PAKS EVENT LESSONS LEARNED

1. PAKS EVENT LESSONS LEARNED Presented By: Chuck Casto U.S. Nuclear Regulatory Commission

2. Agenda • Background • Description of the event • Investigation of the event • Mission Insights • Pictures of the damaged fuel

4. Background • PAKS, 4-unit VVER-440 supplies 40% of Hungary’s electricity • Neglected VVER-440 aging SG feed water sparger operating experience • By 2000, four of six SGs for U-2 could not be ignored (had to replace all 4 in one outage) • Replacement activities hampered by high radiation

5. Background (cont’d) • SG chemical decon introduced crud deposits into RCS • Eventually three units derated (84-98%) • Core replacement did not help • Regulator wanted problem solved

6. 1999 Magnetite deposits in the primary circuit 2000 2001 Unit 1 Background (cont’d)

7. Unit 1 Unit 2 100 95 Unit 3 90 p2 p2 új paraméterek new parameters Reactor scram in December 85 p2 p2 January 2003.: Reactor shutdown (economic reason) 80 new parameters új paraméterek power scale Power loss caused by Magnetite deposition in the primary circuit 94% 94% 92%

8. Background(cont’d) • “Fuel Deposit Team” created to look for solutions • Two options – internal and external fuel cleaning • Vendor worked on internal cleaning SE for months prior to the Unit 2 outage • At last minute changed option to externalcleaning

9. Background(cont’d) • Previous experience of external cleaning seven “cool” assemblies at a time (total 150 assemblies) • Design expanded to 30 assemblies “hot” • The design as considered as “like-for-like” • License application submitted to regulator for “license in principle”

11. System Configuration

12. Unit 2: Location of Cleaning System Refueling machine Interim cover reactor cleaningequipment Pool No. 1. cleaning tank

13. The Event • Unit 2 outage - April 4 - 10, 2003, 5 loads of fuel cleaned (some hot, some cool) • Sixth load was cleaned April 10, completed at 4:00p.m. but crane not available • Shut down of cleaning system and tank remained sealed

14. The Event (cont’d) • 10p.m. reactor building high radiation • 2:00a.m. hydraulic lock opened and lid released • Sharp increase in radioactivity • Classified INES level 2 • April 16, video inspection revealed major damage – re-classified INES level 3

15. Events during the incident Rad Level MBq End of cleaning 16:00 Cover lifting failed: 04:20 Startup of submersible pump 16:40 Area of spent f.p.: 12 mSv/h 02:45 Discharge of water 16:56 Hydraulic lock open, bubble outbursts: 02:15 Spent fuel pool water level increase 19:20 Venting fans started: 23:45 Increase of KR-85 activity in the cleaning system 21:50 Supervisor ordered to leave the R. hall 23:30

16. Investigation of the event • The Paks plant submitted an investigation report on May 10 to the HAEA • The report was published on the plant’s homepage also in Hungarian and English languages (www.atomeromu.hu) • Framatome completed an investigation report • The HAEA final investigation report wasissued at the end of May • HAEA requested a review by the IAEA

17. Mission Insights • Time pressure • Heavy reliance on contractor • Novel technology • Inadequate safety review

18. Mission Insights(cont’d) • Inadequate safety review • Inaccurate bypass flow calculations • Simple thermodynamic calculation • Outlet connection at tank bottom • Undersized submersible pump • Relied upon 12 min 9 sec time to boiling • Single failure criteria not met • Nointernal instrumentation

19. Mission Insights(cont’d) • Fuel deposit team • Not budgeted • Consisted mainly of managers • Solving the problem was the priority not the technique (subcommittee) • Managers from independent groups (QA/NAS) • During safety reviews, same line managers processed the safety evaluation

20. Mission Insights(cont’d) • Safety evaluation assumptions not translated into design, operating procedures and training for workers (OJT) • Inadequate independent safety review by PAKS • Safety Culture assessments by HAEA were not adequately addressed

21. Mission Insights(cont’d) • Inadequate root cause evaluation by PAKS/HAEA • Complex HAEA licensing process • HAEA safety review process did not meet international standards • Failure to verify contractor’s claims • Inadequate technical content of licensing package

22. Mission Insights(cont’d) • Regulator failed to understand relationships between cleaning modification and safety • INES classification changes diminished public confidence

23. AdditionalConfiguration Management Issues • Five types of licenses • Principle modification • Fabrication and import • Installation • Modification (includes fab, import and installation • Operations

24. Additional Configuration Management Issues(cont’d) • License type determined by “safety significance” and “safety class” (design criteria) in that order • Reverse logic from the IAEA 1999 standard • Considered cleaning tank a “cask” but did not follow licensing process for a cask

25. Additional Configuration Management Issues(cont’d) • Content of Licenses not specified • For the tank modification, regulator accepted an incomplete license package

26. Additional Configuration Management Issues(cont’d) • Specific plant issues: • Did not process concerns for undersized pump • Did not use remote verification of fuel assembly alignment • Did not install dedicated crane • Did not provide redundant power supplies for cooling pump • Did not notify of past delays in opening the tank