A SUMMARY OF CDBI FINDINGS. IN SERVICE TESTING OWNERS GROUP December 2010 Clearwater, Florida. Introduction. - PowerPoint PPT Presentation
A SUMMARY OF CDBI FINDINGS
A SUMMARY OF CDBI FINDINGSIN SERVICE TESTING OWNERS GROUPDecember 2010Clearwater, Florida IntroductionComponent Design Bases Inspections (CDBIs) are conducted by the NRC to review risk significant components and ensure that these components are capable of performing their intended safety functions.Inservice Testing (IST) is performed to assess operational readiness and detect and act upon indications of degradation to ensure that components are capable of performing their intended safety functions.Although the objectives are similar, they are not identical.CDBI reports and findings indicate that there is an increasing emphasis on testing and test margins to ensure that design bases are adequately demonstrated to the satisfaction of the inspector.Increasingly, the capacity to meet design requirements has been linked to inservice test (IST) programs.This expectation is heightened when a design basis test has not been developed.
22IST 101IST is intended to assess the operational readiness of components that may be required to place the plant in safe shutdown, maintain safe shutdown or mitigate the consequences of a design basis accident.Assessment is accomplished by testing the component when known to be operating acceptably at a point that may be readily duplicated during subsequent tests.Reference values are established at this test point and subsequent tests are then performed at this reference point with the intent of:Assessing continued operational readiness.Detecting and taking actions in response to degrading component conditions.
3IST 101IST acceptance limits are determined by imposing a specific band around the original reference values. The multipliers used to derive these bands vary dependent on both the component and the design of the component.Limiting values for many IST components may also be found in the UFSAR or Technical Specifications. These limits are usually expressed in terms of hydraulic performance for pumps and limiting stroke time values for power operated valves.UFSAR or Technical Specification limits take precedence over ASME Code derived limits.
4RegulatoryIn December of 1997, the NRC issued Information Notice (IN) 97-090 to alert licensees to potential problems associated with safety-related pump surveillance testingIN 97-090 cited Appendix B, Criterion XI, "Test Control 10CFR Part 50 and stated that licensees have concentrated on inservice testing (IST) requirements without ensuring that design requirements were met. IN 97-090 also stated that there are two applicable primary requirements for safety-related pump testing: To ensure that Criterion XI is met in that each safety-related pump achieves its minimum design-required performance.To ensure that each safety-related pump meets the requirements of the ASME OM Code. 5RegulatoryCriterion XI of Appendix B to 10 CFR Part 50 requires that a test program be established with written test procedures that incorporate the requirements and acceptance limits contained in applicable design documents. Although licensees have established IST acceptance criteria that meet the requirements specified in the ASME Code, the criteria at some plants allowed safety-related pumps to degrade below the performance assumed in the accident analyses.
6RegulatoryIN 97-090 summary:IST is intended to monitor degradation of components; however, does not require that pumps be tested at design-basis conditions.ASME tests may be used to verify compliance with the ASME Code and the pump design requirements contained in plant design-basis documentation such as the FSAR. If the minimum design performance as specified in the plant design documentation is more stringent than the ASME Code acceptance criteria, then the test acceptance criteria must be adjusted to the more conservative requirements.Original plant design-basis calculations, or revisions to these calculations must be properly integrated into surveillance test procedure acceptance criteria.7NRC Inspection GuidanceThe NRC Inspection Manual, Attachment 71111.21 contains prescriptive guidance for the conduct of a Component Design Bases Inspection.This manual defines design margin as the margin in the design calculations related to the performance of the component.For example, the analytical margin for a pump includes flow and head required for the pump to perform its function compared to the calculated capacity of the equipment.The Inspection Manual also requires that the inspector determine whether the design basis is met by the installed and tested configuration.How this requirement is met is somewhat subjective. Without clear guidance, CDBI related conflicts are likely as evidenced by industry OE.
8IN 2008-02, IST SpecificIn March of 2008, the NRC issued IN 2008-02, Findings Identified During Component Design Bases Inspections - Testing.Failure to account for EDG under frequency in pump test acceptance criteria.Failure to appropriately account for instrument uncertainties.Failure to ensure adequate test equipment. Failure to account for valve pressure locking effects.Failure to verify the minimum containment cooling coil fouling factor assumed in analyses.Failure to consider the effects of service water strainer plugging on flow rate.
9The DilemmaThe ASME OM Code does not discuss design basis capability, but does refer to operational readiness. Typically, the IST program is used in conjunction with other programs to confirm operability.Without question, the design basis must be protected; however, the details related to what constitutes an adequate design basis test program, what elements must be considered or where this program should reside are confusing to many. IST limits should be established in a manner that envelopes design limits. For example, IST limits must consider instrument accuracy when establishing limiting values.
10The DilemmaThis example is just one of many that illustrates the conflict that may exist and the basis for the differing expectations between the regulating authority and the IST Engineer.Examples of questions provided on the following slides indicate an increasing need for ISTOG to become involved and provide assistance to IST Engineers. To do this, guidance may be needed or clarifications to existing requirements developed to provide a uniform set of rules. Currently, guidance is being provided in the form of Operating Experience.It is important to maintain perspective - Design Basis testing need not be established in IST Procedures. 11Industry OE- Example #1ConcernInstrument uncertainty is not accounted for in development of IST acceptance criteria.
ConsiderationsInstrument accuracy is addressed by ASME; however, uncertainty is not. What is the overall impact when additional penalties associated with instrument drift, M&TE equipment, temperature changes, orifice plate tolerance, etc. are factored into the total error for a parameter using the square root of the sum of the individual errors squared (SRSS) methodology? Minimize the effects by performing post test calibration checks of test instruments.
12Industry OE- Example #2ConcernInstrument uncertainty is unaccounted for in shaft speed for variable speed pumps.Examples:Steam driven turbine pumps.Variable speed motor driven pumps.
ConsiderationsAccount for instrument accuracy for variable speed pumps.
13Industry OE- Example #3ConcernCheck valve acceptance criteria lack adequate basis and does not ensure design requirements are met.Examples:Differential pressure does not ensure that idle pumps are not rotating.Differential pressure does not consider additional stress on the pump shaft when a start signal is received.
ConsiderationsAssess check valve reverse flow acceptance criteria and tighten limiting values, if possible.Supplement the closure test by including an additional requirement to verify idle pumps are not rotating.For example:The check valve acceptance criteria is met when measured differential pressure is > 80 psid AND the idle pump is observed and is not rotating. Develop calculations to bound the limiting values.14Industry OE- Example #4ConcernThe effects of limit switch settings used in determining the open and closed positions of valves is not factored into IST acceptance limits.
ConsiderationsReduce the limiting value to account for limit switch error. MSIVs closure may provide one of the more limiting challenges.Is this concern only relevant when addressing closure?Does this concern vary dependent on the valve design?Can ISTOG develop a product to address this concern? Input from AOV, MOV Engineers would be helpful.
15Industry OE- Example #5ConcernThe effects of EDG frequency droop on pump and valve performance. Most Technical Specifications permit frequency variations as low as 58.8 hz. Examples:Motor stall for MOVs.Lower EDG frequency translates to slower pump speed. Pump speed is directly proportional to flow rate and pump head squared.
ConsiderationsIncorporate the impact of the lowest allowable EDG frequency into pump and power operated valve calculations.Minimize the impact by revising Technical Specifications to impose a tighter band.Some plants have incorporated a new limit of + 0.5hz. The upper limit restriction is in response to recent findings associated with EDG over frequency concerns.16Industry OE- Example #6ConcernThe station did not have a process in place to evaluate or prevent unacceptable preconditioning of IST components. The NRC utilizes Inspection Procedure, Part 9900 to evaluate a stations ability to prevent unacceptable preconditioning.The Inspection Procedure is more detailed than public information provided in the form of two previous Information Notices. INs 96-024 and 97-016 addressed preconditioning, but did not address the subject in detail and in present terms.