Re-assessment of Cernavoda nuclear power plant design ... · ROMANIA Re-assessment of Cernavoda...

National Commission for Nuclear Activities Control

ROMANIA

Re-assessment of Cernavoda nuclear power plant

design safety in the aftermath of the Fukushima

Daiichi accident

Technical Meeting on Evaluation of Nuclear power Plant Design Safety in the Aftermath of the Fukushima Daiichi

Accident, Vienna, Austria, from 26 to 29 August 2013

Cantemir Ciurea - Ercau, Director, Nuclear Fuel Cycle Division

Technical Meeting on Evaluation of Nuclear power Plant Design Safety in the Aftermath of the Fukushima Daiichi Accident, Vienna, Austria, from 26 to 29 August 2013

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Cernavoda NPP

Reactor Type Gross Capacity

MW(e)

Construction

Start First Criticality Status

Cernavoda-1 CANDU-6 706.5 1980 16th of April

1996 In operation

Cernavoda-2 CANDU-6 706.5 1980 6th of May 2007 In Operation

Cernavoda-3 CANDU-6 720 1980 - Under

Preservation

Cernavoda-4 CANDU-6 720 1980 - Under

Preservation

Cernavoda-5 CANDU-6 - 1980 - Under

Preservation


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Safety re-assessments of Cernavoda NPP

after Fukushima NPP accident

Romania has implemented actions in line with the initiatives taken at

international level:

The first actions taken by the operator were based on the recommendations

in the Significant Operating Experience Report issued by the World

Association of Nuclear Operators (WANO), WANO SOER 2011-2,

“Fukushima Daiichi Nuclear Station Fuel Damage Caused by Earthquake and

Tsunami”.

The actions devised by CNCAN were based on the specifications for “stress

tests” required by the European Commission for all the nuclear power plants

in the European Union, based on a proposal developed by WENRA (Western

European Nuclear Regulators Association) and agreed by ENSREG

(European Nuclear Safety Regulators Group).


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The “stress test” safety reassessment consisted of:

• An evaluation of the response of a NPP when facing a set of extreme situations (e.g.

beyond design basis earthquake, beyond design basis flood, severe weather, etc.);

• A verification of the preventive and mitigative measures chosen following defence-

in-depth logic: initiating events, consequential loss of safety functions, severe

accident management

The following topics were taken into account :

• Topic 1: Initiating events (external events)

• Topic 2: Loss of safety functions

• Topic 3: Severe Accidents Management

In this assessment it was required to consider that the plant has to use only the

on-site resources (conventional and nonconventional equipment, fuel, oil, water,

etc.) for at least 72 hours.

The results of the “stress test” assessment have been subject to a peer-review

and several recommendations were received, in addition to the improvements

already identified and under implementation.

Safety re-assessments of Cernavoda NPP

after Fukushima NPP accident

External Events


External Events

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The following aspects were addressed during the review of design

provisions against seismic, flooding and extreme weather

scenarios:

- Design basis and compliance with the design basis;

- Assessment of plant behaviour for beyond design basis external

events, quantification of safety margins and identification of any

potential cliff-edge effects;

- Identification of measures to increase the robustness of the plant for

extreme external events;

- Planned actions to improve safety.


Design Basis Earthquake

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According to the seismic qualification principles adopted for CANDU

6 NPPs, the design considers two seismic activity levels, both

imposed by nuclear safety requirements, namely:

Design Basis Earthquake (DBE) level - the engineering representation

of earthquakes generating the worst possible severe effects, applicable

to a NPP site and having a sufficiently low probability of being exceeded

during the plant lifetime.

For Cernavoda NPP, the DBE has a return frequency of 1E-03

events/year and based on the site specific hazard curve the intensity

and acceleration are I = VIII degrees MSK-64 and Peak Ground

Acceleration (PGA) = 0.2 g.

Site Design Earthquake (SDE) level - represents the seismic activity

with the period of return for the NPP site 100 years. This is the seismic

design level for the plant systems that must remain operational for a

long period of time after a loss of coolant accident (LOCA).


Validity of Data in Time & Conclusion on the

Adequacy of the Design Basis

In 2004 an update of probabilistic seismic hazard analysis (PSHA)

was carried out for the Cernavoda NPP site.

That PSHA was carried out to support a seismic Probabilistic Safety

Assessment (PSA) for the existing reactors at the Site.

The main conclusions from this study are:

The Vrancea sub-crustal seismic source dominates the seismic hazard at

the Cernavoda NPP.

For the maximum historical recorded event, with a magnitude M = 7.5 the

corresponding PGA at the NPP rock surface is 0.11g.

For the maximum estimated event with a magnitude M = 7.80, the PGA at

the NPP rock surface is 0.18g.


Provisions to protect the plants against the Design

Basis Earthquake

CANDU 6 reactors are designed for safety with a philosophy to deal with

design basis accidents (DBA) and DBE events with significant margins. Both

diverse and redundant systems are implemented to ensure safe reactor

shutdown and fuel integrity.

The safety-related systems, structures and components (SSCs) are divided

into two groups as follows:

Group 1: PHT, shutdown system one (SDS1), main and auxiliary

moderator, steam and feedwater system, emergency core cooling (ECC)

system, shutdown cooling (SDC), Local Air Coolers (LACs), Class I, II, III

and IV power, and the main control room (MCR).

Group 2: shutdown system two (SDS2), Containment Structure,

Containment Isolation System, Dousing, Air locks, Hydrogen Control, EWS,

EPS and the secondary control area (SCA).


Evaluation of seismic margin

The seismic margin analyses have been based on the well established

methodology and on the reports elaborated as part of the Seismic PSA

performed in the period 2004 - 2005 for both Cernavoda NPP Units.

A review level earthquake (RLE) was established at a reasonably high

level seismic ground motion, based on site seismicity and plant specific

design features. The selected RLE has a return period of less than

1/10000 years, with a Ground Motion Response Spectrum (GMRS) with

a PGA of 0.33g.

Based on a review of the DBE qualified systems required for performing

the safety functions, a complete Safe Shutdown Equipment List (SSEL)

has been compiled.

In the framework of the stress test the FRS were pro-rated from 0.33

ZPGA for the targeted value of 0.4 g. to assess the seismic capacity of

SSC. The return frequency for this PGA is 5*E-05.


Conclusions and improvement measures

The plant seismic capacity was assessed for 0.4g (RLE 0.33g).

Up to this value, all the fundamental safety functions can be maintained.

The seismic margin assessment has not revealed a need for any safety

significant design change.

Several recommendations resulted from seismic walkdown, which have

been considered by the licensee as part of the regular plant seismic

housekeeping program.

The robustness of I&C panels has been increased to reduce the relay

chattering effects – (implemented on both units);

The seismic robustness of masonry walls in the CLI/II batteries room

has been increased (currently implemented on both units).


The “stress tests” required also an analysis of cliff-edge effects. For Cernavoda

NPP there are no cliff-edge effects occurring for PGA ≤ 0.4g. Therefore,

assessments of plant behaviour for PGA values greater than 0.4g have not

been performed, meaning that any additional seismic capacity above this value

has not been quantified.

Currently there is no agreed methodology for the performance of assessments

focused on cliff-edge effects rather than of seismic margins expressed in

HCLPF values. Further work will be done in this area, as recommended by the

peer-review, once an internationally agreed methodology becomes available.

Based on peer review recommendations, the adoption of a seismic level

comparable to the SL-1 of IAEA, leading to plant shutdown and inspection, is

currently under consideration.

Currently the actions taken by the licensee following an earthquake are based

on decision-making criteria that include the estimated damage to the plant

(walkdowns using a specific procedure) rather than on pre-defined ground

motion design response spectra.

Recommendations from peer-review


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Reassessment of plant design against flooding events

The assessment started with a systematic review of the original analyses

done for Cernavoda NPP at the siting stage in order to reassess the flooding

level that the plant can withstand without losing any of the main safety

functions that could lead to a severe accident event.

Cernavoda NPP site is located adjacent to the Danube River that is

providing required cooling water flow. The site is 60 km away from the Black

Sea coast.

The site is bordered on the Northeast by Cismelei Valley and on the

Southeast by a bypass channel of Danube-Black Sea Channel (DBSC).

Cooling water for the plant is taken from DBSC through a Bypass Channel,

Intake Channel and Distribution Basin.


Cernavoda site elevations


Cernavoda Area – digital model.

Cismelei Valley.

Cernavoda Area


At the time of the selection of Cernavoda site, it was assumed that

two future dams would be built on the Danube River, one upstream of

Cernavoda and one downstream. These dams were never build but

the supporting studies carried out at that time analysed the different

regimes to determine the maximum (flood) water level of the dam

accumulation lake, and the extreme case of the upstream dam

breaking while the downstream dam holds.

Based on the original study, the maximum design water level for

return period of 1 in 10000 years for Cernavoda NPP is +14.13

mBSL.

The elevation of +16.00 mBSL for Cernavoda NPP site was selected

assuming the extreme postulated failure mode of the planned dams.

Flooding against which the plant is designed


Reassessment of the Design Basis Flood

Potential external flooding sources considered by design for

Cernavoda NPP site are the following:

Extreme Danube River water flow / level;

Extreme local rainfalls.

The original DBF calculation has been reconfirmed by more recent

data and studies, the latest one having been completed in

September 2011, using the modern tool of Digital Topographic

Model (DTM) to create the external flooding hazard map for

Cernavoda NPP site and adjacent area.


Reassessment of the design basis flood has been made considering

the following events:

Extreme Danube River water flow / level;

Flooding due to rainfall on the Cernavoda site platform;

Flooding due to rainfall on catchment area;

Tsunami induced flooding;

Hydro-plant dam failure.

Reassessment of the design basis flood

Technical Meeting on Evaluation of Nuclear power Plant Design Safety in the Aftermath of the Fukushima Daiichi Accident, Vienna, Austria, from 26 to 29 August 2013 19


Worst-case scenario:

Break B4 location in-between Unit 1 and Unit 2

is the worst sensitivity case. The results show

that flowing water could increase up to 1 m

around 110 KV Station and up to 0.5 m behind

the Turbine Buildings were the main output and

unit service transformers are located.

It was conservatively assumed that this scenario

leads to initiating event Total Loss of Class IV power

(loss of off-site power), bounded by the potential

unavailability of Class III Standby Diesel Generators.

Plant response is provided by the existing abnormal

operating procedures at both Unit 1 and Unit 2, since

the buildings housing SSCs required to perform

essential safety functions (EWS/BMW and SCA/EPS)

are not subject to flooding.


Based on the analysis results obtained by making use of the latest

deterministic tools and complemented by probabilistic approach, it

was concluded that the Cernavoda NPP design intent in relation with

flooding hazards provides sufficient safety margins, therefore no

further measures for improvement were envisaged in this area.

Nevertheless, several measures to improve protection against

flooding by flood resistant doors and penetrations sealing have been

implemented for safety related equipment located in rooms below

plant platform level (such as the EPS, SCA, Service building, building

containing the SDGs fuel transfer pumps in Unit1)”. Also, sand bags

have been provided on-site to be used as temporary flood barriers, if

required.



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Extreme Weather Conditions

In order to derive a comprehensive list of severe weather events to be considered for

Cernavoda Units 1 and 2, a review of CNSC regulatory documents and guides, IAEA

guides, ANSI/ANS standards, and US NRC documents and IPEEE experience has been

performed.

The preliminary screening criteria, established in accordance with internationally recognised

standards, consist of the following (any one of these criteria was considered to be sufficient to

screen out the event):

Criterion 1: The event is of equal or lesser damage potential than the events for which the

plant has been designed. This requires an evaluation of plant design bases in order to

estimate the resistance of plant structures and systems to a particular external event.

Criterion 2: The event has a significantly lower mean frequency of occurrence than another

event taking into account the uncertainties in the estimates of both frequencies. The event in

question could not result in worse consequences than the consequences from the other

event.

Criterion 3: The event cannot occur close enough to the plant to affect it. This criterion must

be applied taking into account the range of magnitudes of the event for the recurrence

frequencies of interest.

Criterion 4: The event is included in the definition of another event.

Criterion 5: The event is slow in developing and it can be demonstrated that there is sufficient

time to eliminate the source of the threat or to provide an adequate response.


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Extreme Weather Conditions


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Events screened out based on criterion 5 (slow developing event) have been

addressed in the national stress test report.

Low winter temperature - Ice Cover

Snow

Drought - Low River Level Assessment

Forest fires

Extreme winds and tornadoes

External flooding (addressed in a dedicated chapter in the ST report)

For cases in which the extreme weather conditions could affect the availability of

the off-site power supply and / or the transfer of heat to the ultimate heat sink,

based on the review of severe weather conditions and their impact on the plant,

it was concluded that these would not generate worst accident scenarios as

compared with SBO (Station Black-Out), LOUHS (Loss of Ultimate Heat Sink)

and SBO + LOUHS events.

Although none of the external events related to severe weather has the potential

to induce accident sequences not covered by the existing safety analysis, plant

operating documentation or response capacity of the Cernavoda NPP, the

specific procedure for responding to extreme weather conditions has been

revised to include more proactive actions.


TOPIC 2: Loss of safety functions


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In the “Loss of safety functions” topic the design features have been reassessed

with regard to the fulfilment of the fundamental safety functions in a NPP:

•Control of the reactivity;

•Nuclear fuel cooling;

•Confinement of radioactivity;

•Monitoring of the critical plant parameters.

According to the “stress test” specifications, the assessment results had to

describe the means for maintaining fundamental safety functions in case of:

• loss of power,

• loss of ultimate heat sinks,

and the combination of these scenarios, following external initiating events

considered (earthquake, flooding, extreme weather conditions).

The licensees had to identify the design provisions, the unconventional (mobile)

means, the alternative fuel and water resources and the operating procedures

that can be used in order to ensure the fulfilment of the fundamental safety

functions.

Loss of Safety Functions


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For the “Loss of Power” events, the following scenarios have been analyzed: • Loss of off-site power sources

• Loss of plant generator

• Loss of ordinary back-up generators (diesel generator, gas turbine, etc.)

• Loss of the other diverse back-up sources.

Sequential loss of these sources has been considered in the assessments

performed by the licensees.

For the “Loss of Ultimate Heat Sink” events, the following scenarios have been

analyzed: • Loss of primary Ultimate Heat Sink (UHS) (i.e. access to the water from river or sea,

that represents the primary UHS)

• Loss of primary UHS and the alternate UHS.

In addition, the combination of these events has been considered in the

assessment performed by the licensee, including as a consequence of extreme

external hazards (earthquake or flooding).

Loss of Safety Functions (cont’d 1)


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Cernavoda NPP Electrical power supply system description

There are five levels of electrical power supply at the Cernavoda NPP:

1. Class IV electrical power supplied from the grid or from the plant turbine

generator;

2. Class III electrical power supplied from the first set of diesel generators (SDG)

with 100% redundancy built-in;

3. Class I / II electrical power supplied from batteries for 8 hours;

4. Emergency Electrical Power Supplied (EPS) from the second set of diesel

generators (seismically qualified) known as emergency power supply (EPS)

designed to 100% redundancy and separation requirements;

5. The mobile diesel generators (MDG)

- Two MDG of 1.2 MWe for both Cernavoda NPP units

- Smaller MDG for other purposes (ensure the power for the fire pumps)

Loss of Electrical Power Supply


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Taking into account the design basis, the operating procedures and accident

management measures, the plant units have a high level of defense against the

loss of power and its consequences.

The cliff edge effect for SBO scenario has been defined as the plant

parameter of loss of inventory to all SGs as a heat sink. Design and operational

features, which can avoid these cliff edge effects, are available at the plant:

Eight main steam safety valves (MSSVs) can be open, by the operator or on

the auto-depressurization logic long before the dry-out condition, allowing

timely make-up of water to the steam generators. The MSSVs must remain

blocked open for long term cooling.

After the SGs are depressurized, gravity-fed make-up from the dousing tank

is available through the Boiler Make-up Water system (BMW) pneumatic

valves (PVs) in series, in the medium term.

If the PVs are uncontrolled, the time available for the make-up inventory for

decay heat removal from PHT is 27 hours. If the PVs are controlled, more

than 7 days are available for decay heat removal from PHT.

In the long term, MDGs can power the EWS pumps supplying water to the

SG (or EPS).

Conclusion on the adequacy of protection against

loss of electrical power (cont’d 1)


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Cernavoda Ultimate Heat Sinks (UHS):

The primary Ultimate Heat Sink (UHS) is based on decay power heat removal

using forced cooldown circulation in PHT system.

• PHTS (Primary Heat Transport System)+ SDCS (shutdown cooling system

) + RCW (Recirculating Cooling Water ) + RSW (Raw Service Water) +

Danube River.

The alternate heat sink is based on decay power heat removal using natural

circulation in PHT system.

• PHTS (Primary Heat Transport System)+SGs (Steam Generators) +

“feedwater train” inventory + MSSVs (Main Steam Safety Valves) +

Atmosphere.

The alternate Ultimate Heat Sink is based on decay power heat removal using

natural circulation in PHT system.

• PHTS (Primary Heat Transport System)+SGs (Steam Generators) + BMW

(Boiler Makeup Water – from Dousing Tank)/EWS (Emergency Water

Supply – from Danube River) + MSSVs (Main Steam Safety Valves) +

Atmosphere.

Loss of the decay heat removal capability/Ultimate Heat Sink


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The assessment performed by the licensee demonstrated that there are

sufficient means (especially the dousing tank inventory) to ensure the fulfillment

of safety functions even in the case of total loss of UHS.

The cliff edge effect for this scenario is defined as the plant parameter of loss of

inventory to all SGs as a heat sink. There are sufficient design provisions to

avoid these effects.

SGs inventory will last for 2 hours prior to SGs reaching the dry-out condition.

8 MSSVs will be open based on the auto-depressurization logic long before the dry-out

condition allowing timely make-up of water to the steam generators. The MSSVs must

remain block open for long term cooling.

After the SGs are depressurized, gravity-fed make-up from the dousing tank is

available through two sets of EWS pneumatic valves in series, in the medium term.

If the PVs are uncontrolled, the time available for the make-up inventory for decay heat

removal from PHT is 23 hours.

If PVs are controlled, 7 days continuous heat sink is available.

In the long term, means to make-up water supply to the dousing tank (via on-site fire

water trucks, firewater, water from the river, etc.) either through the EWS or the ECC

would ensure long term cooling.

Conclusions on the loss of the primary ultimate heat sinks(UHS)

(primary and alternate UHS)


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The station response at the loss of primary UHS event coincident with

– or generated by – a SBO, is based on the EWS system, being

powered from the mobile DGs.

For the unavailability of the EWS system (loss of Alternate UHS), the

response consists of fire water trucks connected directly to EWS pipes

through special connections.

The mobile diesel generators can be deployed within 2.5 to 3 hours to

restore the power to EWS.

Loss of the primary ultimate heat sink,

combined with station black out


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Cernavoda NPP performed the assessment of the scenarios required

by “stress test” specifications, including the assessment of the cliff

edge effects;

With respect to electrical supplies, there is a good level of redundancy

and diversity.

The primary and alternative heat sinks provide a good level of

redundancy and diversity.

Following the topical peer review and the country visit, the option of

recharging the batteries or the installation of a supplementary

uninterruptible power supply for the SCA is being considered by the

licensee as a potential improvement.


TOPIC 3: Severe Accident Management


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The assessment of the severe accident management area addressed

the following aspects:

- Current accident management measures in place for preventing and

mitigating core damage;

- Accident management provisions and design features for protecting the

containment after core damage;

- Prevention of H2 deflagration and detonation, prevention of containment

overpressure (in slow overpressurization scenarios), prevention of re-

criticality, prevention of high pressure core melt ejection scenarios,

prevention on basemat melt-through;

- Accident management for scenarios involving loss of cooling to the spent

fuel pool;

Reassessment of Severe Accident Management


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The SAMGs for Cernavoda NPP have been developed based on the

generic CANDU Owners Group (COG) SAMGs for a CANDU-6 type

of plant. In developing the generic SAMGs, COG adopted the

Westinghouse Owners Group (WOG) approach, with the necessary

technical modifications suitable for implementation in CANDU plants,

based on extensive CANDU specific severe accident analysis and

research.

Preparation of plant-specific SAMGs was done by customisation of

the generic COG documentation package for Cernavoda NPP,

removing extraneous information not applicable to the station,

incorporating station-specific details and information and making any

other adjustments required to address unique aspects of the plant

design and/or operation.

Accident management measures in place for preventing and

mitigating core damage


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EOPs & SAMGs

APOP Scope of application

APOP-00 SS / CRO Transient Response Strategy

APOP-E01 Dual Computer Failure

APOP-E02 Loss Of Feedwater

APOP-E03 Loss Of Instrument Air

APOP-E04 Loss Of Service Water

APOP-E05 Loss Of Class IV Power (i.e. loss of off-site power)

APOP-E06 Large LOCA

APOP-E07 Small LOCA

APOP-E08 Steam Generator Tubes Failure

APOP-E09 Partial Loss Of Class IV Power

APOP-E10 Danube Very Low Level

APOP-G01 Generic Heat Sink (MCR – Main Control Room)

APOP-G02 SCA (Secondary Control Area) Operation

APOP-G03 Station Black Out

APOP-G04 Abnormal Spent Fuel Bays Cooling Conditions

SAMG Priority Scope of application

Severe Accident Guidelines

(SAG)

SAG-1 Inject into Heat Transport System

SAG-2 Control Moderator Conditions

SAG-3 Control Calandria Vault Conditions

SAG-4 Reduce Fission Product Release

SAG-5 Control Containment Conditions

SAG-6 Reduce Containment Hydrogen

SAG-7 Inject into Containment

Severe Challenge Guideline

(SCG)

SCG-1 Mitigate Fission Product Release

SCG-2 Reduce Containment Pressure

SCG-3 Control Containment Atmosphere Flammability

SCG-4 Control Containment Vacuum




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EOPs & SAMGs




Conclusion and improvements

in the area of Severe Accident Management

After the Fukushima Daiichi accident, a complex safety review of

the design was undertaken aimed to assess robustness and to

identify solutions to increase the protection against severe

accidents;

Several design improvements have been identified and have been

implemented or are under implementation to maintain fuel cooling

during severe accident conditions and to enhance the capability to

maintain containment integrity in case of severe accidents.

The status of the implementation of the improvements is presented

on the following slides.


Design improvements

in the area of Severe Accident Management - implemented

Actions implemented:

Installation of PARs (passive autocatalytic recombiners) for hydrogen

management in Cernavoda Units 1 and 2.

Accident management provisions for events in the spent fuel pools

(natural ventilation for vapours and steam evacuation, seismically

qualified fire-water pipe for water make-up).

Improvement of the reliability of the on-site emergency control centre

(increased seismic robustness) and of the on-site emergency

organization.

Installation of Special Communication Service phones in each Main

Control Room and Secondary Control Areas.


Design improvements

in the area of Severe Accident Management – in progress (1)

Actions in progress:

Additional instrumentation for severe accident (SA) management

(e.g. hydrogen concentration monitoring in different areas of the

reactor building): to be completed in 2013.

Installation of dedicated emergency containment filtered venting

system for each NPP unit: to be completed in 2013 for Unit 1 and in

2014 for Unit 2.

Improvement of the existing provisions to facilitate operator actions

to prevent a severe accident in the spent fuel pool (water level and

temperature monitoring from outside the SFP building): to be

completed by the end of 2014.

Improvements to the reliability of existing instrumentation by

qualification to severe accident conditions and extension of the

measurement domain: to be completed in 2014 for Unit 1 and in

2015 for Unit 2.


Design improvements

in the area of Severe Accident Management – in progress (2)

Actions in progress:

Implementation of a design modification for water make-up to the

calandria vessel and the calandria vault (completed for Unit 2

calandria vessel): to be finalized in 2013;

Establishment of a new seismically qualified location for the on-site

emergency control centre and for the fire fighters; this location will

include important intervention equipment (mobile DGs, mobile diesel

engine pumps, fire-fighter engines, radiological emergency vehicles,

heavy equipment to unblock roads, etc) and will be protected against

all external hazards: to be completed in 2015;


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Accident management for scenarios involving

loss of cooling to the SFB

In response to the Fukushima accident, based on WANO SOER 2011-2

recommendations, an emergency operating procedure called “APOP G04 -

Spent Fuel Bay cooling abnormal conditions“ was developed, validated and

issued in order to address prolonged/ extended loss of Spent Fuel Bay cooling

capability, main goal being to prevent fuel bundles damage and H2 generation,

due to overheating.

During the worst case scenario (loss of Class IV together with loss Class III,

earthquake or Station Black-Out) when the normal cooling and normal

demineralized water make-up is lost for a prolonged period of time (there are

60h available until water in the bays would start to boil), the APOP G04

procedure guides the operators to establish another means of water make-up in

the Spent Fuel Bay. This is performed using fire trucks or mobile pump via hose

connections, maintaining spent fuel submerged.

To support APOP G04 execution, several design changes and operational

measures have been implemented. It should be noted that on the assumption

than no action is taken to replete the SFB inventory, there would be 15 days

until the first row of fuel bundles become uncovered.

Conclusions


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Design measures: a set of plant modifications have been proposed by the

Cernavoda NPP to be implemented in order to:

Increase the robustness of the plant and avoid the occurrences of severe

accidents following extreme external hazards

Provide different means for the mitigation of severe accidents effects, to

ensure the integrity of the containment and limit the radioactive releases in

case of beyond design basis accidents

To ensure the monitoring of the critical plant parameters and the emergency

response in case of severe accidents determined by extreme external

hazards

Operational measures: review of the abnormal and emergency procedures as

well as Severe Accident Management Guidelines in order to improve the

response of the operators and technical personnel of the plant in case of

extreme external conditions and consequential loss of power/loss of UHS;

training of the personnel in relation with the new operating procedures and

SAMGs.

Stress Test Results (1)


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Some of the proposed modifications or reviews have been already

implemented, others are in progress, approved by CNCAN.

The Romanian National Action Plan is summarised in the annex 2 of

the sixth revision of Romanian National Report under the Convention

on Nuclear Safety (http://www.cncan.ro/assets/stiri/Romanian-Report-

for-the-CNS-6th-Edition.pdf) and provides an outline of the main

improvement activities resulting from the post-Fukushima safety

reviews performed to date.

The action plan has been developed for bringing together the actions

identified from regulatory reviews, self-assessments, peer-reviews

and generic recommendations at international level.

All major design improvements are planned to be completed by the

end of 2015.

Stress Test Results (2)

http://www.cncan.ro/assets/stiri/Romanian-Report-for-the-CNS-6th-Edition.pdf























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As a follow-up to the “stress test”, CNCAN will continue the following

actions:

Verification of the licensee’s implementation of the action plan;

Verification of the implementation of a surveillance and testing programme

of the licensee for the equipment procured to mitigate the consequence of

SBO, loss of UHS and mitigation of the severe accidents;

Verification of the operators’ training programme to include the SAMGs;

Update of the routine inspection package of CNCAN resident site

inspectors to include the verification of the availability of the equipment

procured to mitigate the consequence of SBO and loss of UHS;

Requirements on severe accident management will be included in a new

regulation that is under preparation for publication;

Verification of the implementation of the design modifications which are in

progress and of the update of the relevant operating documentation.

Further Regulatory Actions

Examples of safety improvements

after Fukushima


Flooding resistant doors


Main Steam Safety Valve manual opening kit

hydraulic jack

N2 supplies for

MSSVs pneumatic

actuation


Mobile Diesel Generators


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Thank you for your attention

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