ML19205A490
| ML19205A490 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 07/24/2019 |
| From: | Morgan, Morgan, Lewis & Bockius, LLP, NextEra Energy Seabrook |
| To: | Atomic Safety and Licensing Board Panel |
| SECY RAS | |
| References | |
| 50-443-LA-2, ASLBP 17-953-02-LA-BD01, RAS 55113 | |
| Download: ML19205A490 (9) | |
Text
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION ATOMIC SAFETY AND LICENSING BOARD In the Matter of Docket No. 50-443-LA-2 NEXTERA ENERGY SEABROOK, LLC ASLBP No. 17-953-02-LA-BD01 (Seabrook Station, Unit 1)
Hearing Exhibit Exhibit Number: NER002 Exhibit
Title:
MPR Testimony - Attachment 1 - Glossary
Attachment 1 to MPR Testimony:
GLOSSARY OF TERMS Aggregate Particulate material, commonly gravel and sand, that is mixed with cement and water to produce concrete. Aggregate sizes can be coarse (large) or fine (small), with concrete mixture designs using a spectrum of aggregate sizes.
Alkali-Silica Reaction A chemical reaction that can occur in concrete and produce an expansive (ASR) gel that results in cracking and may eventually cause structural distress.
Axial compression Forces that compress (i.e., squeeze) a structural element together.
Excessive axial compression loading will cause the element to crush.
Beam (one-way) Shearing forces are unaligned forces that push one part of the element in shear one direction and another part of the element in another direction. Forces applied in parallel planes that are some distance apart create compression and tension fields. Excessive one-way shear produces a diagonal failure plane between the unaligned, opposite forces.
Bioshield A concrete structure inside Containment that immediately surrounds the reactor vessel.
Breakout A concrete anchor failure mode where the concrete around the anchor fractures in a cone-like shape emanating from the anchor head.
Capacity Ability of a structural member to withstand applied load.
Chemical In the context of ASR, chemical prestressing is a means for producing Prestressing continuous compressive stress in reinforced concrete by virtue of ASR expansion being restrained by embedded reinforcement.
Commercial Grade A process by which a product or service from a commercial vendor (i.e., a Dedication vendor without a 10 C.F.R. 50, Appendix B Quality Assurance Program) is accepted as equivalent to a product or service produced or performed under a 10 C.F.R. 50 Nuclear Quality Assurance Program. Critical characteristics associated with the product or service are identified and verified to ensure the intended use is satisfied with respect to nuclear safety.
Compression A load applied to a structural member that is in the direction of pushing the constituents together; i.e., crushing. In other words, a compression load works to reduce the size of the component.
Cover Concrete The minimum thickness of concrete that covers the reinforcing cage of a structural member. That is to say, the distance between the outside diameter of an embedded reinforcing bar and the concrete surface of a reinforced concrete member.
Prestressed Concrete A special form of reinforced concrete in which reinforcing steel (i.e.
prestressing steel) is tensioned against the concrete (putting concrete in compression.) The application of compression load to a concrete member improves its service performance by limiting tensile stresses or cracking resulting from those tensile stresses. The compressive stress from prestressing (i.e. precompression) must be completely overcome before the concrete member will be exposed to net tensile stress.
Combined Cracking A term used at Seabrook Station for a combination of Cracking Index Index (CCI) values in both the horizontal and vertical directions.
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Cracking Index A crack width summation technique for quantitatively estimating tensile (CI) strains experienced by a reinforced concrete element. The Cracking Index is the ratio of the sum of crack widths to the length of which the crack summation activity is performed (i.e. the gage length.)
Crack Width A technique for estimating expansion of a reinforced concrete element by Summation measuring the widths of cracks along a line (or lines) of defined length.
Damage Rating A technique for characterizing ASR progression during petrographic Index (DRI) examination by assigning a quantitative score to characterize certain features associated with ASR. The cumulative result is the DRI.
Deflection In the context of the LSTP, deflection refers to displacement of the beam specimens by bending when load was applied during structural testing.
Demand Potential load(s) that could be applied to a structural member.
Development length The minimum length of a given reinforcing bar necessary to ramp up stresses in the bar from zero to the yield strength of the bar. In a typical beam test, this length corresponds to the lap length with which force can be transferred from a bar in tension to another lapped bar.
Engineering strain The amount of unit deformation that occurs in a given direction. The unit deformation is calculated by dividing the change in length with the original length measured. In the context of expansion experienced by a reinforced concrete element, the total expansion can be approximated by adding the widths of the cracks in a given direction, and assuming that the elastic strain in between the cracks is negligible in comparison, and dividing that quantity with the gage length (i.e. original length.) Glossary Figure 1 illustrates this concept.
Expression A relationship in a Design Code between key design parameters. A design equation.
Extensometer A device for monitoring expansion into the depth of a concrete member that is embedded in a borehole drilled into concrete.
Flexure A force that causes a structural element to bend. Compression is applied on the inside radius of the bent member and tension is applied on the outside radius. For a concrete member, which is typically weaker in tension, excessive flexure loading will cause the element to split or tear on the tension side. Glossary Figure 2 depicts a reinforced concrete beam under flexural load.
In-Plane Expansion Expansion that occurs in the two dimensions of a concrete member that are visibly accessible at the surface. At Seabrook Station and in the LSTP test specimens, the in-plane directions are also parallel to the embedded reinforcement mats. Glossary Figure 3 (which is also Figure X from the testimony) illustrates the direction terminology used for the LSTP.
Lap splice Overlapping reinforcing bars to connect multiple segments of reinforcing bars to provide continuous reinforcement over a dimension of a reinforced concrete member that is longer than a single reinforcing bar.
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Limit state A behavioral mode by which a structural response is examined. In structural design, each limit state must be evaluated to confirm structural adequacy. For example, a reinforced concrete component must be sufficiently strong in flexure, shear, etc.
Normal Strength Structural concrete with compressive strength that is greater than 2,500 psi, Concrete but less than 8,000 psi, which is considered to be a threshold for high-strength concrete. Normal strength concrete is more commonly used than high-strength concrete, in particular older reinforced concrete structures.
High-strength concrete is used in particular applications, such as to reduce the weight, improve the durability, or in special architectural considerations.
Normalized Elastic The ratio of the modulus of elasticity of ASR-affected concrete to the Modulus original elastic modulus. This parameter is the input variable for the correlation to determine through-thickness expansion prior to instrument installation.
Plain concrete Concrete without reinforcing bars, or unreinforced concrete.
Pullout A concrete anchor failure mode where there is a loss of load resistance due to local concrete failure at the interface with the anchor, and the anchor slides out of the concrete.
Punching (two-way) For punching shear, force is applied locally, rather than in a uniform plane.
shear In other words, a punching shear condition exists when a structural wall or a reinforced concrete slab is patch-loaded. An excessively patch-loaded area will result in critical levels of shear stresses and will eventually puncture the structural element in the vicinity of the patch-loaded area.
Reinforcement The bond between the concrete to the embedded reinforcement that allows anchorage load to transfer from the concrete to the reinforcing bars. A loss of reinforcement anchorage would cause the reinforcing bars to slip within the concrete element. For reinforced concrete elements to behave in a manner consistent with the design principles, all reinforcement needs to be anchored.
Reinforcing bars Steel bars embedded in concrete to increase the capacity of the structural (Rebar) members to withstand design loads. Since concrete is strong in compression and weak in tension, the primary use of reinforcing bars is to reinforce the tension side of reinforced concrete elements, Reinforcement ratio The cross sectional area of reinforcing bars divided by the entire cross section of the reinforced concrete structural member. This calculation determines the fraction of a reinforced concrete section occupied by reinforcement.
Representativeness The ability to apply conclusions from one application to inform circumstances in another application. In the context of the admitted contention, representativeness refers to the results from the LSTP and their applicability to reinforced concrete structures at Seabrook Station.
Seismic Category I Structures at a nuclear power plant that must fulfill their design function Structures following a design basis seismic event.
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Shear A loading condition where unaligned forces push one part of a structural member in one direction and another part of the member in another direction, creating a diagonal compression and tension field. Excessive shear forces produce a diagonal failure plane that runs between the applied load and a support reaction in a typical shear test. Glossary Figure 4 illustrates this diagonal failure plane and provides further discussion on the applicable forces in a reinforced concrete member that comprise shear.
Tension A load applied to a structural member that is in the direction of pulling the constituents apart. In other words, a tensile load works to elongate, or increase the size of, a structural component.
Through-thickness Expansion that occurs in the dimension of a concrete member that is not expansion visibly accessible at the surface, i.e., expansion in the direction through the surface. At Seabrook Station and in the LSTP test specimens, the through-thickness direction is not reinforced (except for the lower portion of the Containment structure). Glossary Figure 3 (which is also Figure X from the testimony) illustrates the direction terminology used for the LSTP.
Visual Assessment A technique for characterizing ASR progression during petrographic Rating (VAR) examination by assigning a quantitative score to characterize certain features associated with ASR. The cumulative result is the VAR.
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Glossary Figure 1. Illustration of Engineering Strain in Reinforced Concrete Glossary Figure 1 is taken from Seabrooks ASR AMP and shows a diagram of reinforced concrete that has undergone expansion and exhibits cracking. The total expansion is the change in length divided by the original length - i.e., L / L1. Concrete has little tensile strain capacity, so little expansion occurs before cracking occurs. In other words, tensile strains experienced by the uncracked concrete in between the cracks are considered negligible in relation to the contributions that can be attributed to crack openings.
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Glossary Figure 2. Illustration of Flexure Limit State Glossary Figure 2 is from a textbook Prestressed Concrete Structures by Collins and Mitchell (1997). Beam GHIK depicts a reinforced concrete beam with no net loading. Beam LMNO depicts a reinforced concrete beam under flexural loading. The arc length NO is less that its original value whereas the arc length LM is more than its original value.
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Glossary Figure 3. Direction Terminology for Typical Reinforced Concrete Member 7
Glossary Figure 4. Diagram of Forces Contributing to Shear in Reinforced Concrete Glossary Figure 4 is from a textbook, Reinforced Concrete, by MacGregor & Wight (2005).
This figure illustrates various forces that combine to provide the total shear strength of reinforced concrete (Vn). Total shear strength is the sum of the shear strength provided by the concrete (Vc) and the shear reinforcement (Vs). The concrete shear strength is the sum of shear carried in the flexural compression zone (Vcz), the vertical component of the aggregate interlock (Vay), and the dowel action of tension reinforcement (Vd). Aggregate interlock and dowel action are mechanisms for transferring shear forces across a crack. Aggregate interlock refers to the rough surface of the shear crack and the inability of aggregates to slide past one another. Dowel action refers to the shear capacity contribution provided by flexural reinforcement crossing the failure crack and preventing one side of the crack from sliding past the other side. (In Glossary Figure 4, the shear reinforcement runs up and down, whereas the longitudinal reinforcement providing dowel action runs left to right.)
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