IR 05000334/2008009

IR 05000334-08-009, on 11/12-14/2008 and 01/27-29/2009, Beaver Valley Power Station, Unit 1, Special Inspection Team Report

ML090720099
Person / Time
Site:	Beaver Valley
Issue date:	03/13/2009
From:	Doerflein L Engineering Region 1 Branch 2
To:	Sena P FirstEnergy Nuclear Operating Co
References
IR-08-009
Download: ML090720099 (28)

Text

rch 13, 2009

SUBJECT:

BEAVER VALLEY POWER STATION, UNIT 1 - NRC SPECIAL INSPECTION TEAM REPORT 05000334/2008009

Dear Mr. Sena:

On November 12-14, 2008 and January 27-29, 2009, the U.S. Nuclear Regulatory Commission (NRC) conducted the onsite portions of a special inspection at Beaver Valley Power Station, Unit 1. In-office inspection reviews were conducted in the intervening weeks. The enclosed report documents the inspection teams findings and observations which were discussed with Mr. Mark Manoleras and others of your staff on January 29, 2009.

The special inspection was conducted in response to FirstEnergy Nuclear Operating Companys (FENOC) discovery of air voids in the recirculation sump suction piping to the low head safety injection pumps on September 23, 2008. The NRC's initial evaluation of this condition satisfied the criteria in NRC Management Directive 8.3, NRC Incident Investigation Program, for conducting a special inspection. The basis for initiating this special inspection is further discussed in the inspection teams charter that is included in this report as Attachment B.

The inspection examined activities conducted under your license as they relate to safety and compliance with the Commission's rules and regulations and with the conditions of your license.

The team reviewed selected procedures and records, observed activities, and interviewed personnel. Based on the results of this inspection, one NRC-identified finding of very low safety significance (Green) was identified.

In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter, and its enclosures, and your response (if any) will be available electronically for public inspection in the NRC Public Document Room or from the Publicly Available Records (PARS) component of

Mr. NRC=s document system (ADAMS). ADAMS is accessible from the NRC Website at http://www.nrc.gov/reading-rm/adams.html (the Public Electronic Reading Room).

Sincerely,

/RA/

Lawrence T. Doerflein, Chief Engineering Branch 2 Division of Reactor Safety Docket No.: 50-334 License No: DPR-66

Enclosures:

Inspection Report 05000334/2008009 w/Attachment A: Supplemental Information w/Attachment B: Special Inspection Charter w/Attachment C: Independent Operability Evaluation

Mr. NRC=s document system (ADAMS). ADAMS is a

REGION I==

Docket No. 50-334 License No. DPR-66 Report No. 05000334/2008009 Licensee: FirstEnergy Nuclear Operating Company (FENOC)

Facility: Beaver Valley Power Station, Unit 1 Location: Post Office Box 4 Shippingport, PA 15077 Dates: November 12-14, 2008 and January 27-29, 2009 Inspectors: W. Cook, Senior Reactor Analyst, Division of Reactor Safety (DRS)

F. Arner, Senior Reactor Inspector, DRS P. Cataldo, Senior Resident Inspector, Division of Reactor Projects W. Lyon, Senior Reactor Systems Engineer, Office of Nuclear Reactor Regulations J. Staudenmeier, Senior Reactor Engineer, Office of Nuclear Regulatory Research Approved by: Lawrence T. Doerflein, Chief Engineering Branch 2 Division of Reactor Safety

SUMMARY OF FINDINGS

IR 05000334/2008009; 11/12-14/2008 and 01/27-29/2009; Beaver Valley Power Station, Unit 1;

Special Inspection Team Report.

The report covered two on-site inspection visits by a special inspection team consisting of a Senior Reactor Analyst, Senior Reactor Engineer, and a Senior Resident Inspector, with part-time assistance of two headquarters technical reviewers. One finding of very low safety significance (Green) was identified. The significance of most findings is indicated by its color (Green, White, Yellow, or Red) using Inspection Manual Chapter 0609, Significance Determination Process. Findings for which the significance determination process does not apply may be Green or be assigned a severity level after NRC management review. The NRC program for overseeing the safe operation of commercial nuclear power reactors is described in NUREG-1649, "Reactor Oversight Process," Revision 4, dated December 2006.

NRC-Identified and Self-Revealing Findings

• Green: A finding of very low safety significance was identified based upon FENOC not performing adequate extent-of-condition evaluations for voiding events that occurred on-site and for external voiding events evaluated within the corrective action program. This finding is based upon the identification of air voids in September 2008, which were located in accessible portions of both low head safety injection pumps suction piping utilized during accident conditions for recirculation from the containment sump.

The finding was determined to be more than minor, because it was associated with the equipment performance attribute of the Mitigating Systems Cornerstone, and affected the cornerstone objective of ensuring the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences. This finding was evaluated for safety significance using Inspection Manual Chapter (IMC)0609, Significance Determination Process, Attachment 4, Phase 1 - Initial Screening and Characterization of Findings, and determined to be of very low safety significance (Green). The finding screened to Green because the as-found condition constitutes a design or qualification deficiency confirmed not to result in a loss of operability or functionality. The team verified that the voids were effectively removed, periodic ultrasonic testing acceptance criteria for these locations were established, and an extensive analysis that supported past operability was performed. The team also reviewed licensee corrective actions to prevent recurrence which involved initiation of a Condition Report and follow-up using a prepared questionnaire and data sheet of any external operating experience involving emergency core cooling system (ECCS) piping voids. (Section 3.2)

Licensee-Identified Violations

None.

ii

REPORT DETAILS

1. INTRODUCTION

1.1 Background In September 2008, FENOC was conducting ultrasonic testing (UT) of emergency core cooling system piping, in response to Generic Letter 2008-01, Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems, dated January 11, 2008, when the responsible staff identified air voids in the Unit 1 containment sump suction piping to the low head safety injection (LHSI)pumps. The air voids were found in the 12-inch diameter stainless steel suction piping to both trains of LHSI on September 23, 2008. The approximate size of the air voids were 4.1 cubic feet in train A and 3.9 cubic feet in train B. In both trains, the air voids displaced approximately one-half of the water volume in the piping, located in a horizontal length of piping upstream of the sump suction containment isolation valves (MOV-1SI-860A and 860B) and downstream of the sump suction inlet. Upon confirmation of the air voids, the control room operators were notified and per procedure NOP-OP-1009, Immediate and Prompt Operability Determination, an operability determination was initiated by the engineering staff. The initial operability determination concluded that the LHSI pumps would remain operable in the event of a loss-of-coolant accident and subsequent swap-over to containment sump recirculation. The FENOC design engineering staff concluded there was reasonable assurance that the LHSI pumps would remain operable because it was judged that a large percentage of the air void swept into the pump suction would escape upward into the pump suction casing and not be ingested into the pump impellers. Subsequent engineering analysis confirmed the initial operability determination (see Section 3.5 for further details).

1.2 Special Inspection Scope The NRC conducted this inspection to gain a better understanding of the circumstances involving FENOCs identification of trapped volumes of air between the containment sump and the LHSI pump sump suction containment isolation valves. Between October 4 and 5, FENOC took action to vent and fill the approximate four cubic foot air voids in each sump suction line and eliminated the potential for any adverse impact on LHSI pump operability.

The inspection team used NRC Inspection Procedure 93812, Special Inspection, as a guide to complete their review. Additional inspection and review activities were outlined in the special inspection team charter, provided as Attachment B. The special inspection team reviewed procedures, corrective action documents, work requests, engineering calculations and analyses, and the root cause evaluation prepared by FENOC. The team also interviewed key plant personnel regarding the discovery and resolution of the condition. A list of site personnel interviewed and documents reviewed are provided in A to this report.

1.3 Preliminary Conditional Risk Assessment Using Inspection Manual Chapters (IMC) 0309, Reactive Inspection Decision Basis for Reactors, IMC 0609, Significance Determination Process, and the Beaver Valley Unit 1 Standardized Plant Analysis Risk (SPAR) model in conjunction with the Graphical Evaluation Module (GEM), the Region I Senior Reactor Analyst (SRA) evaluated the increase in conditional core damage probability for the voided sump suction piping and postulated impact on LHSI pump operability. Although the immediate operability determination prepared by FENOC concluded that the LHSI pumps would remain functional, if the air voids were ingested with recirculation sump flow, the NRC staff judged that the presence of the air voids, absent more definitive examination and engineering evaluation, may result in both LHSI pumps being rendered inoperable and non-recoverable.

The SRA made the following assumptions to estimate the increase in conditional core damage probability (CCDP): the condition duration was one full year (maximum exposure time); the containment sump recirculation mode of LHSI pumps fail upon ingestion of the air voids (SPAR model event <LPR-MOV-CF-SI860AB>, common cause failure of sump isolation valve SI-860A/B, set to TRUE); calculation truncation was set at 1E-13; an uncertainty factor of 1 in 10 (10 percent) assigned to the failure of the LHSI pumps due to the void ingestion; and, all other model events were set to nominal values.

The results of the GEM evaluation, with the 10 percent LHSI pump failure probability, was an increase in CCDP value in the low 1E-5 range. The dominant core damage sequences involved medium break loss-of-coolant accidents, which are dependent upon the recirculation mode of the LHSI pumps to provide continued core cooling and containment heat removal. Based upon this conservative CCDP value, and having satisfied an IMC 0309 deterministic criterion, this degraded LHSI pump condition fell within the Special Inspection to Augmented Inspection Team overlap range for reactive inspections.

2. EVENT DESCRIPTION

On September 23, 2008, FENOC detected voids in the suction lines for both trains of LHSI at Beaver Valley Unit 1. FENOCs review was being done to complete commitments made in response to Generic Letter (GL) 2008-01, Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems. Approximately four cubic feet of air were detected in each sump suction line by ultrasonic testing (UT) measurement. On September 26, FENOC completed a prompt operability evaluation for this void condition. This operability determination (OD) was reviewed by the resident inspectors and forwarded to the NRC Region I Office on September 30, 2008. NRC regional staff was engaged and had an initial call with the licensee on October 1. Technical questions were developed and asked of FENOC. The questions and other related issues were discussed on a subsequent October 3 conference call. During the call, FENOC acknowledged that they were not able to fully address all of the staffs questions, and initiated action to have the pump vendor conduct a formal analysis of the impact of the voids on LHSI pump operability. The consensus view of the NRC staff was that there was enough uncertainty in FENOCs prompt OD to question the LHSI pumps ability to operate in the low pressure recirculation mode. After follow-up discussions between FENOC and NRC management on October 3, FENOC vented and vacuum filled both LHSI loops, effectively eliminating the voids and resolving any potential safety and operability concerns.

3. SPECIAL INSPECTION AREAS

3.1 Sequence of Events

a. Inspection Scope

The team developed a complete sequence of events related to FENOCs discovery of the voided piping and their follow-up actions to address the condition.

b. Condition Identification and Resolution Chronology The team, with FENOC input, developed the following chronology of events associated with the discovery and removal of the air voids in the LHSI pump suction lines:

June - September 2008 Beaver Valley Operations and Engineering staff conduct an intensive review of emergency core cooling system (ECCS) piping configurations in response to GL 2008-01.

September 23, 2008 Non-Destructive Examination staff conducted ultrasonic examinations of the low head safety injection pump suction piping. Condition Report 08-46771 initiated, identifying the two sections of LHSI pump suction piping from the Unit 1 containment sump having potentially entrapped air voids.

Shift Manager notified by the engineering staff and the immediate operability assessment concluded the LHSI pumps were still operable.

September 26, 2008 Engineering completed a Prompt Operability Determination (POD) per NOP-OP-1009, Immediate and Prompt Operability Determination, concluding that the LHSI pumps would remain operable during and following ingestion of the air voids.

Engineering provided approved POD to the on-watch Shift Manager.

October 1, 2008 Conference call conducted between FENOC and Region I representatives to discuss the POD, dated 9/26/09.

October 3, 2008 Follow-up conference call between FENOC, Region I, and Office of Nuclear Reactor Regulation (NRR) staffs to discuss details of the operability determination.

Discussions between Region I management and Beaver Valley Site Vice President pertaining to the uncertainties associated with LHSI pump operability with the air voids remaining in the recirculation sump suction piping.

October 4-5, 2008 Plant Operations and Engineering personnel conducted a vent and vacuum fill to remove air voids in sump suction piping using available local leak rate connections.

October 6, 2008 FlowServe (pump vendor) documents their evaluation of the impact of air voids on LHSI pump operability.

October 14, 2008 FENOC submitted response to Generic Letter 2008-01.

November 2008 Mancini Consulting Services provided summary of LHSI pump air entrainment analysis to FENOC.

November 12, 2008 Commenced on site Special Inspection Team review at Beaver Valley Power Station.

November 14, 2008 Conducted team debrief with station management December 2008 MPR Associates, Inc. provided Revision 2 of their Beaver Valley Unit 1 LHSI Pump Past Operability Analysis to FENOC.

January 27-29, 2009 Completed on-site inspection activities and conducted exit meeting.

3.2 Review of Operating Experience

a. Inspection Scope

The team reviewed operating experience involving air voiding of emergency core cooling systems (ECCS) and actions taken by the Beaver Valley Power Station (BVPS) staff to identify and address these types of conditions. The team examined the specific issues associated with FENOCs recent void discoveries to assess any new generic issues of industry interest for prompt communication and dissemination.

b. Findings and Observations

Based upon the teams review, no new generic issues were identified pertaining to BVPS air void discovery. However, the teams review of the BVPS Operating Experience Program implementation did identify one finding, as discussed below.

Introduction.

A finding of very low safety significance (Green) was identified based upon FENOC not having performed adequate extent-of-condition evaluations for voiding events that occurred on-site (at Unit 2), and not having identified similar ECCS suction piping voiding vulnerabilities from external events evaluated within the BVPS Corrective Action Program.

Description.

The team identified that from August 2002 to September 2008, FENOC did not evaluate ECCS piping utilized during post-accident long-term recirculation for susceptibility to air or gas voids. In particular, accessible portions of the low head safety injection (LHSI) pump suction piping, located between the pumps and the Unit 1 containment sump, were excluded from consideration during numerous Operating Experience Program evaluations performed by station staff. The team reached this conclusion following an extensive review of Corrective Action Program (CAP)documents to ascertain the scope and adequacy of FENOC's review of the generic communications and industry events that involved ECCS piping gas and air voids.

The team identified a number of missed opportunities by FENOC to identify the subject LHSI pump suction piping air void condition. For example, NRC Information Notice 2006-21, "Operating Experience regarding Entrainment of Air into Emergency Core Cooling and Containment Spray Systems," described events that highlight the need for licensees to understand how changes in plant configuration, such as transitioning from the injection phase to the recirculation phase during a design basis loss-of-coolant accident (LOCA), and the performance of proper engineering analyses, relative to "suction supply lines" of ECCS pumps, are critical to identifying latent plant design and operating vulnerabilities.

The team noted that between 2004 and 2006, multiple ECCS pump voiding events occurred at various United States nuclear power plants and these events were communicated to the industry via various Operating Experience (OE) networks. As described in Section 3.3, FENOC utilized these networks and other similar methods to disseminate information regarding internal events to the industry. FENOC review of external operating events, including NRC generic communications, was captured within the BVPS CAP, evaluated for applicability, and if applicable, corrective actions were established and implemented to address identified adverse conditions or trends. One operating event in particular, the Palo Verde Nuclear Station voided containment suction piping condition, was received via an industry information source, entered into the CAP under Condition Report (CR)-05-02979, and determined to be non-applicable, based in part, on actions already performed or considered resolved by the station. The team viewed FENOCs failure to have more thoroughly examined the lessons learned from this Palo Verde OE as another missed opportunity.

In another example, a gas void was identified in ECCS piping at BVPS Unit 2, in August 2002. The team identified that while FENOC addressed a number of issues regarding the identified gas void at Unit 2, the evaluation did not adequately address the extent-of-condition and potential for voiding of ECCS suction piping at Unit 1. In particular, the team determined that while appropriate standards for evaluation of the voids were identified within the CAP (detailed in CR-02-06831 and the associated root cause evaluation), the extent-of-condition evaluation for Unit 1 was inadequate in one important aspect. Specifically, accessible portions of the low head safety injection (LHSI) pump suction piping located between the pump and the containment sump were not evaluated.

While FENOC was aware that the piping was utilized during the recirculation phase of a LOCA, the focus of the evaluation was limited to similar sections of piping between the LHSI pump discharge cross-connect piping to the high head safety injection pumps.

FENOC was also focused on the issue of piping elevations and high points that would be susceptible to the accumulation of air and gas voids. The team found that FENOC staff only verified the acceptability of existing ultrasonic testing (UT) points for sections of piping that were listed in the void check procedure 3BVT-02.11.01. FENOC did not expand that review. Accordingly, the team considered this event another missed opportunity to have identified the accessible portions of the LHSI system containment sump suction piping. The team noted that FENOCs 2002 evaluation included isometric drawing reviews to verify that UT points identified in the void check procedure were located at the high points of particular piping sections. FENOCs discovery of the air voids on September 23 was based, in part, upon the identification of piping elevation differences initially identified by review of isometric drawings as part of the actions needed to respond to Generic Letter 2008-001.

The team noted that procedure NOP-LP-2100, Operating Experience Program, provides guidance on the review, analyses and dissemination of OE at BVPS. The team determined that between August 2002 and September 2008, FENOC did not perform adequate extent-of-condition evaluations for voiding events that occurred on-site. In addition, FENOC did not identify, via external events evaluated within the BVPS Corrective Action Program, the presence of voids in the Unit 1 LHSI system recirculation sump suction piping. The team determined that these missed opportunities, which culminated in the discovery of air voids in accessible portions of the LHSI pumps suction piping on September 23, 2008, was a performance deficiency.

Evaluation. The team determined that this finding was more than minor, because it was associated with the equipment performance attribute of the Mitigating Systems Cornerstone, and affected the cornerstone objective of ensuring the availability, reliability and capability of systems that respond to initiating events to prevent undesirable consequences. The team determined that there was a reasonable doubt regarding LHSI pump operability with the air voids in the pump suction lines pending engineering analysis, and it resulted in unanticipated unavailability and inoperability for approximately three-and-one-half hours to resolve the identified voids, which were removed approximately 11 days following the initial identification of the air voids. This finding was evaluated for safety significance using Inspection Manual Chapter (IMC) 0609, Significance Determination Process, Attachment 4, Phase 1 - Initial Screening and Characterization of Findings, and determined to be of very low safety significance (Green). The finding screened to Green because the as-found condition constitutes a design or qualification deficiency confirmed not to result in a loss of operability or functionality. The team noted that the identified void was effectively removed, ultrasonic testing acceptance criteria for these suction piping sections was established, and an extensive analysis that supported operability was performed. In addition, a prepared follow-up questionnaire was developed to ensure any future industry operating experience involving ECCS piping voids is appropriately examined for applicability to BVPS and properly resolved.

Enforcement.

This finding did not involve a violation of regulatory requirements.

FENOC has documented this finding and addressed corrective actions to prevent recurrence in BVPS Condition Report CR-08-49518. (FIN 05000334/2008009-01:

Inadequate extent-of-condition and applicability review of Operating Experience involving ECCS pump and piping voids)3.3 Review of Root Cause and Extent-of-Condition

a. Inspection Scope

The team examined the licensees root cause determination for the LHSI system air voids and assessed the condition for evidence of inadequate design and/or system operations. The team independently evaluated plant drawings, procedures, and associated system modifications, including a detailed field inspection of the piping found to be voided and actions taken by FENOC to remove the air voids. The team also examined the licensees efforts to assess the extent-of-condition (including Unit 2) and their self-critique of prior opportunities to have identified this condition.

b. Findings and Observations

No findings of significance were identified.

The team reviewed FENOCs assessment of the potential generic implications regarding the voids identified in September 2008, as detailed in CR 08-46771. The team noted that the potential generic implications were adequately assessed, consistent with station guidance contained in NOBP-LP-2011, FENOC Cause Analysis," Revision 7. The team noted that FENOC had initiated a corrective action to communicate their ECCS void issue and associated consequences to the industry via existing OE networks.

As documented in CR-08-46771, the design and construction of the LHSI recirculation sump suction piping provides a piping configuration that would result in the formation or entrapment of air voids. With the exception of the 12-inch diameter stainless piping exiting the containment wall in the 687-foot elevation valve pit room, the remaining upstream suction piping to the sump is embedded in concrete. In this embedded section of suction piping, a six-inch elevation rise is clearly depicted in the architect-engineering fabrication and welding isometric drawing (No. 11700-6.24-83 Sheet 1-2). Because of the 6-inch upward slope of the 12-inch diameter suction piping, there is no natural vent path back to the containment sump for air to escape. Also, since the issue involves a specific ECCS alignment during a LOCA, it could not manifest itself during routine operations or surveillance testing. As previously discussed, FENOC used a vacuum fill process to remove the air, via the down stream containment isolation valve local leak rate testing connections. No documented explanation could be found by the FENOC staff for this 1971 design configuration/decision. A review of the Unit 2 isometric drawings identified that this piping design vulnerability does not exist. Additional details of FENOCs Unit 2 review and results are documented in their GL 2008-01 response, dated October 14, 2008.

The team concluded that FENOCs historical review and root cause evaluation of this condition was appropriate and thorough.

As required by the Special Inspection Team charter, the team also assessed FENOCs extent-of-condition reviews for previous voiding events and observed that FENOC had numerous Condition Reports (CRs) populated within the station CAP that detailed their assessments of industry operating experience (OE), as well as generic communications from the industry and the NRC. With the exception of the issues discussed in section 3.2, the team observed that the OE program, as detailed in NOP-LP-2100, "Operating Experience Program," was generally effective in evaluating the potential impact of specific events and information regarding gas accumulation and voiding in ECCS pumps and piping. The team noted that, to the extent practicable, there was an appropriate interface between the OE program and the station CAP to identify and resolve issues.

Specifically, the team reviewed FENOCs assessment of industry events that involved gas intrusion of safety-related systems, as detailed in CR 05-02979. This CR utilized attributes of the OE program and requested an "in-depth and thorough evaluation" for applicability of these types of industry events to BVPS. The team determined that, while the evaluation performed under CR 05-02979 was generally effective, missed opportunities were identified that may have led to an earlier identification of the gas voids that were the subject of this special inspection. For example, the engineering staff reviewed selected systems for possible gas intrusion mechanisms and noted that procedures had been developed to ensure the BVPS staff utilized techniques to control gas accumulation. The engineering staff concluded that procedure revisions were not necessary as a result of these existing gas control measures. However, the team found that 3BVT 02.11.01, "Void Monitoring Test Procedure," contains a list of piping segments for performance of void checks, and does not inspect piping utilized for long-term recirculation following the design basis LOCA at either unit.

3.4 Review of Technical Specification Compliance

a. Inspection Scope

The team reviewed station operator compliance with applicable Technical Specifications upon discovery of the sump suction piping voids and through subsequent air void removal activities.

b. Findings and Observations

No findings of significance were identified. Based upon the teams review of the chronology of events and interviews with plant staff, no discrepancies were noted with respect to control room staff compliance with the Unit 1 Technical Specifications.

3.5 Independent Review of Engineering Calculations and Operability Determination

a. Inspection Scope

The team reviewed FENOCs analyses that support their past operability determination for both LHSI pump trains. The team independently evaluated the available plant data and used insights from the FENOC analyses to develop an independent assessment of LHSI pump impact due to suction piping air voids.

b. Findings and Observations

The team observed that FENOC contacted the pump vendor and two independent engineering consulting firms (contractors) to aid in evaluating the potential impact of the as-found air voids on LHSI pump past operability. One of the contractors performed a complex transient thermal-hydraulic analysis to determine the void transport mechanism to the LHSI pumps. This transient analysis included the modeling of the alignment of the pump suction from the refueling water storage tank (RWST) to the containment sump, including the opening of the sump isolation valve and closing of the RWST isolation valve. This modeling characterizes the transition of water flow from the RWST to the containment sump based on the change in system resistance associated with these different suction paths. This analysis also used time dependent assumptions for worst case sump temperature, along with containment pressure, as inputs in calculating/predicting the affect on the air voids found in the sump suction piping. An additional analytical program for air transport mechanisms was used to estimate the transport of the air voids to the pump inlet and then through the pump casing into the pump impeller. This program used theoretical and experimental correlations to determine the movement of the air through the piping and pump suction can, accounting for piping geometry, bubble buoyancy, flow velocities, and the associated Froude numbers (i.e., ratio of inertial to gravitational forces).

The team determined that key design inputs used within the contractors model were generally conservative; in particular, the maximum expected pump flow rate, which has a direct impact on the movement of the air void to the inlet of the pump. The team found that parameters assumed for containment sump temperature and pressure, RWST level, and closing time assumed for the RWST isolation valve were conservative and reasonable. With respect to the assumed flow rate, the team noted that the maximum flow value was conservative, since it accounts for only one LHSI pump in operation vice both pumps. This modeling assumption has the affect of increasing overall system flow rates and the calculated transport of the air void through the pump.

The LHSI pumps at Unit 1 are two-stage, vertically mounted, deep-well, centrifugal pumps. The LHSI pump bowls and impellers are located near the bottom of the pump casing, with the casing inlet approximately six feet above the first stage impeller inlet.

The configuration is such that after the flow enters the casing inlet, it is directed downward by turbulence flow (swirl limiter) vanes. From the exit of the swirl limiter, the flow continues downward around the pump discharge column and two impeller bowls to the first stage impeller inlet. The contractors model calculated that, while a 30% void fraction may enter the pump casing, only a nominal 4% void fraction would travel to the pump impellers. This was based on the vertical configuration and velocity profiles calculated for the pump suction casing flow path. The contractors model shows that a majority of the air void would travel up through an inner annulus area, between the swirl limiter and the pump discharge column, and not travel down to the pump impeller. This is the predicted consequence of the relative air bubble buoyancy velocities and the associated Froude numbers calculated from downward water velocity profiles. Based on this modeling, the contractor and FENOC concluded that the pumps would have always remained operable during and after the ingestion of the air voids.

The team noted that, while the inputs to the model were determined to be reasonable, the team had concerns relative to the accuracy and uncertainty involved with the determination of the air transport mechanism within the pump suction casing.

Specifically, the team was concerned that air transport within the pump may have inaccuracies associated with it based on the unknown configuration of the pocket of air as it progresses through the inlet of the pump, through the swirl limiters, and into the annulus area below. The team noted that bubble transport phenomenon in the vertical direction is, in part, a function of bubble size, which impacts bubble velocity in the upward direction (buoyancy). The contractors analysis acknowledges that the precise size and distribution of the air void/bubbles ingested through the pump casing are not specifically known, but are predicted based upon engineering judgment. Accordingly, the Froude number criteria used in the analysis for vertical transport of air through the pump will propagate the uncertainty of this prediction through the remainder of the analysis. Notwithstanding, the team noted that FENOCs approach to evaluating the issue was not unreasonable and did provide an evaluation of the thermal hydraulics and assumed air transport through the LHSI pumps. However, because of the potential uncertainty involved with the determination of the void fraction transport mechanism within the pump casing and the inherent uncertainty of any analytical model, the team performed an independent bounding analysis to evaluate the air void impact on past operability of the LHSI pumps. The teams results were in general agreement with FENOCs past operability determination. A summary of the teams bounding analysis is documented in Attachment C.

No findings of significance were identified.

3.6 Risk Assessment of the As-Found Condition

a. Inspection Scope

Prior to the initiation of the Special Inspection Team, the Region I Senior Reactor Analyst (SRA) performed a conditional core damage probability (CCDP) assessment which conservatively bounded the potential risk significance of the degraded condition, assuming the as-found air voids may render both LHSI pumps inoperable following swap-over to the containment sump recirculation phase. The initial CCDP estimate was performed in accordance with Inspection Manual Chapter (IMC) 0309, Reactive Inspection Decision Basis for Reactors. The SRA used the Beaver Valley Unit 1 Standardized Plant Analysis Risk (SPAR) model and associated Graphical Evaluation Module (GEM) to evaluate the potential risk significance of this condition. The results of the IMC 0309 assessment are documented in report section 1.3 above.

b. Final Risk Estimate Following team review and independent verification of the impact of the air voids on LHSI pump operability, the team concluded that the LHSI pumps would have remained operable had the air voids been ingested via initiation of sump recirculation flow.

Consistent with IMC 0609 conditional core damage probability assessment methodology, this LHSI system design deficiency did not result in a loss of operability or safety function, and therefore was of very low (less than 1E-6) safety significance.

Accordingly, the identified condition (containment sump suction piping air voids) did not result in any appreciable increase in risk to core damage for postulated design basis events.

4OA6 Meetings, Including Exit

On November 14, 2008, the team conducted a debrief meeting with Mr. Peter Sena and other members of his staff to discuss the status of the teams inspection activities, to date. On January 29, 2009, the team presented the inspection results to Mr. Mark Manoleras and other members of the BVPS staff. Proprietary information that was reviewed during the inspection was returned to FENOC.

ATTACHMENT A

SUPPLEMENTAL INFORMATION

KEY POINTS OF CONTACT

Licensee personnel

Rich Bologna Manager, Plant Engineering

Gary Cacciani Staff Nuclear Engineer

Sam Checketts Manager, Site Operations

Kim DeBerry Staff Nuclear Engineer

Bill Etzel Senior Consultant

Ken Frederick Senior Consultant

Steve Hovanec Supervisor, Nuclear Supply System Engineering

Colin Keller Manager, Regulatory Compliance

Carmen Mancuso Manager, Design Engineering

Mark Manoleras Director, Site Engineering

Jim Mauck Regulatory Compliance Specialist

Dan Mickinac Advanced Nuclear Specialist

Katie Mitchell Senior Nuclear Engineer

Dave Price Supervisor, Nuclear Mechanical Engineering

Mike Ressler Supervisor, Nuclear Engineering Analysis

Brian Sepelak Regulatory Compliance Supervisor

Phil Slifkin Staff Nuclear Engineer

George Storolis Nuclear Shift Manager

LIST OF ITEMS OPENED, CLOSED, AND DISCUSSED

Opened/Closed

05000334/2008009-01 FIN Inadequate extent-of-condition and applicability review of Operating Experience involving ECCS pump and piping voids.