Release Into Containment in AES-2006 Design

Denis Kolchinsky

Project Chief Engineer

Fulfillment of User

requirement UR 1.4 – release

into containment in AES-

2006 design

19-22 November, 2013 INPRO Forum, IAEA, Vienna

State Atomic Energy Corporation ROSATOM

Branch of Joint Stock Company «East-European leading scientific research and design

institute for energy technology»

Saint-Petersburg R&D Institute “Atomenergoproject” (SPbAEP)


All information and data in this presentation take from design

and analytical documents for NPPs of AES-2006 design:

Leningradskaja NPP-2 (LAES-2) - two units are under

construction near Saint-Petersburg (RF)

Baltic NPP (BtAES) – two units in Kaliningrad Region

(RF)

Belorusskaja NPP – construction has recently started in

Republic of Belarus

And also from open information for Balakovo NPP (with

reactor type V-320).

References

The frequency of a major release of radioactivity into the

containment / confinement of an INS due to internal events

should be reduced. Should a release occur, the consequences

should be mitigated.

User requirement UR1.4


Meeting to Criterion CR1.4.1: major release into containment

Activity release into containment atmosphere under LOCA accidents is ever

determined by presence of damaged fuel cladding in the core. The following

acceptance criteria are justified in the design:

For design conditions of category 3 - number of damaged fuel rods shall not

exceed 1 % of the total number of fuel rods in the core

For design conditions of category 4 - number of damaged fuel rods shall not

exceed 10 % of the total number of fuel rods in the core.


In case of design accidents the expected annual irradiation dose of a limited

part of population at the protection zone boundary (NPP site) is:

For category 3 – effective dose below 1 mSv/event

For category 4 - effective dose below 5 mSv/event

The results of accidents analyzes are presented in PSAR,

Chapter 15 for units LAES-2 and BtAES

LOCA accidents are managed by active safety systems ensured reactor

coolant inventory and heat removal.

Meeting to Criterion CR1.4.1: major release into containment (continuation)


If safety systems are working in design basis mode, the acceptance criteria

are implemented. Binding of volatile radionuclides in containment

atmosphere is ensured by adding of chemicals (alcali) into boric water of containment spray system.

Safety systems configuration has forth-

trains configuration and ensures

functional margin as N+2 (in V-320

design it is N+1 only)

Two main reasons which had helped to significantly decrease Core

Damage Frequency (CDF) for AES-2006 in comparison with V-320

design are:

N+2 safety systems configuration;

Using of Passive Heat Removal System via Steam Generators (SG

PHRS) for mitigation some of safety systems multiply failures

consequences (such as: black-out, emergency feed water failure, high

pressure emergency injection failure at small LOCA, etc).

Meeting to Criterion CR1.4.1: major release into containment (continuation)


Multiply failures (included common cause failures) in safety systems may

lead to severe core damage. The frequency of core damage is a

quantitative indicator of criteria CR1.4.1

Main functions of Passive Heat Removal System via Steam Generators


Residual heat removal and reactor shut-down

cooling at full-loss-of-power conditions;

Residual heat removal and reactor shut-down

cooling at full-loss-of-feedwater-supply conditions;

Prevention of radioactive coolant atmospheric

injection through BRU-A or SG safety valves during

accident with coolant leak from primary to

secondary circuit;

Minimization of radioactive coolant release

during accident with coolant leak from primary to

secondary circuit and simultaneously steam pipeline

break in not cutting part out of containment;

Redundancy of active safety systems in the case

of their failure for emergency reactor cool-down

conditions during accidents.


Probability Safety Characteristics of NPP Designs

Operation Mode

CDF, 1/(r *y)

V-320 (BNPP) AES-91

(TNPP)

AES-2006

(LAES-2)

Power operation 2,55·10-5 1,35·10-6 1,36·10-7

Shutdown 2,33·10-5 3,50·10-7 4,58·10-7

BNPP – Balokovskaja NPP (Ref.: PSA-1)

TNPP – Tianwan NPP in China (Ref.: PSA-1)

LAES-2 – Leningradskaja NPP-2 (Ref.: PSA-1)

Conclusion:

Due to new safety measures in AES-2006 design the CDF had been

decreased to almost times in comparison with AES-91 and to

hundred times in comparison with V-320!

Criteria CR1.4.2: processes

Indicator IN1.4.2: Natural or engineered processes

sufficient for controlling relevant system parameters and

activity levels in containment/confinement.


Assurance of containment integrity and containment heat removal


The main aims

Containment

integrity keeping

(at the initial

period of accident

without operator

actions)

Heat removal from

containment at the late

stage of accident

Corium cooling (inside

reactor vessel or in

core catcher)

For mentioned aims reaching the following design basis

are stated:

Steam explosions during interacting between water and

corium is to be excluded;

Direct heating of containment is to be excluded;

Detonation of combustible mixtures is to be excluded;

Formation of non-condensing gases is to be limited


Assurance of containment integrity and containment heat removal (continuation)

Meeting to these statements is approved in PSAR, Chapter

15.

Activity Localization Means Inside the Containment

- Containment spray system

- Chemical injection systems for iodine binding

- Hydrogen removal system

- Passive heat removal system from the containment (in

case if spray system does not efficient)


This function is ensured by:

Emergency Spray System

Intends for:

Pressure reduction in the

containment in case of LOCA

Removal of fission products from

the containment atmosphere .

Control of chemical water

composition in the sump-tank by

adding chemicals.


Passive Heat Removal System from the Containment

Main functions:

Reducing and maintaining pressure inside the

containment within the design limits during BDBA

including severe some with core damage;

Removal to the ultimate heat sink the heat released

into the containment during BDBA including severe

some with core damage;


Redundancy of

containment spray

system.


0 10000 20000 30000

Время (с)

100000

200000

300000

400000

500000

600000

Давление (Па)

Давление в контейнментеDu850 cold (2JND+2JNG+2ГЕ)

С работой системы JMN

Без JMN и JMP

C работой JMP

1) LLOCA (DBA) 2) LLOCA without Spray

system, without PHRS/C 3) LLOCA without

Spray system, with PHRS/C

Pressure in the containment

Design basis:


In DBAs detonation and deflagration is excluded in the Containment.

In BDBAs detonation of hydrogen is excluded and deflagration is

permitted if the localizing safety systems perform their design

functions.

Capacity of Hydrogen removal system is designated as if 1000 kg of

H2 generates in the Containment during 5-7 hours.

Hydrogen safety

Passive catalytic

hydrogen recombiners

Employment of natural

inertization of gas

medium by steam

The Passive catalytic hydrogen recombiners

recombiners

frame

catalytic element

Recombiners arangement in

the containment


0 2000 4000 6000 8000 10000Время, с

0

0.04

0.08

0.12

0.16

0.2

Объем

ная концентрация

водорода,

%10

0 об

.

H2 concentration during accident

0 2000 4000 6000 8000 10000Время, с

0

100

200

300

400

Масса

водорода,

кг

Mass of H2: 1-generated; 2-recobained;

3-not recombined

Criterion CR1.4.3 (accident management)

Acceptance limit AL1.4.3: Procedures, equipment and training

sufficient to prevent large release outside containment /

confinement and regain control of the facility.


Means for BDBA management

1 – PHRS/C, 2 – PHRS/SG, 3 – EHRT, 8 – Core catcher, 5- PARs


BDBA Management Systems Core Catcher [8]

Hydrogen Removal System (passive recombiners) [5]

System of primary circuit overpressure protection and emergency gas removal system [7]

Passive Heat Removal System via Steam Generators [2]

Passive Heat Removal System from Containment [3]

Core Catcher Water Supply System [9]

System of emergency chemical agents supply [4]

Special Measures for Fuel Pool and Emergency Heat Removal Tanks Make-Up

Special electrical train with moving diesel-generator and accumulators;

Special I&C equipment and control panel in the MCR (SAMS).


The Main Functions of the Core Catcher

Reactor vault protected against corium thermomechanical interaction

Reception and localization of solid and liquid corium components

Heat transfer from corium

Сore subcriticality ensuring

Decreased hydrogen and radionuclides release into the containment


Core Catcher Main Technical Solutions

dry, water-cooled, crucible-type, located in the sub-reactor space mixture of iron and aluminum oxides, steel and oxide as part of sacrificial materials two-layer CC vessel resistance to thermal stresses

heat shield for protected the upper part of the vessel against thermal radiation

gadolinium oxide as part of sacrificial material to ensure subcriticality of molten core

1

2

3

4

5

1- reactor vessel, 2 –

dry reactor protection,

3- console framework,

4 – service area, 5 –

core catcher vessel

CC does not require periodic service works. CC equipment and the

measurement system testing should be carried out after accidents, which are

accompanied by leakage in the containment.

1

2

3

4

5

1

2

3

5

4


1 - reactor

2 –core catcher

3 – fuel pool

4 – reactor internals inspection vault

5 – pit-tanks

6 – core catcher flooding pipes (water

supply to the corium surface)

7 –core catcher heat exchanger feeding

pipelines

8 – steam removal (pipes)

Filling and Cooling of Core Catcher


8


Basic Codes for Justification of Passive Systems

KORSAR-B1- best-estimate code a fully non-equilibrium two-fluid model of coolant flow;

SOKRAT/V1 - best-estimate code for modeling severe accident conditions;

KUPOL-M - containment code (lumped paramers);

ANSYS SFX, STAR-CD, PGS-TK, LOGOS, FIRECON special CFD codes for containment calculation;

Program unit KORSAR – KUPOL, SOKRAT-KUPOL integrate codes for joint calculations RV & Conteinment;

DANKO, ANSYS - strength calculations of building constructions, equipment

FIRECON, FIRECON- Calculation of loads on hydrogen

combustion,determination of possible combustion modes


Large-scale test rig “SPOT”

for HRS/SG, CKTI, St.

Petersburg

Test rig “PHRS/C” in OKBM,

Nizhniy Novgorod;

Large-scale test rig “KMS” in

NITI, Sosnovyi Bor;

Experimental validation of Passive Systems

Additional Power Supply Channel from Mobile Diesel Generator


Constantly switched-on switcher

Switched-on by operator switcher

Information and Measurement System


The special control panels for severe accident

management (SAM) are located a the Main and

Emergency Control Rooms

In severe accident at ex-vessel stage the

following parameters are monitoring at the

SAMS panel in MCR:

Temperature in core catcher;

Cooling water level around the core catcher

vessel.

Information and Measurement System (continuation)


Rapid temperature increasing (>

25 oC/s) registered by sensors

in core catcher (or/and their

failure) is the criterion of

reactor vessel brake down and

corium dropping into core

catcher.

BDBA Management Instructions

As a necessary part of design the following documents are developed and

supplied for the NPP owner:

Emergency Operating Procedures (EOPs) – guidance for managing of

design basis accidents and beyond design basis accidents (before core

damage occurs) for core damage prevention.

Severe Accident Management Guidelines (SAMG) - propose a range of

possible mitigating actions and allow make an additional evaluation and

choose alternative actions.


AES-2006 Design has significantly better probabilistic safety characteristic then V-320 design – passive heat removal safety systems allow to decrease the frequency of core damage;

AES-2006 contains the special measures, equipment and procedures for BDBA (including severe accidents) management missing in V-320 design.

AES-2006 fully meets to INPRO criteria 1.4.1-1.4.3

CONCLUSIONS


THANK YOU FOR THE ATTENTION !


Release Into Containment in AES-2006 Design

Documents

Transcript of Release Into Containment in AES-2006 Design