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Eletronuclear ( Brazil) Fukushima Response Plan
Edmundo SelvaticiSite Manager
Mario de Mello Ferreira JuniorManager, Materials Engineering
Technical Meeting on Operational Experience with Implementation of Post-Fukushima Actions in Nuclear
Power Plants
25 - 27 march 2017
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2
Angra Nuclear Power Station (single NPP site in Brazil)
ANGRA 1 PWRPower: 640 MWTechnology: Westinghouse Operation start: Jan. 1985
ANGRA 2 PWRPower: 1,350 MWTechnology: KWU/ Siemens Operation start: Jan. 2001
ANGRA 3 PWRPower: 1,405 MWTechnology: KWU/ Siemens/ Areva Under constructionPlanned start of operation: 2022
(illustrative view)
ANGRA 1ANGRA 2
RADIOACTIVE WASTE STORAGE CENTER 500kV Switchyard
Plan in Full Integration with Nuclear Industry Initiatives Brazilian Nuclear Authority
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Response to Fukushima – Main Safety Goals
629
Response to Fukushima – Evaluation of ST Report
Basis: WENRA Specification for
Stress Test Report
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FORO Angra 1 and Angra 2 NPPs Stress Test Report Evaluation
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Protection from Hazard EventsExternal EventsEarthquakes;Rainfalls;Landslides;Tidal Waves;Tornadoes.
• Assessment of existing DB external event scope and design criteria for completeness and updating
• Assessment of safety margins of existing design in case of BD external events
– 1st step: simplified calculations, engineering/expert judgement
– 2nd step: detailed deterministic and probabilistic analyses.
Internal EventsFire;Internal Flooding.
• Reevaluation consideringup-to-date safety requirements;• Identification of design gaps.
Protection from Hazard Events - Results
Earthquakes
Plants Seismic DesignLow seismicity site (intraplaque region). Largest recorded earthquake 5.2 Richter scale at 300 km (PGA 0.002g at site); Design PGA for SSE: 0.1g (p< 10-
4/yr) based on deterministic seismic response spectrum.
Evaluation of margins• estimated safety margins relative to
Design PGA by expert walkdown and judgement : 2 - 2.5 for Angra 1 and 2.5 -3.0 for Angra 2;
• Extensive updating of geological and seismological database (three-years program completed);
• PGMRS( Probabilistic Ground Motion Response Spectrum) determined for use in the Seismic PSA;
• Seismic PSA for Angra 2 completed(safety margin: up to 4xDesign PGA)
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Slopes very steep around the siteResidual and colluvial soils
High rainfall ratesStation protected by slope stabilization
works and slope monitoring system
Rainfall and Landslides
Protection from Hazard Events - Results
Evaluation of margins
Studies considering heavy rains and consequential or seismic induced landslides concluded. Extreme case of full rupture of slope covering material evaluated.
Results:
For worst case switchyard and discharge channels may be affected however no impact on Plants buildings;
Recommendation for enlargement of slope drainage system and reinforcement of some stabilization works (ongoing)
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External Flooding
0 CNG
Angra1 and 2
+ 5.15m + 5.60m
access to safety buildings
plant construction level
Evaluation of margins: 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, highest sea level).Results:Current design flooding level includes sufficient safety margin (up to 75.000 years rainfall); Recommendation for checking and reinforcement of existing flooding barriers (finished).
Protection from Hazard Events - Results
Tidal Waves Protection from Hazard Events - Results
• calculation of tidal waves for severe metereological conditions( sea storms and hurricanes) at Ilha Grande Bay concluded; largest waves> maximum design wave for wave breaker design
• evaluation of wave breaker stability through physical model by international lab being contracted;
• Results may lead to recommendation of breaker structural reinforcement
Ilha Grande Bay
Angra NP Station
Bay area, natural protection from Atlantic Ocean
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Tornadoes
Protection from Hazard Events - Results
Tornadoes were not originally considered for Angra 1 and 2 due to low probability (~10-7/y);Tornado hazard study developed for Angra 3;Impact on Angra 1 and 2 evaluated and actions plans issued for further evaluation and/or protection of selected structures and components.
Internal FireFire Hazard of Angra 1 revised by EPRI (risk based evaluation); design modification packages under evaluation.
Internal Flooding
Reevaluation of Angra 1 design against internal flooding; Recommendation to increase the safety margins under evaluation
4 x 50% 2 x 100%
M G2x
M G2x
M G4x
M G4x
EDE – 3/4
EAS – 1A/1BULB – D2
UBP – D1
SE500kV
SE138kV
A2 A1 A2 A1
CachoeiraPaulista
SãoJosé
ZonaOeste
SantaCruz
2,5h 4,0h
M G2x
M GM GM G2x
2xM GM GM G
2x
M G4x
M GM GM G4x
M G4x
M GM GM G4x
EDE – 3/4
EAS – 1A/1BULB – D2
UBP – D1
Angra 2 Angra 1
SE500kV
SE138kV
A2 A1 A2 A1
CachoeiraPaulista
SãoJosé
ZonaOeste
SantaCruz
2,5h 4,0h
4 x 50% 2 x 100%
Evaluation of Station Blackout Scenarios (SBO)
1st Emergency Power System
2nd Emergency Power System
Existing power supply conditions forAngra 1 and Angra 2(Design or backfit)
both meet NRC requirements for exclusion of SBO
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Off sitePower
Emergency DieselsAngra 1:
2x100% DG ( Plant Design) + 2x100% DG (backfit)Same cooling system for all DG
Angra 2:4x50% EDG +4x50% EFDG in dedicated bunkered building with independent cooling system.
Minimum batery duration
Existing SBO Emergency Procedures
• SG feeding through steam turbine driven pumps (Auxiliary Feedwater Turbine Pumps) in Angra 1 and Diesel Driven Emergency Feedwater Pumps in Angra 2);
• at least 20 hours in Angra 1 and 33 hours in Angra 2 of feedingfrom, 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 level);
• 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).
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Existing design conditions:• water intake structures protected from open sea hazards (Ilha Grande
Bay);
• water intake structures protected by wave breaker 8.0 m high above average seawater level;
• Availability of alternative heat sink by means of Fire Fighting Water Supply System - FFWS (5,000 m3 reservoir, located on an elevation 110 m above the site level); alternative already incorporated in Emergency procedures for both Plants. Not designed for earthquake..
Main implications for the plants:
• Angra 1: failure of both Emergency Diesel Generator Systems (failure of common cooling system);
• Angra 2: Only EDG fail. Bunkered Emergency Feedwater Diesels (EFDG) not dependent of Service Water;
• impossibility of operating the RHR chain.
Evaluation of Loss of Main Heat Sink
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Provision of Cooling Capacity – extreme conditions
Event Initial Conditions• Loss of Offsite and Onsite Power (SBO) and Loss of Ultimate Heat
Sink (LUHS)
Plant in Power Operation• 100% reactor power;
Plant at Refueling (worst condition for fuel pool temperature)• full core transferred to fuel pool;• full loading of fuel pool storage racks;
Deterministic evaluation approach (WENRA/FORO guidelines)
• no credit given to special design features or former backfits at theAngra plants
• no possibility of external support within 72h after the accident onset;
•Based on the Stress Tests results mobile equipment to provide additional means to supply power and cooling capacity for the core and the fuel pools were identified, specified and purchased, comprising
– different sizes of Diesel Generators, Diesel driven pumps and associated connection fixtures.
•General Concept adopted for Mobile equipment– Equipment stored on site in location that is not affected
by the external events that would affect the site, housed in a light tent-like structure commercial grade equipment;
– Mobile equipment connections specified in accordance to the Requirement Category of the systems where the connection is applied.
– Mobile equipment incorporated to the decision trees of the EOPs;
– Mobile equipment have specific procedures; not incorporated to the Tec Specs.
Stress Test results
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• Design modification processes have been developed for the short and medium term strategies, in case of loss of all AC power and/or UHS, as follows:
Short term (1 to 3 hours): recharging of batteries and Steam Generator feed. – Mobile equipment : one 250 KVA DG and 2 Diesel Driven pumps
per Plant;– Countermeasure: Bleed and Feed through the secondary side.Medium term (1 to 2 days): in case of available UHS.– Countermeasure: repowering one RHR cooling train– Mobile equipment: 3 large DG, of 600 KVA each for Angra 1; 2
large DG, of 600 KVA each for Angra 2.Medium term (1 to 2 days): in case UHS is unavailable– Countermeasure: continue Secondary B&F and replenish source of
water for SG cooling (tank/pool) with sea water;– Mobile equipment: 2 submergible Diesel powered pumps
Stress Test results
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•The implementation of a new water reservoir of 4000 m3
meeting seismic requirements located at a height able to provide means of feeding the steam generators in a totally passive way, is in phase of design completion.
•An alternative means of cooling the Diesel Groups in Angra1, in case of loss of the Service Water System (SWS), was developed by installing a connection in the SWS piping for sea water injection with a mobile Diesel powered pump.
Stress Test results
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Overview of Additional Emergency Supply Alternatives
Mobile DG (Emergency Power Supply for essential
Safety Systems)
Mobile DG (Emergency Power Supply for essential
Safety Systems)
Interconnection of Diesel Systems D1 and D2 (intended)
ANGRA 2 ANGRA 1
Alternative coolingchain for Angra 1
Emergency Power DG
Mobile DG (extension of
batteries autonomy)
Mobile DG (extension of
batteries autonomy)
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2017 status (completed)
2017 status (completed)
2017 status (design
concluded)
2017 status (final
implementation)
2017 status (final
implementation)
Additional Alternatives for Reactor Cooling
Alternatives for Reactor Cooling Via Steam Generators
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Angra 1 and Angra 2: Secondary side “bleed-and-feed” through the Steam Generators. (2017 status – final implementation)
Alternatives for Direct Reactor Cooling Angra 2 Primary side“bleed-and-feed”: Installation of additional valves in the Pressurizer valve station with dedicated power supply and I&C. (2017 status – completed). Ensures depressurization of Primary System(bleed).
Mobile Ar Compressor for Remote
Valve Actuation (Angra 1)
Mobile Pumps for SG Feeding Mobile Pumps for Refilling Water Reservoirs
Fire Hoses
Additional Alternatives for Reactor Cooling
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Mobile Equipment maintenance and storage
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Testing and Maintenance activities:
- All tests and maintenance are being performed according the equipmentsupplier manuals;
- Weekly sequence of DG performance tests, mobile pumps and mobile aircompressor;
Loss of Fuel Pool Cooling
Unit Plant condition Time until start boiling
Time until fuel element exposure
Angra 1Power Operation 28 h 179 h
Refueling (*) 9 h 56 h
Angra 2Power Operation 23 h 136 h
Refueling (*) 5 h 31 h
(*) Full core unloaded and full occupation of pool racks
Fuel Pool Temperature Increase after Loss of Cooling
Fuel Pool Cooling alternatives :
• Angra 1 (SFP in external Fuel Building): Feedto the SFP from outside – fire fighting FF) water reservoir or FF truck. (2017)
• Angra 2( SFP inside Containment): fuel pool cooling using fire fighting water – 2018)
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Mitigation of Radiological ConsequencesContainment Protection:
Passive H2 catalytic
recombiners (PARs) already
installed in Angra 1 and 2 (completed)
Containment Filtered Venting (CFV):• AREVA CFV (wet option) under
design for Angra 2. Implementation in steps due to budget limitations
• Not yet decided for Angra 1.
Severe Accident Management Guidelines (SAMGs):•Angra 1: WOG SAMGs have been implemented and integrated with the Emergency Planning (EP) procedures.
• Angra 2: AREVA SAMGs have been developed, implemented and integrated with the Emergency planning procedures.
Other improvements of the infrastructure for Emergency Planning
• Implementation of trails in emergency planning zones (completed)• Improvements in Emergency Centers (underway)• Improvements in radiological protection controls for Severe accident situations(
underway)
