GENERIC SAFETY ISSUE (GSI) 189 - SUSCEPTIBILITY OF 

ICE CONDENSER AND MARK III CONTAINMENTS TO EARLY 

FAILURE FROM HYDROGEN COMBUSTION DURING A 

SEVERE ACCIDENT

 

TAC Nos: MB7245, MD5986 Last Update: 02/04/09 

 Lead NRR Division: DSS 

 Supporting Division: DPR 

 Supporting Office: RES 

 MILESTONES DATE 

Target (T) 

Complete (C) 

1. SPLB staff briefed DRIP/DSSA management to obtain 

management endorsement for actions to implement voluntary 

industry initiatives through issuance of generic letter. 

11/15/04 (C) 

2. SPLB staff, with assistance from SPSB & RPRP, briefed the 

ET/LT on closure plans for GSI-189. A consensus was reached 

at the ET/LT meeting to go forward with letters (in lieu of a 

generic letter) to the owners to capture voluntary licensee 

initiatives for providing backup power sources to the hydrogen 

igniters. 

11/29/04 (C) 

3. The NRC staff met with senior representatives of the six affected 

PWR and BWR licensees to discuss safety-security-related 

insights and briefed the industry regarding potential changes to 

the voluntary actions. 

03/30/05 (C) 

4. Issued memorandum to the Commissioners from the EDO to 

inform the Commission of the regulatory analysis results and 

staff=s plans for resolution of GSI-189. 

06/14/05 (C) 

5. Update Commission regarding licensee plans for voluntary 

measures. 03/01/06 (C) 

6. Conduct closed meetings with affected licensees to consider 

security insights. 

01/17/07 (C) 

7. Evaluate licensee commitments and inform Commission 04/23/07(C) 

8. Issue letters to accept commitments and inform licensees of 

plans for verification 06/15/07(C) 

9. Complete Temporary Instruction for TI 2515/174, “Hydrogen 

Igniter Backup Power Verification,” verification inspections 

02/12/08(C) 

10. Complete verification inspections at one unit per site 08/31/2010(T) 

11. Closeout issue 09/30/2010(T) 
Description: NUREG/CR-6427, AAssessment of the Direct Containment Heat (DCH) Issue for 

Plants with Ice Condenser Containments," showed that the early containment failure probability 

of ice condensers is dominated by non-DCH hydrogen combustion events. The staff 

subsequently extended the issue to include BWR MARK III containments because their relatively 

low free volume and strength are comparable to PWR ice condensers. Following a severe 

accident concurrent with station blackout (SBO), the PWR ice condenser containment and BWR 

Mark III containment are vulnerable to failures from hydrogen deflagrations and detonations 

because the hydrogen igniters rely on AC power. The staff opened a generic safety issue, GI189, in response to SECY 00-198, "Status Report on Study of Risk-Informed Changes to the 

Technical Requirements of 10 CFR Part 50 (Option 3) and Recommendations on Risk-Informed 

Changes to 10 CFR 50.44 (Combustible Gas Control)." To resolve the generic safety issue, 

GSI-189, the staff recommended the addition of a backup power supply for the combustible gas 

igniters for the plants with Ice Condenser or Mark III containments. The affected plants are the 

four dual-unit PWR nuclear stations with ice condenser containments - McGuire, Catawba, DC 

Cook, and Sequoyah; a single-unit PWR nuclear station with ice condenser containment - Watts 

Bar; and four single-unit BWR nuclear plants with Mark III containments - Grand Gulf, River 

Bend, Clinton, and Perry. 

Historical Background: The staff conducted studies to determine whether providing an 

independent power supply for the igniter systems provides a substantial increase in the overall 

protection of the public health and safety with implementation costs that are justified in view of 

the increased protection. The staff continued work on this issue following an initial screening in 

accordance with MD 6.4. 

The staff briefed the ACRS on June 6, 2002, and again on November 13, 2002. The ACRS 

recommended that the form of regulatory action should be through the plant-specific severe 

accident management guidelines. RES provided its technical assessment for resolving GI-189 

to NRR in a memorandum dated December 17, 2002. RES concluded that further action to 

provide back-up to one train of igniters was warranted for both ice condenser and MARK III 

plants. 

On January 30, 2003, NRR prepared a reply memorandum that outlined the next steps in the 

resolution of this GI. NRR prepared a Task Action Plan to complete MD 6.4, Stage 4, 

Regulation and Guidance Development, based on a preliminary decision to issue an Order. The 

staff reviewed the proposed regulatory actions and associated draft documents with senior 

management and OGC, and senior management decided to pursue Rulemaking rather than an 

Order. The staff held a public meeting on June 18, 2003, to receive feedback from licensees 

and other stakeholders regarding the need to provide a backup power supply to the hydrogen 

igniters and NRR's consideration of rulemaking for the resolution of GI-189. NRR staff briefed 

the ACRS on November 6, 2003, and recommended providing a backup power supply to the 

hydrogen igniters. On November 17, 2003, the ACRS Chairman wrote the NRC Chairman 

recommending the NRC proceed with rulemaking to require a backup power supply to the 

hydrogen igniters for PWR ice-condenser and BWR MARK III plants. The ACRS recommended 

that rulemaking include a small pre-staged generator with installed cables, conduit, panels, and 

breakers, or an equivalent diverse power supply. The ACRS also recommended that the 

rulemaking be accompanied by guidance that specifies the design requirements. 

NRR developed design criteria for the backup power supply, and administered a contract to 

merge and enhance the existing technical assessment into a regulatory analysis. NRR held a 

public meeting with the public and industry on September 21, 2004, to get external stakeholders' 

input on the draft design criteria. The BWR owners indicated a willingness to make 
modifications to supply power from the existing HPCS diesel generator, and agreed to provide 

additional information regarding implementation cost for the prestaged generator and relative 

risk contribution of SBO events at each of the four Mark III plants. Duke power, representing two 

PWR ice condenser sites, Catawba 1 & 2, McGuire 1 & 2, indicated a willingness to make 

modifications to an existing safe shutdown diesel generator that could manually connect to 

provide backup power source as needed. American Electric Power representatives indicated a 

willingness to provide backup power source for D. C. Cook 1 & 2 from the large diesel 

generators intended to support an increased allowed outage time for the emergency diesel 

generators. TVA, representing two PWR ice condenser sites, Sequoyah 1 & 2, Watts Bar 1, 

also indicated a willingness to provide a backup power source from a supplemental diesel 

generator. In November 2004, the staff reached a consensus to evaluate the proposed 

voluntary initiatives and pursue that path as a preferential solution. 

In February and early March 2005, the NRR staff met with representatives of RES, NSIR, and 

OEDO to develop an understanding of newly identified safety/security interface issues and 

actions initiated in the security arena that could impact the solution of the issue. On March 30, 

2005, the staff met with senior representatives of the six affected utilities to present securityrelated insights. 

On June 14, 2005, the EDO issued a memorandum to the Commissioners to inform the 

Commission of the regulatory analysis results and recent staff activities on GSI-189. The 

regulatory analysis indicated that the backup power modification may provide a substantial 

safety benefit at a justifiable cost for the PWRs with an ice-condenser containment, and the 

proposed voluntary actions provide the majority of the benefit. The costs exceed the benefits for 

all BWR regulatory options, and none of the options for the BWRs provides a substantial 

increase in the overall protection of public health and safety. However, external events and 

security insights were not fully evaluated in the regulatory analysis, and defense-in-depth 

considerations in improving the balance among accident prevention and mitigation provide an 

additional un-quantified benefit for both containment types. 

Current Status: Based on an understanding that many of the voluntary physical modifications 

had been completed, the staff elected to delay seeking specific commitments while securityrelated reviews of the facilities were ongoing. On March 1, 2006, the EDO issued a memo 

informing the Commission of the staffs intent to delay the request for commitments until after the 

security-related reviews were completed in September 2006. Because this issue was not 

incorporated in the scope of security-related modifications, the staff has held closed meetings in 

December 2006 and January 2007 to further explore the proper consideration of security 

insights in the design of the modifications. The staff received industry proposals for 

modifications that incorporate security insights in late February and early March 2007. The staff 

reviewed the industry proposals and concluded that the proposed modifications would resolve 

GSI-189 and provide benefit for some security scenarios. On April 23, 2007, the EDO issued a 

memo informing the Commission of the staffs intent to accept the commitments and perform 

verification inspections at the affected sites. On June 15, 2007, the NRC staff issued letters to 

affected licensees accepting the commitments. The NRC staff also notified licensees of the 

intent to perform verification inspections at the affected sites and clarified the scope of the 

inspection relative to the commitments. 

Modifications are complete on all but two units, Catawba Units 1&2, which are expected to be 

completed in early 2010. 
Contacts: 

NRR Lead Project Manager: Joseph Golla, DPR, 415-1002 

NRR Lead Technical Reviewer: Steven Jones, DSS, 415-2712 

NRR Technical Contact: Bob Palla, DRA, 415-1095 

References: 

1. SECY-00-0198, "Status Report on Study of Risk-Informed Changes to the Technical 

Requirements of 10 CFR Part 50. 

2. NUREG/CR-4551, Vol. 3, Rev. 1, Part 1, "Evaluation of Severe Accident Risks: Surry 

Unit 1, Main Report," October 1990. 

3. NUREG/CR-4551, Vol. 3, Rev. 1, Part 3, "Evaluation of Severe Accident Risks: Surry 

Unit 1, External Events," December 1990. 

4. NUREG/CR-4551, Vol. 5, Rev. 1, Part 1, "Evaluation of Severe Accident Risks: 

Sequoyah, Unit 1, Main Report," December 1990. 

5. NUREG/CR-4551, Vol. 6, Rev. 1, Part 1, "Evaluation of Severe Accident Risks: Grand 

Gulf, Unit 1, Main Report," December 1990. 

6. NUREG-1150, "Severe Accident Risks: An Assessment for Five U.S. Nuclear Power 

Plants," December 1990. 

7. Letter from V. Mubayi, Brookhaven National Laboratory, to H. VanderMolen, NRC, 

"NUREG-1150 Consequence Calculations," July 20, 1994. 

8. T. D. Brown et. al., "NUREG-1150 Data Base Assessment Program: A Description of the 

Computational Risk Integration and Conditional Evaluation Tool (CRIC-ET) Software and 

the NUREG-1150 Data Base," letter report, March 1995. 

9. NUREG/BR-0184, "Regulatory Analysis Technical Evaluation Handbook," Final Report, 

January 1997. 

10. 10 CFR 50.44, "Standards for combustible gas control system in light-water-cooled 

power reactors," January 1, 2000 (last revised 1987). 

11. NUREG/CR-6427, "Assessment of the DCH Issue for Plants with Ice Condenser 

Containments," April 2000. 

12. NUREG/BR-0058, "Regulatory Analysis Guidelines of the U.S. Nuclear Regulatory 

Commission," July 2000. 

13. Memorandum to Samuel Collins, Director, Office of NRR, from Ashok Thadani, Director, 

Office of RES, September 29, 2000, regarding Research Information Letter RIL-0005, 

"Completion of Research to Address Direct Containment Heating Issue for All 

Pressurized Water Reactors." (ML003755724). 

14. Memorandum to Ashok Thadani, Director, Office of RES, to Samuel Collins, Director, 

Office of NRR, November 22, 2000, regarding Research Information Letter RIL-0005, 

"Completion of Research to Address Direct Containment Heating Issue for All 

Pressurized Water Reactors." ML003761979). 

15. NUREG-1742, "Perspectives Gained from the Individual Plant Examination of External 

Events (IPEEE) Program, Main Report," Draft Report for Public Comment, April 2001. 
16. Memorandum to John Flack, Chief, Regulatory Effectiveness and Human Factors 

Branch, Division of Systems Analysis and Regulatory Effectiveness, RES, from Mark 

Cunningham, Chief, Probabilistic Risk Analysis Branch, Division of Risk Analysis and 

Applications, RES, "Information Concerning Generic Issue on Combustible Gas Control 

for PWR Ice Condenser and BWR Mark III Containment Designs," August 15, 2001 

(ML012330522). 

17. Memorandum to M. Snodderly (NRC) from M. Zavisca and M. Khatib-Rahbar (ERI), 

"Combustible Gas Control Risk Calculations (DRAFT) for Risk-Informed Alternative to 

Combustible Gas Control Rule for PWR Ice Condenser, BWR Mark I, and BWR Mark III 

(10 CFR 50.44)," October 22, 2001. 

18. Management Directive 6.4 (MD 6.4), "Generic Issues Program," December 4, 2001. 

19. Management Directive 6.3 (MD 6.3), "The Rulemaking Process," July 31, 2001. 

20. Memorandum from John H. Flack, Chief, REAHFB:DSARE:RES to Jack E. Rosenthal, 

Chief, SMSAB:DSARE:RES and Mark A. Cunningham, Chief, PRAB:DRAA:RES, dated 

February 6, 2002, regarding "Panel Review of GSI-189, Susceptibility of Ice Condenser 

and Mark III Containments to Early Failure from Hydrogen Combustion During a Severe 

Accident." 

21. Memo from Farouk Eltawila, Director, RES, to Ashok C. Thadani, Director RES, dated 

February 13, 2002, regarding RES Task Action Plan for Resolving Generic Safety Issue 

189: "Post Accident Combustible Gas Control in Pressure Suppression Containments." 

22. Memorandum from William Travers, EDO, to The Commissioners, dated May 13, 2002 

(SECY-02-0080), Proposed RulemakingBRisk Informed 10CFR50.44, "Combustible Gas 

Control In Containment", (WITS 20010003). 

23. Advisory Committee on Reactor Safeguards Meeting Minutes, 493rd Meeting, June 6, 

2002, regarding Technical Assessment Generic Safety Issue (GSI)-189. 

24. Backup Power for PWRs with Ice Condenser Containments and for BWRs with Mark III 

Containments under SBO Conditions: Impact Assessment, Rev. 2, September 24, 2002, 

by Information Systems Laboratories, Inc., Rockville, MD. 

25. Hydrogen Control Calculations for the Sequoyah Plant, draft letter report, Rev. 3, 

September 30, 2002, by Sandia National Laboratories. 

26. Memorandum from Ashok Thadani, RES to William Travers, EDO, dated October 1, 

2002, regarding, "Revision to NRC=s Regulatory Analysis Guidelines [NUREG/BR-0058] 

and RES Office Letter 1 to Conform to OMB=s Information Quality Guidelines." 

27. Benefit Cost Analysis of Enhancing Combustible Gas Control Availability at Ice 

condenser and Mark III Containment Plants, draft letter report, October 4, 2002, by 

Brookhaven National Laboratory. ADAMS ML022880554. 

28. Advisory Committee on Reactor Safeguards Subcommittee on Thermal-Hydraulic 

Phenomena and Subcommittee on Reliability and Probabilistic Risk Assessment Meeting 

Minutes, November 5, 2002, regarding Generic Safety Issue (GSI)-189. 

29. Advisory Committee on Reactor Safeguards Meeting Minutes, 497th Meeting, 

November 7, 2002, regarding Technical Assessment Generic Safety Issue (GSI) -189. 

30. Memo from George E. Apostolakis, Chairman Advisory Committee on Reactor 

Safeguards, to the Commission Chairman Richard A. Meserve, dated 

November 13, 2002, regarding "Recommendations Proposed by the Office of NRR for 

Resolving Generic Safety Issue -189, Susceptibility of Ice Condenser and Mark III 

Containments to Early Failure from Hydrogen Combustion During a Severe Accident. 

ML023230513 

31. Memo from Ashok C. Thadani, Director RES, to Samuel J. Collins, Director, Office of 

Nuclear Reactor Regulation, dated December 17, 2002, regarding RES Proposed 

Recommendation for Resolving Generic Safety Issue 189: "Susceptibility of Ice 

Condenser and Mark III Containments to Early Failure from Hydrogen Combustion 
During a Severe Accident." ML023510161 

32. Attachment to Memo from Ashok C. Thadani, Director RES, to Samuel J. Collins, 

Director, Office of Nuclear Reactor Regulation, dated December 17, 2002, "Technical 

Assessment Summary for GSI-189: Susceptibility of Ice Condenser and Mark III 

Containments to Early Failure from Hydrogen Combustion During a Severe Accident." 

33. Memo from John A. Zwolinski, Director, Division of Licensing Project Management, NRR 

to Farouk Eltawila, Director, Division of Systems Analysis and Regulatory Effectiveness, 

RES, dated January 21, 2003, regarding, "Resolution Process for Generic Safety Issue 

(GSI) 189, "Susceptibility of Ice Condenser and Mark III Containments to Early Failure 

from Hydrogen Combustion During a Severe Accident." 

34. Memo from Jack Rosenthal, Branch Chief, Safety Margins and Systems Analysis 

Branch, Division of Systems Analysis and Regulatory Effectiveness, Office of Nuclear 

Regulatory Research to John Hannon, Branch Chief, Plant Systems Branch, Division of 

Systems Safety and Analysis, Office of Nuclear Reactor Regulation dated June 19, 2003, 

regarding, Final Contractor=s Reports: Generic Safety Issue 189: "Susceptibility of Ice 

Condenser and Mark III Containments to Early Failure from Hydrogen Combustion 

During a Severe Accident." 

35. Benefit Cost Analysis of Enhancing Combustible Gas Control Availability at Ice 

Condenser and Mark III Containment Plants, Final Letter Report, Energy Sciences and 

Technology Department, Brookhaven National Laboratory, December 23, 2002 

(ML031700011). 

36. Backup Power for PWRs with Ice Condenser Containments and for BWRs with Mark III 

Containments under SBO Conditions: Impact Assessment, Revision 2, Information 

Systems Laboratories, Inc., September 24, 2002 (ML031700015). 

37. Hydrogen Control Calculations for the Sequoyah Plant, Final Letter Report, March 2003, 

Prepared By Sandia National Laboratories, March 2003 (ML031700025). 

38. Memorandum from Luis A. Reyes, EDO, to The Commissioners, dated June 14, 2005, 

AStatus of Staff Activities to Resolve Generic Safety Issue 189, >Susceptibility of Ice 

Condenser and Mark III Containments to Early Failure from Hydrogen Combustion 

During a Severe Accident= (WITS 20010144) (ML051440875). 

39. Attachment to Memorandum from Luis A. Reyes, EDO, to The Commissioners, dated 

June 14, 2005, ABackground - Status of Staff Activities to Resolve Generic Safety Issue 

189, >Susceptibility of Ice Condenser and Mark III Containments to Early Failure from 

Hydrogen Combustion During a Severe Accident= (WITS 20010144) (ML051590380). 

40. Regulatory Analysis for Proposed Action to Address Generic Safety Issue 189: 

Susceptibility of Ice Condenser and Mark III Containments to Early Failure from 

Hydrogen Combustion During a Severe Accident, May 24, 2005 (ML051450060). 

41. Memorandum from Luis A. Reyes, EDO, to The Commissioners, dated March 1, 2006, 

AUpdate on Status of Staff Activities to Resolve Generic Safety Issue 189, >Susceptibility 

of Ice Condenser and Mark iii Containments to Early Failure from Hydrogen Combustion 

During a Severe Accident=@ (WITS 200600039 ) (ML060390122). 

42. Memorandum from Luis A. Reyes, EDO, to The Commissioners, dated April 23, 2007, 

ALicensee Commitments and Staff Actions Addressing Backup Power for Hydrogen 

Igniters@ (WITS 200700082 ) (ML070890613).