ML12089A645
| ML12089A645 | |
| Person / Time | |
|---|---|
| Site: | Indian Point  |
| Issue date: | 02/29/2012 |
| From: | Pitkin L Indian Point |
| To: | Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| Shared Package | |
| ML12089A633 | List: |
| References | |
| RAS 22135, 50-247-LR, 50-286-LR, ASLBP 07-858-03-LR-BD01 IP-PRT-12-00003, Rev 0 | |
| Download: ML12089A645 (42) | |
Text
ENT000326 Submitted: March 29, 2012 ATTACHMENT 9.1 ENGINEERING REPORT COVER SHEET & INSTRUCTIONS SHEET 1 oF2 Engineering Report No. IP-RPT-12-00003 Rev 0 Page IA of 42 ENTERGY NUCLEAR Engineering Report Cover Sheet Engineering Report
Title:
DISCUSSION ON AGING OF THE INDIAN POINT 2 SPENT FUEL PIT Engineering Report Type:
New r2l Revision 0 Cancelled 0 Superseded 0 Superseded by:
Applicable Site(s)
IPI 0 IP2 r2l IP3 0 JAF 0 PNPS 0 VY 0 WPO 0 ANOI 0 AN02 0 ECH 0 GGNS 0 RBS 0 WF3 0 PLP 0 EC No. 34889 Report Origin: o Entergy r2l Vendor Vendor Document No.:_A11357-R-001 Quality -Related: DYes r2l No Prepared by: Lucius Pitkin Date: 2-16-12
~---------------------
Responsible Engineer (Print Name/Sign)
Design Verified: _________________-.:::..N'-'-A~______________ Date:
Design Verifier (if required) (Print Name/Sign)
Reviewed Date: 2-17-12 Approved by: ___R_ic_'h-=-D_ra_k...,.e-,: Date: 2-17-12 Supervis,~,-,~==
Lucius Pitkin, Inc. Consulting Engineers Advanced Analysis Fitness-For-Service Failure & Materials Evaluation Nondestructive Engineering DISCUSSION ON AGING OF THE INDIAN POINT 2 SPENT FUEL PIT Report No: A11357-R-001 Revision No: 0 February, 2012 Prepared for ENTERGY NUCLEAR OPERATIONS, INC.
Indian Point Energy Center Prepared by Paul Bruck Thomas Esselman New York Office and Laboratory:
304 Hudson Street, New York, NY 10013-1015 Tel: 212-233-2737 Fax: 212-406-1417 www.luciuspitkin.com New York, NY Boston, MA Richland, WA Ensuring the integrity of todays structures for tomorrows world TM
DOCUMENT RECORD Document Type: Calculation Report Procedure Document No: A11357-R-001 Document
Title:
Discussion on Aging of the Indian Point 2 Spent Fuel Pit Client: Entergy Nuclear Operations, Inc.
Client Facility: Indian Point Energy Center (IPEC) (Unit 2)
Client PO No: 2011-0817-01 Quality Nuclear Safety Related? No Yes Assurance:
Computer NO1 1. Check NO when EXCEL, MathCAD and/or similar programs are used Software since algorithms are explicitly displayed.
Used: YES2 2. Include Software Record for each computer program utilized.
NO Instrument Used: 3. Include Document Instrument Record.
YES3 Approval Design Revision Preparer Checker Approver4 Date Verification 0 02/16/12 Paul Bruck Thomas Esselman Paul Streeter N. A. Paul Bruck 4
The Approver of this document attests that all project examinations, inspections, tests and analysis (as applicable) have been conducted using approved LPI Procedures and are in conformance to the contract/purchase order.
(Include any Title Sheet and Attachments in page count. Document Back Page 2 of 40 Total Pages Cover, if utilized, not included in page count)
This document is rendered upon the condition that it is not to be reproduced wholly or in part for advertising or other purposes over our signature or in connection with our name without special permission in writing. Be advised that all materials submitted for evaluation will be retained for six months. After such time, all material will be discarded unless otherwise notified in writing to retain beyond six months Form: LPI-3.1-Rev-4-Fig-5-2
REVISION RECORD Revision Date Description of Change Reason No.
0 See Original Issue Document Record Form: LPI-3.1-Rev-4-Fig-5-7 Report No: A11357-R-001 Page 3 of 28 Revision: 0
TABLE OF CONTENTS Cover Sheet..1 Document Record2 Revision Record...3 Table of Contents.4 1.0 INTRODUCTION......................................................................................... 5
2.0 BACKGROUND .......................................................................................... 5
2.1 Design Details .......................................................................................... 5
2.2 Fabrication Details ................................................................................... 6
2.3 Historical Leakage ................................................................................... 7
2.3 SFP Inspections ....................................................................................... 8
3.0 AGING OBSERVATIONS ......................................................................... 16
3.1 Time Dependent Aging ......................................................................... 16
3.2 Spent Fuel Pit Aging ............................................................................. 17
3.2.1 Degradation of the Stainless Steel Liner ......................................... 17
3.2.2 Degradation of the Reinforced Concrete Structure ......................... 19
3.3 Specific IPEC Unit 2 SFP Observations................................................ 21
4.0
SUMMARY
AND CONCLUSIONS ............................................................ 25
5.0 REFERENCES ......................................................................................... 27
APPENDICES:
A Calculation of Potential Volume in Interstitial Space (4 pages total)
B Estimation of Concrete Service Life based on Hypothetical Corrosion (2 pages total)
C Estimation of Percentage Areas Covered by NDE (6 pages total)
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1.0 INTRODUCTION
In the past, leakage of inventory from the Indian Point Energy Center (IPEC) Unit 2 Spent Fuel Pit1 has occurred. Entergy, together with the prior owner of the Plant have taken steps to identify the source of leakage and implement repairs intended to preclude additional leakage. This White Paper is prepared to assess the likelihood of future leakage as a result of aging of the structure.
2.0 BACKGROUND
The background discussion provides information associated with the design and construction of the Unit 2 Spent Fuel Pit, identification of prior leakage locations, repairs, and inspection observations.
2.1 Design Details The Spent Fuel Pit (SFP) is a reinforced concrete structure located in the Fuel Storage Building (FSB). The FSB is a framed structural steel superstructure with metal roof and siding. The walls and floor of the SFP are stainless steel lined. The pit is filled with borated water with the submerged spent fuel contained in approximate 15 high fuel racks that sit on the floor of the pit.
The SFP has concrete walls that are 4-0 and 6-3 thick with a 3-0 thick concrete base mat; the pit is approximately 40 deep. The structure is founded on rock beneath the base mat at EL. 51-7 (see Figure 2-1 and Figure 2-2). The SFP is partially embedded in the ground. The ground level outside of part of the east wall is at EL. 79-0 and the ground level outside the north wall is at EL. 95-0. The portion of the east wall above EL. 79-0 is exposed. The south wall is internal to the FSB and is exposed down to a slab at EL. 77-6, i.e. the truck bay floor (see Figure 2-2). The west wall is partially exposed to the foundation slab.
1 Indian Point 2 design documents refer to the Spent Fuel Pit. Common industry terminology is Pool. The term Pit is used herein.
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The SFP walls and floor are lined with multiple interconnected 1/4 thick stainless steel plates. Each plate has a nominal dimension of approximately 6-0 by 20-02 and is attached directly to the concrete by the use of embedded steel (T beam) sections in the concrete as shown in Figure 2-4.
The embedded steel sections are at every plate seam and run both vertically and horizontally. Each liner plate is welded to the adjacent liner plate and to the embedded steel sections. Each embedded steel section is welded to the adjacent embedded steel section and form a cross where they meet (see Figure 2-4). Once the liner plates are welded to the embedded steel section and to each other, they effectively create individual cells (majority being 6-0 by 20-0) comprising any irregular space behind the liner plate and the concrete surface if the liner plate does not sit flush with the concrete. Within the interior area of a typical liner plate, there are approximately 15 to 20 plug welds to the embedded steel sections, as shown in Figure 2-4. The plug welds provide additional attachment points to the concrete walls.
The liner plates are fabricated from stainless steel ASTM A240 Type 304 plate. The embedded steel sections are carbon steel. Stainless to carbon steel welding was performed in two passes [1, 3a]3 to minimize carbon steel exposure to the pool water.
2.2 Fabrication Details Fabrication and installation of the SFP stainless steel plates was performed in accordance with the specification requirements [1]. Items of note identified in the specification include:
x Plates were in accordance with ASTM A240 Type 304 x All seam welds and plug welds were performed with a minimum of two passes, using stainless electrode E308.
2 Plates of smaller dimensions occur in certain locations because of overall SFP geometry and the practicalities of fabrication/installation.
3 Numbers in [xx], refer to references listed in Section 5.0.
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x All welds were required to be sound throughout, with full penetration of plate thickness. No cracks or zones of incomplete penetration in any weld pass were permitted.
x All slag or flux remaining on any bead or layer or welding was to be removed before applying the next layer.
x Cleaning of each bead or layer was to be performed by a stainless steel power brush. All defects or irregularities disclosed by inspection would prevent proper disposition of succeeding bead were to be removed.
x Visible defects, such as cracks, pinholes, and incomplete fusion were required to be completely removed and the welds repaired by rewelding.
x All plate welds were tested for leak tightness using a vacuum box and soap bubble test. The box was specified to be evacuated to at least a 5 psi pressure differential with the atmospheric pressure. The vacuum was specified to be held for a minimum of 5 minutes with zero leakage.
2.3 Historical Leakage In May 1992, efflorescence-like deposits were observed on the outer surface of the SFP wall at the northeast corner [4a]. The deposits were located on the exposed portion of the east wall of the SFP and the northeast extension of the north wall, which supports a steel column above the SFP. With the help of divers, a small hole was discovered in the stainless steel liner approximately at EL. 88 ft., about 5 below the water surface in the northeast corner. Maintenance records on the SFP indicated that work was performed on the liner in October of 1990. An attachment to the liner was burned off during maintenance work. It was postulated that the liner was punctured at that time [4a, 4b] allowing water to penetrate the wall and then evaporate on the outer surface leaving the observed efflorescence-like boron deposits. The root cause of the defect was an inadvertent maintenance error. Following identification of the leak location, the liner was repaired in June 1992 by welding a steel box over the liner perforation.
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In August 2005, during construction activities associated with the Independent Spent Fuel Storage Installation (ISFSI) Project, moisture was observed on the outer surface of the SFP wall on the south end of the SFP at EL. 64 ft at an indication in the wall [5a]. The moisture was observed on the western-most end of a mostly horizontal 9-2 long hairline crack. As the excavation continued, another mostly horizontal hairline crack at approximately Elevation 59-11 did not dry out upon being exposed to the air and an approximate 3 ft.
length remained damp. Radiochemical analysis was performed on the fluid emanating from the cracks. It was determined to be consistent with spent fuel pit water that was approximately 6 to 10 years old [5a], indicating that the leaking fluid may have been from past leaks. As a result, on September 1, 2005, Condition Report CR-IP2-2005-03557 [5a] was issued. As part of the investigative work, a permeability assessment of the concrete was performed
[8g] to assess potential transport time of the water through the concrete.
Additionally, the potential volume of liquid from leaks that might be resident in the interstitial space between the liner and concrete surface was estimated to be as much as 1,400 gallons, based on the assessment summarized within Appendix A herein. Entergy designed and installed a collection box for this location [6], shown in Figure 2-5, to collect and drain off moisture prior to backfilling the region to complete the necessary ISFSI infrastructure.
In 2011, it was hypothesized that SFP water could have migrated into the interstitial space between the back side of the liner and concrete surface through electrical junction boxes mounted on the wall of the liner if the SFP was filled to the level of the high water level alarm (see Figure 2-6).
Administrative controls and a temporary modification have been enacted to ensure that the SFP is not filled to a level where water could enter these electrical junction boxes. A design change has been designed and is planned to permanently seal this potential leakage path [7]. Installation of this design change is scheduled for 2012.
2.3 SFP Inspections In 2005 a remote visual inspection of the accessible areas of the SFP was performed [5b], with the intent to locate any potential source of leakage. This inspection covered the cask loading area (region inside the SFP close to Report No: A11357-R-001 Page 8 of 28 Revision: 0
observed leakage on the south wall outside the SFP), together with the SFP walls from approximately 2 feet above the fuel racks to the water surface.
The fuel racks are approximately 15 feet above the floor of the pit. This inspection identified three areas with brown staining as possible leak locations. Following this inspection a diver entered the pool and performed a vacuum box test of the upper two locations. No detectable leakage was identified. As part of the inspection by the diver, a coat of epoxy material (Bio-Dur561) was applied over any identified weld anomalies [5c], even though leakage had not been detected. The third indication was subsequently tested with no indication detected [5d].
An Underwater Construction Corporation diver examined the SFP walls to a depth of approximately 20 feet from the surface [5d] - a distance to maintain safety for the diver. Any identified indications were reviewed by Entergys metallurgist and seven indications were identified as having the greatest potential for through-wall leakage. The locations were vacuum box tested with no signs of leakage identified.
In 2006, the walls of the Spent Fuel Pit down to the top of the racks were remote visually inspected by ROV Technologies [5f]. This inspection did not reveal any indications that the inspection team would expect to be a through-wall leak location.
A Nondestructive Examination (NDE) of the SFP transfer canal region (Figure 2-3) was also performed. The transfer canal was drained for this inspection.
This inspection used a combination of vacuum box testing, ultrasonic testing (UT), penetrant testing (PT), and visual inspections (VT) to identify any indications. All inspections were performed by qualified Nondestructive Examination (NDE) personnel. This inspection identified a through-wall indication at a plug weld (P-10) in the north wall of the transfer canal liner, approximately 25 feet below the surface [5g]. A typical plug weld configuration is shown in Figure 2-4, and the identified indication is shown in Figure 2-7. This indication was repaired in 2007 after the inspection.
The identified through-wall indication was removed for laboratory failure analysis [8a]. The findings of the laboratory analysis concluded that the Report No: A11357-R-001 Page 9 of 28 Revision: 0
identified through-wall leakage at the plug weld was the result of interconnected bubble porosity that extended through the thickness of the plug weld metal. The porosity was introduced at the time of the welding during construction. The canal side end of the porosity channel was likely opened by the plug weld being ground flush to the plate surface during construction. Thus, the apparent root cause of this leak was a welding defect that occurred during the initial installation of the SFP liner.
The examined location that included the through-wall leak contained no discernible indications of corrosion, supporting the hypothesis that the leak existed from original fabrication. The failure report [8a] identified numerous superficial rust staining or spotting on the liner plates, identified as resulting from handling of the stainless steel plates during fabrication. The report stated that microbiological influenced corrosion (MIC) may have contributed to some degradation of the canal floor. Indication of MIC in examination of the walls of the transfer canal was not identified. Additionally, MIC could not exist in the floor of the SFP due to the radiation from the fuel. Examination of the floor of the transfer canal did not identify any unsatisfactory indications.
No other progressive degradation mechanisms were detected based on both in-situ inspections, and laboratory examination of the removed weld sample.
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Ele v ation Crane z.-122' '()O" Rail 95'.()O" SPENT FUEL-f/'
PIT 51 ' -7" Figure 2-1: Fuel Handling Building Looking North ELEVATION 135'.()O" CRANE TRUCK BAY 95'.()O"
~
TRANSFER FAN HOUSE CANAL 51'-7" .
OBSERVED CRACK SPENT INDICATION FUEL PIT Figure 2-2: Fuel Handling Building Looking East Report No: A11357-R-001 Page 11 of 28 Revision: 0
Figure 2-3: Spent Fuel Pit Looking Northeast Report No: A11357-R-001 Page 12 of 28 Revision: 0
Cut Section T Beam Periphery continuous weld Interior plug weld Cut Section T Beam Figure 2-4: SFP Steel Plate Fabrication Liner Details [1, 2]
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Figure 2-5: Collection Box on South Side of Spent Fuel Pit Outer Wall Report No: A11357-R-001 Page 14 of 28 Revision: 0
Potential Leak Path Figure 2-6: Configuration of Electrical Light Enclosures Figure 2-7: Plug Weld Flaw in Transfer Canal Report No: A11357-R-001 Page 15 of 28 Revision: 0
3.0 AGING OBSERVATIONS 3.1 Time Dependent Aging A component or structure life may be related to time in service. The life and the timing of failure are dependent on the stressors that are acting on the component or structure and the degradation mechanisms that are active in the component or structure. The life of a specific component or structure is classically defined by a bathtub curve. This is shown in Figure 3-1. In general, three distinctive ranges can be identified on this curve. In the majority of cases, failures are more frequent in the beginning of service than at later stages.
Structural failures early in life can be caused by improper construction, flaws, improper materials, and other similar defects. The higher probability of failures early in life is referred to as the early failure period or run-in period.
After the passage of time, such failures become less likely and the probability of failure decreases and becomes stable. The failure rate is low and becomes relatively constant. This is termed the constant failure or useful life period. Eventually, time dependent aging mechanisms manifest themselves and the failure rate starts increasing. This increasing probability of failure range of the bathtub curve is termed the wear-out period. Bath-tub curve properties (run-in, constant failure and wear-out) are directly related to the concepts of structural reliability [9]. The bathtub curve for a specific structure or component is really an envelope of specific time dependent degradation mechanisms. If a degradation mechanism is not active, it will not contribute to a late-in-life increase in the probability of failure. For a structural system like a spent fuel pit that is comprised of the liner, the concrete, and the reinforcing steel, the shape of the bathtub curve will depend on specific degradation mechanisms that are either active or inactive. The three distinct regions are evident for such a structural system, but the time that the probability of failure starts to increase is highly dependent on the mechanisms of degradation.
The degradation mechanisms that occur in the run-in period are different than the ones that occur in the wear-out period. In the run-in period, failures are controlled by misalignment, construction defects, bad welds, and other similar mechanisms. In the wear-out period, the mechanisms are more likely to be Report No: A11357-R-001 Page 16 of 28 Revision: 0
fatigue, corrosion, stress corrosion cracking, and irradiation embrittlement.
These are the types of mechanisms that can eventually lead to an increase in probability of failure in even a well-made and well-maintained component or structure. In order to predict the time that the likelihood of failure of a component begins to increase, the one or two dominant mechanisms that are likely to manifest themselves need to be known and understood. If those mechanisms can be determined and it is possible to define the behavior of those mechanisms, then the failure likelihood versus time can be defined for the structure.
3.2 Spent Fuel Pit Aging The spent fuel pools of pressurized water reactors (PWRs) such as Indian Point contain borated water. The IPEC Unit 2 pool utilizes a stainless steel liner attached to a reinforced concrete structure, with the use of stainless steel intended to minimize corrosion from the contained borated water. The IPEC Unit 2 reinforced concrete SFP structure is supported directly on a foundation founded on rock. The concrete walls of the SFP structure are above and below grade.
Degradation of the primary subcomponents of the SFP -- namely the stainless steel liner and steel reinforced concrete -- is discussed below.
3.2.1 Degradation of the Stainless Steel Liner The failure analysis report [8a] concluded that a discovered pin-hole leak in the fuel transfer canal was caused by porosity introduced during initial welding. The leak path was most likely present from the time of construction of the fuel transfer canal.
The report states that the evaluation:
..found no evidence of the following corrosion modes:
Crevice (occlusion cell) corrosion
Intergranular corrosion Report No: A11357-R-001 Page 17 of 28 Revision: 0
Weld decay
Chloride-induced stress corrosion cracking (Chloride -SCC)
Dissimilar weld metal corrosion And that: . . . uniform corrosion was below detection limits.
These are the degradation mechanisms that are most likely to cause an increase in the probability of failure. The fact that they were not active is important to the definition of the bathtub curve for the spent fuel pit.
The failure analysis report also states that a contribution from microbiologically influenced corrosion (MIC) on the floor of the fuel transfer canal portion of the SFP could not be ruled out. There was some evidence of corrosion products that appeared similar to those that would be found from MIC. However, there were no leaks found on the floor of the fuel transfer canal. So if MIC were occurring on the floor of the fuel transfer canal, it had not caused any leakage. MIC would not be a viable corrosion mechanism on the majority of the floor of the fuel storage portion of the SFP because of radiation from the spent fuel. No indications of MIC were identified in examination of the transfer canal walls or on the walls of the SFP above the fuel storage racks.
Based on the inspection of the SFPs Transfer Canal and of the associated failure analysis report [8a], there is currently no active time-dependent aging mechanism occurring in the stainless steel liner of the canal. The direct inspection of the transfer canal represents 22% of the total surface area of the liner4 and the inspection of the SFP walls and Cask Load area represent an additional 45% of the total surface area. As a result, it is reasonable to conclude the comprehensive inspection of 67% of the total liner surface area is a representative sample for the spent fuel pit. Inspection findings would be directly relatable to the 33% of the total surface area that was not inspected.
In reference to the Bathtub Curve depicted in Figure 3-1, the current state of the pool liner is depicted by the flat part of the curve. There is no indication 4
Total surface area covers the SFP area and Transfer Canal area, (see Appendix C).
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that an increase in the likelihood of failure - the start of the wear-out period -
is occurring or would be expected to occur soon. Further, absent an active degradation mechanism, this also indicates that no new cracks would be expected to develop. Any flaws or pin-hole leaks in the stainless steel liner that have been present since construction or occurred later from maintenance/fuel storage activity will remain, but they will not grow.
The concrete floor and walls of the SFP are significant, being 3-0 thick for the floor slab and 4-0 to 6-3 thick for the walls. Typically, leakage through large concrete structures does not follow a continuous path, unless a defined path is present. The flow quantity along a path in the concrete structure may decrease considerably with time depending on the potential for specific paths to autogenously heal [10]. This process is dependent upon items such as further hydration of the concrete, expansion of the concrete in the crack flanks, crystallization, and closing of the cracks by particles in the flowing water. Autogenous healing can lead to the water finding alternate leakage paths, with the process repeating. Autogenous healing of the leakage path leading to the moist region along the south wall of the SFP (where the collection box is present) could result in differing flow rates to the collection box. This also has the potential for leakage to find other migration paths outside of the collection box.
3.2.2 Degradation of the Reinforced Concrete Structure Degradation of the reinforced concrete structure has previously been evaluated for the Unit 2 SFP.
Following the identification of leakage from the pool in 1992, an investigation was performed of potential concrete degradation and reinforcement corrosion that resulted from pool borated water migrating through the reinforced concrete structure [8d, e]. This study concluded that the strength of the concrete had not degraded, and that no corrosion of the steel reinforcement had occurred.
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In 2005, rebar was intentionally exposed and inspected in the observed crack locations; there was little or no corrosion observed. A photo of the exposed rebar is provided in Figure 3-2.
Following the identification of moisture migration through the south wall of the SFP in 2005, an investigation of the structural capability of the SFP was performed [8e]. The conclusion was that the pool structure would have sufficient strength throughout the period of extended operation, i.e. greater than 60 years of life (see further discussion on this item in Appendix B). The corrosion rate selected for the assessment was a conservative bounding estimate even though there were no indications of pool structure corrosion. If corrosion were occurring, it would only be in the early stages of formation and not observable.
Additionally, Entergy has performed concrete and reinforcement steel assessments at other IPEC structures subjected to borated water migration through the concrete [8f]. These include:
x The Unit 2 reactor refuel cavity concrete wall was inspected, sampled and tested to assess any potential damage to the concrete and reinforcement steel as a result of cavity water containing boric acid migrating through the refuel cavity concrete during periods of reactor refueling. As concluded within the report [8f], and is evident in Figure 3-3, no indication of concrete damage beyond some superficial surface leaching in some samples, was evident. There was no indication of reinforcement steel corrosion.
x The Unit 1 spent fuel pool concrete wall was inspected, sampled, and tested to assess any potential damage from contained spent fuel pool water migrating through the walls as a result of leakage. Such leakage has been identified dating back to the early 1990s [8f]. As concluded in the report [8f], no indication of concrete damage or steel reinforcement corrosion was evident.
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3.3 Specific IPEC Unit 2 SFP Observations Three prior indications of spent fuel pool liner leakage have been identified (see Section 2.0).
- 1. 1992 - Efflorescence deposits were observed on the northeast corner of the SFP. These were identified as resulting from a liner tear occurring in 1990 as a result of maintenance activities. The defect was repaired in 1992.
- 2. 2005 - Moisture-like indications on the south wall of the SFP were identified during excavation work for ISFSI project infrastructure. A through-wall flaw in the transfer canal was identified as the potential source, and repaired in 2007. A collection box was added to the south wall to collect, channel and monitor leakage from this region [6].
- 3. 2011 -- A potential leakage path through underwater lighting electrical outlet boxes was identified when pool water might be at a high level.
Administrative controls were added to maintain pool level below this potential leak path and a temporary repair was implemented, with a permanent repair [7] scheduled for 2012.
The above three identified leak paths are not associated with age-related degradation mechanisms and are not indications that the likelihood of failure is increasing.
From the inspections of the Unit 2 SFP already performed, the following observations are made.
- 1. Fuel Transfer Canal - The canal has generally been filled during the life of the plant. To perform the extensive examination of the transfer canal, it was drained and examined in detail for 100% inspection using a combination of vacuum box testing, UT, PT and VT. This represented approximately 22% of the total wall and floor area of the Spent Fuel Pit (with the transfer canal included). During this examination, a single through-wall indication was identified, which was categorized, weld repaired and subsequently tested as acceptable.
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- 2. Spent Fuel Pit - the region above the fuel racks in the SFP plus the cask load pit area were remotely inspected using visual techniques.
This represented approximately 45% of the total wall and floor area.
- 3. Spent Fuel Pit - the floor and walls of the SFP adjacent to and below the racks. This area was not examined.
- 4. The resulting inspected area (SFP and Transfer Canal) is approximately 67% of the total surface area.
No active corrosion mechanisms were detected in the 67% of the pool and transfer canal that was inspected. Given the large percentage area of the pool that has been inspected with no active corrosion mechanism identified, it would be highly unlikely there is an undetected age-related mechanism occurring in the non-inspected portions of the pool. Assessment of inspection areas are summarized in Appendix C.
The presence of MIC as an active corrosion mechanism in the transfer canal could not be ruled out [8a], but would generally only occur at the floor. If MIC were occurring in the transfer canal, it did not penetrate the floor liner in 35 years of operation. The presence of MIC on the floor or walls of the fuel storage portion of the SFP is not viable, since MIC would be unable to survive in the radiation fields. On these bases, it is unlikely that MIC could become an active contributor to leakage anywhere in the SFP.
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'0 Run*in I Level or declining failures Wear*out
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Figure 3-3: Exposed Rebar from IPEC 2 Reactor Cavity Showing Rebar Condition with No Corrosion Report No: A11357-R-001 Page 24 of 28 Revision: 0
4.0
SUMMARY
AND CONCLUSIONS The Indian Point Unit 2 Spent Fuel Pit (SFP) has leaked in the past. A leak was identified in 1992, dating back to 1990 which was subsequently repaired. As a result of leakage identified in 2005, a collection box was attached to the south wall of the SFP to collect any leakage local to this area and drain the collected water for sampling and appropriate treatment and disposal. It is likely that any leakage that migrates through a liner flaw or hole will collect and fill an interstitial space between the back side of the liner and the concrete surface.
Based on sampling and collected volume from the collection box, continued leakage from the pool into the collection box appears to be occurring. This leakage could be a result of draining of collected water in the interstitial space from prior liner flaws or it could be from a current leak path.
Extensive inspection of the SFP and the attached transfer canal has been performed in the past covering approximately 67% of the total surface area. Past nondestructive examination (NDE) inspections have included ultrasonic, penetrant and direct and remote visual (UT, PT VT) methods, together with vacuum box testing of welds and indications. A maintenance inflicted tear in the liner was identified and repaired in 1992. In 2007 the transfer canal was drained and inspected, and a weld flaw identified as being from original construction was found and subsequently repaired. Examination of the drained transfer canal, together with failure analysis of the identified weld flaw did not identify any time dependent aging mechanisms occurring, providing additional confidence in the condition of the SFP liner. Absent a time-dependent active degradation mechanism, the only leakage paths through the pool would be weld defects that have been there since construction or maintenance/fuel storage activity inflicted damage that could have occurred at a later date. These would not be expected to increase in size as the flow rate through such a flaw or hole is very small and the driving pressure is also very small. At very low flow rates and with no active mechanisms that would open up an existing defect, it is likely that the spent fuel pool liner will be stable. No new leaks or increases in leakage rates through any existing flaws/holes in the stainless steel liner are expected.
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The concrete walls of the SFP have been structurally assessed for integrity conservatively considering corrosion occurring in the reinforced concrete as a result of borated water migrating through the concrete matrix. Corrosion rates used in this study were conservatively selected. This evaluation derived a life of the SFP walls that exceeds the design life through the period of extended operation. Based on all current available information, examination results, and testing performed on other IPEC structures, active corrosion of the SFP concrete structure does not appear to be occurring at this time.
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5.0 REFERENCES
- 1. Entergy Indian Point 2 Specification 9321-01-225-6 Specification for Installing Stainless Steel Plates for Spent Fuel Pit and Transfer Canal.
UE&C January 1967.
- 2. Entergy Indian Point 2 Specification No. 9321-01-13-1, Concrete Work
- 3. Entergy Drawings:
- a. 9321-1301 and 1302, Fuel Storage Building Tank Liner Plates - Sheet 1 and 2.
- b. 9321-F-1026 Concrete and Foundation Notes
- c. 9321-F-1196, 1197, 1198, 1199, 1200 Fuel Storage Building Concrete Details
- 4. 1992 Leak Information:
- a. (ConEdison) SAO-132 Condition Report Leak in the Spent Fuel Pool East Wall, Event Date 5/7/1992.
- b. UE&C Report No. 8904.019-S-S-002 Rev. 0 Indian Point Unit 2 Evaluation of the Spent Fuel Pool Walls, March 1993.
- c. LPI Technical Report No. 8281, Report No. ME-3802, Evaluation of Spent Fuel Pools Walls - Indian Point 2 Nuclear Power Plant
- 5. 2005 Leak Information:
- a. Entergy Condition Report CR-IP2-2005-03557, Hairline crack several feet in length was found at approximately 60 foot level of Unit 2 spent fuel pool south wall on the loading bay side, Dated 09/07/2005.
- b. Entergy Work Order WO IP2-05-25553 Remote Visual Inspection -
Cask Load Area, plus Liner Walls surface to 2 feet above rack
- c. Entergy Work Order WO IP2-05-26413 Diver Applied Epoxy to Indications
- d. Entergy Work Order WO IP2-05-26214 Underwater Construction Inspection - Surface to 20 feet below, including Vacuum Box of Indications
- e. Entergy Work Order WO IP2-06-20176 ROV Technologies 20 ft below surface to Rack Wall Inspection Report No: A11357-R-001 Page 27 of 28 Revision: 0
- f. Entergy Work Order WO IP2-06-23700 ROV Technologies under Rack Inspection
- g. Entergy Condition Report CR-IP2-2007-03550 During NDE inspection of Unit 2 transfer canal, a small leak was identified during vacuum box testing.
- 6. Entergy Modification ER-05-2-108, Rev. 0 IP2 Spent Fuel Pool Liquid Collection System.
- 7. Entergy Engineering Change (EC) 31357, Removal of Spent Fuel Pool Flood Light Electrical Boxes from the Spent Fuel Pool
- 8. Entergy Engineering Reports:
- a. Honeywell Document No. 146986-TS1354P-01, Rev. 0 Indian Point Unit 2 Transfer Canal Liner Indication and Degradation Root Cause Report
- d. Report No. 8904.019-S-S-002 Rev. 0 Indian Point Unit 2 Evaluation of the Spent Fuel Pool Walls, March 1993.
- e. IP-RPT-05-00313, Rev. 0 Evaluation of Spent Fuel Pools Walls -
Indian Point 2 Nuclear Power Plant
- f. IP-CALC-05-00952, Rev. 0 Assessment of Concrete Aging from Selected Indian Point Structures
- g. IP-RPT-05-00392, Rev. 0 Study of the Spent Fuel Pool Pit Permeability.
- 9. Tichy, M. Applied Methods of Structural Reliability, Springer Press, 1993.
- 10. Ramm W, & M. Biscoping Autogenous Healing and Reinforcement Corrosion of Water-Penetrated Separation Cracks in reinforced Concrete, Nuclear Engineering & Design #179, 1998. Elsevier Science.
- 11. American Concrete Institute ACI 117-06 Specification for Tolerances for Concrete Construction and Materials and Commentary Report No: A11357-R-001 Page 28 of 28 Revision: 0
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APPENDIX A Evaluation of Volume in Interstitial Space (4 pages total)
Report No: A11357-R-001 Page A1 of 4 Revision: 0
A1. Calculation of Volume in Interstitial Space A leak in the liner could result in SFP water filling any space between the backside of the liner and the concrete surface, as a result of imperfections of flatness of the concrete surface when the wall was originally poured. The wall was formed using normal concrete forms, bolted directly to the embedded T beams. When the forms were unbolted the surface may or may not be perfectly flat. Additionally, the liner plates (typically 6 ft x 20 ft x 1/4 thick) may not have been flat also. As a result a space may be present between the liner and the concrete surface. This space, referred to as the interstitial space may result in leaked water filling this space as a result of water pressure from the SFP equalizing across a leak location.
Surface finish of the concrete is not identified within the concrete specification [2]
or concrete drawings [3b, c]. ACI 117 [11] provides typical construction guidance. For such a hidden wall, a Class B finish would provide for a 1/4 gap over the typical 5 to 6 feet span between the embedded T beams.
Figure A1-1 shows a typical liner cell as described in Section 2.1, based on liner drawing details [3]. Calculate volumes as follows:
Area of one liner plate section or cell (shown in Figure A1-1):
Area = 72.375 x 240.75 = 17424.3 in2
= 121 ft2 Calculate volume of water5 in interstitial space between steel liner and concrete:
Case 1 - 1/4 gap behind entire liner plate:
17424.3 in2 x 1/4 in = 4356.1 in3 = 18.9 gallons Case 2 - liner tight to concrete on both vertical edges with 1/4 bulge in center of plate 12.6 gallons (Calculated using AutoCAD layout) 5 1 cubic inch of water equals 0.004329 (us) gallons.
Report No: A11357-R-001 Page A2 of 4 Revision: 0
Case 3 - liner tight to concrete on all four edges with 1/4 bulge in center of plate 8.4 gallons (calculated using AutoCAD)
Calculate total volumes for spent fuel pit and transfer canal.
Total liner surface area = 8877 ft2 (this is to the high alarm level)
(Including all sides and floor - see Appendix C)
Top of fuel pit liner = EL. 95 [3]
Hi-Alarm level = EL. 94-3 (see Figure 2-6)
Using ratio approach to calculate total volume of water between liner and concrete:
Case 1:
18.9 gallons x x = 1369 gallons 121 ft 2 8767 ft 2 Case 2:
12.6 gallons x x = 913 gallons 121 ft 2 8767 ft 2 Case 3:
8.4 gallons x x = 609 gallons 121 ft 2 8767 ft 2 Report No: A11357-R-001 Page A3 of 4 Revision: 0
Figure A1-1: Typical Liner Plate Cell [3a]
Figure A1-2: SFP Floor Plan [3a, c]
Report No: A11357-R-001 Page A4 of 4 Revision: 0
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APPENDIX B Estimation of Years of Service Based on Hypothetical Corrosion Rate (2 pages total)
Report No: A11357-R-001 Page B1 of 2 Revision: 0
B1.1 Estimation of Years of Service Based on Hypothetical Corrosion Rate A study was performed to estimate remaining years of service considering the reinforcing steel in the south wall of the SFP was corroding as a result of water migration through the wall in the area of the collection box [8e].
As established within this calculation the design basis for the SFP, per IPEC 2 UFSAR, is the 1963 Edition of the ACI 318 Code. Within [8e], it was noted ACI 318-63 permits required areas of reinforcing steel to be lower than code minimum recommendations, provided sufficient steel remains for strength requirements. The calculation of the wall strength, considering the enveloping rate of corrosion, at the location where moisture was identified on the south wall resulted in an estimate of 69 and 68 years (Columns under Note 1 and Notes 3 of Table 2 [8e].
If the following conservative hypothesis is made:
- Leakage initiated as a result of original construction fabrication flaw.
- Leakage through the region where collection box is located commenced from original construction.
- Corrosion is current and actively occurring (no evidence)
- The years of service is estimated to be a minimum of 68 years.
This will encompass the original design life plus the period of extended operation (i.e. 60 years).
Report No: A11357-R-001 Page B2 of 2 Revision: 0
APPENDIX C Estimation of Percentage of SFP Covered During Inspections (6 pages total)
Report No: A11357-R-001 Page C1 of 6 Revision: 0
C1. Estimation of Percentage of SFP Covered During Inspection Inspections of portions of the SFP were performed as outlined in Section 2.3.
This Appendix performs surface area calculations, such that calculations of percentage of inspections performed can be determined.
The SFP layout is shown in Plant drawings [3c] and the liner plate layout is shown in [3a].
Using the figures shown (Figures C1-1 through C1-3) the following calculations are made to derive inspection percentages:
SpentFuelPoolSurfaceAreaCalculation
Floorelevation 655 in 54'7" Floor
HiLevel
Topelevation 1131 in 94'3" AlarmEL
Fuelpoolheight(Ht) 476 in 39.67 ft
Area4:SFPFloorsurfacearea (27*25+8*36)ft^2= 963 ft^2
(FigureC11andC13)
Transfercanalsurfaceareaatfloor [(23*12+3)*4*12)]/144ft^2= 93 ft^2
(EL54'7")
Report No: A11357-R-001 Page C2 of 6 Revision: 0
Steellinersurfacearea:
Note:SeefigureC13forareanumbering
Area1(36ftside) (36*Ht)= 1428 ft^2
Area2(33ftside) (33*Ht)= 1309 ft^2
Area3(27ftside) (27*Ht)= 1071 ft^2
Area5(8ftside) (8*Ht)= 317.3 ft^2
Area6(25ftside) (25*Ht)= 991.7 ft^2
Area7 (Ht*927.25*2.375)= 292.3 ft^2
Area8 (4*29.2)= 116.8 ft^2
Area9 (4.6*4)= 18.4 ft^2
Area10 (8.42*4)= 33.68 ft^2
Area11:floorareaofslot (4*2.375+1*1.54)= 11.04 ft^2
Area12(bothsides) 2*(26*1)= 52 ft^2
2*(27.25*4)
Area13(bothsides) = 218 ft^2
Area14 (Ht*41.54*26)= 118.6 ft^2
2*(20*29.2+(20+23.25)*3.25/2+
Area15(seefigure2)(bothsides) 8.6*23.25)= 1709 ft^2
Area16 (2.375*27.251.54*26)= 24.68 ft^2
Steellinertotalsurfacearea(sumArea1toArea16) 7711 ft^2
Totalsurfacearea(includesfloor, (Area4+TCFloor+(A1toA16))
transfercanal,andsteelliner) = 8767 ft^2
Wallfromfloorto190" 190/12*(27+33+36+8+9+25)= 2185 ft^2
Area4
SFPFloor above 963 ft^2
TransferCanal Floor 93 ft^2
Walls Area15 1709 ft^2
Walls Area8 116.8 ft^2
Walls Area9 18.4 ft^2
Walls Area10 33.68 ft^2
Sum 1971 ft^2
Report No: A11357-R-001 Page C3 of 6 Revision: 0
CalculatePercentagesofSFPandTransferCanalthathasbeeninspected:
TotalAreaofLiner(SFP&TC) TotalArea 8767 ft^2 1
TotalAreaofTransferCanal(TC) TCTotalArea 1971 ft^2 2
TCFlooralone TCFloor 93 ft^2 3
PerWOIP20620176&IP20623700,region RackwallArea 2185 ft^2 4
couldnotbeinspected UnderrackArea 963 ft^2 5
Netuninspected 3148 ft^2 6=4+5
PerWOIP20525553Caskareawasinspected CaskArea8x8 16 ft^2 7
8x8floorplussouthandeastwall walls2x8x190/12 253.3 ft^2 8
Totalcaskarea 269.3 ft^2 9=7+8
Uninspected=(NetCaskArea) Totaluninspected 2879 ft^2 10=69
Inspected=(TotalAreaUninspected) TotalInspected 5889 ft^2 11=110
Total(SFP+TransferCanal)Inspected %ofTotal 67% 12=11/1
TransferCanalInspected %ofTotal 22% 13=2/1
SFPAloneInspected(TotalTCinspected) %ofTotal 45% 14=1213
TCFloorInspected %ofTotal 1% 15=3/1
Report No: A11357-R-001 Page C4 of 6 Revision: 0
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36 ft 9 ft 27 ft Figure 1: Fuel Pool Floor Dimension Figure C1-1: Fuel Pit Floor Dimension
. - - - - -20'- - - - - , - - - --
' ~----
3'3"L ~
3'3" Figure C1-2: Transfer Canal South Wall Report No: A11357-R-001 Page C5 of 6 Revision: 0
Figure C1-3: SFP Surface Area Numbering Report No: A11357-R-001 Page C6 of 6 Revision: 0
Lucius Pitkin, Inc. Consulting Engineers Advanced Analysis Fitness-For-Service Failure & Materials Evaluation Nondestructive Engineering Main Office & Laboratory:
304 Hudson Street New York, NY 10013-1015 Tel: 212-233-2737 Fax: 212-406-1417 Boston Area Office:
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