POLICY ISSUE 

(Information) 

October 23, 2009 SECY-09-0156

FOR: The Commissioners 

FROM: R. W. Borchardt 

 Executive Director for Operations 

SUBJECT: STATUS OF APPLYING LESSONS LEARNED FROM PRESSURIZED 

WATER REACTORS TO EMERGENCY CORE COOLING SYSTEM 

SUCTION STRAINER PERFORMANCE FOR BOILING WATER 

REACTORS 

PURPOSE: 

This paper summarizes the activities of the U.S. Nuclear Regulatory Commission (NRC) staff to 

examine and apply lessons learned from the evaluation of pressurized water reactor (PWR) 

emergency core cooling system (ECCS) suction strainer performance to boiling water reactors 

(BWRs). This paper was prepared in response to Staff Requirements Memorandum (SRM) 

M081107, “Meeting with Advisory Committee on Reactor Safeguards (ACRS),” dated 

January 8, 2009. 

SUMMARY: 

The efforts to address Generic Safety Issue (GSI) 191, “Assessment of Debris Accumulation on 

PWR Sump Performance,” have led to new information on the phenomena that could be 

relevant to previous assessments of ECCS suction strainer performance in BWRs. Both the 

NRC staff and the Boiling Water Reactor Owners Group (BWROG) are examining the GSI-191 

lessons learned for significance and applicability to BWRs even though modifications to improve 

suction strainer performance were made by BWR licensees in the 1990s. Currently, BWR 

ECCS operability is not in question and continued operation of BWRs does not pose an undue 

risk to public health and safety. 

CONTACT: Stewart N. Bailey, NRR/DSS 

 301-415-1321 
The Commissioners 2 

BACKGROUND: 

In SRM M081107 the Commission directed the staff to consider lessons learned from the 

analyses of PWR sump strainer performance and to determine if issues have arisen that call for 

revisiting sump strainer performance in BWRs. The staff engaged the BWROG on this question 

in 2007, and there have been several interactions since. 

DISCUSSION: 

From 1992 to 2001, the NRC and the nuclear industry addressed the issue of potential debris 

blockage of ECCS suction strainers in BWRs. The NRC and industry conducted research and 

testing and developed guidance documents, and the industry made hardware and procedure 

changes. The NRC staff issued NRC Bulletin (NRCB) 95-02, “Unexpected Clogging of a 

Residual Heat Removal Pump Strainer While Operating in Suppression Pool Cooling Mode,” 

dated October 17, 1995, and NRCB 96-03, “Potential Plugging of Emergency Core Cooling 

Suction Strainers by Debris in Boiling-Water Reactors,” dated May 6, 1996. Both bulletins dealt 

with ensuring that debris generated during a loss-of-coolant accident would not clog ECCS 

suction strainers. The BWROG supported licensees by developing resolution guidance, 

referred to as the Utility Resolution Guide (URG), which the staff endorsed with conditions and 

limitations in an August 1998 safety evaluation. 

BWR licensees performed plant-specific evaluations to determine necessary mitigation 

measures. Most BWR licensees installed larger strainers and established measures to clean 

and maintain the suppression pool free of foreign materials. In October 2001, the NRC staff 

concluded that generic and plant-specific activities associated with NRCB 95-02 and 

NRCB 96-03 were complete on the basis that licensees had designed their ECCS suction 

strainers with sufficient margin to remain operable even with the debris loads anticipated during 

a loss-of-coolant accident. 

The NRC initiated GSI-191 in 1996 to examine whether the events and research associated 

with the BWR strainers warranted similar evaluations and/or changes for PWRs. The NRC staff 

concluded that plant-specific analyses should be conducted to determine whether debris 

accumulation in PWR containments could impede recirculation operation of the ECCS or 

containment spray system and that licensees should take any appropriate corrective actions. 

Generic Letter 2004-02, “Potential Impact of Debris Blockage on Emergency Recirculation 

during Design Basis Accidents at Pressurized-Water Reactors,” dated September 13, 2004, 

communicated this expectation to licensees. The industry developed guidance, submitted by 

the Nuclear Energy Institute (NEI) as NEI 04-07, “Pressurized Water Reactor Sump 

Performance Evaluation Methodology,” Volume 2, dated May 28, 2004, for evaluating PWR 

recirculation issues. The NEI based its guidance, in part, on the methods and techniques 

previously used in the BWROG URG. The staff issued a safety evaluation dated 

December 6, 2004, endorsing the NEI guidance with certain conditions. 

The efforts to address GSI-191 have led to new insights that could be relevant to previous 

assessments of ECCS suction strainer performance in BWRs. Both the NRC staff and the 

BWROG are examining the GSI-191 lessons learned for applicability to BWRs. 
The Commissioners 3 

RECENT DEVELOPMENTS: 

Staff Activities 

The NRC staff is developing a revision to Regulatory Guide 1.82, “Water Sources for Long-Term 

Recirculation Cooling Following a Loss-of-Coolant Accident.” The staff is updating this 

document, in part, to reflect the latest available guidance on acceptable methods for evaluating 

ECCS strainer performance. The public comment period is scheduled to begin in November 

2009, with issuance of the final regulatory guide in late 2010. 

The NRC staff is also developing a report that evaluates the differences in treatment of the 

various phenomena in sump strainer evaluations. The intent is to focus attention on those 

lessons learned that could reduce margin in the BWR strainer evaluations. The staff expects to 

publish the report in the first quarter of 2010. 

Further, the staff is consolidating the knowledge base that has been gained in evaluating GSI191. It completed a similar effort for BWRs in report LA-UR-01-1595, “BWR ECCS Strainer 

Blockage Issue: Summary of Research and Resolution Actions,” dated March 2001. The staff 

plans for the knowledge base to build on the 2001 BWR report and include international 

experience, as applicable. The staff also plans to lead an international effort through the 

Nuclear Energy Agency Committee on the Safety of Nuclear Installations to develop a 

comprehensive summary of knowledge and operating experience related to sump performance 

issues. 

Finally, the NRC staff is planning the necessary resources to support review of the technical 

documents developed by the BWROG in 2010 and 2011 and to review a sample of 

plant-specific evaluations. 

BWROG Activities 

In a letter dated July 17, 2009, the BWROG outlined its plans for evaluating the impact of the 

GSI-191 lessons learned on BWRs. The NRC staff met with the BWROG on July 23 and 

July 30, 2009, to discuss the plans in more detail. The BWROG has developed the ECCS 

Suction Strainer Committee and four subcommittees, discussed below. 

Source Term Subcommittee 

This subcommittee will address new insights regarding the debris that is generated during a 

loss-of-coolant accident, including chemical effects. For chemical effects, the BWROG plans to 

submit a position paper in fall 2009, conduct testing in spring 2010, and perform plant-specific 

evaluations in summer 2010. For the zone of influence, the BWROG plans to submit a position 

paper in fall 2009 on the conservatism of the air-jet testing that was used as basis for the URG. 

The staff has informed the BWROG that submittal of licensing topical reports (LTRs) would be 

necessary for the staff to review and potentially approve the information in the position papers. 

Regarding debris sources, the NRC staff has reviewed the containment walkdown guidance, 

and the BWROG plans to complete walkdowns by 2011. 
The Commissioners 4 

Head Loss Subcommittee 

This subcommittee will address new insights regarding the pressure drop across a debris-laden 

strainer. BWR licensees generally used correlations that were based on generic testing to 

predict head loss, while PWR licensees employed plant-specific testing. The BWROG will 

ensure that the testing database adequately covers limiting debris cases, considering the NRC 

staff’s strainer testing guidance provided in a letter to the Nuclear Energy Institute, “Revised 

Guidance for Review and Approval of Final Licensee Responses to Generic Letter 2004-02,” 

dated March 28, 2008. The BWROG has not determined whether additional head loss testing is 

needed. 

Downstream Effects - Components Subcommittee 

This subcommittee will address the adverse effects of debris that bypasses the suction strainer 

and enters downstream components such as pumps and valves. This subcommittee is 

developing an LTR, similar to the one for PWRs, for submittal in summer 2011. 

Downstream Effects - In-Vessel Subcommittee 

This subcommittee will address the effects of debris and chemicals on the reactor core. The 

BWROG is developing an LTR with generic analysis and testing protocol for Global Nuclear 

Fuels (GNF) fuel bundle designs. Testing of the GNF fuels will follow NRC staff approval of the 

LTR. A separate LTR will compare the analysis of GNF fuel with other BWR fuel types, and 

additional LTRs will cover testing if necessary. The subcommittee expects to submit the first 

LTR before May 2010. 

STAFF EVALUATION: 

Based on the evaluation of currently available information, the staff believes that, although 

uncertainties in the technical areas discussed above warrant further evaluation, BWR ECCS 

operability is not in question and continued operation of BWRs does not pose an undue risk to 

public health and safety. 

The staff considered the need for a generic communication and determined that no generic 

communications are needed at this time. The BWROG is actively addressing the insights 

gained from GSI-191 efforts identified by the NRC in its April 10, 2008, letter and the NRC staff 

generally agrees with the licensees’ approach and the established schedules. The NRC staff 

will periodically reassess the need for generic communications. 

CONCLUSIONS: 

The staff has found that the BWROG is generally addressing the lessons learned from GSI-191 

with sufficient timeliness and rigor. The staff concludes that the issues identified as a result of 

GSI-191 evaluations, as discussed in this paper, do not pose an undue risk to public health and 

safety and that continued plant operation is justified. Furthermore, the staff does not believe 

there is a need at this time for plant-specific regulatory actions or generic communications. The 

staff will periodically reassess the BWROG progress and will reconsider the need for additional 

regulatory measures as part of that reassessment. 
The Commissioners 5 

RESOURCES: 

The staff’s efforts to evaluate lessons learned from GSI-191 for implications on the performance 

of BWR ECCS suction strainers will require resources in fiscal year (FY) 2010 to FY 2013. As 

stated in industry correspondence, the BWROG expects to submit at least two and probably 

four LTRs in FY 2010 and two in FY 2011. The staff will need eighteen months and two full-time 

equivalents (FTEs) for each LTR review. The staff also plans to review plant-specific 

evaluations on a sampling basis in FY 2012 and FY 2013. In summary, the staff expects to 

spend the following resources: 

Fiscal Year NRR Budget RES Budget Total 

FY 2010 3 FTE 1 FTE, $185K 4 FTE, $185K 

FY 2011 3 FTE 1 FTE, $184K 4 FTE, $184K 

FY 2012 6 FTE 

FY 2013 1 FTE 

FY 2010 and FY 2011 resources have been requested and FY 2012 and FY2013 resources will 

be requested through the respective PBPM process. This budget estimate assumes that the 

staff will only need to review a sample of plant-specific evaluations, similar to what was done for 

the BWRs in the 1990s, and not detailed plant-specific reviews similar to those that are currently 

being conducted for PWRs. 

COORDINATION: 

The Office of the General Counsel has reviewed this paper and has no legal objection. The 

Office of the Chief Financial Officer has reviewed this paper for resource implications and 

concurred. 

 /RA Bruce Mallett for/ 

R. W. Borchardt 

Executive Director 

 for Operations 
The Commissioners 5 

RESOURCES: 

The staff’s efforts to evaluate lessons learned from GSI-191 for implications on the performance 

of BWR ECCS suction strainers will require resources in fiscal year (FY) 2010 to FY 2013. As 

stated in industry correspondence, the BWROG expects to submit at least two and probably 

four LTRs in FY 2010 and two in FY 2011. The staff will need eighteen months and two full-time 

equivalents (FTEs) for each LTR review. The staff also plans to review plant-specific 

evaluations on a sampling basis in FY 2012 and FY 2013. In summary, the staff expects to 

spend the following resources: 

Fiscal Year NRR Budget RES Budget Total 

FY 2010 3 FTE 1 FTE, $185K 4 FTE, $185K 

FY 2011 3 FTE 1 FTE, $184K 4 FTE, $184K 

FY 2012 6 FTE 

FY 2013 1 FTE 

FY 2010 and FY 2011 resources have been requested and FY 2012 and FY2013 resources will 

be requested through the respective PBPM process. This budget estimate assumes that the 

staff will only need to review a sample of plant-specific evaluations, similar to what was done for 

the BWRs in the 1990s, and not detailed plant-specific reviews similar to those that are currently 

being conducted for PWRs. 

COORDINATION: 

The Office of the General Counsel has reviewed this paper and has no legal objection. The 

Office of the Chief Financial Officer has reviewed this paper for resource implications and 

concurred. 

 

 /RA Bruce Mallett for/ 

R. W. Borchardt 

Executive Director 

 for Operations 

WITS 200900007/EDATS: SECY-2009-0020 

ADAMS Accession No.: ML092600377 * concur by e-mail 

OFFICE BC(A):NRR/DSS/SSIB Tech Editor* D:NRR/DSS D:NRR/DCI* OGC* 

NAME SBailey KAzariah-Kribbs WRuland MEvans MSmith 

DATE 10/08/09 09/22/09 10/09/09 10/07/09 10/08/09 

OFFICE D:RES* D:OCFO* NRR EDO 

NAME BSheron 

(JLyons for) 

JDyer 

(GPeterson for) 

ELeeds 

(JGrobe for) 

RBorchardt 

(BMallett for)

DATE 10/09/09 10/14/09 10/16/09 10/23/09 

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