brazilian nuclear operator’s · 2013-08-29 · iaea technical meeting on evaluation of npp design...

IAEA Technical Meeting on EVALUATION OF NPP DESIGN SAFETY IN THE AFTERMATH OF THE FUKUSHIMA DAIICHI ACCIDENT 26–29 August 2013 Vienna International Centre

Brazilian Nuclear Operator’s Response to Fukushima Accident ELETRONUCLEAR – Paulo Carneiro

Contents

1. Angra Nuclear Power Station

2. Brazilian Operator’s Approach to Fukushima

Accident

3. Reevaluation of Hazard Events

4. Reinforcement of Cooling Capacity

5. Mitigation of Accident Consequences

(updated and complementary information to the paper

submitted for the Technical Meeting)

3

1. Angra Nuclear Power Station

ANGRA 1 PWR

Power: 640 MW

Technology: Westinghouse

Operation start: Jan. 1985

ANGRA 2 PWR

Power: 1,350 MW

Technology: KWU/ Siemens

Operation start: Jan. 2001

ANGRA 3 PWR

Power: 1,405 MW

Technology: KWU/ Siemens/ Areva

Under construction

Planned start of operation: May 2018

(illustrative view)

ANGRA 1

ANGRA 2

RADIOACTIVE

WASTE STORAGE

CENTER 500kV Switchyard


Working groups of specialists under guidance of a

Fukushima Response Management Committee;

o gathering and evaluation of information about the accident

onset, development and consequences;

o identification of lessons learned applicable to Brazilian

NPPs;

o safety assessments;

o establishment and management of an execution plan

(studies and projects consolidated in the

ELETRONUCLEAR Fukushima Response Plan);

o participation in national and international discussion forums

about the lessons learned and safety initiatives.

Full Integration with Nuclear Industry Initiatives Brazilian Nuclear Authority


1st Document - Preliminary Report: submitted to CNEN in August, 2011

• Plant Comparison Angra x Fukushima;

• Design Criteria for Protection Against External Events;

• Preliminary Evaluation of Plant Behavior for SBO and LUHS;

• Measures for Mitigation of Consequences from Severe Accidents

2nd Document – Fukushima Response Plan: submitted to CNEN in Dec, 2011

• 58 initiatives (studies and projects, including performance of Stress Tests)

• Protection Against Hazard Events, Reinforcement of Cooling Capacity and

Mitigation of Accident Consequences

• Budget estimation: around US$ 150 million to be applied from 2012 to 2016

3rd Document – Stress Test Report: submitted to CNEN in April, 2012

• According to specification issued by Iberoamerican Forum of Regulatory

Bodies, Nuclear and Radiological (request from CNEN in January 2012)

• Compliance with WENRA Specification for Stress Tests

• Same cross-checking procedure by different regulators as WENRA.


Earthquakes

Low seismicity site

Largest earthquake 5.2 mb at

250 km (PGA 0.002g at site)

Design PGA 0.10g (p< 10-4/yr)

Slopes very steep around the site

Residual and colluvial soils

High rainfall rates

Station protected by slope stabilization

works and slope monitoring system

Rainfalls


Ilha Grande Bay

Angra NP

Station

Bay area, natural protection

from Atlantic Ocean

Tidal Waves

Favorable

geological

characteristics

of the South

Atlantic coast

to


Verification and enlargement of safety margins

Seismic hazard

• updating of geological and seismological database already

started; probabilistic seismic spectra expected for 2016

(preliminary spectrum already available);

• methodology for evaluation of the seismic design margin

under discussion; preliminary results expected for 2014;

Landslides

• reevaluation of slope stabilization works and slope

movement monitoring system concluded, taking earthquakes

in consideration;

• recommendation of reinforcement of some slopes, additional

measures for proper soil drainage and extension of the slope

monitoring system; implementation until 2015;



Tidal waves

• reevaluation of jetty stability, considering severe

meteorological conditions, to be concluded until end of 2013;

• expected indication of reinforcement measures;

implementation until 2016;

Site flooding

• reevaluation of flooding level under more severe conditions

concluded (rainfall rate higher than 10,000 years rainfall,

blockage of site drainage channels and circulating water

discharge tunnel due to landslides and continued operation of

circulating pumps);

• current design flooding level includes sufficient safety margin;

no plant changes necessary.



Tornadoes

• tornadoes were not originally considered for Angra 1 and 2

(few data for defining a design basis for tornadoes);

• tornado hazard study developed for Angra 3 (10-7/yr);

•impact on Angra 1 and 2 under evaluation; affected

components and recommended protective measures until the

end of 2013; implementation until 2016;

Conclusions:

Design basis for external events confirmed;

Opportunity for enlarging safety margins;

Additional protective measures under definition for

implementation in 2 to 3 years.

Event Initial Conditions

• Loss of Offsite Power - LOOP;

• failure to switchover to supply by plant main generator;

• no possibility of external support within 72h after the accident

onset;

Plant in Power Operation

• 100% reactor power;

• reactor and turbine trip after LOOP;

Plant Refueling (worst condition for fuel pool temperature)

• full core transferred to fuel pool;

• full utilization of fuel pool storage racks;

Basic Assumptions for Safety Evaluation

4. Reinforcement of Cooling Capacity

4 x 50% 2 x 100%

M G

2x

M G

2x

M G

4x

M G

4x

EDE – 3/4

EAS – 1A/1B ULB – D2

UBP – D1

SE

500kV

SE

138kV

A2 A1 A2 A1

Cachoeira

Paulista

São

Jos é

Zona

Oeste

Santa

Cruz

2,5h 4,0h

“ Off - Site

Power ”

M G

2x

M G M G M G

2x

2x

M G M G M G

2x

M G

4x

M G M G M G

4x

M G

4x

M G M G M G

4x

EDE – 3/4

EAS – 1A/1B ULB – D2

UBP – D1

Angra 2 Angra 1

SE

500kV

SE

138kV

A2 A1 A2 A1

Cachoeira

Paulista

São

Jos é

Zona

Oeste

Santa

Cruz

2,5h 4,0h

“ Off - Site

Power ”

4 x 50% 2 x 100%

Evaluation of Station Blackout Scenarios (SBO)

special design conditions for

Angra 1 and 2 (12 diesel

groups for 2 reactors !!!)

normal design condition

(2 diesel groups per

reactor)

1st Emergency

Power System

2nd Emergency

Power System

Favorable power supply

conditions in

Angra 1 and Angra 2

both meet NRC

requirements for

exclusion of SBO

Very conservative approach of

considering loss of all AC power

Evaluation of Station Blackout Scenarios (SBO)

• possibility of SG feeding through mechanically driven

pumps (Auxiliary Feedwater Turbine Pump AF-2 in Angra 1

and Diesel Driven Emergency Feedwater Pumps LAS in

Angra 2);

• at least 20 hours in Angra 1 and 33 hours in Angra 2 of

feeding from, respectively, Auxiliary Feedwater Tank - AFT

and Demineralized Water Pools - DWP;

• possibility of AFT and DWP refilling from Fire Fighting

Water Supply System - FFWS (5,000 m3 reservoir, located

on an elevation 110 m above the site grade);

• possibility of full passive secondary B&F from the FFWS

reservoir (connection before SG becomes empty, in case

AF-2 or LAS pump fails, about 50 minutes).

Very conservative approach:

• water intake structures in an area of protected sea water (Ilha

Grande Bay);

• water intake structures protected by jetty 8.0 m high above

average seawater level;

• very low probability of water intake blockage to the extent of

impairing minimum flow for residual heat removal;

Main implications for the plants:

• failure of both Emergency Supply Diesel Generator Systems

in Angra 1 (bunkered Emergency Feedwater Diesels in Angra

2 not dependent on Service Water);

• impossibility of operating the RHR chain.

Evaluation of Loss of Heat Sink Condition

Loss of Fuel Pool Cooling

Unit Plant condition Time until start

boiling

Time until fuel

element

exposure

Angra 1

Power

Operation

18 h 190 h

Refueling (*) 9 h 63 h

Angra 2

Power

Operation

23 h 155 h

Refueling (*) 5 h 35 h

(*) limit condition, full core unloaded and full occupation of pool racks

Fuel Pool Temperature Increase after Loss of Cooling

Improvements in Design / Implementation Phase

Conditions for restoring AC power supply:

• possibility of manual inter-train connection in Angra 1;

• possibility of EPSS1 feeding EPSS2 consumers in Angra 2;

• possibility of manual connection of emergency power busbars

of Angra 1 and Angra 2 (use of large installed DG reserve

capacity);

• alternative for cooling Emergency Power System Diesels of

Angra 1 in case of failure of service water;

• mobile diesel generators for emergency supply of essential

systems and components (1,800 kVA in Angra 1 and 1,000 kVA

in Angra 2);

• mobile diesel generators for recharging batteries (250 kVA for

Angra 1 and for Angra 2)

2014 / 2015

Improvements in Design / Implementation Phase

Conditions for Reactor and Fuel Pool Cooling:

• mobile compressor for operating Angra 1 MS-valves;

• mobile diesel engine driven pumps for feeding SGs (27 kg/s and

75 m head, two pumps for each plant);

• mobile diesel engine driven pumps for refilling AF Tank in Angra 1

and DW Pools in Angra 2 (20 kg/s and 20 m head, two pumps for

each plant);

• additional 4,000 m3 seismic reservoir, located on the elevation

70m above site grade, connected to the plant by seismic designed

piping;

• autonomous mobile cooling unit for fuel pool cooling in Angra 1;

• possibility of fuel pool cooling and residual heat removal

connecting FFWS to the RHR heat exchanger in Angra 2

2014 / 2016

5. Mitigation of Accident Consequences

Containment Protection:

• passive H2 catalytic recombiners already purchased for

Angra 1 and Angra 2 (until 2015)

• filtered venting under technical evaluation for Angra 1 and

commercial clarification for Angra 2 (until 2016);

Severe Accident Management Guidelines:

• pre-Fukushima SAMGs are being implemented in Angra 1

(planned for the middle of 2014);

• post-Fukushima SAMGs are in preparation for Angra 2

(planned for the end of 2014);

Other improvements in the infrastructure for emergency

planning are being planned and performed.

Focus of the 2nd Semester of 2013

• conclude all hazard external event studies and define

additional protective measures (exception: earthquakes);

• define methodology and start seismic margin evaluation;

• finish detailed design for plant modifications related to the

control of SBO and LUHS;

• technical and commercial definitions for purchasing filtered

containment venting;

• finalize safety design concept for BDBA systems and

equipment (plants with different safety design concepts);

• start preparation of procedures for utilization of mobile

equipment (equipment already purchased).

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THANKS FOR THE ATTENTION!

Paulo Carneiro

[email protected]

brazilian nuclear operator’s · 2013-08-29 · iaea technical meeting on evaluation of npp design...

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