning outside of g y gthe plant.

EC-1 ... clear lifecycle-cost advantages over other energy sources.

EC-2 ... comparable financial risk to other energy projects.


Generation IV Initiative – Aims (2/2)

Nuclear energy-systems including fuel cycles of the 4th generation shouldshould ...

SU-l ... produce sustainable energy, following regulations for air

pollution prevention and enhancing the long term availability

of the system and efficient usage of fuel.

SU-2 ... minimise the nuclear waste and disposing it, especially they

will reduce administration efforts on a long term scale and g

hence improve the protection of health and environment.

SU-3 ... increase the certainty that they are an undesirable and

difficult source to obtain dangerous materials for usage in

weapons.


8

Selected Generation IV Concepts (out of 21)

GEN IV Concepts Acronym Spectrum Fuel cycle TemperaturePressure

[°C] [bar]

Sodium Cooled Fast SFR Fast Closed 530-550 1

Lead Alloy-Cooled LFR Fast Closed 550-800 1

Gas-Cooled Fast GFR Fast Closed 490-850 90

Very High Temperature VHTR Thermal Once-Through 640-1000 70

Supercritical Water Cooled SCWR Th.&Fast Once/Closed 280-510 250

Molten Salt MSR Thermal Closed 565-850 < 5


The Roadmap Addresses Viability and Performance R&D Phases Viability

K f ibilit d f f i i l d i i Key feasibility and proof-of-principle decisions

Performance Engineering-scale demonstration and optimization to desired levels

of performance

Demonstration Mid to large scale system demonstration Mid- to large-scale system demonstration

[Commercialization]


9

VHTR - Technology gaps

Process-specific R&D gaps exist to adapt the chemical process and the nuclear heat source Qualification of high-temperature alloys and coatingsheat source Qualification of high temperature alloys and coatings.

Producing hydrogen using the I-S process

Performance issues includedevelopment of a high-performance helium turbine.

Modularization of the reactorand heat utilization systems isanother challenge foranother challenge forcommercial deployment ofthe VHTR.


Concept of a modular HTR (1/3)

Fuel element and restraining the fission products up to 1600°C Brennelement 10-1

1600°C Brennelement

SiCBeschichtung

Graphit

10000 bis

1300 1500 1700 1900 2100 2300 2500Temperatur / °C

10-7

10-5

10-3

10

Kr85

- F

reis

etzu

ng

10-210000 bis20000 coated particles

Graphit

Kern

SiC

Graphit

Sr 90

Cs 137

Kr 85

10-7

10-6

10-5

10-4

10-3

0

0 100 200 300 400 500Heizdauer bei 1600 °C / h

Fre

iset

zung

sant

eil


10

Concept of a modular HTR (2/3)

15

Thermal power 300MW

Circular core

11

125

32

910

feedwater

steam

Pre stressed primary loop as an burst prove inclusion

Interior concrete cell with a limitation on air amount

Underground arrangement of the reactor building

filter

to the

16

13 14

7

4

8

6

1

G

M

Use of the primary loop to steam production, gas turbines and process heat applications (with in-between heat exchanger)


Concept of a modular HTR (3/3)Underground arrangement of the reactor

20

18

Frischdampf

Speisewasser

20

0 019

15

11

10

39

12 5

p

M

G

3

8

717

14

641316

1

2

9


11

Accident behaviour of a modular HTR (1/10) Accident assumptions

external

• Full loss of coolant

• Full loss of the active residual heat removal

• Massive water ingress into the

internalCauses

• Crash of a plane (phantom)

• Gas cloud explosion

• Earthquake (b < 0,3

• Terrorist attacks with planes (Booing 747)

• Sabotage

• Impacts of war (missiles)

externalCauses

externalcauses(beyond

licensing)

Massive water ingress into the primary system

• Massive air ingress into the primary system

• Extreme reactivity disturbances

• Massive damage of reactor components

Earthquake (b 0,3 g)

• Fire

• Tornados, hurricanes and floods

pacts o a ( ss es)

• Extreme earthquakes(b > 0,3 g)

• Meteorites


Accident behaviour of a modular HTR (2/10)

Stabilitäts-i i

WirkungRequirements for a non melting inherent safe modular HTR

nukleareStabilität

thermischeStabilität

selbsttätige Begren-zung von nuklearerLeistung und Brenn-stofftemperaturen

selbsttätige Nach-wärmeabfuhr ausdem Reaktorsystem nichtschmelz-

bare Brenn-elemente undC t kt

prinzip

Fulfilment of the principles for all accidents due to internal and foreseeable external cause (requirements from licensing)

Fulfilment of the principles for all accidents including

inherent safe modular HTR

chemischeStabilität

mechan-ische

Stabilität

selbsttätiger Schutzgegen Korrosion

selbsttätiger Schutzgegen mechanischeCorezerstörung

Corestrukturen unforeseeable occurrences such as terrorist attacks or extreme earthquakes

12


Automatic removal of the residual heat in the case of failing of all active heat removal

1600

1400

1200

1000

800

600

TBrennst.max

(°C)

TBrennst.max

Fuel elements can never melt

Maximum fuel temperature remains below 1600°C

failing of all active heat removal (for example: PBMR, additionally the total failure of the first shut down system was assumed)

600

400

200

00 20 40 60 80 100 120

Zeit (h)

TBrennst. Most fuel elements stay far below this temperature

Total fission product release stays below 10-5 of the inventory


Biological analogue for the automatic residual heat removal and limitation of accident temperaturep

QN

Tmax

T °Cmax < 1600

Tw °C < 400

Q A T - TuN a w ( )

T - T Q H

4max o N

c

/

Q kWN 600

Q

T

T °Cmax < 38

T °Co < 37

Q A T - T ( ) a o u

T - T Q H

4max o

i

/

To

Tu

Tw

QN

(entspricht der Nachwärmeeines Cores mit 300 nach etwa 30 )

P = MWh

th

Tmax

To

Tu

Q W 60

(entspricht der Wärmeabgabeeines Menschen unter“normalen” Bedingungen)


13


New safety requirements for nuclear technologynuclear technology

zukünftigeAnnahmen

h ti

K (t) 10 5 t

1,1 104 t Flammen-temperatur( )°C

max. 1200 °C

heutige zukünftigeheutigeAnnahmen

t

Schutz der Gebäude gegenPenetration und Zerstörung

t

800 °C

0 30 min 2 h

Schutz gegen langandauerndeFlammeneinwirkungen mit hohenTemperaturen bei Kerosinbrand

heutigeAnnahmen

zukünftigeAnnahmen



Reaktor

Bauschutt

Automatic removal of the residual heat after the destruction of the

t b ildi (f lBauschutt(mit Isolations-wirkung)

Reactor totally covered with rumble

Residual heat is still removed

Core (maximum)1500

T (°C)

reactor building (for example caused by an extreme earthquake or a plane crash caused by terrorists)

es dua eat s st e o edautomatically, but slowed down

Maximum fuel temperature stays below 1600°C

Total fission product release stays below 10-5 of the inventory

Behälter zu 60% isoliertBehälter zu 99% isoliert

Reaktordruckbehälter

1000

500

00 20 40 60 80 100 120 140 160 180 200 220 240

Zeit (h)


14


6000

Leistung des

0.1 sP/P(%)

O Automatic limitation of nuclear power and fuel temperature

0

2000

4000

0 10 20

1300

t/s

1.0 s

10.0 s

Leistung desReaktors

TB

Strongly negative temperature coefficient ends the excursion

T i t h t i i kl d f

when faced with extreme reactivity transient (total loss of the first shut down system: ρ = 1,2 % in a short period of time)

0 10 20700

800

900

1000

1100

1200

1300

t/s

1.0 s10.0 s

Brennelement-temperatur

0.1 s

(°C) Transient heat is quickly and for the most part stored in the fuel element graphite

Maximum fuel temperature stays below 1600°C



Granulat

V 5000mluft3 Concepts for minimising the

consequences of an air ingress accident:

1

2

8

7

354

6 Draining the primary Helium through pipes over a filter

Automatic limitation on the amount of air within the concrete cell (V < 5000 m3) by automatic closing mechanisms (flaps and pouring granulate)

Limitation of possible graphite1) Internal concrete cell (sealed against outside air)

acc de t

Limitation of possible graphite corrosion to < 500 kg C and therefore no radiological consequences

Limitation of possible graphite corrosion to < 100 kg by simple intervention methods (protection of investment)

1) Internal concrete cell (sealed against outside air)

2) Reactor building

3) Draining channel

4) Sealing flaps (gravity)

5) Sealing plug

6) Granulate silo

7) Filter

8) Flue


15


Begrenzung Begrenzungder Mengen

Verhin-derung derK i

g gder Menge

an Luft

der Mengen-rate an

Luft

Korrosionvon Brenn-elementen

Volumen der inneren Betonzelle ist begrenzt (<5000m³)

h f l t D k

Vorgespannter Reaktor- druckbehälter mit kleinen Öffnungen

Korrosionsbeständige SiC-beschichtete Brennelemente

i B t ll nach erfolgter Druck-entlastung schließt eineKlappe oder ein Granulat-

vorrat den Kanal ab

innere Betonzelle wird mit Inertgas gefüllt

Berst-Schutz für die Behälter

Intervention in innerer Betonzelle

innere Betonzelle ist mit Inergas gefüllt


Accident behaviour of a modular HTR (10/10)Comparison of the fuel behaviour after loss of the active residual heat removal.

~ 105Ci

Brennstab

UO2-Tablette

TB

t0 1 h

T°C

=2850

melt

T ~°C

C 600

Brennstoff-temperatur

( )°C ~ < 1CiPartikel

C

SiC

UO2-Kern

TB

30 h t

<1600 °C

Brennstoff-temperatur

PWR HTR

Zr-Canning S

t1 h

1

Schäden an denBrennelementen

C Matrix

C

S

t

10-5

Schäden an denBrennelementen

30 h


16

Total Assessment of Safety (1/2)

l kt i h

Simulation of the residual heat in a graphite-sphere-pile by electrical

i t h ti ( 2 MW f 300

Integral proof of safety behaviour

elektrischeWiderstandsheizung

resistance heating. (~ 2 MW for a 300 MWth - Core)

Analysis of all assumable accidents (total loss of coolant, air ingress, water ingress, pressure discharge, mechanical impacts on the elements of the shut down system, component

f)damage when pressure relief)

Validation of all calculating programs for extreme accidents (heat transfer throughout all structures, flow phenomena, acts of pressure discharge).


Total Assessment of Safety (2/2)

Fuel elements can never melt; there is no heating up of the fuel elements to a temperature above 1600°C

The principal of automatic residual heat removal can never fail, even after the destruction of the reactor building it stays intact.

The reactor would even stay resistant against extreme reactivity transient. There is no temperature raise of the fuel elements to above 1600°C

The pre-stressed reactor containment can not burst; It is impossible that an unacceptable amount of air enters the primary loop, graphite corrosion is minimal.

The ingress of larger amounts of water into the primary loop will not lead to unacceptable states of the reactor; in the case of gas turbines operating thisunacceptable states of the reactor; in the case of gas turbines operating this accident is not applicable.

Against extreme, in future even more severe external impacts, the underground way of building with covering mound, and fast removal of spherical fuel elements as protection

There is no accident in which case a significant amount of radiation is released


Documents

Safety of Nuclear Power Plants - ETH Zurich: Herzlich Willkommen