© Lars HögbergASME Workshop 2012-12-04

The Swedish approach to severe accidentmanagement from 1979 onwards

Lars HögbergDirector General (retired)

1. The primary lesson learned after TMI, Chernobyl and Fukushima2. Swedish conclusions after TMI3. Design objectives for severe accident management backfits after TMI4. Swedish actions after Fukushima and EU stress tests5. Conclusions

ASME Workshop on A New Nuclear Safety Construct

© Lars HögbergASME Workshop 2012-12-04

TMI, Chernobyl, Fukushima: ”the Primary Lesson Learned”

All three accidents had their root causes in system deficiencies indicative of poor safety management and poor safety culture in both the nuclear industry and government authorities.– TMI: Instrumentation, procedures, training, feedback of operating 

experience– Chernobyl: Design features, respect for tech specs, feedback of 

operating experience– Fukushima: Design basis (feedback of tsunami experience), state‐of‐

art accident management procedures and training

Thus, maintaining high global standards of safety management and safety culture including a “questioning mindset” must always have first priority, or else…

© Lars HögbergASME Workshop 2012-12-04

Swedish conclusions after TMI

Severe accidents, including core melt, can occur. 

Should a severe accident occur, a containment with preserved integrity can protect against significant releases to the environment.

Swedish emergency planning studies indicatedthat source terms of several thousand TBq of Cs‐137 or more (>1 % of core content) mightcause ground contamination calling for evacuation and land usage restrictions with significant socio‐economic impacts at distanceswell beyond 20 km from the plant.

So, severe accident management should aim at limiting source terms to less than ~150 TBq

Parliament endorsed in 1981 an overarching, qualitative cost/benefitassessment of measures to be taken based on socio‐economic considerations

Source: NRC

© Lars HögbergASME Workshop 2012-12-04

1 – 3 MBq/m23 – 30 MBq/m2

Barsebäck NPP(closed in  2005)

Population within 40 km radius(solid line yellow circle):Denmark: ~2 millionSweden : ~1 million

Justification: Hypothetical impact of a 10 000 TBq Cs-137 release (~ Fukushima) from Barsebäck

SOARCA 2012:Peach Bottom SBO unmitigated: ~7 500 TBq Cs‐137

Map source: Google Maps

© Lars HögbergASME Workshop 2012-12-04

1 – 3 MBq/m23 – 30 MBq/m2

Barsebäck NPP(closed in  2005)

Population within 40 km radius(solid line yellow circle):Denmark: ~2 millionSweden : ~1 million

Justification: Hypothetical impact of a 100 TBq Cs-137 release (”FILTRA-type”) from Barsebäck

SOARCA 2012:Peach Bottom SBO unmitigated: ~7 500 TBq Cs‐137

Map source: Google Maps

© Lars HögbergASME Workshop 2012-12-04

Severe accident management measures after TMI

Key overall objectives in case of a severe accident:• reach a stable state without undue delay, with damaged 

core covered by water and preserved containment integrity; • keep releases of radionuclides that cause long‐term land 

contamination below the equivalent of ~150 TBq Cs‐137.Specific functional requirements include:• Design basis includes: 

– 24h total station blackout; – single failure in BWR pressure suppression function (based on lessons

learned)

• Pressure relief shall not need operator action if containmentintegrity is threatened (but manual relief possible)

– No political or regulatory approval of venting needed under stress

• Capability to flood containments above core level (requiresventing in BWR) combined with protection of vulnerablecontainment penetrations against molten core.

• Appropriate procedures and training

Barsebäck(pebble bed filter, operational in 1985)

Remaining ten reactors(multi‐venturi scrubbers, operational in 1988)Government decisions in 1981 and February

1986 on measures to be implemented

Source: Sydkraft/E.ON

Source: Vattenfall AB

© Lars HögbergASME Workshop 2012-12-04

Lessons learned: Socio-economic impact of Cs-137 deposits in Sweden in 1986

0      100    200 km    

Total amount of Cs‐137 depositedover Sweden:~4000 Tbq

Max. 200 kBq/m2

Total amount of Cs‐137 releasedfrom Chernobyl:~85 000 Tbq

Mapping deposits and implementingappropriate food control measures toppedagendas of governments, media and foodindustry in Europe in most of 1986.Source: Swedish Radiation Protection Institute

© European Commission

© Lars HögbergASME Workshop 2012-12-04

Swedish actions after Fukushima and EU stress tests

Safety upgrades (and power upgrades) continue based on periodic safety reviews: redundancy, diversity, separation 

Reassessment of capabilty to cope with extreme naturalevents (seismic, flooding, weather) 

Reassessment of I&C response to extreme voltage transients Continuation of work started after Forsmark and other incidents

Separate ”last resort” feedwater and emergency power trainconsidered Totally independent and possibly bunkered, also for security reasons

Upgrading existing severe accident management capabilities:Long‐time endurance (>>24h). Simultaneous failures at several reactors.

Reassessment of fuel pool cooling capabilitiesRegulatory decisions on new requirements expected in 2013

© Lars HögbergASME Workshop 2012-12-04

ACCIDENT TYPE RELEASE OF Cs‐137 (TBq) 

EVACUATED  ESTIMATED COSTS million US$ 

Three Mile Island 1979 

Core melt << 1  Voluntary short‐term evacuation of nearby communities

~6 500

Tjernobyl 1986  Runaway fission process destroying the reactor

85 000  >300 000 relocated 250 000 ‐ 500 000

Fukushima 2011  Three cores severely damaged, probably melted 

12 000  ~150 000 evacuated, prospects to return still unclear after 20 months

100 000 ‐ 500 000 

Present Swedish release mitigation objective for station blackout sequence

Core melt <150 Precautionary short term evacuation in the vicinity of the plant?

< 20 000 ? 

My conclusions: Robust protection against socio-economicimpacts intolerable to both society and industry is justified

A New Nuclear Safety Construct should include a call for severe accident management preparedness based on Best Available Technology (BAT) with the objective to reach a stable state with preserved containment integrity without undue delay, and  keep releases of radionuclides that cause long‐term land contamination below the equivalent of about 100 TBq Cs‐137 in case of a core melt.