Action Plan
Fukushima2013

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Table of contents

1

Introduction

32

Reports relating to Switzerland

5

2.1

Report by the NSC: "The Fukushima reactor catastrophe follow-up measures in Switzerland"5

2.2

EU stress tests: peer review team report for Switzerland

8

2.3

Assessment of the Mühleberg nuclear power plantby the Environment Agency Austria (Umweltbundesamt GmbH)

8

2.4

3

4

Expert report by the Institute for Applied Ecology, Darmstadt:
analysis of the results of the EU stress tests for the Fessenheim and Beznau
nuclear power plants, part 2: Beznau
9

Retrospective of 2012

10

3.1

Earthquakes

10

3.2

Flooding

11

3.3

Extreme weather conditions

12

3.4

Prolonged loss of power supply (Station Blackout, SBO)

12

3.5

Loss of ultimate heat sink

13

3.6

Containment venting and hydrogen management

13

3.7

Emergency management at Swiss national level

14

3.8

Safety culture

15

3.9

Experience feedback

15

3.10

International supervision and cooperation

16

3.11

Reitnau external storage facility

17

Key issues in 2013

19

4.1

Earthquakes

19

4.2

Containment integrity

20

4.3

Extreme weather conditions

21

4.4

Increase in safety margins

21

4.5

Hydrogen management

23

4.6

Severe Accident Management (SAM)

23

4.7

Emergency management at Swiss national level

24

4.8

Experience feedback

26

4.9

EU stress tests follow-up

27

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5Annexes28

5.1

Annex 1: List of checkpoints from "Lessons Learned"

28

5.2

Annex 2: List of open points from the EU stress tests35

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1

Introduction

Immediately after the reactor accidents at the Fukushima Dai-ichi nuclear power plant in Japan on
11 March 2011, ENSI initiated measures to review the safety of Switzerland's nuclear power plants.
These measures were contained in four formal orders issued by ENSI. The first three formal orders(dated 18 March, 1 April and 5 May 2011) called for immediate measures and supplementary
analyses.
The immediate measures comprised the construction of a joint external emergency storage facility
for the Swiss nuclear power plants, including the necessary plant‐specific hook-up points for
Accident Management (AM) equipment, and backfits to provide external injection into the spent
fuel pools. The additional reassessments focused on the design of the Swiss nuclear power plants
against earthquakes, external flooding and a combination thereof. Screening investigations werealso requested regarding the coolant supply for the safety and auxiliary systems and the spent fuelpools.
In parallel with these investigations by the licensees, ENSI itself conducted topical inspections
during 2011, entailing reviews of the cooling systems already in place for spent fuel pools, protection
against external flooding and systems for filtered containment venting. These topical inspections
were continued during 2012: they included the plants' strategies in case of a prolonged loss of power
supply, processes for the assessment of external occurrences, and the emergency rooms available in
the Swiss plants.
The results of ENSI's reviews confirmed that the Swiss nuclear power plants display high levels ofprotection against the impacts of earthquakes, flooding and combinations thereof, and thatappropriate precautions have been put in place to cope with a loss of power supply and of theultimate heat sink. The safety case has been demonstrated for all the analysed accidents on thebasis of the hazard assumptions that are currently applicable. This means that compliance with thebasic statutory requirements for fulfilling the fundamental safety functions (reactivity control,
cooling of the fuel elements and confinement of radioactive substances) is guaranteed. In order tocontinue improving safety, however, ENSI has stipulated a series of additional requirements for
substantial backfits, e.g. a requirement for a flood-proof and earthquake-resistant diversified
ultimate heat sink. ENSI is supervising the work carried out by the nuclear power plants to meetthese requirements in the course of its ongoing supervisory activities, either by drawing up reviews,
issuing permits or carrying out on-site inspections and checks.
In its fourth formal order issued on 1 June 2011, ENSI requested the licensees to take part in the EU
stress tests. ENSI reviewed the documentation for the EU stress test submitted by the licensees in
the Swiss country report on the EU stress tests (ENSI-AN-7798 dated 31 December 2011). On 10
January 2012, further formal orders were issued requiring clarification of three major open points
arising from the analysis of the final reports by the Swiss nuclear power plants for the EU stresstests. Switzerland's submissions for the EU stress tests then underwent a peer review process. The
results of the peer review at European level confirm ENSI's conclusions regarding the safety of Swiss
nuclear power plants, and they also provide an overview of the condition of plants in Europe. ENSI iscurrently implementing the two recommendations made by the peer review team for Switzerland,
which relate to scenarios beyond the design basis. In addition, ENSI is participating in the follow-up
work on the EU stress tests in order to track implementation of the recommended measures in
Europe, and it is actively collaborating on the optimisation of the WENRA Safety Reference Levels.

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In parallel with the activities mentioned above, ENSI published four reports during 2011 in relation to
the event analysis of the Fukushima accident:--

Fukushima sequence 11032011, Event Sequences at Fukushima Dai-ichi and Dai-ni following the
Tohoku-Chihou-Taiheiyou-Oki Earthquake on 11.03.2011, ENSI-AN-7614 Rev. 1 (26 August 2011)
Fukushima analysis 11032011, In-depth Analysis of the Accident at Fukushima on 11 March 2011,
With Special Consideration of Human and Organisational Factors, ENSI-AN-7669 (29 August
2011)
Fukushima lessons 11032011, Lessons Learned and Checkpoints based on the Nuclear Accidents
at Fukushima, ENSI-AN-7746 (29 October 2011)
Fukushima impact 11032011, Radiological Effects of the Nuclear Accidents at Fukushima on
11.03.2011, ENSI-AN-7800 (16 December 2011)

The knowledge obtained from analysing the events of the accident at Fukushima was reviewed todetermine its applicability to Switzerland, and a summary was compiled in the ENSI report entitled"Lessons Learned" in the form of a series of checkpoints. Further points were added on completionof the analyses for the EU stress tests. The current overview can be found in Annexes 1 and 2. The
list of points identified is reviewed continuously on the basis of the latest findings and is updated asnecessary (see the comments on this aspect in section 2). Processing of the checkpoints willprobably be completed by 2015.
The Mühleberg nuclear power plant (KKM) intends to carry out the backfits ordered on the basis of
Fukushima and those required for the purposes of long-term operation within the overall DIWANAS
project. ENSI has reviewed this overall project with respect to long-term operation and has
requested that both the backfits ordered due to Fukushima and those required for long-term
operation should be implemented with a staggered schedule by the end of the 2017 annual
refuelling and maintenance outage, at the latest. A detailed planning for the implementation ofthese backfits must be submitted to ENSI by 30 June 2013.
The Fukushima action plans serve the purpose of ensuring transparency as regards processing of theidentified points until they are implemented. They also provide an instrument for the planning ofsupervisory work and the assessment of new knowledge gained from the Fukushima accident.
Progress with processing the identified points is documented and published. The action plan itself is
updated by February of the year in progress by identifying key issues for that year. ENSI's annual
reporting also provides information about the processing status. Beyond that, the public may be
informed on specific issues should the need arise.
ENSI report

Publication

Fukushima Action Plan

February

Oversight Report, Radiological Protection Report,
Research and Experience Report

April - June

National Action Plan for Follow-Up to the EU Stress Tests

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2

Reports relating to Switzerland

2012 saw the publication of four reports regarding the situation in Switzerland, which are detailed in
the following subsections. These are: the report on Fukushima by the Federal Nuclear Safety
Commission (NSC) , the report by the EU stress tests peer review team for Switzerland, the reportby the Environment Agency Austria (Umweltbundesamt GmbH) on the Mühleberg nuclear power
plant, and the report by the Öko-Institut (Institute for Applied Ecology, Darmstadt, Germany) on the
Beznau nuclear power plant.

2.1

Report by the NSC: "The Fukushima reactor catastrophe follow-up measures in Switzerland"

In its report published in March 2012, the NSC provides an overview of the events at Fukushima andthe formal orders which ENSI then issued in Switzerland. For this purpose, the NSC sets the accident
in the context of the fundamental safety concept for nuclear power plants and in summary reaches
the conclusion that ENSI's action list is an appropriate and comprehensive means of learning thelessons that may be drawn for nuclear power plants in Switzerland. The NSC considers that theschedule set by ENSI for reviews and measures imposes very demanding requirements on thelicensees and on ENSI itself.
The NSC sets out seven formal recommendations which ENSI has added to the action plans. The
NSC report also contains various suggestions which ENSI is incorporating into its ongoingsupervisory activities.
Detailed comments on the NSC's recommendations are given below.
The effectiveness of internal emergency preparedness measures (defence-in-depth level 4) should be
reviewed at regular intervals. Such reviews should take more account of combinations of events andpossible follow-on events. (NSC recommendation 4.3)
The NSC's report makes specific reference to natural events beyond the design basis, in respect ofwhich the adequacy of internal emergency preparedness measures should be reviewed. ENSI
recognises the special significance that extreme natural events have acquired in the light ofFukushima, and has already assessed the margins available at the Swiss nuclear power plants byparticipating in the EU stress tests. Further analyses will focus on improving safety margins andemergency management in case of severe accidents as key issues in 2013 (see sections 4.4 and 4.6).
Extreme drought was also listed as a case to be considered in connection with proof for extreme
weather conditions (see section 3.3).
As regards current conditions in Switzerland, it should be noted that the internal emergency
preparedness measures at defence-in-depth level 4 are mapped and evaluated in the probabilistic
safety analyses. These analyses also take account of all potential combinations of subsequent errors
which could lead to core damage. Combinations of triggering events are also taken into
consideration for the definition of the deterministic accident spectrum. In 2012, for instance, ENSI
assessed the proof submitted by the licensees of the Swiss nuclear power plants for the combinationof a 10,000-year earthquake and earthquake-induced flooding.

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Guideline ENSI-B11 ("Emergency exercises") already states that staff emergency exercises should
generally be conducted for scenarios beyond the design basis where possible. Furthermore, incompliance with the requirements in Guideline ENSI-B12 ("Emergency preparedness in nuclear
installations"), written plant-specific technical decision-making aids (Severe Accident Management
Guidance (SAMG)) should be available in every plant to mitigate the effects of a severe accident.
These documents have undergone a SAMG validation exercise and are included in regular training
activities. Knowledge gained from the exercises and training activities is taken into account when
the SAMG is updated. Regular reviews of the SAMG are carried out as part of the Periodic Safety
Review (PSR) which takes place at least once every ten years.
The investigations to determine the seismic hazard for the Swiss nuclear power plants (PEGASOS
Refinement Project) must be brought to a prompt conclusion, and the applicable seismic hazards must
be defined by ENSI. (NSC recommendation 5.1.1)
According to the current schedule, the "PEGASOS Refinement Project" will be completed in 2013.
ENSI will then carry out a final review of the project results and will redefine the seismic hazard
assumptions to be used in the safety case. The definition of the methodology for the demonstrationof the safety case has already been added as a key issue for 2013 (see section 4.1).
New knowledge regarding the flooding hazard, e.g. studies on historic hydrology, must be taken into
account for the periodic safety reviews. (NSC recommendation 5.1.2)
According to the "Hazard assumption ordinance" (SR [Systematic Collection of Federal Law]
732.112.2 article 5, paragraph 3), historic data acquired through current scientific knowledge have to
be considered in order to determine the hazards. When available and applicable, data of this sort
was also used for the latest safety case demonstration regarding the 10,000-year flood, drawn up in2011 for the Swiss nuclear power plants’ sites. Furthermore, the hazard due to debris blockages wasassessed in detail. For this purpose, ENSI ordered additional investigations which are being followed
up in the course of ongoing supervisory activities (see section 3.2).
In ENSI's view, a high technological level (as compared to other countries) has already been attainedin the analysis of the flooding hazard for Swiss nuclear power plants. Further refinements to theseanalyses are possible, in particular including greater use of coupled hydraulic-sedimentological 2-D
calculations for specific scenarios and a more extensive evaluation of historic floods. However, thelatter requires research work. ENSI intends to encourage development work of this sort.
In order to strengthen provisions for a prolonged loss of AC power supply, there should be a review ofthe optimisation potential for extending battery lifetimes obtained from targeted management ofconsumer loads in connection with emergency preparedness measures. (NSC recommendation 5.1.3)
During the fourth quarter of 2012, ENSI carried out inspections in all the plants focusing on the issueof "Control of a prolonged loss of AC power supply" (station blackout, SBO). Among other aspects,
these inspections also considered the supply of direct current for key consumers by means ofbatteries. Assessment of the results of these inspections has not yet been completed. ENSI endorses
the NSC's recommendation and will also review the optimisation measures planned by the plants toextend battery lifetimes as part of its review of the measures to bring an SBO under control.

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Control of fully developed rapid hydrogen production in the Swiss nuclear power plants must be
reviewed. As a potential strategy, filtered venting should be optimised with the help of the following
measures :–––Adequate numbers of accident-proof devices should be installed at relevant locations in
the primary containment in order to measure hydrogen and oxygen concentrations. Bothmeasured variables should be taken as criteria for triggering early filtered venting in orderto prevent the formation of ignitable gas mixtures to a potentially damaging extent.
In the light of the events at Fukushima, it is necessary to review and ensure the error-proof
operation of filtered venting under more difficult conditions (including more severeradiological conditions) by remote control and, if necessary, by local manual actions.
The procedures for filtered venting must be defined in advance. The decision-making
pathways for this purpose must be specified so that authorisation is obtained promptly,
even under more difficult conditions.

In addition, the NSC advises reviews of the following aspects: situations in which hydrogen can escape
into adjacent rooms, the hazard that this would create and the measures which could be used to bring it
under control, where necessary. (NSC recommendation 5.2.1)
ENSI immediately re-addressed the issues of hydrogen management and filtered venting in theaftermath of Fukushima. On the one hand, analyses regarding the release and control of hydrogenin the spent fuel pool buildings were ordered in May 2011, and ENSI completed its assessment ofthese analyses in February 2013 (see section 3.6). On the other hand, ENSI has critically analysed theinformation supplied by the licensees for the reviews in connection with the EU stress tests, as wellas other data. Related open points which call for in-depth consideration were identified andgradually incorporated into the processing work. ENSI stipulated new requirements regardinghydrogen management for all plants in the first quarter of 2013. The topics of hydrogen control andcontainment integrity are key issues for 2013: the planned activities cover all of the individual
aspects raised by the NSC (see sections 4.2 and 4.5).
The NSC recommends that the concept of the external storage facility for operational resources should
be validated and optimised as necessary by means of exercises, in order to ascertain the prompt
availability of the materials required. (NSC recommendation 5.2.2)
ENSI is entirely in agreement with the NSC that the procedures for the external storage facility can
only be validated by deployments that simulate actual practice. ENSI's activities are described in
section 4.6.
In case of an accident or an accident, ENSI is responsible for the task of assessing the licensees'
procedures. For this purpose, the emergency situation and the adequacy of the measures must undergo
constant assessment, independently of the licensees. Suitable means should be in place to ensure thesecapabilities on a permanent basis. (NSC recommendation 5.4)
ENSI has a broad-based emergency preparedness organisation which integrates all the specialist
disciplines required in order to assess malfunctions and accidents in nuclear power plants. In case ofa deployment, the measures initiated by the plants must be assessed quickly for the purpose ofprotecting the population.

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The International Atomic Energy Agency (IAEA) is currently proposing amendments to the General
Safety Requirements, GSR Part 1, " Governmental, Legal and Regulatory Framework for Safety”,
which would cover (among other aspects) the adequacy of training and practice for all players
involved in an emergency, and maintenance of the emergency preparedness organisation over a
prolonged period. In this context, ENSI is examining whether further measures are required for its
own emergency preparedness organisation.

2.2

EU stress tests: peer review team report for Switzerland

The peer review team, which consists of international experts, has carried out a review of theinformation provided by Switzerland in connection with the EU stress tests (information is available
in the country report for Switzerland on the EU stress tests, ENSI-AN-7798 dated 31 December 2011,
and in the reports by the Swiss licensees). During the so-called topical review the experts madetopic-related cross-comparisons with other countries. The review was completed by a so-called
country review with a discussion of the open points and a visit to the Beznau nuclear power plant.
The peer review team identified two issues as offering potential for improvements. It is
recommended that further progress should be made in the determinination of the margins for
extreme weather conditions, i.e. the safety reserves with respect to hazards in the range beyond thedesign basis, for example in the course of the periodic safety reviews.
ENSI has followed this recommendation and has defined a key issue for 2013, starting with hazards
in the design range (see sections 3.3 and 4.3). In connection with hydrogen management, the peer
review team also commented that the use of passive systems in case of severe accidents should be
reviewed, as well as the behaviour of hydrogen in the venting system pipes. These specific aspects
addressed in the second recommendation have been incorporated into the "Hydrogen
management" key issue (see section 4.5).

2.3

Assessment of the Mühleberg nuclear power plant by the Environment Agency
Austria (Umweltbundesamt GmbH)The Environment Agency Austria (Umweltbundesamt GmbH) has drawn up a technical assessment
report on behalf of the Federal Ministry for Agriculture and Forestry, Environment and Water
Management, which is the competent authority in this regard. The report covers technical safety
aspects of the Mühleberg nuclear power plant (KKM) "...which, from the Austrian viewpoint, requirein-depth bilateral discussion". ENSI has reviewed the report and has issued a statement on it for theattention of the coordinating office in Switzerland of the bilateral Austrian-Swiss committee. ENSI
was unable to identify any new aspects in connection with the safety issues that were raised. The
question of requirements for equipment to deal with severe accidents is addressed in the context ofthe present Action Plan 2013 (see section 4.4).

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2.4

Expert report by the Institute for Applied Ecology, Darmstadt: analysis of theresults of the EU stress tests for the Fessenheim and Beznau nuclear power
plants, part 2: Beznau

On behalf of the Baden-Württemberg Ministry of the Environment, Climate Protection and theEnergy Sector, the German Institute for Applied Ecology (Ökoinstitut) has drawn up an assessmentof the results from the EU stress tests for the Fessenheim and Beznau nuclear power plants, which
are located close to the border. For this purpose, the Institute for Applied Ecology proceeded
according to the investigative method of the German Reactor Safety Commission (RSC) which wasapplied in parallel with the EU stress test in Germany, and on the basis of the specific additional
studies for the States of Baden-Württemberg and Bavaria. For the assessment of the Fessenheim
and Beznau plants, these methods are therefore based on specific German safety standards.
The approach adopted by the Institute for Applied Ecology focused on the robustness of thesystems that are permanently installed in order to perform safety functions. In ENSI's view, thetechnical characteristics of the permanently installed safety systems at the Beznau plant arepresented correctly in the report for the most part, and the results of the assessment (based on acomparison with specific German safety requirements) are essentially correct. However, the resultsof the comparison did not provide ENSI with any new knowledge. In response to the criticism madethat the maintenance criterion (according to German requirements) is not met, it must be statedthat no maintenance may be carried out on Swiss nuclear power plants during normal operation if
the maintenance criterion is not met. In the latter case, there is consequently no need to assume for
accident analyses that maintenance is performed.
Furthermore, the report by the Institute for Applied Ecology only gives reduced consideration to thewide-ranging preventive and mitigative Accident Management measures implemented at the
Beznau nuclear power plant. The consideration given to level 4 of the defence-in-depth concept istherefore inadequate. Until recently, German safety requirements focused on the safety equipment
at level 3 of the defence-in-depth concept, whereas the Swiss safety regulations have for a long timerequired the plants to comply with high standards at all defence-in-depth levels. Consequently, theexpert report by the Institute for Applied Ecology does not provide a complete picture of the Beznau
nuclear power plant's ability to withstand accidents beyond the design basis.

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3

Retrospective of 2012

3.1

Earthquakes

By the end of March 2012, in accordance with the specified deadline, the Swiss nuclear power plants
supplied ENSI with their safety case demonstrating adequate protection against a 10,000-year
earthquake and a combination of earthquake and flooding, as required by the formal order dated 1
April 2011. Seismic fragilities for all the relevant structures, systems and components had alreadybeen determined in advance. In addition to analyses of the safety of the nuclear reactor, the primarycircuit and the containment, ENSI's formal order dated 5 May 2011 also required design
reassessments of the spent fuel pools, their buildings and cooling systems, and proof of compliancewith the permitted dose limits for these accidents. In their deterministic proof, the plants
demonstrated that such accidents are safely terminated in compliance with the boundary conditions
stipulated by ENSI, and that a value lower than the permitted limit of 100 mSv as per theRadiological Protection Ordinance (SR 814.501) is attained. Based on its review of the submitted
documentation, ENSI concluded that core cooling and cooling of the spent fuel pools is guaranteed
under the impact of a 10,000-year earthquake and a combination of earthquake and seismicallyinduced flooding, in compliance with the single failure criterion. The dose limit of 100 mSv isrespected during such accidents. The criterion as per article 3 of the "DETEC Ordinance on the
Methodology and Boundary Conditions for Checking the Criteria for the Provisional Shut-Down of
Nuclear Power Plants" (SR 732.114.5) is not met. In ENSI's statements on the seismic safety case thatwas submitted, additional requests were identified; these relate in general to individual components
in the nuclear installations for which more detailed analyses are required or whose seismic behaviour
can be improved by minor structural adaptations. All the additional requests were incorporated into
individual follow-on tasks so that their processing will continue as part of the normal supervisory
activities.
The licensees of the nuclear power plants at Beznau (KKB), Leibstadt (KKL) and Mühleberg (KKM)
submitted the results of their assessments of the seismic robustness of the containment’s andprimary circuit’s isolation in line with the deadline of 30 September 2012. ENSI granted the licenseeof the Gösgen nuclear power plant (KKG) an extension of the deadline for submission of the
supplementary assessment until 31 December 2012, and the documentation was submitted incompliance with this new deadline. The licensees conclude that the integrity of the primary circuitand the containment is guaranteed on the basis of the seismic hazard assumptions defined in ENSI's
formal order of 1 April 2011.
ENSI carried out a cursory examination of the assessment reports on seismic robustness submitted
by the licensees. As regards KKB, it can be stated that the seismic robustness of the isolation of thecontainment and the primary circuit was already covered by the seismic safety case requested in
ENSI's formal order dated 1 April 2011, which KKB submitted by 31 March 2012 and which wasreviewed and accepted by ENSI. For the other nuclear power plants, the review of the seismicrobustness of the containment isolation (in particular) must also include additional buildings anditems of equipment which are not covered by the seismic safety case submitted by 31 March 2012and belong now to the scope of the analysis.

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3.2

Flooding

In its formal order dated 1 April 2011, ENSI required all the Swiss nuclear power plants to submit
their safety case demonstrating adequate protection against the 10,000-year flood. After submittal
the safety case was reviewed by ENSI. In its statements, ENSI concluded that all the plants can bebrought into a safe condition even if the external power supply fails at the same time. The applicable
does limits are respected by all the plants. In connection with the analyses of seismically induced
flooding, ENSI identified new requests in 2012, although they do not cast doubt on the overall resultof that review. In order to complete its analyses regarding seismically induced flooding, the Gösgen
nuclear power plant (KKG) must consider the effects of a failure of the dam installations locatedupstream in the relevant area surrounding the KKG. The Mühleberg nuclear power plant (KKM) mustcomplete the seismic safety calculations for dam installations in the power station's zone ofinfluence in accordance with the requests contained in the review reports of the Swiss Federal Officeof Energy (SFOE). KKM submitted the requested documents by the deadline. The relevant
statement by the authorities is expected in the first quarter of 2013.
In connection with the Swiss country report on the EU stress tests, ENSI asked KKG and KKM toconsider flood-induced debris blockages of hydraulic engineering installations by means of asensitivity study of accident scenarios beyond the design basis. KKB had already submitted
documentation on this aspect and it submitted a revised version based on coupled water/sedimentcalculations (hydraulic-sedimentological 2-D calculations) in 2012. Due to its elevated location, KKL
is not affected by any debris blockages. In ENSI's view, the studies available from KKB, KKG and
KKM indicate that debris blockages cannot trigger a cliff-edge effect for these plants. On the basis
of ENSI's statement on long-term operation, KKM was requested to analyse the safety margins forflooding in greater detail (see the "Safety evaluation report on the long-term operation of the
Mühleberg nuclear power plant", ENSI 11/1700 dated 20 December 2012). ENSI has requested
further information for a conclusive assessment of the situation at the Gösgen and Beznau nuclear
power plants. Work still outstanding was incorporated by ENSI into individual follow-on tasks sothat their processing will continue as part of the normal supervisory activities.
In ENSI's view, the technological standard attained for the analysis of the flooding hazard at Swiss
nuclear power plants is already high when compared to other countries. Additional refinements ofthese analyses are possible, but they should be supported by research results. This applies inparticular to the assessment of historic flooding and the extended use of coupled hydraulicsedimentological 2-D calculations for specific scenarios. Furthermore, ENSI advocates the initiation
with other Federal authorities of a research project on the flooding hazard for the catchment area of
the Aare, into which the results of the development work should be incorporated.

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3.3

Extreme weather conditions

In its letter to the licensees dated 4 July 2012, ENSI specified the requirements for the probabilistic
hazard analyses and the safety case needed to demonstrate adequate protection of the plant
against extreme weather conditions.
Quantitative analyses must be carried out for the hazards of extreme winds, tornados, extreme air
and river water temperatures, heavy rainfall on the plant site and deep snow.
On the other hand, the following hazards may be given qualitative treatment provided that theirimpact on the plant does not result in a demand for safety systems: hail, freezing rain, drought (i.e.
low river and groundwater levels), forest fire, icing caused by low outdoor or river watertemperatures, and combinations of:-

exceptionally harsh winter conditions with snow (snowdrifts), low temperatures and icing; andextremely acute summer conditions with high temperatures, drought, forest fires and low river
and/or groundwater levels.

The design values of the structures (buildings) and equipment (e.g. exhaust stacks of emergency
diesel generators, air intakes, etc.) required to cope with the hazard in question must be presented
so as to prove that the plant has adequate protection. It must also be demonstrated that they canwithstand the expected loads. If the resultant loads are covered by other load cases, such cases may
be adduced in order to provide proof. The margins in relation to the design values must also be
indicated.
The concept for proving adequate protection against extreme weather conditions was submitted by
the licensees by the end of 2012 in accordance with the deadline. Due to the large number ofanalyses, the licensees were granted one more year for completing the assessment than wasenvisaged in the Action Plan 2012.

3.4

Prolonged loss of power supply (Station Blackout, SBO)ENSI conducted team inspections in all plants during the fourth quarter of 2012 in order to review
the precautionary measures to cope with a prolonged loss of AC power supply (Station Blackout,
SBO).
The purpose of these inspections was to review the strategies in place at the plants for coping withan SBO accident beyond the design basis, the Accident Management (AM) resources available toterminate the accident, the hook-up points for emergency supply of cooling water and electricity,and the emergency procedures relating to an SBO. After technical discussions on the plant-specificstrategies and the situation regarding time and resources, the planned operational resources such as
mobile AM emergency power units, pumps, fire water trucks and motorised sprays, as well as theirstorage and deployment locations, were assessed on the basis of an inspection walkdown of theplants. The presence and accessibility of feed and hook-up points under SBO conditions were also
checked. In addition, the scope of the inspections included a review of the necessary quantities, andthose held in readiness, of service products such as diesel fuel and lubricating oil in order toguarantee operation of AM equipment for seven days, and the stocks held of other auxiliarymaterials such as cables, plugs and transportation facilities for equipment, as well as tanks for local

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refilling.
The inspections demonstrated that the plants have effectively continued to develop their existing
strategies, and that adequate AM resources are available to prevent core damage after an SBO. The
results of the inspections will also be assessed in detail during the first quarter of 2013. Dependingon the results of the assessment, ENSI will decide whether further actions are required in addition to
the measures regarding SAM equipment already stipulated for the Action Plan 2013 (see section
4.4).

3.5

Loss of ultimate heat sink

In order to meet the requirements arising from ENSI's formal order dated 5 May 2011, KKM
submitted an application for "permit of concept" by the stipulated deadline of 30 June 2012. Thisapplication covers three back-fitting projects which should be combined to deliver an overallsolution (the DIWANAS project).
Among other activities, the DIWANAS project includes the construction of an alternate (diverse)
ultimate heat sink to the river Aare. According to the "permit of concept" application, a feed pipe
from a groundwater intake in the Saane valley will be added to the SUSAN special emergency
system. Should the Aare not be available, this will serve as a heat sink to ensure the removal ofresidual heat from the reactor and the spent fuel pool. The transfer point for the feed pipe from thegroundwater intake in the Saane valley will be located in a new building to be constructed on the
power plant site.
ENSI has carried out first a cursory review of the submitted application documents. ENSI considers
that the proposed concept for the Saane groundwater intake is basically suitable in order to meetthe requirement for an alternate, diverse cooling water supply. The additional supply of coolingwater can be operated independently of the existing river water supply (from the Aare) and should
be protected against a 10,000-year earthquake and a 10,000-year external flood. The cursory review
yielded some further requests regarding additional documents to be submitted. These documents
were submitted by KKM in mid-December 2012, in compliance with the specified deadline, and weretaken into consideration by ENSI when it issued the "permit of concept" at the end of January 2013.
As regards scheduled dates for the implementation of measures included in the DIWANAS project,
ENSI requested (in its statement on the long-term operation of KKM) that the backfits covered by
the DIWANAS project must be implemented at the latest by the end of the 2017 annual refuellingand maintenance outage, and a binding implementation plan for this purpose must be submitted by
30 June 2013.

3.6

Containment venting and hydrogen management

Provisions against the hazard caused by hydrogen were taken into account in the design of Swiss
nuclear power plants at an early stage. Various aspects of these provisions were reviewed again in
the light of events at Fukushima.
Relevant work during 2012 focused on investigations of protective measures against the hydrogen

ENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 14

hazard in the spent fuel pools, the seismic resistance of the containment venting systems and thefollow-up activities arising from the inspections regarding containment venting. The status of therelevant work is presented in brief below.
The licensees have submitted their investigations regarding protection against hydrogen hazards inthe area of the spent fuel pools. Based on its review of the submitted documentation, ENSI has
concluded that the quantities of hydrogen produced by radiolysis are not sufficient to generate an
ignitable mixture in the area of the spent fuel pools. The investigations also show that in the event of
a 10,000-year earthquake/flood combined with a loss of the emergency power supply, at least threedays are available to initiate appropriate measures in all the plants. In ENSI's view, prevention takes
precedence over mitigation and, for this reason, ENSI has imposed specific additional requirements
for each plant to ensure monitoring of the spent fuel pools, upgrading of the spent fuel pool coolingsystems and extension of the relevant on-site emergency preparedness measures. These measures
additionally reduce the risk of a severe accident in the area of the spent fuel pools.
The Gösgen and Leibstadt nuclear power plants have submitted their studies regarding the seismic
resistance of the containment venting systems together with proposals for improvements, if
needed.
The requests identified during the topical inspection of filtered containment venting have beenprocessed by the licensees and analyses have been submitted to ENSI. In this regard, KKG
submitted the required concept for improvements to displays in the emergency control room, andKKB updated the Post-LOCA study on the investigation of radiation exposure at workplaces in caseof severe accidents.

3.7

Emergency management at Swiss national levelOn 4 July 2012, the Federal Council took note of the report by IDA NOMEX (the Interdepartmental
Working Group to Review Emergency Preparedness Measures in case of Extreme Events in
Switzerland) and instructed various Federal agencies to draft organisational and legislative
measures. In this context, ENSI collaborated with representatives of the Federal Office for Public
Health (FOPH), the Swiss Accident Insurance Fund (SUVA) and the Group of Swiss Nuclear Power
Plant Operators (GSKL) in 2012 to compile a report on the prevailing situation regarding support andtreatment for persons exposed to severe radiation and the agreements with the plants, and specificalternative solutions were proposed.
The current status of measurement and forecasting systems was assessed in collaboration with
Federal agencies and the power plant operators. The requirements for these systems were redefinedon the basis of this analysis and the lessons learned from Fukushima.
Completion of the review of reference scenarios and related assumptions for emergency
preparedness was delayed due to the extensive documentation submitted by the licensees at theend of September 2012. This task is to be carried out as a project together with the review of thezoning concept in the areas surrounding nuclear power plants, in conjunction with the cantons andFederal agencies.
In November and December 2012, moreover, ENSI carried out inspections of the emergency control
center (ECC) and substituted ECC at nuclear power plant sites. The inspection reports are being

15 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSI

drawn up. Human and organisational aspects of emergency management by nuclear power plant
licensees are also addressed here. ENSI's emergency center in Brugg was inspected to determine its
seismic resistance. Specific improvements have already been implemented and additional options
for upgrading are under review. The option for an alternative location for ENSI's protected
emergency center is also being followed up under the auspices of Business Continuity Management.
The measures for 2013 are set forth in sections 4.6 and 4.7.

3.8

Safety culture

The accident at Fukushima entails potential implications at multiple levels for the safety culture of
Swiss nuclear power plants. On the one hand, the findings from the analysis of the accident should
be considered to determine whether they can be applied to the safety culture of Swiss nuclear
power plants. On the other hand, the political consequences of the accident in Switzerland, i.e. thedecision to phase out from nuclear energy, should be considered to determine their potential impact
on the safety culture. This self-examination and the implementation of any specific measures is the
responsibility of the licensees of the Swiss nuclear power plants. In 2012, ENSI assured itself that thelicensees are actually fulfilling this responsibility, during the "specialist discussions on safety
culture", as they are known. These are open, constructive and discursive discussions on a chosen
topic with the primary aim of encouraging the licensees to consider their own safety culture.
Specialist discussions of this sort were conducted at all the nuclear power plants between July andDecember 2012. The topic proposed by ENSI was considered and discussed in the first session ofeach discussion. ENSI then made an evaluation of the discussions and reported the results to thelicensees during a second discussion. The overall assessment of the specialist discussions andreports on them will be completed in the first quarter of 2013.
In addition to these specialist discussions, a specialist meeting was held at the Mühleberg nuclear
power plant (KKM) on the subject of Personnel and Organisation. During this specialist meeting,
ENSI obtained information about measures implemented by KKM or by BKW (the licensee) to deal
with uncertainties regarding the timeframe for continued operation of the plant, and personnel
policy in view of the decommissioning of the plant.
As the accident at Fukushima has shown, the safety culture of a licensee organisation is heavily
influenced by the safety culture of the responsible supervisory authority (i.e. the supervisory
culture), among other factors. By launching an internal project that will run for several years, ENSI
has initiated a self-examination process to consider its supervisory culture. This project should help
ENSI to learn the right lessons from the Fukushima accident for its own supervisory activities. New
guiding principles for ENSI should also be drafted against this background.

3.9

Experience feedback

To examine the issue of experience feedback, topical inspections were carried out in all the nuclear
power plants during the fourth quarter of 2012, focusing on the processes for the assessment of
external occurrences. These inspections showed that suitable specified guidance documents are inplace at the plants so that the external occurrences of relevance to each plant can be assessed inENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 16

greater detail. The interfaces to the relevant processes for the implementation of derived measures
have also been defined throughout. As regards guidance documents for the analysis and derivationof measures, the relevant documents are in some cases available in the plants only in draft form. The
plants have already recognized the need for improvement on this issue. The definitive documents,
and the documents stipulating the reporting requirements to ENSI as per Guideline ENSI-B02, have
yet to be submitted and will then be reviewed by ENSI. The review of documentation on experience
feedback and any improvement measures that may be required are followed up in the Action Plan
2013.

3.10

International supervision and cooperation

Internationally harmonised assessment scales
The primary purpose of cooperation among international authorities to ensure the safety of nuclear
technology is to continue the development and harmonisation of safety requirements so that thosecountries which utilise nuclear energy will have a set of regulatory instruments at their disposal.
These include the Safety Standards of the International Atomic Energy Agency (IAEA) and the
Safety Reference Levels of the Western European Nuclear Regulators' Association (WENRA). At theend of 2011, ENSI's Director was elected as Chairman of WENRA. ENSI is using this circumstance tomake further progress with the development of harmonised Safety Reference Levels for all areas of
nuclear energy, and to advance their implementation in European countries that use nuclear energy.
ENSI's formal order dated 1 June 2011 required the licensees of Swiss nuclear power plants to takepart in the EU stress tests. These were carried out in Switzerland in the same way as in the EU
countries with nuclear power plants. ENSI also took part in the peer review process which wascompleted by April 2012, whereby international teams assessed the country reports in overall terms
and on a topic-by-topic basis according to standard criteria. At the technical level, WENRA set itself
the goal of adopting the key findings from the EU stress tests immediately after publication of themain peer review report. The Safety Reference Levels are being examined to determine potential for
improvements in this context. The results from the EU stress tests should also be incorporated into
follow-up activities. For this purpose, the European Nuclear Safety Regulators' Group (ENSREG, theassociation of supervisory authorities in the EU member states) has adopted an action plan forfollow-up measures.
Switzerland takes part in the IAEA's Safety Standards Groups on an ongoing basis. Switzerland also
participated in the IAEA General Conference in September 2012 and the Ministerial Conference on
Nuclear Safety at Fukushima in December 2012. As elements of the IAEA action plan, these events
aim to help strengthen the international nuclear safety regime.

International reviews and transparency for supervision and licensees
A two-week IRRS mission with a team of 24 experts from 14 countries visited Switzerland in
November 2011. The International Atomic Energy Agency (IAEA) completed the final report by thereview mission, under the auspices of the Integrated Regulatory Review Service (IRRS), in May 2012.
It contains 19 "Good Practices", 12 recommendations and 18 suggestions. By the end of 2012, ENSI
drafted an action plan for the suggested improvements in view of the IRRS follow-up mission which
is likely to take place in 2015.

17 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSIAn OSART (Operational Safety Review Team) mission visited the Mühleberg nuclear power plant(KKM) in October 2012. A team of experts from the International Atomic Energy Agency (IAEA)
inspected operational safety for a period of more than two weeks. The OSART team drew up 21
recommendations and proposals regarding further improvements to operational safety at KKM. Ten
Good Practices were also identified. ENSI observed the mission but did not participate in it directly.
The IAEA published the final report in January 2013. An OSART follow-up mission to assess themeasures implemented by KKM is likely to take place in 2014.

Convention on Nuclear Safety
An extraordinary conference on the Convention on Nuclear Safety (CNS) took place in August 2012.
Switzerland submitted its country report for this event in May 2012, in compliance with the specified
deadline; this was published on ENSI's website (see http://www.ensi.ch/de/2012/05/11/swiss-national
report-to-the-second-cns-extraordinary-meeting/). In advance of the extraordinary conference,
eleven countries (including Switzerland) submitted suggested changes to the CNS GuidanceDocuments, and they went on to develop joint proposals for changes at two Consultancy Meetingsin June and July 2012. The Conference accepted at least the basic content of most of the proposals,
including the changes desired by Switzerland. These changes bring about practical improvements tothe content of the reports and their discussion during the conferences, but do not make any
substantial or binding changes to the international safety regime.
Russia and Switzerland also submitted proposals to amend the Convention itself. In particular,
Switzerland wanted to introduce binding status for the international peer reviews, theimplementation of periodical safety reviews and improvements to transparency. Unfortunately, theproposals submitted to the Convention were unable to attract a consensus in this form. Instead, theparties to the Convention agreed to set up a working group (the "Effectiveness and Transparency
Working Group"). By the next regular Review Meeting in 2014, this group will endeavour to draft
broad-based proposals to improve the CNS and its processes.

3.11

Reitnau external storage facility

The central storage facility for Severe Accident Management equipment at Reitnau (canton of
Aargau), which was the subject of a request by ENSI to all licensees of Swiss nuclear power plants in
March 2011, was commissioned on 1 June 2011. On 20 January 2012, the operating company for the
storage facility submitted the concept for the external storage facility for the Swiss nuclear power
plants (ExLaReitnau) to ENSI, within the specified period. After assessing the submitted
documentation and on the basis of an ENSI inspection report dated 31 May 2011, ENSI was able todetermine from its initial assessment that the Reitnau external storage facility is a viable facility forthe purposes of storing equipment and auxiliary supplies in order to extend the emergency
preparedness of the Swiss nuclear power plants in case of severe accidents. ENSI's only criticism waslevelled at the wired communication via a cable route which is buried but not redundant, because
this connection is assessed as too unsafe on the assumption that the mobile telephone network
would no longer be available due to overload or outage.
On 27 September 2012, ENSI carried out an inspection of inventory management at the Reitnau
external storage facility with satisfactory results because the Accident Management equipment

ENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 18

indicated on the inventory list was fully present, in maintained condition and ready for deployment.
The three underground buildings of the storage facility were in a clean, dry and tidy condition, andboth the loading ramps and transport areas were ready to handle outbound transport by truck orhelicopter at any time of the day or night.
Although there was no doubt that the buildings, erected for military purposes, are resilient toearthquakes, confirmation from a civil engineer expert was obtained at ENSI's request in January
2013; this states that the building complies with the seismic requirements for structures in class
BWK III as per SIA standard 261.
The gradual deployment of Accident Management resources mentioned in the concept dated 20
January 2012 largely corresponds to ENSI's notion. Subsequently, however, it will be necessary toinspect the numerous interfaces for the deployment of the stored equipment and auxiliary supplies
from the Reitnau external storage facility; these are currently being incorporated into theemergency procedures for the nuclear power plants on a gradual basis. These procedures will beassessed and their practicability will be verified by means of emergency exercises during the coming
years (see 4.6). On the basis of these exercises, and in response to additions and changes in the
Swiss nuclear power plants, necessary adaptations to the concept and the inventory will be
implemented.
The assessment of the Reitnau external storage facility to date was summarised by ENSI in a reportpublished in the first quarter of 2013.
An emergency exercise involving the deployment of the Reitnau external storage facility emergency
team planned for November 2012 had to be postponed until 2013 because of unplanned repair
works, which prolonged the refuelling outage 2012 at KKL (see 4.6).

19 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSI

4

Key issues in 2013

Based on their importance in relation to safety, and on synergies with ongoing projects, thefollowing key issues were specified for ENSI's follow-up activities in view of Fukushima during 2013:
1. Earthquakes
2. Containment integrity
3. Extreme weather conditions
4. Increase in safety margins
5. Hydrogen management
6. Severe Accident Management
7. Emergency management at national Swiss level
8. EU stress tests follow-up
9. Experience feedback

4.1

Earthquakes

In compliance with formal orders from ENSI regarding protection against the 10,000-year
earthquake, the Swiss nuclear power plants submitted new safety cases for the safe shutdown
earthquake (SSE) in 2012. For this purpose, use was made of the seismic hazard assumptions (PRP
Intermediate Hazard) current at the time in question based on the new earthquake catalogue issued
by the Swiss Seismological Service (SED) and the site specific data acquired during the Pegasos
Refinement Project (PRP). The calculation was based on current results from attenuation modelling.
Completion of the PRP project is planned in the second quarter of 2013. ENSI will then review theresults and define new hazard assumptions. By the fourth quarter of 2013, the methodology and thetimeline for the seismic safety case to be provided by the Swiss nuclear power plants will be
redefined in detail. Following this, the safety case submitted by the licensees of nuclear power
plants must be revised or a new one must be furnished. These activities conform to the "Hazard
Assumption Ordinance" (SR 732.112.2, article 13), which states that in case of new hazard
assumptions or of changes to the hazard assumptions on which the construction license is based,
the licensee must carry out new deterministic and probabilistic safety analysis with the new
assumptions, and must assess their impact on the safety of the plant and on the risk in particular.
In the course of analyses for the EU stress tests, ENSI became aware of a circumstance that proved
advantageous during the severe earthquakes which occurred in Japan: in the Japanese nuclear
power plants, automatic scrams were triggered upstream by means of the seismic instrumentation.
Triggering of this sort has not yet been implemented in the Swiss nuclear power plants. In 2013,ENSI will set up a working group to examine whether automatic scrams should take place upstream,by means of the seismic instrumentation, in Swiss nuclear power plants.

ENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 20

Milestones for licensees:
2nd quarter of 2013:

Completion of the Pegasos Refinement Project (PRP)

Milestones for ENSI:
4th quarter of 2013:

Stipulation of the methodology and timeline for new seismic safety case
Concept regarding the advantages and drawbacks of upstream automatic
scrams by means of seismic instrumentation

4.2

Containment integritya) Seismic robustness of the containment venting systems at Gösgen andLeibstadt nuclear power plants
Following the cursory review completed at the end of 2012, the detailed review of the submitted
documentation by ENSI will continue into the second quarter of 2013. The first step will be to assess
the actual state of the systems on the basis of updated documents. ENSI will then review the
improvement measures proposed by the licensees.

b) Seismic robustness of the isolation for the containment and the primary circuit
The cursory review was completed for the plants in question at the start of 2013 (for KKB, the review
was already completed within the seismic safety case supplied in 2012, see section 3.1). The cursory
review produced certain further requests regarding the submission of additional documents. These
documents will be submitted in the first quarter of 2013 and will be taken into account by ENSI in its
statement to be issued in the second quarter of 2013.

c) Requirements for containment integrity
The main report of the peer review team in connection with the EU stress tests (April 2012) includes
a recommendation at European level that the containment, as the final barrier before the release ofradioactive substances, plays a key role in severe accidents. Switzerland's nuclear power plants
already have equipment and measures in place which largely guarantee attainment of the"Confinement of radioactive substances" fundamental safety function; their rating in the review byinternational experts was therefore good. ENSI is actively involved in the technical working group of
WENRA (a sub-group of the Reactor Harmonization Working Group), which is currently focusing on
containment integrity in case of severe accidents. In particular, the group will review the existing
WENRA requirements and will adapt them where necessary. ENSI will then examine whether therequirements for the revised Safety Reference Levels are met in Switzerland.

21 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSI

Milestones for licensees:
1st quarter of 2013:

Submit documentation from cursory review

Milestones for ENSI:
2nd quarter of 2013:

Statement by ENSI on seismic robustness of the isolation of thecontainment and the primary circuit
Statement by ENSI regarding the seismic robustness of the containment
venting systems at KKG and KKL

End of 2013:

4.3

Review of Safety Reference Levels for containment integrity

Extreme weather conditions

ENSI defined the requirements for the probabilistic hazard analyses and safety case needed todemonstrate adequate protection of plants against extreme weather conditions in greater detailduring 2012.
At the end of 2012, in compliance with an ENSI request to this effect, the plants submitted a concept
for proving adequate protection; this is currently under review. The probabilistic hazard analyses
and safety case for extreme weather conditions, including statements of safety margins, must be
submitted to ENSI by the end of 2013.
Milestones for licensees:
End of 2013:

Safety case for extreme weather conditions

Milestones for ENSI:
1st quarter of 2013:

4.4

Statement by ENSI regarding the concept

Increase in safety margins

Following the events at Fukushima, investigations were conducted and demonstrations were
provided during 2011 and 2012 in connection with external natural events and sequences entailingthe failure of essential safety systems which create increased autonomy requirements for the
nuclear power plants; these activities confirmed that the Swiss nuclear power plants display a highlevel of protection against the impact of the accidents that were analysed. The requirements forsafety provisions stipulated by law to comply with the fundamental safety functions (control ofreactivity, cooling of fuel elements and confinement of radioactive substances) are met. Moreover,the safety margins are available. These are mainly attributable to the robust design of the special
emergency systems at the plants, which are specially protected against external events.

ENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 22

In the Swiss country report on the EU stress tests (December 2011), the concept of "safe shutdown
paths" was used to supply deterministic proof for the first time; safe shutdown paths enable theplants to be brought into a safe shutdown state after accidents. Swiss nuclear power plants havethree safe shutdown paths. The first path comprises the conventional safety systems. The special
emergency systems constitute the second safe shutdown path, which is designed primarily to copewith extreme external events and sabotage acts. The preventive accident management measures
implemented in all the nuclear power plants form the third safe shutdown path. These comprisemanual measures to be carried out locally by the operating staff; they are defined in specificemergency procedures and are carried out with the use of permanently installed or mobile
equipment. This approach (deterministic demonstration by means of safe shutdown paths) allows
an assessment of the robustness of the individual safe shutdown paths and therefore provides anadditional analytical tool to increase safety margins.
As a consequence of the accident at Fukushima, ENSI ordered specific backfitting measures to cope(in particular) with severe accidents at the Swiss nuclear power plants; some of these measures havealready been implemented, while others are still in the planning phase. In addition, the Swiss nuclear
power plants have implemented further improvements such as the procurement of additional
mobile power supply units for the specific purpose of improving autonomy in case of severe
accidents.
Increasing safety margins in case of accidents beyond the design basis is a key issue for analysis
work in 2013. Based on the results of probabilistic and deterministic analyses, the objective is to
identify areas where backfits could contribute the most towards a further reduction of the hazard,
taking account of the principle of adequacy. The licensees of the Swiss nuclear power plants willdraft potential solutions to increase the safety margins in these areas. There will be a special focus
on strengthening the third safe shutdown path. A systematic overview will be used to show that, asa result of the measures developed, all appropriate precautions have been implemented to bringabout a further reduction of the hazard by means of permanently installed systems or preparedmeasures that are available at short notice.
This year, as the third safe shutdown path is strengthened, ENSI will also review extended
requirements (e.g. design requirements or testing intervals) for accident management equipment
under conditions resulting from extreme external events. These include, for example, theemergency power supply for the instruments required for severe accident management.
Milestones for licensees:
End of 2013:

Analyses for increasing safety margins

Milestones for ENSI:
2nd quarter of 2013:

Drafting of requirements and boundary conditions for the analyses on
increasing safety margins

4th quarter of 2013:

Requirements for accident management equipment are defined

23 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSI

4.5

Hydrogen managementa) Containment venting
ENSI's review of the studies submitted by KKG and KKB in 2012 (regarding the improvement of
displays in the emergency control room and the updated post-LOCA study) is scheduled for 2013.

b) Hydrogen management
As already noted in connection with the EU stress tests, various aspects of the hydrogen hazard incase of severe accidents in the reactor should be reconsidered. Extensive studies have already been
carried out in connection with the probabilistic safety analysis, so important basic material is alreadyavailable. Based on the review in connection with the EU stress tests and the NSC's report, thefollowing analyses are to be carried out by the Swiss nuclear power plants:


Review of robustness and scope of measuring equipment in connection with the assessment of
the hydrogen hazard

Updating of analyses regarding the hydrogen hazard and investigation of the propagation ofhydrogen from the containment into other nuclear power plant buildings

Review of the measures and procedures in place for protection against the hydrogen hazard



Review of the containment venting path in respect of the hydrogen hazard.

Milestones for licensees:
End of 2013:

Submission of studies regarding the hydrogen hazard in case of severereactor accidents

Milestones for ENSI:
1st quarter of 2013:

4.6

Specification of requirements for the review of the hydrogen hazard in caseof severe accidents

Severe Accident Management (SAM)

Severe Accident Management (SAM) includes the implementation of measures following coredamage accidents to cool the damaged reactor core and to limit or reduce the release of radioactive
substances into the surrounding area. As the reactor accident at Fukushima shows, these activities
have to be carried out for prolonged periods under unfavourable radiological conditions, thereby
creating the requirement to provide an infrastructure that remains operable in the long-term under
accident conditions.
In connection with infrastructure, in 2012 ENSI requested the plants to submit a report on the longterm operability of the emergency control center (ECC) and substituted ECC to ENSI by the end of
the first quarter of 2013. The plants submitted these reports by the specified deadline and they are
currently under review. On the basis of these reports, ENSI will carry out follow-up inspections of theemergency accommodations for prolonged deployments this year, and will order additional
measures as required.

ENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 24

The procedures of the activation of the Reitnau external storage facility and the provision of SAM
equipment and its transportation from the external storage facility to the plant will also be tested
during the course of this year. These tests will be carried out as part of an unannounced alarm
exercise and an emergency exercise in one plant.
Milestones for licensees:
1st quarter of 2013:

Submission of reports on long-term operability after core damage accidents
with large releases (all plants)

4th quarter of 2013:

Operational readiness of the external storage facility is tested and SAM
equipment is transported to a plant as part of an emergency exercise

Milestones for ENSI:
4th quarter of 2013:

Completion of inspections of the emergency accommodations for prolonged
deployment after core damage accidents with massive releases
Procedures for the deployment of the equipment from the external storage
facility are tested

4.7

Emergency management at Swiss national levela) IDA-NOMEXENSI coordinates its activities with other Federal agencies and cantons on the basis of the measures
adopted by the Federal Council and included in the final report of IDA NOMEX (theInterdepartmental Working Group to Review Emergency Preparedness Measures in case of Extreme
Events in Switzerland) issued in July 2012. ENSI will also devote attention to the implementation ofinternational recommendations and the problem of liquid radioactive discharges as a consequenceof reactor accidents. ENSI's work for 2013 is as follows:
The reviews of existing reference scenarios for emergency preparedness will be completed, in
collaboration with representatives of the cantons, Federal agencies and nuclear power plants. The
results will be incorporated into the review of emergency preparedness zones which will then be
carried out by the same working group.
In case of accidents at nuclear power plants, deployments of external emergency preparedness
organisations and notifications to neighbouring countries are linked to specified levels on theInternational Nuclear Event Scale (INES). The IRRS issued a recommendation to Switzerland thatthe classification of emergencies and the ensuing deployment of emergency preparedness
organisations should be geared to a special IAEA classification system created for emergencies;
ENSI will therefore carry out a study regarding the implementation of the IAEA emergency
classification system in the nuclear power plants and at ENSI itself in 2013.

25 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSI

The importance of redundant and fail-safe communication equipment in order to terminate an
emergency was addressed in the final report by IDA NOMEX. One of the measures taken in thisregard was to task the Federal Office of Civil Protection (FOCP) / Department of Defence, Civil
Protection and Sport (DDPS) with the definition of requirements for redundancy and fail-safe
operation of communication equipment. For its part, ENSI is examining various options such as
satellite-based communication in order to be able to compensate for the decrease in redundancy
originated by the loss of the AF network in 2011. This year, ENSI will introduce the "safety radio
network" offered by Polycom (Switzerland) AG as an alternative communication system.
Even in the case of an accident at a nuclear power plant triggered by an external extreme event (e.g.
a severe earthquake), the availability of measurement and forecasting systems must be ensured. For
this purpose, for example, it is necessary to examine the acceleration sensitivity of the measurement
electronics. In the course of 2013, ENSI will inspect the dose rate measurement sensors currently inoperation to determine whether they are able to function in case of the accelerations which canoccur during severe earthquakes. By the end of 2013, ENSI will also determine whether Guideline B12 adequately defines the requirements related to seismic resistance of accident instrumentation(including the emergency power supply) for the implementation of AM measures in particular, andfor the plant parameters transmitted to ENSI.

b) Dispersion of contaminants in watercourses
As a result of the Fukushima accident, significant quantities of radioactively contaminated water
were discharged into the sea in addition to the airborne releases of radioactive substances. ENSI will
require the licensees to examine those cases in which large quantities of radioactively contaminatedwater can be expected in their plant, the routes by which these quantities of water can reach thesurrounding area, and the methods that can be used to retain and/or minimise them.
In 2o12, ENSI drafted a report on the situation in Switzerland in case of a discharge of large
quantities of radioactivity into the rivers Aare and Rhine; the Federal agencies and cantons
concerned are carrying out the consultation process regarding this report until the end of February
2013. The need for action to optimise protective measures for the population in such cases will be
determined after completion of the consultation process in 2013, in liaison with the cantons andFederal agencies.
Milestones for licensees:
4th quarter of 2013:

Studies on plant-specific application of the IAEA emergency classification
system are completed (for all plants)
Studies of scenarios, release paths and possibilities for minimisingwaterborne radioactive discharges are completed

Milestones for ENSI:
2nd quarter of 2013:

Report on the review of the reference scenarios

4th quarter of 2013:

Report on the review of the zoning concept
The POLYCOM communication system has been fully introduced at ENSIENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 26

4th quarter of 2013:

The need for action to optimise measures to protect the population in caseof waterborne radioactive discharges is determined
The functional capability of dose rate measurement sensors in case ofearthquakes has been reviewed
Guideline B12 has been reviewed to determine necessary adaptations

4.8

Experience feedback

The plants must finalise those guidance documents for the analysis of external occurrences and forthe derivation of measures which were only available in draft form when ENSI carried out its topicalinspections in 2012. The requirements for reporting to ENSI as per Guideline ENSI-B02 must be
revised where a need for improvements was identified during the inspections. The aforementioned
documents must be submitted to ENSI by the deadlines in the second half of 2013. ENSI will thenassess the submitted documents.
Switzerland assesses operational experience from foreign nuclear power plants. On the one hand,
statutory requirements oblige the licensees to evaluate events abroad for the purpose of gaining
knowledge for their own plants. On the other hand, ENSI keeps track of the key issues atinternational level (in bilateral committees and international working groups of the NEA (Nuclear
Energy Agency) and the IAEA). ENSI is also a member of the "European Clearinghouse on NPP
Operational Experience Feedback", a body of experts which focuses on knowledge gained fromoperational experience on the basis of event analyses, assessments and reporting. ENSI plans tosubject its own process for the assessment of foreign operating experience to a review in order to
identify potential for improvement and, as an option, to initiate closer collaboration with theClearinghouse.
Milestones for licensees:
4th quarter of 2013

Updated guidance documents are available (all plants)

Milestones for ENSI:
4th quarter of 2013

Review of the ENSI process for the assessment of foreign operating
experience27 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSI

4.9

EU stress tests follow-up

The European Nuclear Safety Regulators' Group (ENSREG) approved an action plan for follow-up
measures to the EU stress tests in 2012. Its objective is to request the participating countries to draw
up their own national action plans for the implementation of the measures resulting from the EU
stress tests. Switzerland participates actively in this process. ENSI has drawn up a status report for
the implemented and planned measures (as per end of 2012) and will continue to take part in thefollow-up actions. ENSREG will review and compare the implementation measures by theparticipating countries during a workshop at the end of April 2013. ENSREG currently plans to issue
an action plan every year.
Milestones for licensees:
Milestones for ENSI:
2nd quarter of 2013

Peer review of the national action plans (ENSREG workshop)

4th quarter of 20132013 status report to ENSREGENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 28

5

Annexes

Legenda to column 3 (status/action plan)2013 Key issue in the action plan for 2013
LA
Issue incorporated into ongoing supervisory activities
NI
Issue yet to be initiatedB
Issue dependent on IDA NOMEX

5.1
No

1

Annex 1: List of checkpoints from "Lessons Learned"
Designation

PP1

Status /action plan2013

Description

The hazard assumptions for earthquake and external flooding, and also for
extreme weather conditions, must be re-evaluated to take account of thelatest knowledge.

Implementation text

Earthquakes: the first review of the seismic safety case based on intermediate hazard
assumptions (PRP Intermediate Hazard) was completed in June 2012. Determination of
the definitive hazard will be completed in the course of the PRP project in 2013,
followed by new seismic analyses by the NPP licensees.
External flooding: hazard assumptions were reviewed in 2011. Combination ofearthquakes/earthquake-induced flooding was covered in 2012.
Extreme weather conditions: the licensees will submit their safety case in 2013.

2

PP2

LA

The coping strategies for a prolonged loss of electric power supply must be reevaluated on the basis of knowledge gained from Fukushima.

The strategies were reviewed during topical inspections in all NPPs at the end of 2012:
the plants have effectively continued to develop their existing strategies, and adequate
resources for AM are available in order to prevent core damage after an SBO. Work will
be followed up as part of ongoing supervisory activities.

29 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSINo

Designation

Status /action plan

Description

Implementation text

3

PP3

LA

Screening analyses of coolant supply were completed in 2012; at all plants except
It should be checked whether the coolant supply for the safety systems and the
Mühleberg, adequate redundancies are available in order to guarantee the coolant
associated auxiliary systems is guaranteed from a diverse source which is safe
supply. KKM must backfit a diverse heat sink. The work will be followed up as part of theagainst earthquakes, flooding and contamination.
DIWANAS project.

4

PP4

LA

It should be checked whether the requisite tightness of buildings containing
important safety equipment is guaranteed in case of flooding of the site.

5

6

7

8

9

PP5

2013

On the basis of experience gained from the Fukushima accident, it should bechecked whether the availability of the instrumentation required to assess thecondition of the plant is guaranteed adequately even in extreme situations.

The safety case for the 10,000-year flood was accepted by ENSI in 2011. Work still
outstanding was incorporated by ENSI into individual follow-on tasks so that theirprocessing will continue as part of the normal supervisory activities.
Backfitting of instrumentation to monitor the spent fuel pools was required in theformal order dated 05.05.2011. Backfitting projects for this purpose are in progress in all
NPPs; permits for these have been issued by ENSI, which also supervises theimplementation.
In 2013, activities are planned with regard to accident instrumentation, as defined in
ENSI-B12 (see section 4.6). In addition, ENSI will address extended requirements for
SAM equipment (see section 4.4).

LA

It should be checked whether control of leaks and long-term cooling of the
spent fuel pools are guaranteed in case of severe accidents.

2013

In 2013, ENSI requires a reconsideration of various aspects of the hydrogen hazard in
It should be checked whether tests and inspections regarding the prevention of case of severe accidents in the reactor (see section 4.5). Topics are: analyses of thehydrogen explosions should be extended to additional areas of the plantshydrogen hazard including propagation of hydrogen from the containment into otherbeyond the primary containment.
buildings of the nuclear power plant, robustness and scope of measuring equipment,
measures and procedures in place, review of the containment venting path.

PP8

2013

The design and operation of the systems for filtered venting of thecontainment must be addressed again.

PP9

B
2013

It is necessary to carry out a new review of the earthquake and flood design ofthe monitoring network for automatic dose rate measurement in the vicinity of ENSI has reviewed the specific requirements on the basis of the knowledge obtained
nuclear power plants (MADUK), in relation to experience gained from thethough IDA NOMEX. Compliance with the requirements will be examined in 2013.
Fukushima accident.

PP6

PP7

Reviews took place in 2011 and 2012. Permits for backfitting projects at the Beznau andMühleberg NPPs are being issued by ENSI, which also supervises the implementation.

The filtered venting system was examined both in the EU stress tests ("Measures anddesign to protect containment integrity") and in the course of topical inspections by
ENSI which relate specifically to knowledge gained from the accident at Fukushima-Daiichi. Containment integrity continues to be a key issue in 2013.

ENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 30

No

Designation

10 PP1011 PP1112 PP12

Status /action plan

Description

Implementation text

B2013

It should be checked whether the emergency control center (ECC) and thesubstitute ECC at the Swiss nuclear power plants still meet the requirements,
based on the experience gained from the Fukushima accident.

Requirements for technical emergency preparedness equipment at nuclear installations
are stipulated in ENSI Guideline B12. On the basis of knowledge gained frominvestigations of the accident at Fukushima, from IDA NOMEX and from newinspections, ENSI will review the specific requirements for ECC and substitute ECC andcheck their implementation in practical terms.

LA

The access control system for nuclear power plants and the associatedarrangements must be reviewed to determine the accessibility of rooms where This issue was initially addressed in the course of existing supervisory activities taking
intervention is required in case of severe accidents, while maintaining
into consideration the additional knowledge gained from the Fukushima accident.
appropriate plant security. Monitoring of radiation protection must continue to Follow-up will continue in the course of ongoing supervisory activities.
be guaranteed in this context.

2013

The emergency measures for heat removal in case of a complete failure of thecooling water supply must be reviewed and verified under conditions resulting
from the disruption of the infrastructure and the power supply.

After the construction of the Reitnau external storage facility, resources were alreadymade available for use in a situation of this sort in order to maintain the cooling function
independently of the permanently installed safety systems. In addition, this issue isincluded in the scope of the EU stress tests ordered by ENSI on 01.06.2011.
A comprehensive review of the deployment of resources from the Reitnau external
storage facility will take place in 2013 in connection with an emergency exercise.

13 PP13LA

It should be checked how the alternative supply of water and power for
emergencies is ensured.

Operational resources have been held in readiness at a central point at the Reitnau
storage facility since 2011; in addition, storage facilities have been set up at the NPP
sites. Hook-up points at the NPPs have been backfitted as necessary. Their review will
be part of the regular emergency exercises. In addition, this topic will be consideredagain as part of the "Increased margins" key issue (see section 4.4).

14 PP14LA

It is necessary to examine the water resources that can be made available tosupply the reactor pressure vessel, the spent fuel pools and the containment.

Available reserves of water have already been reviewed and are already documented in
the existing emergency procedures. This topic will be considered again as part of the"Increased margins" key issue (see section 4.4).

15 PP15

B
2013

Emergency management must be reviewed to determine further potential for
improvement.

Implementation will take place under the auspices of IDA NOMEX. The resultant specificrequirements for nuclear installations will be supervised by ENSI.

31 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSINo

Designation

Status /action plan

Description

Implementation text

ENSI has identified the following issues for improving emergency planning andemergency exercises:

16 PP16LAa The decision-making guidance for emergency management in case of
severe accidents (SAMG) at nuclear power plants, including the newly
planned checkpoints to deal with severe accidents, must be reviewed on thebasis of knowledge gained from the Fukushima accident. In this regard, it is
The Swiss NPPs have a comprehensive system of accident and emergency procedures,
particularly necessary to check:complemented by the SAMG. ENSI considers that a new assessment in the light ofevents at Fukushima would serve the interests of safety. In the course of ongoing- whether adequate consideration is given to a prolonged Station Blackout
supervisory activities, there will be re-assessments of the regulatory requirements(SBO) and the simultaneous occurrence of events in multiple-unit plants(ENSI-B12) and the implementation of SAMG in the plants.
-

whether there is any need for measures, auxiliary resources andequipment that must be available to ensure subcriticality in the longterm in case of severe accidents.

b Consideration given to accidents involving a prolonged SBO in the planningof emergency exercises.

In connection with the implementation of ENSI's formal order dated 18.03.2011, an
external emergency storage facility (Reitnau) for all NPPs in Switzerland was alreadyestablished on 01.06.2011. Among other items, stocks of boron compounds are kept inreadiness here to ensure the long-term maintenance of subcriticality.

c Examination of whether the processes are trained often enough during
emergency exercises. Particular attention should be given here to afunctioning inter-organisation chain of communication across the variousorganisations.

17 PP17B
2013

It should be checked whether and to what extent the communication facilities
are designed with adequate redundancy and diversity.

Implementation will take place under the auspices of IDA NOMEX. The resultant specificrequirements for nuclear installations will be supervised by ENSI.

18 PP18

B
2013

It must be ensured that adequate staff is available at all times to accomplish allnecessary emergency management activities.

Implementation will take place under the auspices of IDA NOMEX. The resultant specificrequirements for nuclear installations will be supervised by ENSI.

19 PP19

LA

Measures that increase the organisation's ability to react to unexpected events
must be reviewed again on the basis of experience gained from Fukushima.

Actions related to this issue are followed up by the Human and Organisational Factors
section in the course of ongoing supervisory activities.

20 PP20

B
2013

Transmission of plant parameter data must be re-evaluated with respect to analternative, independent means of data transmission.

The specific requirements are being drawn up by ENSI on the basis of knowledge
acquired through IDA NOMEX. ENSI will introduce the " safety radio network" of
POLYCOM Switzerland AG as an alternative communication system.

ENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 32

Status /action plan

Description

Implementation text

21 PP21B
2013

The evacuation concepts must be reviewed, taking account of knowledge
gained from the Fukushima accident.

Implementation will take place under the auspices of IDA NOMEX.

22 PP22

B
2013

Coordination with other international partners is required to determine
Implementation will take place under the auspices of IDA NOMEX. The resultant specificwhether and how an international network for central international emergency
requirements for nuclear installations will be supervised by ENSI.
support can be set up.

23 PP23B
2013

It should be checked whether the necessary information regarding forecasts ofreleases and radiation exposure is provided in a timely and continuous mannerin case of accident.

No

Designation

The specific requirements are being drawn up by ENSI on the basis of knowledge
acquired through IDA NOMEX.

The following improvement measures were identified regarding information
provided to the general public:

24 PP24

B
2013

a It must be ensured not only that the requisite infrastructure and thenecessary individuals and/or organisations and equipment are available forcrisis communication, but also that the necessary means of communication
are in place. The relevant precautions must be taken. Regular training must
be provided on the associated procedures. This point also includes afunctioning network of experts who are available to the media to supply
neutral and objective information.

Implementation will take place under the auspices of IDA NOMEX. The resultant specificrequirements for nuclear installations will be supervised by ENSI.

b It should be checked whether the organisational responsibilities for
informing the public as well as the local authorities and support staff areclearly stipulated, and are uniformly understood by all involved parties.
c It should be checked whether the timely communication of radiologicaleffects, including calculated forecasts, is also ensured beyond Switzerland's
borders.

25 PP25

NI

It is necessary to examine the extent to which the release of non-nuclear
hazardous substances in case of beyond design basis accidents could exert an
additional influence on the accident sequence, and which counter-measures
are required.

26 PP26

2013

The process of evaluating and examining the applicability of national andinternational operating experience must be optimised on the basis ofknowledge gained from the Fukushima accident.

-

ENSI has continued to optimise the relevant internal structures. Activities related tooperating experience feedback from international occurrences are planned in 2013.

33 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSINo

Designation

27 PP27

Status /action plan

Description

Implementation text

2013

It must be guaranteed that the knowledge gained from national andinternational operating experience (event analysis) in the licensees'organisations reaches all the relevant individuals and units (including those atgroup level).

Inspections of this aspect were carried out by ENSI at all NPPs in the fourth quarter of2012. Follow-up measures will receive further attention from ENSI as a key issue activity
in 2013.

Switzerland collaborates continuously in the Safety Standards Groups (SSC) and otherimportant IAEA bodies.

28 PP28LA

It must be ensured that internationally harmonised assessment criteria for
nuclear safety are established at the highest level of safety.

Under the auspices of WENRA, ENSI advocates the development of harmonised Safety
Reference Levels (SRL) and their implementation in European countries that use nuclear
energy. Six new working groups within the RHWG (Reactor Harmonisation Working
Group ) are to draft proposals in 2013 for the integration of new knowledge from the EU
stress test into the SRLs.
An OSART (Operational Safety Review Team) mission was carried out at KKM in
October 2012.

29 PP29

LA

Greater importance should be accorded also at international level to therecommendations resulting from international reviews (IRRS, OSART) andfrom the regular Periodic Safety Reviews (PSR). The transparency of ENSI's
supervision and of the operators' safety-related activities must be increased.

On the basis of the recommendations and suggestions ENSI got during the 2011 IRRS
mission, ENSI has (by the end of 2012) developed an action plan for the follow-up
mission which will probably take place in 2015.
In May 2012, by the specified deadline, Switzerland submitted its country report for the
extraordinary conference on the Convention on Nuclear Safety (CNS). At the conferencein August 2012, Switzerland advocated further improvements to the international safety
regime. A working group is to draft proposals to improve the CNS and its processes by
the time of the next regular conference in March/April 2014. Switzerland is participating
actively in this work.

30 PP30LAENSI is reviewing the significance of the lessons learned from the Fukushima
accident for its supervisory activities.

ENSI worked to adopt an analytical approach regarding its own supervisory strategy
well before the accident in Japan. In this context, ENSI is currently carrying out aninternal project on the topic of supervisory culture.
The review of the regulatory framework will continue in the course of ongoingsupervisory activities. Specific issues are covered by other checkpoints.

31 PP31LA

Additional operational resources must be kept in readiness for radiation
protection in case of severe accidents.

Establishment of the Reitnau external storage facility in 2011. Reviews of the adequacyof the resources to be kept in readiness are carried out at regular intervals.

32 PP32

B
2013

It is necessary to examine whether the emission and immission measurements
in place on the power plant sites in order to determine the activity releases areguaranteed in case of loss of offsite power or loss of normal emergency power.

The specific requirements for checking adequate implementation in relation to thisissue are being drawn up by ENSI on the basis of knowledge acquired through IDANOMEX. Accident instrumentation will be reviewed again in 2013 (see section 4.7).

ENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 34

Status /action plan

Description

Implementation text

33 PP33

B
2013

It is necessary to examine the extent to which the availability of themeteorological data required for dispersion calculations is guaranteed in caseof extreme natural events.

The specific requirements for checking adequate implementation in relation to thisissue are being drawn up by ENSI on the basis of knowledge acquired through IDANOMEX.

34 PP34

B
2013

It is necessary to stipulate arrangements for dealing with contamination in thearea surrounding nuclear installations following severe accidents.

On the basis of knowledge from IDA NOMEX, it is planned to define the specificrequirements for checking adequate implementation in relation to this issue inconnection with the revision of the Radiological Protection Ordinance.

35 PP35

2013

It is necessary to examine how to deal with large volumes of contaminatedwater, radioactive waste or environmentally hazardous substances in case of
severe accidents.

In 2013, the NPPs will present the envisaged scenarios, including the requisite technicalequipment, to retain large quantities of contaminated water.

36 PP362013

As part of the emergency planning for severe accidents, it must be ensured
that sufficient radiation protection staff is available on site.

In 2013, inspections will be carried out and supervisory discussions will be conductedwith the NPP licensees on this aspect.

37 PP37LA

The knowledge gained from the Fukushima accident must be taken into
account in the programmes to foster and develop the safety culture in Swiss
nuclear power plants.

Knowledge from the accident at Fukushima was integrated into the activities related tosafety culture in the NPPs and at ENSI during 2012, and this will be continued insubsequent years as part of the regular activities related to safety culture.

No

Designation

35 | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | ENSI

5.2

Annex 2: List of open points from the EU stress tests
Status /action plan

Description

Implementation text

38 OP2-1

2013

ENSI will follow up on the question as to whether in the Swiss nuclear power
plants automatic scrams should be triggered by the seismic instrumentation.

An upstream automatic scram by means of seismic instrumentation has not yet been
implemented in Swiss nuclear power plants. A working group at ENSI will draft aconcept in 2013 regarding the advantages and drawbacks of an upstream automatic
scram by means of seismic instrumentation.

39 OP2-2

2013

In respect of seismic proof that has still to be supplied, ENSI will follow up on amore detailed examination of the seismic robustness of the isolation of thecontainment and the primary circuit.

Proof was submitted by the licensees in 2012 and the cursory review by ENSI wascompleted. Further processing will take place in 2013.

40 OP2-3

2013

ENSI will follow up on measures to improve the seismic stability of theProof was submitted by the licensees in 2012 and the cursory review by ENSI was
containment venting systems in case of beyond-design basis accidents for KKG
completed. Further processing will take place in 2013.
and KKL.

41 OP3-1

LA

ENSI will follow up on the impacts of a total debris blockage of hydraulicengineering installations.

Proof was submitted by the licensees (KKB, KKG and KKM) in 2012. For KKB and KKM,ENSI determines that no cliff-edge effects from debris blockage are to be expected.
Further processing will take place in 2013.

42 OP4-1

2013

ENSI will follow up on the proofs of protection against extreme weather
conditions, including combinations thereof.

Requirements were defined by ENSI in 2012. Proof of adequate protection against
extreme weather conditions is to be furnished by the licensees in 2013.

43 OP5-1

LA

ENSI will follow up on the development of a compre-hensive strategy for thetargeted deployment of the mobile accident management emergency diesels
in order to secure selected direct current and/or alternating current consumers
in the long term under total SBO (resp. SBO) conditions.

Inspections of this aspect were carried out by ENSI in the fourth quarter of 2012. The
results will be assessed in the first quarter of 2013. Any follow-up measures will be
implemented by ENSI in the course of its ongoing supervisory activities.

44 OP6-1

2013

From the point of view of risk minimisation, ENSI will follow up on the extent
to which the current deployment strategies for the venting systems in severe
accidents should be retained.

Containment integrity is a key issue in 2013.

45 OP6-2

NI

ENSI will follow up on whether restoring containment integrity during
shutdown in the case of a total SBO represents a time-critical measure.

-

No

DesignationENSI | F u k u s h i m a A c t i o n P l a n 2 0 1 3 | 36

No

Designation

46 PRT-1

47 PRT-2

Status /action plan

Description

Implementation text

2013

The peer review team recommends considering the assessment of margins
with respect to extreme weather conditions exceeding the design bases, e.g.
by extending the scope of future PSRs.

ENSI specified detailed requirements for the probabilistic hazard analyses and the proofof adequate protection of plants against extreme weather conditions in 2012. In 2013,
the licensees will submit proof (including statements on the available safety margins) to
ENSI.

2013

It is recommended that the regulator assesses the opportunity of requiring
more reliance on passive systems for hydrogen management for severe
accident conditions. It is also recommended that the regulator considers
further studies on hydrogen management for the venting systems.

In 2013, ENSI requires a reconsideration of various aspects of the hydrogen hazard incase of severe accidents in the reactor. The topics are: analyses of the hydrogen hazard
including the propagation of hydrogen from the containment into other buildings of thenuclear power plant, robustness and scope of the measuring equipment, measures andprocedures in place, and review of the containment venting path.

Issued by
Swiss Federal Nuclear Safety Inspectorate ENSI
Industriestrasse 19
CH-5200 Brugg
Phone +41 (0)56 460 84 00
Fax+41 (0)56 460 84 99
info@ensi.ch
www.ensi.ch
ENSI-AN-8283
Published 28.02.2013