Generic Safety Issue (GSI) 191 Pressurized Water Reactor (PWR) Sump Performance

1. Generic Safety Issue (GSI) 191Pressurized Water Reactor (PWR)Sump Performance Presented by: Donnie Harrison Office of Nuclear Reactor Regulation Presented to: Advisory Committee on Reactor Safeguards October 2, 2008

2. Today’s Discussions • Generic Letter (GL) 2004-02 Closure Process and Overview of Current Status • Discussion of Selected Technical Areas • Emergency Core Cooling System (ECCS) Sump Strainer Head Loss Testing • Chemical Effects • In-vessel Downstream Effects • Fuel inlet blockage TRACE Calculation

3. Background • GSI-191 • Assessment of Debris Accumulation on PWR Sump Performance • Bulletin 2003-01 • Licensees who chose not to confirm regulatory compliance were asked to describe any interim compensatory measures that would be implemented to reduce risk until the analysis could be completed • All licensees responded to Bulletin 2003-01, but it was recognized that the methodology to perform the evaluations was not available at the time • GL 2004-02 • Most licensees requested and received extensions to GL 2004-02 to support the completion of testing, analyses, and implementation of corrective actions

4. Current Status of GSI-191 • All licensees have installed significantly larger ECCS sump strainers • Licensees have done, or will do, other modifications, for example: • insulation modifications • replace sump buffer • debris interceptors • water management • Strainer testing activities have been performed for nearly all licensees

5. Current Status (Continued) • Most licensees requested extensions beyond December 2007 to complete certain corrective actions • Integrated head loss testing, including chemical effects • Downstream effects analyses • Plant modifications • The staff is nearing completion of the review of the licensees’ initial supplemental responses

6. Licensee Submits GL 2004-02 Information Detailed Staff Review Draft RAIs Integration Review Team Management Decision IRT Determination Request Additional Information (RAIs) Document Licensee Closure Closure Process

7. License Submittal • Each licensee will provide, as applicable: • Initial response to GL • All plants submitted supplemental responses to GL in February/March 2008 • Responses to RAIs on the licensee’s GL supplemental submittals • Responses to open items identified in NRC staff audits • Final supplemental response after all testing and evaluations completed • Submittal addressing in-vessel downstream effects after WCAP-16793-NP issued, if appropriate

8. Break selection Debris generation Debris characteristics Latent debris Debris transport Head loss and vortexing Net positive suction head Coatings Debris source term Screen modifications Structural analysis Upstream effects Downstream effects Chemical effects Detailed Staff Reviews • Technical staff performs area-specific detailed reviews • Reviews involve 10 staff members from DSS, DCI, & DE • Output of initial review is draft RAIs • - 60% of plants through detailed reviews • Plan to have completed initial reviews of all plants by • end of October

9. Integration Review Team • Consists of 3 senior technical staff (including senior level scientist) • Performs holistic review of licensee information and staff detailed review and draft RAIs • Interactions with detailed technical reviewers to ensure staff views and IRT recommendations understood • Makes determination regarding need for RAIs/issue closure • Recommendation to Management includes minority opinions • Detailed reviewers can appeal IRT recommendation to Management • 50% of plants through IRT phase • Staff has informed several licensees with “low-fiber” that the staff has few RAIs • Most other plants have received, or will receive, RAIs • Most plants receive a “Placeholder” RAI for in-vessel downstream effects if they are relying on WCAP-16793-NP

10. Closure Activities • The staff reviews supplemental information/RAI responses in accordance with the closure process • The Regions inspect implementation of modifications and other commitments • The staff will issue a closure letter to each licensee when sufficient information is provided to close the issue for that plant • After all licensees have been issued closure letters, GL 2004-02 will be formally closed • Some modifications will be made after planned issue closure • NRC will track all commitments to completion • The staff expects to complete all technical review activities to support closure next year

11. ECCS Sump Strainer Testing Presented by: Stephen Smith Office of Nuclear Reactor Regulation Presented to: Advisory Committee on Reactor Safeguards October 2, 2008

12. Strainer Testing Overview • Strainer testing is being conducted to ensure adequate net positive suction head (NPSH) margin for emergency core cooling system (ECCS) and containment spray system (CSS) pumps under accident conditions • The staff’s assessment of testing has been refined as observations of additional testing allowed understanding of how various test parameters affect results • To be discussed: • Staff observation and review of strainer testing • Lessons learned regarding head loss testing • Review guidance for head loss testing and evaluation • Staff review of GL 2004-02 responses in the head loss area • Path forward

13. Head Loss TestingStaff Observations • Staff has witnessed a number of head loss tests at each vendor • Lessons learned have been incorporated into review guidance for testing, staff review of licensee test activities, and staff review of GL 2004-02 submittals • Most strainer vendors/testers have now developed procedures that the staff agrees are capable of producing conservative head loss results • Some vendors have not provided adequate assurance that their current protocols are conservative • Some licensees may be able to justify the use of head loss results from testing that does not meet the current guidance • Some licensees will likely have to retest using procedures that meet staff guidance

14. Head Loss TestingLessons Learned • Debris Preparation • Fibrous debris sizing • Debris sizing should match transport evaluation • Debris Introduction • Agglomeration • Thin Bed Test Protocol • Debris introduction order • Debris amounts not conservative • Debris sizes not conservative • Test Flume Flow Patterns • Stirring • Similarity to plant (e.g. floor or sump location, volume, circumscribed velocity) • Lessons learned are reflected in the staff review guidance for strainer testing

15. Example of inappropriate debris addition • Excessive agglomeration due to high fibrous debris concentration • Excessive settling of debris could occur • Agglomerated debris less likely to uniformly cover strainer

16. Video of Appropriate Debris Preparation and Introduction • Finer debris, more uniformly covering strainer will lead to higher head losses

17. Head Loss TestingReview Guidance • Staff Issued Updated Head Loss Testing Review Guidance in March 2008 • Incorporates recent lessons learned from industry head loss testing discussed previously • Publically available • Tests and evaluations conducted per this guidance should result in conservative results that may be used for plant strainer qualification

18. Path Forward • Plants that have RAIs will have to provide acceptable responses, additional analyses, or retest to assure adequate strainer performance • Some licensees that have had unacceptable test results using conservative protocols are “testing for success” by identifying and testing several contingency plans until success is achieved, e.g.: • Analytical changes to reduce calculated debris loading • Physically removing debris sources from containment • Installing debris interceptors or other plant modifications • Plant will be modified at upcoming outage to be consistent with successful test condition

19. Conclusions • Strainer testing methods have improved • Some licensees have demonstrated acceptable strainer performance as shown by conservative tests • Some licensees are working to reduce debris loads • Retesting with reduced debris loads is required • Some licensees will attempt to stand on current test results by responding to staff RAIs • Staff will consider the additional information provided on a case by case basis

20. Chemical Effects Presented by: Paul Klein Office of Nuclear Reactor Regulation Presented to: Advisory Committee on Reactor Safeguards October 2, 2008

21. Chemical Effects Activities • NRC Staff evaluation of industry chemical effects testing • Different approaches by multiple industry vendors • Pre-mixed precipitates, precipitates formed in-situ, and “evolving chemistry” tests • Staff commenting on test procedures and observing testing • Issued review guidance in chemical effects, Sept. 2007 • Issued safety evaluation report for WCAP-16530, Dec. 2007 • Technical Support From Argonne National Laboratory, Dr. Robert Litman • Relative head loss from various precipitates • Investigate aluminum solubility in alkaline, borated water • Licensee GL 2004-02 supplement review

22. Argonne Vertical Loop Test Results • Industry Test Precipitates Characteristics • Per unit mass of Al removed from the solution, the WCAP AlOOH surrogate caused greater head loss than aluminum hydroxide precipitate from aluminum coupon dissolution. • Increasing head loss for ANL test loop conditions: • WCAP AlOOH • WCAP Sodium Aluminum Silicate – “tap water” • In-situ formation of aluminum hydroxide by chemical addition • 6061 Aluminum, 1100 Aluminum • WCAP Sodium Aluminum Silicate – high purity water

23. Long-term Al Hydroxide Precipitation Tests: Al Hydroxide Precipitation Map Long-term solubility test results for various pHs and Al concentrations represented in a Al hydroxide precipitation map that plots pH and Al concentration vs. temperature. Solubility increases with pH and temperature Loop tests with Al alloy plates seem to suggest lower solubility than the chemical Al tests. This may be due to heterogeneous nucleation of Al hydroxide on intermetallic particles and/or on the surfaces of preexisting precipitates pH of 8 at 140F 10 ppm 50 ppm 100 ppm

24. Summary Chemical Effects Status • NRC Staff has observed tests at each vendor facility • Vertical head loss loop tests are typically more susceptible to large head losses from chemical precipitates compared to larger scale strainer tests • Most plants are using test methods that are acceptable to the staff, although some technical issues remain that will be resolved with individual licensees • Testing at Argonne and at vendor facilities continues to indicate that the WCAP-16530-NP methodology is conservative with respect to the amount and the properties of precipitates • NRC staff to perform a few chemical effects audits to assess overall evaluations at selected plants

25. In-Vessel Downstream EffectsFlow Resistance due to Potential Debris Accumulation Presented by: Stephen Smith Office of Nuclear Reactor Regulation Presented to: Advisory Committee on Reactor Safeguards October 2, 2008

26. Introduction • Background • Debris in the core • How debris loads are determined • Diablo Canyon testing • PWROG testing

27. Debris Effects on Reactor Core - Background • WCAP-16793 issued to provide guidance to plants on in-vessel debris effects • ACRS raised concerns with adequacy of the WCAP methodology and assumptions • Only one significant set of tests for fuel head loss had been conducted • Some assumptions used in WCAP evaluation were not validated • PWROG is working to provide more rigorous guidance in the WCAP • An outstanding concern is potential head loss within core due to debris accumulation • PWROG is conducting testing with representative fuel inlet types and varying debris loads • Staff will review revised WCAP when it is completed

28. Debris at Fuel Inlet • Debris load is plant specific • Fibrous bypass (pass through) determined by strainer testing • Fibrous test debris characteristics are similar to actual bypassed debris • Testing to date has assumed no filtering of particulate or chemical debris by strainer • This is a conservative assumption because some debris will filter out on the strainer • Chemical loading determined per WCAP-16530

29. Vendor Fiber Bypass Testing • Vendor, and in some cases, plant specific • Downstream sampling methods • Sample is dried and weighed to determine mass • Size distribution of sample is determined • PWROG to provide fiber bypass data

30. Diablo Canyon Fuel Testing • Westinghouse Alternate P-grid • Testing Performed at CDI • Witnessed by staff • Prototypical Debris for Plant • Varied Debris Loads • Bottom Nozzle and One Intermediate Grid Strap • Hot Leg and Cold Leg Flows Tested • Tested head losses were within allowable limits

31. PWROG Test Observations • Testing has just begun • Staff observed early testing at Westinghouse • Standard P-grid was tested • Testing used hot leg break flow rate • Debris preparation and introduction was appropriate • Observations indicate that test program can result in conservative results

32. PWROG Test Plans • Other Westinghouse fuel designs will be tested to ensure that results are bounded • Testing of Areva fuel designs to be conducted in the future • PWROG plans to increase debris loads to bound as many plants as possible • Staff will continue to review data and test information as it becomes available • PWROG to determine limiting core head losses allowable for various breaks to be applied as acceptance criteria for tests

33. Conclusions • Westinghouse and CE fuel testing is currently underway • Areva fuel testing is scheduled to begin later this year. • Testing will determine acceptable debris loading for various fuel designs, postulated conditions, and debris mixtures • WCAP-16793 to be revised based on test results

34. Core Inlet Blockage AssessmentGSI-191 In-Vessel Review Presented by: Ralph R. Landry Senior Level Advisor Office of New Reactors Presented to: Advisory Committee on Reactor Safeguards October 2, 2008

35. Core Blockage Assessment - Background • March 2008 T/H Subcommittee • Presented TRACE analysis based on 95% core inlet blocked • Core heatup calculated to be less than 300 ºF • Questions raised concerning coolant dispersal beyond core entrance plane • RES Performed Additional Calculations • TRACE based on porous medium at core entrance • “Hand calc” using Excel spreadsheet solution

36. Core Blockage Assessment -TRACE Model • Core entrance flow passing through porous medium • Uniform Nukon/CalSil debris bed instantaneously present • Debris bed form loss developed from test data in NUREG-1862 and NUREG/CR-6917; Δpbed = f(bed thickness, approach velocity) • Debris bed thicknesses of 1.2, 2.4, and 4.8 inches

37. Core Blockage Assessment -Core Collapsed Level

38. Core Blockage Assessment -PCT

39. Core Blockage Assessment -Hand Calc Model

40. Core Blockage Assessment -Hand Calc

41. Conclusion • The staff has established a process for closure of GL 2004-02 • Licensees have implemented significant modifications to prevent unacceptable strainer blockage • Guidance has been developed to ensure conservative test protocols and evaluations • In-vessel downstream effects will be resolved as part of WCAP-16793 review