ML11214A137
| ML11214A137 | |
| Person / Time | |
|---|---|
| Site: | Boiling Water Reactor Owners Group |
| Issue date: | 08/26/2011 |
| From: | Joe Golla NRC/NRR/DPR/PSPB |
| To: | Stewart Bailey NRC/NRR/DSS |
| References | |
| Download: ML11214A137 (7) | |
Text
August 26, 2011 MEMORANDUM TO: Stewart N. Bailey, Chief Safety Issues Resolution Branch Division of Safety Systems Office of Nuclear Reactor Regulation FROM:
Joseph A. Golla, Project Manager
/RA/
Licensing Processes Branch Division of Policy and Rulemaking Office of Nuclear Reactor Regulation
SUBJECT:
SUMMARY
OF JULY 20, 2011, CATEGORY II PUBLIC MEETING WITH THE BOILING WATER REACTOR OWNERS GROUP (BWROG)
On July 20, 2011, U.S. Nuclear Regulatory Commission (NRC) staff met with representatives of the BWROG, in a public meeting at NRC Headquarters in Rockville, Maryland. The purpose of the meeting was to discuss the review of boiling water reactor (BWR) emergency core cooling system (ECCS) suction strainer issues.
The Enclosure provides a list of those in attendance.
The BWROG presented information on program update, zone of influence (ZOI) adjustment for air jet testing, chemical effects resolution strategy, status of headloss and coatings surveys, status of containment walkdowns, boron precipitation, downstream effects on fuel, and strainer bypass testing. The NRC staff presented information on ZOI adjustment for air jet testing.
These presentations may be viewed on the Agencywide Documents Access and Management System at accession number ML11214A140.
Mr. Steve Scammon, ECCS Suction Strainers Committee Chairman for the BWROG, presented an overall program update. Mr. Scammon indicated that the BWROGs response to Action Item No. 6, BWROG to provide a calculation comparing ZOIs for BWRs and PWRs
[pressurized water reactors] based on the RCS [reactor coolant system] pressure differences, identified during the August 10-11, 2010, meeting between the BWROG and the NRC staff (meeting summary at ML102360056), is under technical review with completion expected by October. The NRC staff acknowledged this and looks forward to obtaining the response.
Mr. Scammon addressed the status of Action Item No. 11, The staff stated that it would providea clear statement of intention on whether it plans to revise its position on spherical ZOI, identified at the September 22, 2010, meeting between the BWROG and the NRC staff (meeting summary at ML102800152). Mr. Scammon stated that the BWROG is awaiting official notice from the NRC staff regarding this item.
The NRC staffs position, as documented in the 2004 Safety Evaluation (SE) of Nuclear Energy Institute (NEI) 2004-07 for PWRs, and the Utility Resolution Guide (URG) SE for BWRs, and in NUREG/CR-7011, Evaluation of Treatment of Effects of Debris in Coolant on ECCS and CSS
[core spray system] Performance in Pressurized Water Reactors and Boiling water Reactors, is that spherical ZOIs are acceptable. Slide number 13 of the presentation given by the BWROG at the September 22-23, 2010, meeting with the NRC titled ECCS Suction Strainers Spherical ZOI, Issue No. 12, (presentation at ML102800091) in part, states the following: Although the spherical ZOI remains conservative, the BWROG will address this issue by providing enhanced guidance in the area of debris generation, specifically looking at problematic targets.
Slide 13 of the BWROG presentation presents a method that the NRC staff considers acceptable for resolving Issue No. 12. Therefore, the NRC staff agrees with this approach and maintains the position stated above on spherical ZOI. Action Item No. 11 is closed. Issue No. 12 remains open and will be addressed as described above by Slide 13, i.e., the BWROG will provide guidance on how to address problematic materials just outside the ZOI.
Mr. Scammon also addressed Action Item No. 13 which was identified during the October 20, 2010, meeting (meeting summary at ML103010393). This action item requests that a separate guidance document be developed that addresses how utilities will resolve differences between the debris characteristics established in their current strainer qualification analysis and a guidance document the BWROG is developing that will identify acceptable debris characteristics for use in BWR strainer qualification analysis and testing. The BWROG proposes instead to include this guidance in the final URG supplement which will be reviewed by the NRC staff. The NRC staff agrees with this approach. Action Item No. 13 is closed.
Mr. Scammon addressed Action Item No. 18 identified during the November 17, 2010, meeting (meeting summary at ML110110307). This action item reads as follows: Mr. Mendiola [Chief, Nuclear Performance & Code Review Branch, Division of Safety Systems (DSS), Office of Nuclear Reactor Regulation (NRR)] asked about the representative nature of the testing, that is, the testing of one fuel bundle representing a core. The BWROG took an action to describe this.
This action will be done at a near future follow-on meeting. Mr. Scammon requested moving the due date for this to the end of September 2011 and discuss this as part of the BWROGs response to some of the requests for information on the in-vessel downstream effects Topical Report currently in the review process. The NRC staff agrees with this approach. The target date for Action Item No. 18 is now September 30, 2011.
Mr. Stewart Bailey, Chief, Safety Issues Resolution Branch (SSIB)/DSS/NRR then addressed Issue No. 7, ZOI Adjustment for Air Jet Testing. This issue has been the subject of Action Items 2 and 3 originating with the August 10-11, 2010, meeting (summary at ML102360056) and reiterated in the September 22, 2010, meeting (summary at ML102800152), the October 20, 2010, meeting (summary at ML103010393), and the November 17, 2010, meeting (summary at ML110110307). The NRC staffs position was that the 40 percent reduction in damage pressure used for ZOI determination for PWRs should also be applied to ZOI determination for BWRs because prior ZOI determinations described in the URG for BWRs are based on air jet tests, the destructive properties of which may differ from those of an actual two-phase blowdown from a high-energy line break in a power plant. Because of this concern, the NRC initiated a joint test program in 2004 with Ontario Power Generation (OPG).
As of this meeting, July 20, 2011, the NRC staff has re-reviewed the available test results (air jet intrusion test results presented in the URG and the OPG results) and has determined that they are not conclusive (i.e., it is not clear whether two-phase jets are more damaging at a given target stagnation pressure (ZOI is normalized to stagnation pressure)). The NRC staff reached this determination because there are no direct test comparisons (air versus water), there are large uncertainties in comparing test results (scaling and target configuration differences), there is limited data (destruction pressure was not always identified during testing), results likely are significantly affected, and there are apparent inconsistencies in damage thresholds (e.g.,
insulation jacket seam to jet orientation).
The NRC staff concurs with the BWROG position that the 40 percent reduction factor does not need to be applied to BWR ZOI determinations across the spectrum of postulated break locations/debris sources. However, due to the uncertainties cited above, the NRC staff believes that margin should be added to the damage pressure of some materials based on the damage observed in the air jet testing. Mr. Stewart Baileys presentation (ADAMS Accession No. ML11203A432) indicates preliminary recommended damage pressures for a number of materials.
Action Item 20: The BWROG will review the URG and provide feedback on the NRC staff-proposed damage pressures. (Target date is October 26, 2011.)
Mr. Tony Borger, ECCS Suction Strainers Committee Source Term Vice Chairman for the BWROG, presented the status of the Chemical Effects Resolution Strategy, Issue No. 4.
Mr. Borger stated that the chemical effect strategy outline document will be available for NRC review in September 2011.
Mr. Paul Klein of the Steam Generator Tube Integrity & Chemical Engineering Branch, Division of Component Integrity, NRR, asked if the chemical effect tests planned are single effect or multiple effect. Mr. Borger stated that the testing will comprise both single and multiple effects.
Mr. Klein also asked if tests would be conducted with and without boron to represent some BWRs that inject sodium pentaborate from the standby liquid control injection system. Mr.
Borger stated that the BWROG will look at both chemistries.
Mr. Steve Scammon addressed the boron precipitation issue. NRC management asked the BWROG, at the May 26, 2011, BWROG Executive Committee Meeting, to examine the implications of standby liquid control (SLC) system initiation on long-term core cooling due to possible boron precipitation in the reactor vessel. At that meeting, the BWROG stated it would follow-up on this request. At this, July 20, 2011, meeting, the BWROG stated that the upcoming chemical effect test for the ECCS suction strainer effort will evaluate the impact of the sodium pentaborate buffer, from SLC injection on chemical effects with respect to strainer performance.
The BWROG further stated though that the effects of boron precipitation in the core is beyond the scope of current ECCS program investigations. The BWROG will address this question through its licensing subcommittee. Mr. Stewart Bailey stated that the NRC staff will seek to have good communication with the licensing subcommittee on the issue.
Further, the BWROG indicated it would seek to understand more of the NRC staffs concerns at this, July 20, 2011, meeting. The NRC staff briefly discussed its concerns with the BWROG.
The following captures the NRC staffs concerns:
Boron Precipitation within the Core Upon SLC Injection If SLC injection leads to boron precipitation conditions within the core, this would lead to blocked fuel channels and cause heat up. The distribution of the sodium pentaborate in the core and containment is highly dependent on the timing of SLC injection in accordance with plant procedures, the break location, and the SLC injection point (above core, below core, etc.).
The highest powered bundles would be of most concern as these hot bundles are highly voided and may not take much sodium pentaborate to cause precipitation or at least inhibit cooling intended from the injection systems. Addition of debris will also cause the sodium pentaborate to concentrate even faster as there would be less liquid for dilution.
The NRC staff would need to understand the injection rate and concentration of the sodium pentaborate added and the manner in which it is injected as this will affect how much of it enters specific bundles. The NRC staff assumes that the concentration entering the bundles could be asymmetric (not perfectly mixed) and sodium pentaborate could concentrate very quickly in some areas. Addition of sodium pentaborate in the bundles could cause the two-phase levels in the core to be lower, potentially impacting peak cladding temperatures for small breaks as well.
Core inlet blockage reduces the inventory of water in the core, so chemicals concentrate faster.
Debris Blockage therefore exacerbates the issue of boron precipitation within the core (the BWROGs Topical Report on the issue assumes 100 percent blockage). The staffs concern is that sodium pentaborate and other chemicals would concentrate in the core due to boil-off conditions.
Radiochemical Effects on the Source Term The above effect would be further deleterious because sodium pentaborate that concentrates in the core is not available for controlling pH in the suppression pool. More radioiodine could therefore be released, possibly challenging the licensing basis of plants licensed with an alternate source term.
Members of the public were not in attendance, therefore, no Public Meeting Feedback forms were received.
Enclosure:
List of Attendees cc w/encl: See attached page
Package: ML11214A140 Memo: ML11214A137 OFFICE PM:DPR:PLPB LA:DPR:PLPB BC:DSS:SNPB BC:DCI:CSGB BC:DSS:SSIB NAME JGolla JG DBaxley DB TMendiola TM RTaylor PK for SBailey SB DATE 8/2/2011 8/11/2011 8/23/2011 8/25/2011 8/26/2011
BWR Owners Group Project No. 691 cc:
BWROG Chairman Frederick P. Schiffely Exelon Generation Co., LLC Cornerstone II at Cantera 4300 Winfield Road Warrenville, IL 60555 frederick.schiffley@exeloncorp.com BWROG Vice Chairman Michael H. Crowthers PPL Susquehanna, LLC 2 North Ninth Street Allentown, PA 18101-1179 mhcrowthers@pplweb.com BWROG Project Manager Robert Whelan GE-Hitachi Nuclear Energy PO Box 780 M/C F-12 3901 Castle Hayne Road Wilmington, NC 28402 Robert.whelan@ge.com BWROG Program Manager Craig J. Nichols GE-Hitachi Nuclear Energy PO Box 780 M/C F-12 3901 Castle Hayne Road Wilmington, NC 28402 craig.nichols@ge.com GEH Senior Vice President Jerald G. Head Senior Vice President, Regulatory Affairs GE-Hitachi Nuclear Energy PO Box 780 M/C A-18 Wilmington, NC 28401 jerald.head@ge.com
List of Attendees for the July 20, 2011 Public Meeting with the BWROG James Furman Alion Rob Choromokos Alion Alan Fanning GEH/BWROG Tony Borger PPL Susq/BWROG Larry Fleischer GEH/BWROG Dan Fouts Entergy/BWROG Rob Whelan GEH/BWROG Steve Scammon ENW/BWROG Ralph Architzel NRC/NRR Paul Klein NRC/NRR Emma Wong NRC/NRR Matt Yoder NRC/NRR George Thomas NRC/NRO John Burke NRC/RES Ervin Geiger NRC/NRR Steve Smith NRC/NRR Stewart Bailey NRC/NRR John Lehning NRC/NRR Tony Mendiola NRC/NRR John Jolicoeur NRC/NRR Joe Golla NRC/NRR Phillip Grissom*
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