sweden’s lwr activities · 400kv for f1 and f2 ... •equipment on safety and non-safety busbar...

© Forsmarks Kraftgrupp AB

Sweden’s LWR activities

IAEA TWG-LWR meeting Vienna, 18-20 June, 2013

Sekretessklass: Öppen (S1)

2013.06.19


| Sweden's LWR activities | Patrik Svantesson | 2013-06-19 |

Contents

• Regulatory activities

• Swedens Post-Fukushima actions

• R & D program - Reactor Safety

• The phase-event at Forsmark 3

• Future Role & Initiatives on LWRs in Sweden

• Proposals for future IAEA-activities



Regulator activities

• Swedish government requested in 2010 SSM to make a safety

evaluation of the existing plants called ”Investigation of long-term safety

in the Swedish nuclear power industry and measures regarding the

accident at Fukushima Dai-ichi”

• The scope was:

- Compliance and effect of the implemented safety upgrades

- Operation beyond 50 years. Identify necessary safety upgrades.

- Key parameters for long term operation (LTO)

- Evaluation of the Swedish regulatory framework (ie. international bench mark)

- International experience of safety enhancements to allow LTO

- Addition 2011: Fukushima: Stress test, actions taken and further investigations



Conclusions of Regulatory evaluation

1. Needs for further safety improvements:

• Up until 30 June 2012, altogether for the ten reactors’ modernisation programmes, approximately 60 per cent of the decided measures had been implemented to fulfill the requirements in the regulations

• The power plants needs to strengthen resilience against extreme natural phenomena, a loss of power and a loss of main heat sink

• Systems for independent coolant makeup needs to be built

• Protection against sabotage needs to be strengthened further



Conclusions of Regulatory evaluation

2. Ageing management and long-term operation

• Establishment of programmes that effectively detect early indications of safety deficiencies due to ageing

- Special attention to effects that can substantially increase the

rate of embrittlement of reactor pressure vessels for PWRs

- The condition of tendons and steel liners in reactor

containments

- Degradation mechanisms that can influence reactor

containments’ concrete and metal parts

- Possibilities for reliable inspections and testing of reactor

containments

- The validity of environmental qualifications of electrical,

instrumentation and control equipment as well as parts with

polymer construction materials



Conclusions of Regulatory selfassessment

3. Needs for changed regulation and regulatory supervision

• The model stands up relatively well in relation to international standards and practice, but it needs to be developed in various respects

• The results of the IRRS review points out areas for improvements such as regulatory framework, in the form of regulations and regulatory supervision

- The regulatory framework needs to become more comprehensive and be based on international safety standards and European practice

- Define the areas of supervision for which different supervisory strategies are to be developed

|


Overview Post-Fukushima Actions

• Present investigations to determine measures,

how they shall be implemented and when.

• Investigations to be completed 2013, 2014 and

2015

• Fukushima actions are considered in relation

to other safety upgrades that are in progress or

are planned

• Recognise the importance of strategy for core

melt mitigation



New postulated events

New postulated events are needed for the design of back fitting

measures to enhance prevention of severe accidents.

• “Extended Loss AC Power” (ELAP) and “Loss of DC-power”

• Loss of ultimate heat sink (LUHS, total loss of the plants connection to

all sea water sources)



Suggested principles for a independent ECCS


Probability

Consequence

Compensatory measure

Instructions

Mobile equipment

Functions Fixed installations

SAR 4.8

External impact

SAR 4.6

SAR 4.7

Initiating events and accepted consequences

SAR 4.10

Protection against sabotage

Countermeasures

Permanent safety functions

Independent ECCS Mitigating

system

DB Slow sequences BDB

Implemented measures

Further actions

PC2,3 PC4 PC5 Complex sequences (CCF)

ELAP, LUHS

Core mealtdown


| Sweden's LWR activities | Patrik Svantesson | 2013-06-19 | 10

R & D program - Reactor Safety

Network Issues Partners

NPSAG Risk assessment

PSA, Failure data

SSM, Fortum, TVO, OKG, RAB,

FKA (SAFIR- contact,OECD-

contacts)

NORTHNET Thermohydraulic

In fuel, In-vessel,

Containment

SSM, Fortum, Westinghouse, OKG,

RAB, FKA, KTH, CTH, VTT, (SAFIR-

contact)

APRI Severe Accident SSM,KTH, RAB,OKG, FKA

(SAFIR-contacts, SARNET-contacts)

NBSG Fire prevention SSM, RAB, OKG, FKA

( OECD-contacts)

BWR-club Support

R & D activities

20 different utilities and vendors in

Europe and Japan


The event at Forsmark 3 2013-05-30

Switchyard FT46 –

400kV for F1 and F2

Forsmark 1

Forsmark 3

Forsmark 2

Switchyard –

FT47 400 kV for

F3

Gasturbine 70 kV

Switchyard - 70kV

Forsmark 3 was

in outage with

external 400 kV

busbars

connected to the

plant




400 kV

Maintanance work

on the generator




400 kV

Signal to open the

400kV breaker

was sent

unexpected

The reason is

an inaccurate

instruction




400 kV

Two out of

three breakers

opens

The reason is

a loose cable

to the 400kV

breaker

tripping device

Pumps for

residual heat

removal stops




What happened?

• Equipment on safety and non-safety busbar with protection for “phase-disconnection” stopped

automatically. This includes the pumps for residual heat cooling. Electrical machines lacking protection

for “phase-disconnection” did not stop and some of them got minor damages.

• The under-voltage protection on the diesel busbar did not measure < 65 % voltage with only one phase

connected (the internal voltage is above 65 % due to the generator step-up transformer coupling.

- No automatic signal to start the Emergency Diesel Generators (EDG) on any trains

• Operators separated manually the safety busbar from the external grid (opened the breakers).

- The load on the busbar was automatical disconnected and protection safety device was manual

and automatic reset and the EDG:s started as expected and energized the safety busbars

• The residual heat cooling was in operation after 16 minutes

• Analyses shows that there was time in the day scale to restore cooling before start of boiling



Future Role & Initiatives on LWRs in Sweden

• Modernisation aim at 50 -60 years life time of Swedish

plants

- New regulations to support licensing of new reactors

- New strategy for the regulatory work

- Safety enhancements to support Long term Operation

• Actions after Fukushima

- Power supply: Improved reliability (grid, gas turbine etc)

- Spent fuel pool cooling

- Independent core cooling

- Handle events with all units affected



Proposals for future IAEA activities

Identify new events outside design base

• Support member states to achive better understanding of not yet fully

assessed events

- Experience shows that the events that occurred in reality is often a

complex combination of events that not have been foreseen.

• Create methods to combine probabalistic and deterministic safety

assessments by comparing differences and similarities between

member states

- Support development of methodologies to identify critical complex

event scenarios by dynamic PSA or other methodologies

- Increase benchmarking between countries on identificaion of critical

complex scenarios (Benchmarking of PSAs and FSAR)

sweden’s lwr activities · 400kv for f1 and f2 ... •equipment on safety and non-safety busbar...

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