Multinational Design Evaluation Programme
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MDEP Design-SpecificCommon Position
CP-HPR1000WG-01
HPR1000 WORKING GROUPCOMMON POSITION ADDRESSING FUKUSHIMADAIICHI NPP ACCIDENT-RELATED ISSUES

Participation
Regulators involved in the MDEP working group
discussions:

ARN (Argentina), NNSA (China),
NNR (South Africa), ONR (UK)

Regulators which support the present common position:

ARN (Argentina), NNSA (China),
NNR (South Africa), ONR (UK)

Regulators with no objection:

none

Regulators which disagree:

none

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Multinational Design Evaluation Programme
Design-Specific Common Position
CP-HPR1000WG-01 FOR PUBLIC USE

Date: November 2020
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Multinational Design Evaluation Programme
HPR1000 Working GroupCOMMON POSITION ADDRESSING FUKUSHIMA DAIICHI NPP ACCIDENTRELATED ISSUES

Context:
A severe accident involving several units took place in Japan at Fukushima Daiichi Nuclear
Power Plant (NPP) in March 2011. The immediate cause of the accident was an earthquake
followed by a tsunami coupled with inadequate provisions against the consequences of such
events in the design. Opportunities to improve protection against a realistic design basis tsunami,
such as taking into account analyses providing frequency/magnitude information on tsunamis in
the region, were not taken.
As a consequence of the tsunami, safety equipment and the related safety functions were lost at
the plant, leading to core damage in three out of the four units and subsequently to large
radioactive releases (INES 7).
Several studies have already been performed to better understand the accident progression anddetailed technical studies are still in progress in Japan and elsewhere. In the meantime, on-goingstudies on the behaviour of NPPs in very severe situations, similar to that experienced at
Fukushima Daiichi NPP during and after the accident, seek to identify potential vulnerabilities inplant design and operation; to suggest reasonably practicable upgrades, or to recommend
enhanced regulatory requirements and guidance to address such situations. Likewise, agencies
around the world that are responsible for regulating the design, construction and operation of
HPR1000 plants are engaged in similar activities.
Based on the MDEP Common Position CP-STC-02, issued by steering technical committee(STC) in September 2016, this common position is developed by the MDEP HPR1000 Working
Group (HPR1000 WG) members, consisting of regulators from Argentina, People's Republic ofChina, South Africa and the United Kingdom. This report supplements CP-STC-02 and should
be read in conjunction with that document. Since the regulatory reviews of the HPR1000 design
have not yet been completed by all of the member countries, this paper identifies common
preliminary approaches and regulatory expectations to address potential safety improvements for2

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HPR1000 plants, as related to lessons learned from the Fukushima Daiichi accident or
Fukushima Daiichi-related issues. In seeking a common position, regulators will provide input tothis paper to reflect their regulatory expectations regarding the HPR1000 design and how thedesign could be enhanced to address Fukushima Daiichi issues. This paper can be updated as
appropriate to reflect regulatory conclusions when the relevant member countries havecompleted their regulatory reviews. This report is organized into six sections, namely,
evolutionary improvements in safety, hazards, reliability of safety functions, accidents withcore melt, spent fuel pools, and emergency preparedness in design, in line with CP-STC-02.
CP-STC-02 also includes a “STATEMENT REGARDING THE VIENNA DECLARATION ON
NUCLEAR SAFETY”. HPR1000 MDEP working group members intend to consider a separate
Technical Report/Common Position on the issue.
It should be noted that the HPR1000 design includes two specific options; Option 1 is currently
under construction at Fangchenggang, and Option 2 is currently under construction at Fuqing.
Designs being considered outside of China are variations on one of these two options.
Differences between the two options that are relevant to this common position are described in
the following sections. Different regulators within the HPR1000 WG are assessing different
options and therefore the common positions outlined in this paper are high level principles that
relate to both options.
Lessons Learned from the Fukushima Daiichi Accident:
The Fukushima Daiichi NPP accident demonstrates the importance of reinforcing the Defencein-Depth (DiD) principle, correctly identifying external hazards including their magnitude andcredible combinations, and design provisions to protect the installation. This should be reflected
in licensing requirements and detailed in the installation safety case. The accident also reinforced
the need to have a comprehensive safety analysis using both deterministic and probabilistic
methods in a complementary manner to provide coverage of all safety factors. In the safetyassessment, specific consideration needs to be given to both multi-unit sites and to address longterm measures protecting the plant.
One has to bear in mind that the specific nature of individual events and challenges can never becompletely taken into account in design and operation of a nuclear power plant (or indeed anyother industrial facility). However, a robust design based on DiD with reliance on passive
design principles, sizeable safety margins and diverse means for delivering critical safetyfunctions as well as flexible, symptom-based operator response plans will help to address
accidents beyond the current design basis (i.e. latest licensing basis).
The design, construction, manufacturing and installation of Structures, Systems and Components(SSCs) should rely on appropriate engineering measures and sufficient margin beyond the design
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criteria required for a design basis accident to avoid cliff edge effects 1. Operation, including
examination, maintenance inspection and testing, must not undermine these engineered measuresand margins. Such an approach will help to ensure an appropriate response, should a beyond
design basis accident occur. Provisions aiming at facilitating the repair/recovery of impaired
safety functions should also be considered.
EVOLUTIONARY IMPROVEMENTS IN SAFETY
I. The Fukushima Daiichi NPP accident confirms the relevance of the general safety objectives
that have been considered for Generation III reactors, such as the HPR1000 (lower probabilityof core melt, limitation of releases, management of severe accident situations…)
Design Features
As compared to most current operating reactors, the HPR1000 applies the DiD concept andincorporates design features to address the learning obtained from the Fukushima Daiichi
accident. The reactor has safety systems using both active and passive features, which aredesigned with the capability to cool the core, containment, and spent fuel pool for 72 hours
without the need for off-site support. Loss of Ultimate Heat Sink (LUHS) and Station Blackout(SBO) are also considered in the design. In addition, there are systems to provide for severe
accident management and protection against external events such as earthquakes and flooding.
In order to enhance the emergency response capability, as a post-Fukushima Daiichi resiliencemeasure, mobile diesel generators and mobile pumps are also included in the HPR1000 design.
The mobile diesel generator provides power to limited safety functions upon extended total lossof alternating current (AC) power (i.e. loss of off-site power + loss of Emergency Diesel
Generators (EDGs) + loss of SBO generators), and the mobile pump provides water to theprimary circuit, the secondary circuit and the spent fuel pool. The HPR1000 design has
considered the need for mobile equipment to be protected from potential common cause failurescaused by internal and external hazards.
Common Positioni.

The regulators of the HPR1000WG expect that the independence between levelsof DiD is achieved to the extent that is reasonably practicable.

Cliff edge effects are the effects of those hazards for which a minimal increase in the hazard’s magnitude can havea much higher impact. For example, the external flooding hazard may have little to no impact to a nuclear power
plant below a prescribed flood level. However, a small increase beyond that prescribed flooding level could impact
many of the nuclear power plant’s functions and lead to a severe accident.
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ii.

The regulators of the HPR1000WG expect that equipment for severe accident
response is designed with appropriate integrity, availability and robustness toensure resilience to all relevant external hazards.

iii.

Mobile pumps and power supplies play a positive role in accident mitigation. The
regulators of the HPR1000WG expect that measures will be taken to protect
mobile equipment from common cause failures. However, considering that theseare supplementary measures which are not part of the generic design, different
member countries may have different requirements and expectations for ensuring
the availability of mobile equipment in emergency situations.

HAZARDS
II. While acknowledging that external hazards are primarily site dependent and that theadequacy of the design has to be reviewed on a case-by-case basis considering the sitecharacteristics, it is important that the safety systems of reactors are designed and protected totolerate external hazards and internal events, mostly by applying adequate physical separationand protection against dynamic loads.
Design Features
The accident at Fukushima Daiichi has reinforced the need to undertake a comprehensive
analysis of external hazards, including consideration of relevant combinations of events. Thisshould include analysis that addresses how these hazards could impact areas of the proposed
NPP where significant amounts of radioactive material are expected to be present.
The designers claim that the HPR1000 design considers external events and defines aconservative design basis with appropriate margin (e.g. seismic events, external flooding,extreme temperature, extreme wind, tornado, etc.), as well as the extreme scenario resulting frombeyond design basis external events.
a) Seismic Design
For the HPR1000 design, the peak ground acceleration adopts 0.3g in the horizontal direction
and 0.2g in the vertical direction for Safety Shutdown Earthquake (SSE) (IAEA SL-2 seismic
design basis). The safety-related structures are designed to defend against SSE using site,
national and/or international design response spectra. Safety classified SSCs including
mechanical and electrical equipment are designed using resultant floor response spectra towithstand SSE.
b) External Flood Design

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For the HPR1000 design, a risk assessment of flooding has been undertaken, and the plant layout
has been designed to protect against or eliminate the possibility of flooding inundation.. Design
Basis Flood (DBF) has been used to determine the height of the plant/site and considers theinfluence of the coastal flooding hazard including tsunami. The NPP drainage design protects thesite from accumulated ponding with analysis undertaken to check that the capacity of thedrainage system in the plant area is sufficient.
Important equipment such as EDG is located at higher elevations. The design basis flood levelshould be used to superimpose the 1 in 1000 years’ precipitation hazard to assess the depth ofwater entering the plant. According to the assessment results, flood defence measures both atground-level and underground are adopted. Generally, permanent waterproof sealing should be
adopted. For cases where permanent waterproof sealing is not possible, temporary waterproof
flooding measures can be adopted after evaluation.
c) Extreme wind and extreme temperature
The HPR1000 has been designed against a range of extreme environmental conditions. Extreme
wind speed is determined by the relative low return period gust wind speed. For example,
64.3m/s and 68.4m/s are set as the design basis of the nuclear island buildings at the
Fangchenggang (Option 1) and Fuqing (Option 2) sites respectively. Extreme high/low
temperatures are determined by the statistical value of the relative low return period. For
example, 38.5ºC/-1.8 ºC and 42℃/-4.4℃ are set as design basis at the Fangchenggang (Option
1) and Fuqing (Option 2) sites respectively.
Common Positioniv.

The regulators of the HPR1000WG expect all relevant external hazards to besystematically identified and characterised, screened using defined criteria andanalysis of those screened-in hazards to enable the selection of design basis inaccordance with national regulations and guidance. For those external hazards
characterised by a hazard curve (i.e. typically natural hazards), the analysis could
extend the hazard curve to an appropriate, low frequency to support beyond
design basis, probabilistic and severe accident analyses. Credible combinations
should be defined as additional design basis events.

v.

The plant will be assessed against these hazards in accordance with establishedassessment methodologies and criteria, including consideration of beyond designbasis hazards and cliff-edge effects to demonstrate the robustness of the plant andavailability of margin. The hazard assessment should consider combined andconsequential hazards that may increase the plant challenge.

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Multinational Design Evaluation Programme
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External events could exceed the assumptions used in the design and licensing ofa plant, as demonstrated by the events at Fukushima Daiichi. International
practice is to establish design input parameters by both deterministic andprobabilistic methods, but to proceed with the design in a deterministic manner(e.g. selection of a design basis value from the hazard curve). There is a “beyond
design basis” component to consider for those hazards which can be evaluated tovery low return periods (albeit with increasing levels of uncertainty), well below
the design basis frequency. External events beyond those accounted for in thedesign basis are unlikely to occur, but could present challenges to NPPs should
they transpire. In order to address these challenges, licensees need to enhancetheir ability to cope with conditions resulting from external events exceeding
those considered for design.

vii.

It is generally accepted that there are two aspects of beyond design basis analysis.
Firstly, the design is analysed for cliff-edge effects just beyond the design basis
and to identify the margin to the point(s) where safety functions are no longer
achieved, as a function of increasing hazard severity. Second is consideration of
extreme events that could severely challenge plant safety functions across the site
to understand how SSCs required for nuclear safety respond, the failure modes
that can occur and how the ability of SSCs and operators to deliver safetyfunctions degrades.

viii.

Design basis definitions differ between member countries. The design basis
external events for the HPR1000 design have been derived according to extreme
conditions at the candidate sites. These particular design basis values should becompared with the specific expectations in different countries to assess theadequacy of the HPR1000 design for specific sites.

RELIABILITY OF SAFETY FUNCTIONS
III. It is observed to date, from those regulators who have made safety findings in the review of
their design applications, that since most safety functions depend on electric power that thereactors could suffer cliff-edge effects after a limited period of time following infrequent andsevere external hazards, particularly those involving a common-cause failure that results inlong-term loss of power and cooling. Those regulators acknowledge that safety improvements
have been proposed to address those situations. Continued discussions, detailed design, andanalysis will be needed to make final approvals of these improvements.
Design Features

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The key safety functions that should be protected are reactivity control, reactor cooling andcooling of spent fuel in the spent fuel pool and confinement of radioactive material. Ensuring
adequate protection, through appropriate design, plant layout, electrical and physical separationand segregation, electrical isolation, etc. of the power supplies against infrequent and severe
external hazards is a lesson from the Fukushima Daiichi NPP accident.
The designers claim that in order to achieve the safety functions for HPR1000 the principle of
DiD is applied, and SSCs important to safety will be capable of withstanding identified initiating
events with sufficient robustness which is ensured by redundancy, diversity, and independence.
The HPR1000 design uses active and passive design features to achieve robustness andreliability of safety functions. Different trains of safety functions are physically separated where
possible, as are SSCs among the enhanced DiD levels. It is noted that the details of thesesystems differ between Options 1 and 2 of the HPR1000 design and each member country willassess the design against relevant national requirements and expectations.
At DiD Level 3 the HPR1000 design includes at least two active safety systems to protect against
design basis accidents (DBA). These include medium head safety injection, low head safety
injection, and auxiliary feed water system. These are supplemented by passive components suchas accumulators.
The HPR1000 has additional DiD measures which provide diverse ways to deliver safetyfunctions should the DBA safety measures not be available. For Option 1, the safety measures
include secondary passive heat removal system (SPHRS), SBO diesel generators and extra
cooling system (ECS). For Option 2, the safety measures include SPHRS, turbine-driven
auxiliary feedwater system, air-cooled chilled water system and the passive containment coolingsystem (PCS).
Ensuring the energy supply and heat removal is an important lesson learned from the Fukushima
Daiichi Accident, the HPR1000 designers claim that the following design measures are
considered correspondingly.
For both Option 1 and Option 2, the power is supplied by two independent external sources
during normal operation. EDG and SBO DG are provided to increase the reliability of power
supplies, and mobile DG and severe accident batteries are provided to ensure power supplies tosafety systems are maintained under extreme conditions. The EDG and SBO DG are diverse andseparated from others to avoid the potential common cause failure, and the capacities of thesediesel generators are long enough to withstand a long term of loss of offsite power event.
For both Option 1 and Option 2 the cooling chains for accidents are safety classified andredundant trains are incorporated for residual heat removal; that is, a diversified Extra Cooling
System for option 1, and the air-cooled chilled water system and the PCS for option 2.
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Common Positionix.

A robust and independent DiD concept should be established to ensure the reliability ofsafety functions.

x.

Quality management arrangements covering processes throughout the lifecycle including
design, manufacture, supply, installation, operation and maintenance of safety related SSCs
in the design should be established.

xi.

Systems performing the same safety function(s) should be designed with appropriate
redundancy and diversity to ensure independence and reliability. Any exceptions to thisshould be justified.

xii.

Redundant safety systems should be designed with adequate separation and segregation to
avoid propagation of failures between systems.

xiii.

LUHS and SBO should be considered in order to ensure continued delivery safety functions
for extended periods. Reliability of associated support systems (such as heating, ventilation,
air conditioning and water sources) should also be considered.

xiv.

Probabilistic safety targets (CDF) should be established in the design to determine adequate
reliability of safety functions.

xv.

Different member countries may have different requirements and expectations; a typicalexample is that, anticipated transient without scram (ATWS) is a design basis accident in the UK
but a beyond design basis accident in China.

ACCIDENTS WITH CORE MELT
IV. The regulators recognise that the generic design includes measures to mitigate theconsequences of severe accidents. The design benefits from reinforced measures to prevent
accident situations such as high pressure core melt, global hydrogen detonations and in-vessel
and ex-vessel steam explosions, which would lead to large or early releases. Nevertheless, assome severe accident management systems rely on AC and direct current (DC) power, at least
after a few hours, regulators recognise the need to reinforce existing or proposed provisions toincrease the time available before cliff-edge effect. Due consideration to those cliff edge effects
is to be given while tailoring long term loss of electrical power mitigation strategies.
Design Features
The designers claim that safety features have been incorporated to mitigate the potential forsevere accidents in the design of HPR1000. These safety features are designed to have adequate
independence from the other plant safety provisions, and also to be adequately protected against
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internal and external hazards. The anticipated ambient environmental conditions have been
calculated and the necessary equipment and instruments have been qualified to ensure that they
could perform their functions.
The HPR1000 design includes two trains of severe accident dedicated valves (SADVs) designed
to depressurise the primary circuit during a hypothetical severe accident event. The SADVs aredesigned to reduce pressure below that in which a high pressure melt ejection can occur, thus
avoiding direct containment heating.
The layout of the containment building has been designed with the principle of promoting natural
circulation and mixing, in order to reduce the risk of local build-up of combustible gases. This
principle has also been applied to determining the location of passive autocatalytic recombiners
for the containment combustible gas control system design scheme.
The In-Vessel Melt Retention external reactor vessel cooling strategy (IVMR-ERVC) has been
incorporated in the design of the HPR1000 to avoid Molten Core Concrete Interaction (MCCI).
The reactor cavity injection system based on passive and/or active injection (depending on
Option 1 or Option 2) has been designed to remove corium decay heat.
Containment Heat Removal Systems have been designed to actively (Option 1) or passively(Option 2) remove heat independent of the HPR1000 designs. The HPR1000 containment design
includes an additional containment filtration and exhaust system for when the dedicated severe
accident mitigation systems have failed, which is used to prevent structural failure of thecontainment.
The HPR1000 is also designed with a dedicated severe accident Instrumentation and Control(I&C) system. These safety features are designed with DC batteries, which provide differing
mission times dependent on the philosophy (12-24 hr for Option 1, and 72 hr for Option 2).
Common Position
xvi.

Event sequences and conditions such as direct containment heating, steam explosions, largehydrogen detonation, and basemat melt-through or containment excessive pressure, should
be considered in the design.

xvii.

The design features for the above event sequences and conditions should be sufficiently
reliable. The selection of "event sequences and conditions" should be based on engineering
judgement, deterministic assessments and probabilistic assessments.

xviii.

For severe accidents, maintaining the containment integrity is the main objective. This also
implies that the cooling and stabilization of the molten fuel, and the removal of heat from thecontainment, need to be achieved in the long term
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xix.

Reasonable channels for circulation and diffusion should be considered in design, to prevent
large volumes of local hydrogen accumulation. Layout principles should be defined for
combustible gas control equipment, to control the concentration of combustible gas incontainment, and supplemented by adequate assessment to demonstrate its adequacy.

xx.

In accordance with the DiD approach, these safety features should be independent as far as
reasonably practicable from the other plant safety provisions, and they should also be
designed to be adequately protected against internal and external hazards.

xxi.

The necessary equipment and instruments should be capable of performing their safetyfunctions in the severe accident environmental conditions.

xxii.

Severe accident management guidelines should be developed to inform the crisis team totake appropriate actions.
SPENT FUEL POOLS
V. The Fukushima Daiichi NPP accident also highlighted the need to fully consider safety in thedesign of spent fuel pools. This implies that single initiating events, multiple failure events,
internal hazards as well as external hazards should be properly addressed. In particular, thecooling and structural integrity of the spent fuel pools needs to be ensured with adequate margin
in case of external hazards.
Design Features
During normal operations and some design basis accidents, the Fuel Pool Cooling and Treatment
System (FPCTS) is designed to remove heat from the Spent Fuel Pool (SFP). The FPCTS has
been designed with the principle of redundancy and is classified as a safety related system. The
heat exchangers are cooled by the Component Cooling Water System (CCWS). For option 1, an
Extra Cooling System is provided which is actuated upon loss of the CCWS.
The SFP is designed to the highest seismic categorisation, and the designer claims that ponddraining as a result of pond liner leakage will be slow enough to be compensated by makeup
water sources. In addition, the HPR1000 SFP has been designed to avoid the likelihood of
unacceptable drainage events through major pipework by placing connection points above safe
water levels, and fitting those pipes with siphon breakers. During and following an accident
scenario, the SFP is designed to retain sufficient water inventory to ensure the covering of thefuel stored in the SFP such that no immediate action is required.
The HPR1000 SFP is designed so that it can be provided with makeup water upon total loss ofcooling chain or pond drainage faults. Makeup water measures considered include thedemineralized water system, fire protection system and cask loading pit. For Option 1, the11Multinational Design Evaluation Programme
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SPHRS tank is designed to be manually aligned with the FPCTS to passively provide makeup
water when necessary. In addition, the emergency mobile water injection can be aligned with the
FPCTS to provide makeup water.
The HPR1000 has safety-related SFP level measurement instrumentation. The data can bedisplayed on the screens in the main control room (MCR).
Common Positionxxiii.

The SFP should be designed to maintain the coverage of stored fuel in the event of internaland external hazards.

xxiv.

The SFP should be designed with adequate cooling capability to ensure the safe storage ofspent fuel in normal operations and design basis accident conditions.

xxv.

The design should have the capability to provide make up water to the SFP.

xxvi.

SFP should have reliable water level indication, the specific requirements of which (forexample the depth of level measurement) should be considered on a country by country
basis.
EMERGENCY PREPAREDNESS IN DESIGN
VI. The accident at the Fukushima Daiichi NPP highlighted how complicated emergency
response can be if multiple reactors on the same site are affected at the same time and electrical
power is unavailable. For such large accident scenarios there is a need to ensure that allreasonably practical measures are in place to mitigate accident consequences, and to ensurethat the design of the installation will minimize any radiological consequences. Additional
reviews should consider the need for additional emergency staff and the power requirements ofemergency response equipment.
Design Features
While many aspects of emergency preparedness in design will be country and site specific, theHPR10000 designers have considered features to support emergency management response.
Emergency response facilities are designed to coordinate and manage site actions under normal
and emergency conditions, such as the MCR, Remote Shutdown Station (RSS), and on-site
Emergency Control Centre (ECC).
The MCR Air Conditioning System maintains the environment (including temperature, humidity,
concentration of radioactive materials) of the MCR and associated rooms in normal operating
condition and accident condition. The system has two iodine filtration trains with a fresh air andreturn air filtering function that consist of pre-filters, HEPA filters, and iodine absorbers. The on12

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site ECC shares the same dose acceptance criteria as MCR, which considers the protection
measures against external hazards and radioactive releases.
Systems are provided in the on-site ECC for collation, storage and display of data for multiple
units. The communication channels and distribution points of communication systems are set in
the MCR, RSS and ECC and other important locations at the plant to meet the requirements for
emergency response.
Radiation monitoring equipment is incorporated, and equipment locations are distributed to bereasonable and representative for the HPR1000. A severe accident I&C system is provided tomonitor important plant parameters during and following a beyond design basis accident.
Common Position
xxvii.

An on-site Emergency Control Centre (ECC), separate from both the Main Control Room
(MCR) and the Remote Shutdown Station (RSS), should be provided from which an
emergency response can be directed at the NPP.

xxviii.

The importance of the accessibility and habitability of MCR and on-site ECC under accident
conditions in the HPR1000 design is fully recognized by the regulators. The regulators
expect that accessibility and habitability assessment should be undertaken for both DBAs
and also beyond design basis accidents.

xxix.

The MCR and the ECC should be sufficiently protected against internal and external hazards
to ensure the plant can be taken to a safe state and remain there.

xxx.

Suitably reliable I&C monitoring and emergency communication equipment should be
provided in the reactor building and SFPs to survive beyond design basis accidents andenable continued monitoring and communication of important plant parameters. Information
about these important plant parameters and radiological conditions should be provided to therelevant emergency facilities. Each unit should be provided with means of communication
with important locations at the plant as appropriate, and with on-site and off-site emergency
organisations. The robustness of necessary off-site communications for severe accidents
involving widespread disruption may require provision of equipment with satellite
communications capability.

xxxi.

Access to appropriate locations to implement mobile means to recover safety functions
should be possible when necessary. Access and connection points should be clearly
identified.

xxxii.

Events that may simultaneously affect several units should be explicitly considered in theemergency preparedness on multi-unit sites, if applicable.
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CONTRIBUTORS TO DRAFTING AND REVIEWT Parkes

ONR, UK

Robert Whitham

ONR, UK

Mark Drummond

ONR, UK

Aidan Parkes

ONR, UK

Chai Guohan

NNSA, China

Sun Zaozhan

NNSA, China

Pan Rong

NNSA, China

Yang Zhiyi

NNSA, China

Adriana Politi

ARN, Argentina

Jean Joubert

NNR, South Africa

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ABBREVIATIONSAC

Alternating Current

ATWS

Anticipated Transient Without Scram

CCWS

Component Cooling Water System

DBA

Design Basis Accident

DBF

Design Basis Flood

DC

Direct Current

DG

Diesel Generator

DiD

Defence-in-Depth

ECC

Emergency Control Centre

ECS

Extra Cooling System

EDG

Emergency Diesel Generator

FPCTS

Fuel Pool Cooling and Treatment System

HPR1000WG

MDEP HPR1000 Working Group

LUHS

Loss of Ultimate Heat Sink

MCCI

Molten Core Concrete Interaction

MCR

Main Control RoomMDEP

Multinational Design Evaluation Programme

NPP

Nuclear Power Plant

PMP

Probable Maximum Precipitation

RSS

Remote Shutdown Station

SADV

Severe Accident Dedicated Valves

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SBO

Station Black Out

SFP

Spent Fuel PoolSPHRSSecondary Passive Heat Removal System

SSCs

Structures, Systems and Components

SSE

Safety Shutdown Earthquake

STC

Steering Technical Committee

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