ML033370903
| ML033370903 | |
| Person / Time | |
|---|---|
| Site: | Cook  |
| Issue date: | 11/12/2003 |
| From: | Nazar M Indiana Michigan Power Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| AEP:NRC:3520-01, FOIA/PA-2005-0075 | |
| Download: ML033370903 (32) | |
Text
NV0 Indiana Michigan Power Company 500 Circle Drive Buchanan, MI 49107 1395 INDIANA MICHIGAN POWER November 12, 2003 AEP:NRC:3520-01 10 CFR 50.90 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Mail Stop O-P1-17 Washington, DC 20555-000 1
SUBJECT:
Donald C. Cook Nuclear Plant Units I and 2 Docket Nos. 50-315 and 50-316 License Amendment Request to Use Yield Strength Determined From Measured Material Properties for Reinforcing Bar in Structural Calculations for Control Rod Drive Missile Shield
Dear Sir or Madam:
Pursuant to 10 CFR 50.90, Indiana Michigan Power Company (I&M), the licensee for Donald C. Cook Nuclear Plant (CNP) Units I and 2, proposes to amend Facility Operating Licenses DPR-58 and DPR-74. I&M requests review and approval, pursuant to 10 CFR 50.59(c)(2)(viii), of a change to the CNP licensing basis as described in the CNP Updated Final Safety Analysis Report (UFSAR). The change allows the use of reinforcing bar (rebar) yield strength based on measured material properties as documented in certified material test reports (CMTRs) in structural calculations for the control rod drive missile shield (missile shield).
During the period between September 1997 and December 2000, I&M performed a reanalysis of the containment structures. The Nuclear Regulatory Commission (NRC) subsequently reviewed the reanalysis and concluded that, with the exception of the missile shield, I&M used acceptable methods and appropriate assumptions and design parameters. In Reference 1, I&M informed the NRC that structural calculations for the missile shield used conservative yield strength based on measured material properties as documented in CMTRs. Such use is allowed by the code of construction for concrete structures at CNP and by equivalent current code versions. The safety factors applied to the calculated loads were consistent with the CNP licensing basis; therefore, the safety margins in the missile shield design were unaffected.
This methodology was incorporated into the CNP UFSAR under the provisions of 10 CFR 50.59 for use on a case by case basis.
C)
U. S. Nuclear Regulatory Commission AEP:NRC:3520-01 Page 2 In Reference 2, the NRC staff stated that they have reasonable assurance that the missile shield will perform its intended function.
However, the NRC staff questioned the change to the CNP UFSAR made under the provisions of 10 CFR 50.59 to use actual yield strength of rebar, in lieu of specified material properties, in the structural calculations. In Reference 3, I&M informed the NRC it would submit a license amendment requesting NRC approval of the CNP use of this provision of the applicable code for the missile shields. This request for amendment satisfies that commitment. provides an affirmation statement pertaining to this letter. Enclosure 2 provides I&M's evaluation of the submitted change. Attachment 1 provides the Definitions section of ACI 318-63. Attachment 2 provides Chapter 20 of ACI 318-95. Attachment 3 provides Chapter 20 of ACI 349-01. Attachment 4 provides Page 3.8-22 of the Diablo Canyon Nuclear Power Plant UFSAR. provides Pages 3-49 and 3-50 of Supplement 7 to the Diablo Canyon Nuclear Power Plant Safety Evaluation Report.
Copies of this letter and its attachments are being transmitted to the Michigan Public Service Commission and Michigan Department of Environmental Quality, in accordance with the requirements of 10 CFR 50.91.
This letter contains no new commitments.
Should you have any questions, please contact Mr. Brian D. Mann, Acting Manager of Regulatory Affairs, at (269) 697-5806.
Sincerely, Ak./ 41 M. K. Nazar Senior Vice Prident and Chief Nuclear Officer RV/rdw
U. S. Nuclear Regulatory Commission Page 3 AEP:NRC:3520-01
References:
- 1. Letter from Scot A. Greenlee, Indiana Michigan Power Company, to Nuclear Regulatory Commission Document Control Desk, "Donald C. Cook Nuclear Plant Units I and 2, Response to Nuclear Regulatory Commission Request for Additional Information Regarding. Containment Structure Conformance to Design Basis Requirements (TAC Nos.
MB3603 and MB3604)," submittal AEP:NRC:2520, dated July 16, 2002.
- 2. Letter from John F. Stang, Nuclear Regulatory Commission, to A. Christopher Bakken, III, Indiana Michigan Power Company, "Donald C. Cook Nuclear Plant, Units 1 and 2 -
Regarding Containment Structure Conformance to Design and Licensing Basis Requirements," dated March 21, 2003.
- 3. Letter from J. B. Giessner, Indiana Michigan Power Company, to Nuclear Regulatory Commission Document Control Desk, "Donald C. Cook Nuclear Plant Units 1 and 2, Containment Structure Conformance to Design and Licensing Basis Requirements,"
submittal AEP:NRC:3520, dated April 24, 2003.
Enclosures:
- 1. Affirmation
- 2. Evaluation of the Proposed Change Attachments:
I. ACI 318-63 Building Code for Reinforced
- Concrete, Chapter 3 - Definitions
- 2. ACI 318-95 Building Code Requirements for Structural Concrete, Chapter 20 - Strength Evaluation of Existing Structures
- 3. ACI 349-01 Code Requirements for Nuclear Safety Related Concrete Structures Chapter 20 - Strength Evaluation of Existing Structures
- 4. Diablo Canyon Nuclear Power Plant UFSAR Revision 15 Page 3.8-22
- 5. Supplement 7 to Diablo Canyon Nuclear Power Plant Safety Evaluation Report Pages 3-49 and 3-50
U. S. Nuclear Regulatory Commission AEP:NRC:3520-01 Page 4 c:
J. L. Caldwell, NRC Region III K. D. Curry, Ft. Wayne AEP, w/o enclosures/attachments J. T. King, MPSC, w/o enclosures/attachments MDEQ - WHMD/HWRPS, w/o enclosures/attachments NRC Resident Inspector M. A. Shuaibi, NRC Washington, DC to AEP:NRC:3520-01 AFFIRMATION I, Mano K. Nazar, being duly sworn, state that I am Senior Vice President and Chief Nuclear Officer of American Electric Power Service Corporation and Vice President of Indiana Michigan Power Company (I&M), that I am authorized to sign and file this request with the Nuclear Regulatory Commission on behalf of I&M, and that the statements made and the matters set forth herein pertaining to I&M are true and correct to the best of my knowledge, information, and belief.
American Electric Power Service Corporation M. K. Nazar Senior Vice Pre dent and Chief Nuclear Officer SWORN TO ND SUBSCRIBED BEFORE ME JULIE E. NEWMILLER TW la/
DY_
DAY OF
, 2003 Notary Public, Berien Count2 2M
~~~-// I ~~~~~~~My Commiission Expires Aug 22,2004
/ /
Nota'ry Public My Commission Expires N
to AEP:NRC:3520-01 Evaluation of the Proposed Change
1.0 DESCRIPTION
Indiana Michigan Power Company (I&M), the licensee for Donald C. Cook Nuclear Plant (CNP)
Units 1 and 2, proposes to amend Facility Operating Licenses DPR-58 and DPR-74.
I&M requests review and approval, pursuant to 10 CFR 50.59(c)(2)(viii), of a change to the CNP licensing basis as described in the CNP Updated Final Safety Analysis Report (UFSAR). The change allows the use of values of yield strength for reinforcing bar (rebar) in structural calculations for the control rod drive missile shield (missile shield) based on the measured yield strength documented in certified material test reports (CMTRs), in lieu of specified yield strength.
2.0 PROPOSED CHANGE
I&M proposes the addition of the following statement to UFSAR Section 5.2.3.
"Additionally, as-tested reinforcing bar strength was utilized for the determination of design structural capacity for the control rod drive missile shield."
The proposed change will allow the use of values of yield strength for rebar in structural calculations for the missile shield based on the measured yield strength derived from CMTR data, in lieu of specified yield strength.
3.0 BACKGROUND
During the period between September 1997 and December 2000, I&M performed a reanalysis of the containment structures.
The Nuclear Regulatory Commission (NRC) subsequently performed a detailed review of the methods and calculations used for the reanalysis and performed a design audit in January 2002. Based on the results of their review and audit, as augmented by a Request for Additional Information and I&M's responses, the NRC staff concluded that, with the exception of the missile shield, I&M used acceptable methods and appropriate assumptions and design parameters.
The reanalysis of the missile shield required the use of provisions of the relevant design codes which allow the use of measured yield strength documented in CMTRs, to accommodate calculated loads with required safety factors.
In a letter to I&M dated March 21, 2003, the NRC staff stated that they have reasonable assurance that the missile shield above the upper reactor cavity will perform its intended function. However, the NRC staff questioned the use of the actual rebar yield strength, in lieu of code specified material properties, in the structural calculations for the missile shields. By letter to AEP:NRC:3520-01 Page 2 dated April 24, 2003, I&M informed the NRC it will submit a license amendment requesting NRC approval of the CNP use of this provision of the code for the missile shield.
4.0 TECHNICAL ANALYSIS
The design of the concrete structures at CNP was in accordance with American Concrete Institute (ACI) 318-63, "Building Code for Reinforced Concrete," (Attachment 1). ACI 318-63 defines rebar yield strength as "Specified minimum yield strength or yield point of reinforcement in pounds per square inch. Yield strength or yield point shall be determined in tension according to applicable American Society for Testing and Materials (ASTM) specifications." For CNP, the applicable ASTM specification for reinforcing steel is ASTM A615-68. I&M believed that the use of measured yield strength for rebar was allowed by the CNP design basis because ACI 318-63 allows the use of rebar strength up to the yield point based on measured CMTR data.
ACI 318-63 does not provide specific guidance on evaluation of existing concrete structures.
However, later editions of relevant concrete codes do have provisions for such evaluations. ACI 318-95, "Building Code Requirements for Structural Concrete" (Attachment 2), and ACI 349-01, "Code Requirements for Nuclear Safety Related Concrete Structures" (Attachment 3) both provide guidance on strength evaluations of existing structures.
Section 20 of ACI 318-95 discusses "Strength Evaluation of Existing Structures," and Section 20.2.4 states, "If required, reinforcement or tendon strength shall be based on tensile tests of representative samples of the material in the structure in question."
The most recent concrete code for nuclear safety related structures, ACI 349-01, Chapter 20, "Strength Evaluation of Existing Structures," provides further technical support for this approach in nuclear applications. Paragraph 20.2.4 of ACI 349-01 states, "If required, reinforcement or tendon strength shall be based on tensile tests of representative samples of the material in the structure in question." This confirms the applicability of measured yield strength to nuclear applications.
In the reanalysis of the missile shield, I&M used a conservative estimate of rebar yield strength based on measured data. Rebar received at CNP during construction is traceable to specific locations in the plant via mark numbers, and by "How to Be Used" notes on Material Receipts.
However instead of using the specified yield strength as allowed by ASTM A615-68, I&M used a conservative yield strength based on the lowest value of the CMTR data compiled for all missile shield rebar of both units. All relevant rebar used in the missile shield have been traced to their respective heats and have traceable CMTR values. The compilation of the CMTR yield and tensile strength data for each heat of material relevant to the rebar used in the missile shields is presented in Table 1. As noted in Table 1, the yield strength used by CNP (50.6 ksi) is significantly less than corresponding average ultimate strength values determined by the tests.
The use of a value for yield strength based on CMTR measured data does not affect the safety margins for the missile shield. The margin of safety for structures is provided by the safety to AEP:NRC:3520-01 Page 3 factors that are applied to the separate loads when performing structural calculations. In other words, the margin of safety is provided by increasing the estimated loads, not by decreasing the estimated yield strength. I&M continues to use the same safety load factors specified in the applicable codes that were used to license CNP and, therefore, the margin of safety is unaffected.
Precedents A precedent for the use of measured material strength for reinforcing and structural steel for containment structures exists for Diablo Canyon Nuclear Power Plant (Diablo). The Diablo UFSAR documents that "the yield strength of steel and the ultimate strength of concrete for the HE [Hosgri (seismic) event] are taken as the average values of properly substantiated test results," (Attachment 4).
The use of material test data in other Diablo applications has also been accepted. Supplement No. 7 to the Safety Evaluation Report (SER) by the Office of Nuclear Reactor Regulation for Pacific Gas and Electric Company for the seismic reevaluation of Diablo, dated May 26, 1978 (Attachment 5) discusses the use of actual material test strengths for design of mechanical equipment and systems in several passages. For example, the SER notes that, "In some cases, where material test data were available, actual material properties were used in lieu of code specified properties to establish allowable stress limits to justify structural integrity where the calculation stress exceeded the limits of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)." The SER further notes, "The general methods used by the applicant in this reevaluation as described above contain few variations from the usual procedures as defined by our usual criteria.... Another is the use of actual material test strengths.
As discussed above, the code safety factors have been retained in using these material test data to establish allowable stress levels."
to AEP:NRC:3520-01 Page 4 5.0 REGULATORY SAFETY ANALYSIS 5.1 No Significant Hazards Consideration Indiana Michigan Power Company (I&M) has evaluated whether a significant hazards consideration is involved with the use of yield strengths in structural calculations for the missile shield based on measured material properties as documented in certified material test reports (CMTRs). The I&M evaluation was performed by focusing on the three standards set forth in 10 CFR 50.92, "Issuance of Amendment," as discussed below:
- 1. Does the proposed change involve a significant increase in the probability of occurrence or consequences of an accident previously evaluated?
Response: No Probability of Occurrence of an Accident Previously Evaluated The failure of missile shield to perform as designed is not an initiator of any accident previously evaluated. As a result, the probability of any accident previously evaluated is not significantly increased.
Consequences of an Accident Previously Evaluated The ability of missile shield structures to perform their assumed mitigation functions is not affected by this change as the calculations continue to demonstrate that the structures will perform as designed when subjected to conservatively calculated loads.
As a result, the consequences of any accident previously evaluated are not significantly increased.
Therefore, the proposed change does not involve a significant increase in the probability or consequences of an accident previously evaluated.
- 2. Does the proposed change create the possibility of a new or different kind of accident from any accident previously evaluated?
Response: No The missile shield will continue to perform as designed under all analyzed conditions. No new failure mechanisms have been introduced. No changes in plant operation are required. This change does not adversely affect any current system interfaces or create any new interfaces that could result in an accident or malfunction of a different kind than previously evaluated.
Therefore, the proposed changes do not create the possibility of a new or different kind of accident from any previously evaluated.
to AEP:NRC:3520-01 Page 5
- 3. Does the proposed change involve a significant reduction in a margin of safety?
Response: No The margin of safety for the missile shield is provided by the factors that are applied to the separate loads when performing structural calculations. These code safety factors are sufficient to ensure that anticipated and unanticipated loads can be withstood by the concrete structures.
The use of yield strengths based on measured material properties as documented in CMTRs has no effect on margin of safety provided by the load safety factors. I&M continues to use the same safety load factors that were used to license the Donald C. Cook Nuclear Plant (CNP).
Therefore, the proposed change does not involve a significant reduction in the margin of safety.
In summary, based upon the above evaluation, I&M has concluded that the proposed amendment involves no significant hazards consideration under the standards set forth in 10 CFR 50.92(c),
and, accordingly, a finding of "no significant hazards consideration" is justified.
5.2 ApplicablC Regulatorv Requirements/Criteria The following criterion, which is contained in Updated Final Safety Analysis Report Section 1.4.1, is applicable to the missile shield:
"Those structures, systems and components of reactor facilities which are essential to the prevention, or the mitigation of the consequences, of nuclear accidents which could cause undue risk to the health and safety of the public shall be identified and then designed, fabricated, and erected to quality standards that reflect the importance of the safety function to be performed."
The missile shield will continue to meet applicable code requirements, thereby satisfying this criterion.
Based on the considerations discussed above, (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Nuclear Regulatory Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
In conclusion, the use of yield strengths based on measured material properties as documented in CMTRs in structural calculations for the missile shield is consistent with the applicable CNP design code, ACI 318-63, and meets the regulatory requirements.
to AEP:NRC:3520-01 Page 6
6.0 ENVIRONMENTAL CONSIDERATION
S A review has determined that the proposed amendment would change a requirement with respect to installation or use of a facility component located within the restricted area, as defined in 10 CFR 20, or would change an inspection or surveillance requirement. However, the proposed amendment does not involve (i) a significant hazards consideration, (ii) a significant change in the types or significant increase in the amounts of any effluent that may be released offsite, or (iii) a significant increase in individual or cumulative occupational radiation exposure.
Accordingly, the proposed amendment meets the eligibility criterion for categorical exclusion set forth in 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the proposed amendment.
I I.
I I.-
I to AEP:NRC:3520-01 Page 7 Table I
_CMTR Data for Missile Shield Rebar Heat Bar Size Yield Point, Tensile Strength, psi pounds per square inch (psi)
Unit I C34105
- 11 53,205 89,423 B37160
- 11 54,487 83,333 C35157
- 8 57,468 85,316 A36448
- 5 54,193 79,677 Lowest for Unit 1 53,205 83,333 Average for Unit 1 54,838 84,437 Unit 2 B36171
- 11 54,487 89,423 A37151
- 11 50,641 84,615 B37340
- 11 51,602 83,012 A36334
- 11 55,769 85,576 C35157
- 8 57,468 85,316 C34982
- 5 57,741 79,354 Lowest for Unit 2 50,641 83,012 Average for Unit 2 54,618 84,549 A common yield strength value of 50,600 psi was utilized for shield calculation (lowest CMTR value is 50,641 psi).
both of the units in the missile to AEP:NRC:3520-01 ACI 3 18-63 BUILDING CODE FOR REINFORCED CONCRETE CHAPTER 3 - DEFINITIONS
ACI Standard Building - Code Requirements for Reinforced Concrete
- (ACI 318-63)
JUNE 1963 N,
PUBLICATION
DEFINITIONS 318-11 CHAPTER 3-DEFINITIONS 301-General definitions (a) The following terms are defined for general use in this code; specialized definitions appear in individual chapters:
Admixture-A material other than portland cement, aggregate, or water added to concrete to modify its properties.
Aggregate-Inert material which is mixed with portland cement and water to produce concrete.
Aggregate, lightweight-Aggregate having a dry, loose weight of 70 lb per cu ft or less.
Building official-See Section 102(c).
Column-An upright, compression member the length of which ex-ceeds three times its least lateral dimension.
Combination column-A column in which a structural steel member, designed to carry the principal part of the load, is encased in concrete of such quality, and in such manner that the remaining load may be allowed thereon.
Composite column-A column in which a steel or cast-iron structural member is completely encased in concrete containing spiral and longi-tudinal reinforcement.
Composite concrete flexural construction-A precast concrete member and cast-in-place reinforced concrete so interconnected that the compo-nent elements act together as a flexural unit.
Compressive strength of concrete (f,') * -
Specified compressive strength of concrete in pounds per square inch (psi). Compressive strength shall be 'determined by tests of standard 6x12-in. 'cylinders made and tested in accordance with ASTM specifications at 28 days or such earlier age as concrete is to receive its full service load or maximum stress.
Concrete-A mixture of portland cement, fine aggregate, coarse aggre-gate, 'and water.
Concrete, structural lightweight -A concrete containing lightweight aggregate conforming to Section 403.
Deformed bar-A reinforcing bar conforming to "Specifications for Minimum Requirements'for' the Deformations of Deformed Steel Bars for Concrete Reinforcement" (ASTM A 305) or "Specifications for Special Large Size Deformed Billet-Steel Bars for Concrete Reinforce-ment" (ASTM A 408). Welded wire fabric with welded intersections not farther apart than 12 in. in the direction of the principal reinforce-ment and with cross wires not more than six gage numbers 'smaller in wherever this quantity appears under a radical sign the root of only the numerical value s Intended; all values are In pounds per square inch (psi).
318-12 ACI STANDARD-BUILDING CODE Chapter 3 size than the'principal reinforcement may be considered equivalent to a deformed bar when used in slabs.
Effective area of concrete-The area of a section which lies between the centroid of the tension reinforcement and the compression face of the flexural member.
Effective area of reinforcement-The area obtained by multiplying the right cross-sectional area of the reinforcement by the cosine of the angle between its direction and the direction for which the effectiveness is to be determined.
Pedestal-An upright. compression member whose height does not exceed three times its average least lateral dimension.
Plain bar-Reinforcement that does not conform to the definition of deformed bar.
Plain concrete-Concrete that does not conform to the definition for reinforced concrete.
Precast concrete-A plain or reinforced concrete element cast in other than its final position in the structure.
Prestressed concrete-Reinforced concrete in which there have been introduced internal stresses of such -magnitude and distribution that the stresses resulting from service loads are counteracted to a desired degree.
Reinforced concrete-Concrete containing reinforcement and designed on the assumption that the two materials act together in resisting forces.
Reinforcement-Material that' conforms to Section 405, excluding prestressing steel unless specifically included.
Service dead load-The calculated dead weight supported by a member.
Service live load-The live load specified by the general building code of which this code forms a part.
Splitting tensile strength-(see Section 505)
Stress-Intensity of force per unit area.
Surface water-Water carried by an aggregate except that held by absorption within the aggregate particles themselves.
'Yield strength or yield point (f,)-Specified minimum yield strength or yield point of reinforcement in pounds per.square inch. Yield strength or yield point shall.be'determined in -tension according to applicable ASTM specifications.
to AEP:NRC:3520-01 ACI 3 18-95 BUILDING CODE FOR REQUIREMENTS FOR STRUCTURAL CONCRETE CHAPTER 20 - STRENGTH EVALUATION OF EXISTING STRUCTURES
ACI 318-95 ACI 318R-95 r1C.,
ACI BUILDING CODEICOMMENTARY 31 8131 8R-279 PART 6 SPECIAL CONSIDERATIONS CHAPTER 20 -
STRENGTH EVALUATION OF EXISTING STRUCTURES CODE COMMENTARY 20.0 -Notation D
= dead loads or related Internal moments and forces fe'
= specified compressive strength of concrete, psi h
= overall thickness of member, In.
L
= rive loads or related Internal moments and forces Att
= span of member under load test, In. (The shorter span for two-way slab systems.)
Span Is the smaller of (a) distance between centers of supports,, and (b) clear distance between supports plus thickness h of mem-ber. In Eq. (20-1), span for a cantilever shall be taken as twice the distance from support to cantilever end, In.
= measured maximum deflection, In. See Eq.
(20-1) 4max= measured residual deflection, In. See Eq.
(20-2) and (20-3)
Amaf = maximum deflection measured during the second test relative to the position of the structure at the beginning of the second test, In. See Eq. (20-3) 20.1 -
Strength evaluation -
General 20.1.1 - If there Is doubt that a part or all of a struc-ture meets the safety requirements of this code, a strength evaluation shall be carried out as required by the engineer or building official.
R20.1-Strength evaluation -
General Chapter 20 does not cover load testing for the approval of new design or construction methods. (See 16.10 for recom-mendadons on strength evaluation of precast concrete mem-bers.) Provisions of Chapter 20 may be used to evaluate whether a structure or a portion of a structure satisfies the safety requirements of this code. A strength evaluation may be required if the materials are considered to be deficient in quality, if there is evidence indicating faulty construction, if a structure has deteriorated, if a building will be used for a new function, or if, for any reason, a structure or a portion of it does not appear to satisfy the requirements of the code.
In such cases, Chapter 20 provides guidance for investigat-ing the safety of the structure.
If the safety concerns are related to an assembly of elements or an entire structure, it is not feasible to load test every ele-ment and section to the maximum for the applied load inten-sity. In such cases, it is appropriate that an investigation plan be developed to address the specific safety concerns. If
318/31 8R-280 ACI STANDARDICOMMITTEE REPORT CODE COMMENTARY a load test is described as part of the strength evaluation process, it is desirable for all parties involved to come to an agreement about the region to be loaded, the magnitude of the load, the load test procedure, and acceptance criteria before any load tests are made.
20.1.2 -
If the effect of the strength deficiency Is well understood and if It Is feasible to measure the dimen-sions and material properties required for analysis, analytical evaluations of strength based on those mea-surements shall suffice. Required data shall be deter-mined In accordance with 20.2.
R20.12 -
In the practice of reinforced concrete building design, it is currently assumed that strength considerations related to axial load, flexure, and combined axial load and flexure are well understood. There are reliable theories relating strength and short-term displacement to load in terms of dimensional and material data for the structure.
If it is decided to determine the strength of the structure by analysis, calculations must be based on data gathered on the actual dimensions of the structure, properties of the materi-als in place, and all pertinent details. Requirements for data collection are in 20.2.
20.1.3 -
If the effect of the strength deficiency Is not well understood or If It Is not feasible to establish the required dimensions and material properties by mea-surement, a load test shall be required if the structure Is to remain In service.
R20.13 ' If the shear or bond strength of an element is critical in relation to the doubt expressed about safety, E physical test may be the most efficient solution to eliminate or confirm the doubt. A physical test may also be appropri-ate if it is not possible or feasible to determine the materiai and dimensional properties required for analysis even if the cause of the concern relates to flexure or axial load.
Wherever possible and appropriate, it is desirable to suppor the results of the load test by analysis.
20.1.4-If the doubt about safety of a part or all of a structure Involves deterioration, and If the observed response during the load test satisfies the acceptance criteria, the structure or part of the structure shall be permitted to remain In service for a specified time period. If deemed necessary by the engineer, periodic reevaluations shall be conducted.
R20.1A -For a deteriorating structure, the acceptance pro.
vided by the load test may not be assumed to be withou limits in terms of time. In such cases, a periodic inspectior program is useful. A program that involves physical test!
and periodic inspection can justify a longer period in ser.
vice. Another option for maintaining the structure in ser.
vice, while the periodic inspection program continues, is tc limit the live load to a level determined to be appropriate.
The length of the specified time period should be based o0 consideration of (a) the nature of the problem, (b) environ mental and load effects, (c) service history of the structure and (d) scope of the periodic inspection program. At the enc of a specified time period, further strength evaluation i required if the structure is to remain in service.
With the agreement of all concerned parties, special proce dures may be devised for periodic testing that do not neces sarily conform to the loading and acceptance criteri:
specified in Chapter 20.
20.2 -
Determination of required dimen-sions and material properties R20.2 -
Determination of required dimen-sions and material properties This section applies if it is decided to make an analytica evaluation (20.1.2).
ACI BUILDING CODEICOMMENTARY 318/31 8R-281 CODE COMMENTARY 20.2.1 -
Dimensions of the structural elements shall be established at critical sections.
20.2.2 -
Locations and sizes of the-reinforcing bars, welded wire fabric, or tendons shall be determined by measurement. It shall be permitted to base reinforce-ment locations on available drawings if spot checks are made confirming the information on the drawings.
20.2.3 -
If required, concrete strength shall be based on results of cylinder tests or tests of cores removed from the part of the structure where the strength Is In doubt. Concrete strengths shall be determined as specified In 5.6.4.
20.2.4 -
If required, reinforcement or tendon strength shall be based on tensile tests of representative sam-ples of the material In the structure In question.
20.2.5 -
If the required dimensions and material properties are determined through measurements and testing, and If calculations can be made In accordance with 20.1.2, It shall be permitted to Increase the strength reduction factor In 9.3, but the strength reduc-tion factor shall not be more than:
Flexure, without axial load............................
1.0 Axial tension, and axial tension with flexure....... 1.0 Axial compression and axial compression with flexure:
R20.2.1 -
Critical sections are those at which each type of stress calculated for the load in question reaches its maxi-mum value.
R20.2.2 -
For individual elements, amount, size, arrange-ment, and location must be determined at the critical sec-tions for reinforcement and/or tendons designed to resist applied load. Nondestructive investigation methods are acceptable. In large structures, determination of these data for approximately five percent of the reinforcement or ten-dons in critical regions may suffice if these measurements confirm the data provided in the construction drawings.
R202.3 -
The number of tests may depend on the size of the structure and the sensitivity of structural safety to con-crete strength for the problem. In cases where the potential problem involves flexure only, investigation of concrete strength can be minimal for a lightly reinforced section (pf, IYc 5 0.15 for rectangular section).
R120.24 -
The number of tests required depends on the uniformity of the material and is best determined by the engineer for the specific application.
R20.2.5 -
Strength reduction factors given in 20.25 are larger than those specified in Chapter 9. These increased values are justified by the use of accurate field-obtained material properties, actual in-place dimensions, and well understood methods of analysis.
Members with spiral reinforcement conforming to 10.9.3............
0.9 Other members.............................................. 0.85 Shear and/or torsion.1.......................... 0.9 Bearing on concrete.............
0.85 20.3 -
Load test procedure 20.3.1 -
Load arrangement -
The number and arrangement of spans or panels loaded shall be selected to maximize the deflection and stresses In the critical regions of the structural elements of which strength Is In doubt. More than one test load arrange-ment shall be used if a single arrangement will not simultaneously result in maximum values of the effects (such as deflection, rotation, or stress) necessary to demonstrate the adequacy of the structure.
R20.3 -Load test procedure R20.3.1 -It is important to apply the load at locations so that its effects on the suspected defect are a maximum and the probability of unloaded members sharing the applied load is a minimum. In cases where it is shown by analysis that adjoining unloaded elements will help carry some of the load, the load must be placed to develop effects consis-tent with the intent of the load factor.
318/31 BR-282 ACI STANDARDICOMMITTEE REPORT CODE 20.3.2 - Load intensity-The total test load (includ-ing dead load already In place) shall not be less than 0.85 (1.4D + 1.7L). It shall be permitted to reduce L In accordance with the requirements of the applicable general building code.
COlMENTARY
.R20.3.2 - The required load intensity follows previous load test practice. The live load L may be reduced as perrait.
ted by the general building code governing safety consider-ations for the structure. The live load should be increased to compensate for resistance provided by unloaded portions of the structure in questions. The increase in live load is deter.
mined from analysis of the loading conditions in relation to the selected pass/fail criterion for the test.
20.3.3 -
A load test shall not be made until that por-tion of the structure to be subject to load is at least 56 days old. If the owner of the structure, the contractor, and all Involved parties agree, it shall be permitted to make the test at an earlier age.
20.4 -
Loading criteria 20.4.1 -
The Initial value for all applicable response measurements (such as deflection, rotation, strain, slip, crack widths) shall be obtained not more than one hour before application of the first load Increment.
Measurements shall be made at locations where max-imum response Is expected. Additional measurements shall be made If required.
20.4.2 -
Test load shall be applied In not less than four approximately equal Increments.
20.4.3 -
Uniform test load shall be applied In a man-ner to ensure uniform distribution of the load transmit-ted to the structure or portion of the structure being tested. Arching of the applied load shall be avoided.
R20.4 -
Loading criteria R20.42 -
It is advisable to inspect the structure after each load increment.
R20.43 -
"Arching" refers to the tendency for the load to be transmitted nonuniformly to the flexural element being tested. For example, if a slab is loaded by a uniform arrangement of bricks with the bricks in contact, "arching" would results in reduction of the load on the slab near the midspan of the slab.
20.4.4 -
A set of response measurements shall be made after each load increments applied and after the total load has been applied on the structure for at least 24 hr.
20.4.5 -Total test load shall be removed Immediately after all response measurements defined In 20.4.4 are made.
20.4.6 -
A set of final response measurements shall be made 24 hr after the test load Is removed.
20.5 -
Acceptance criteria 20.5.1 -
The portion of the structure tested shall show no evidence of failure. Spalling and crushing of compressed concrete shall be considered an indica-tion of failure.
R20.5 -
Acceptance criteria R20.5.1 -
A general acceptance criterion for the behavior of a structure under the test load is that it shall not show "evidence of failure." Evidence of failure will include cracking, spalling, and/or deflection of such magnitude and extent that the observed result is obviously excessive and incompatible with the safety requirements of the structure.
No simple rules can be developed for application to all types of structures and conditions. If sufficient damage has occurred that the structure is considered to have failed that test, retesting is not permitted since it is considered that
ACI BUILDING CODEICOMMENTARY 318131811-283 CODE COMMENTARY damaged members should not be put into service even at a lower rating.
Local spalling or flaking of the compressed concrete in flex-ural elements related to casting imperfections need not indi-cate overall structural distress. Crack widths are good indicators bf the state of the structure and should be observed to help determine whether the structure is satisfac-tory. However, exact prediction or measurement of crack widths in reinforced concrete elements is not likely to be achieved under field conditions. It is advisable to establish criteria before the test, relative to the types of cracks antici-pated, where the cracks will be measured, how they will be measured, and to establish approximate limits or criteria to evaluate new cracks or limits for the changes in crack width.
20.5.2 -
Measured maximum deflections shall satisfy one of the following conditions:
max 20,000h (201)
Ann Ampex (20-2) i m x 4 If the measured maximum and residual deflections do not satisfy Eq. (20-1) or (20-2), It shall be permitted to repeat the load test.
R20.5.2 -
Specified deflection limits and the retest option follow past practice. If the structure shows no evidence of failure, "recovery of deflection" after removal of the test load is used to determine whether the strength of the struc-ture is satisfactory. In the case of a very stiff structure, how-ever, the errors in measurements under field conditions may be of the same order as the actual deflections and recovery.
To avoid penalizing a satisfactory structure in such a case, recovery measurements are waived if the maximum deflec-tion is less than L21(20,000h). The residual deflectiori-A,,.
is the difference between the initial and final (after load removal) deflections for the load test or the repeat load test.
The repeat test shall be conducted not earlier than 72 hr after removal of the first test load. The portion of the structure tested In the repeat test shall be considered acceptable if deflection recovery satisfies the condI-tion:
,,Atmax Amx5 (20-3) where Afmax Is the maximum deflection measured dur-ing the second test relative to the position of the struc-ture at the beginning of the second test.
20.5.3 -
Structural members tested shall not have cracks Indicating the Imminence of shear failure.
R205.3 -
Forces are transmitted across a shear crack plane by a combination of aggregate interlock at the inter-face of the crack which is enhanced by clamping action of transverse stirrup reinforcing and by dowel action of stir-rups crossing the crack. As crack lengths increase to approach a horizontal projected length, equal to the depth of the member and concurrently widen to the extent that aggre-gate interlock cannot occur, and as transverse stirrups if present begin to yield or display loss of anchorage so as to threaten their integrity, the member is assumed to be approaching imrninent shear failure.
318131BR-284 ACI STANDARDICOMMITTEE REPORT CODE 20.5.4 -In regions of structural members without transverse reinforcement, appearance of structural cracks inclined to the longitudinal axis and having a horizontal projection longer than-the depth of the member at midpoint of the crack shall be evaluated.
20.5.5 -
In regions of anchorage and lap splices, the appearance along the line of reinforcement of a series of short Inclined cracks or horizontal cracks shall be evaluated.
20.6 -
Provision for lower load rating If the structure under Investigation does not satisfy conditions or criteria of 20.1.2, 20.5.2, or 20.5.3, the structure shall be permitted for use at a lower load rat-ing based on the results of the load test or analysis, If approved by the building official.
COMMENTARY R20.5.4 -The intent of 20.5.4 is to make certain that the professionals in charge of the test will pay attention to the structural implication of observed inclined cracks that may:
lead to brittle collapse in members without transverse rein-forcement.
R20.S.5 -
Cracking along the axis of the reinforcement in anchorage zones may be related to high stresses associated with the transfer of forces between the reinforcement and the concrete. These cracks may be indicators of pending brittle failure of the element if they are associated with the main reinforcement. It is important.that their causes and consequences be evaluated.
R20.6 -
Provision for lower load rating Except for load tested members that have failed under a test (see 20.5), the building official may permit the use of a structure or member at a lower load rating that is judged to be safe and appropriate on the basis of the test results.
20.7-Safety 20.7.1 -
Load tests shall be conducted In such a manner as to provide for safety of life and structure during the test.
20.7.2 -
No safety measures shall Interfere with load test procedures or affect results.
"I to AEP:NRC:3520-01 ACI 349-01 CODE REQUIREMENTS FOR NUCLEAR SAFETY RELATED CONCRETE STRUCTURES CHAPTER 20 - STRENGTH EVALUATION OF EXISTING STRUCTURES
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ACI SIANUAKU PART 6-SPECIAL CONSIDERATIONS CHAPTER 20-STRENGTH EVALUATION OF EXISTING STRUCTURES 20.0-Notation D
=
dead loads or related internal moments and forces f
=
specified compressive strength of concrete, psi h
=
overall thickness of member, in.
L
=
live loads or related internal moments and forces 4
=
span of member under load test, in. (The shorter span for two-way slab systems.) Span is the smaller of (a) distance between centers of sup-ports, and (b) clear distance between supports plus thickness h of member. In Eq. (20-1), span for a cantilever shall be taken as twice the dis-tance from support to cantilever end, in.
Azax=
measured maximum deflection, in. See Eq.
(20-1)
A,,,,= measured residual deflection, in. See Eq. (20-2) and (20-3) 4,ma.~ maximum deflection measured during the second test relative to the position of the structure at the beginning of the second test, in. See Eq. (20-3) ;-
20.1-Strength evaluation: General 20.1.1 If doubt develops concerning the safety of a struc-ture or member, and/or low-strength concrete is confirmed in accordance with 5.6.4.4 and computations indicate that load-carrying capacity has been significantly reduced, the engineer may order a strength evaluation. (For approval of special systems of design or construction, see 1.4 regarding use of tests.)
20.12 If the effect of the strength deficiency is well un-derstood and if it is feasible to measure.the dimensions and material properties required for analysis, analytical evalua-tions of strength based on those measurements shall suf-fice. Required data shall be determined in accordance with 20.2.
20.13 If the effect of the strength deficiency is not well understood or if it is not feasible to establish the required dimensions and material properties by measurement, a load test shall be required if the structure is to remain in service.
20.1.4 If the doubt about safety of a part or all of a struc-ture involves deterioration, and if the observed response during the load test satisfies the acceptance criteria, the structure or part of the structure shall be permitted to re-main in service for a specified time period. If deemed nec-essary by the engineer, periodic reevaluations shall be conducted.
2 0.2-Analytical Investigations: General 20.2.1 If strength evaluation is by analysis, a thorough field investigation shall be made of dimensions and details of members, properties of materials, and other pertinent conditions of the structure as actually built.
20.2.2 Locations and sizes of the reinforcing bars, weld-ed wire fabric, or tendons shall be determined by measure--
ment. It shall be permitted to base reinforcement locations.
on available drawings if spot checks are made confirming the information on the drawings.
20.2.3 If required, concrete strength shall be based on re-sults of cylinder tests or tests of cores removed from the part of the structure where the strength is in doubt. Con-crete strengths shall be determined as specified in 5.6.4.
20.2.4 If required, reinforcement or tendon strength shall be based on tensile tests of representative samples of the material in the structure in question.
20.2.5 If the required dimensions and material properties are determined through measurements and testing, and if calculations can be made in accordance with 20.1.2 aId subject to the special requirement of 1.4, it shall be permit-ted to increase the strength reduction factor in 9.3, but the strength reduction factor shall not be more than:
Flexure, without axial load..............................
1.0 Axial tension, and axial tension with flexure............. 1.0 Axial compression and axial compression with flexure:
Members with spiral reinforcement conforming to 10.9.3 0.9 Other members 0.85 Shear and/or torsion 0.9 Bearing on concrete 0.85 20.3-Load tests: General 203.1 If strength evaluation is by load tests, a qualified engineer authorized by the Owner and engineer shall con-trol such tests.
20.3.2 A load test shall not be made until that portion of the structure to be subject to load is at least 56 days old. If the Owner, engineer, and all other involved parties agree, it is permitted to make the test at an earlier. ge.
20.3.3 When only a portion of the structure is to be load tested, the questionable portion shall be load tested in such a manner as to adequately test the suspected source of weakness.
20.3.4 Forty-eight hours prior to application of test load, a load to simulate effect of that portion of the dead loads not already actir)g shall be applied and shall remain in place un-til all testing has been completed.
20.3.5 Load tests are not confined to the complete con-crete structure; tests may be utilized to determine strength characteristics of specific elements such as anchorages and
- embedments. The engineer shall specify the appropriate testing parameters.
20.4-Load test procedure 20.4.1-Load arrangement The number and arrangement of spans or panels loaded shall be selected to maximize the deflection and stresses in the critical regions of the structural elements of which strength is in doubt. More than one test load arrangement
NUCLEAR SAFETY STRUCTURES CODE 349-73 shall be used if a single arrangement will not simultaneous-ly result in maximum values of the effects (such as deflec-tion, rotation, or stress) necessary to demonstrate the adequacy of the structure.
20.4.2-Load Intensity The test load shall be of a magnitude and in the direction of interest necessary to fully evaluate the structural behavior and response of the member or portion thereof. The total test load (including dead load already in place) shall not be less than 0.85 (IAD + 1.7L).
20.5-Loading criteria 205.1 The initial value for all applicable response mea-surements (such as deflection, rotation, strain, slip, crack widths) shall be obtained not more than one hour before ap-plication of the first load increment. Measurements shall be made at locations where maximum response is expected Additional measurementishall be made If required.
205.2 Test load shall be applied in not less than four ap-proximately equal increments.
205S3 Uniform test load shall be applied in a manner to ensure uniform distribution of the load transmitted to the structure or portion of the structure being tested. Arching of the applied load shall be avoided.
205.4 A set of response measurements shall be made after each load increment is applied and after the total load has been applied on the structure for at least 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
205.5 Total test load shall be removed immediately after all response measurements defined in 205.4 are made.
205.6 A set of final response measurements shall be made 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after the test load is removed.
where Aflna, is the maximum deflection measured during the second test relative to the position of the structure at the be-ginning of the second test.
20.63 Structural members tested shall not have cracks in-dicating the imminence of shear failure.
20.6.4 In regions of structural members without transverse reinforcement, appearance of structural cracks inclined to the longitudinal axis and having a horizontal projection longer than the depth of the member at midpoint of the crack shall be evaluated.
20.65 In regions of anchorage and lap splices, the appear-ance along the line of reinforcement of a series of short in-clined cracks or horizontal cracks shall be evaluated.
20.6.6 The engineer shall also consider the original design and functional requirements of the structure in question when establishing acceptance criteria for testing.
20.7-Safety 20.7.1 Load tests shall be conducted in such a manner as to provide for safety of life and structure during the test. The load testing shall not interfere with the operating status of the nuclear plant, or violate any plant Technical Specifications.
20.7.2 No safety measures shall interfere with load test procedures or affect results.
~.. A 20.6-Acceptance criteria 20.6.1 The portion of the structure tested khall show no ev-idence of failure. Spalling and crushing of compressed con-crete shall be considered an indication of failure.
20.62 Measured maximum deflections shall satisfy one of the following conditions.
20, OO0h Armax~gA.
(20-1)
(20-2)
If the measured maximum and residual deflections do not satisfy Eq. (20-1) or (20-2), it shall be permitted to repeat the load test.
The repeat test shall be conducted not earlier than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> after removal of the first test load. The portion of the struc-ture tested in the repeat test shall be considered acceptable if deflection recovery satisfies the condition; Ana ax (20-3) 5 to AEP:NRC:3520-01 SUPPLEMENT 7 TO DIABLO CANYON NUCLEAR POWER PLANT SAFETY EVALUATION REPORT PAGES 3-49 AND 3-50
May 26. 1978 SUPPLEMENT NO. 7 TO THE SAFETY EVALUATION REPORT BY THE OFFICE OF NUCLEAR REACTOR REGULATION U.S. NUCLEAR REGULATORY COMMISSION IN THE MATTER OF PACIFIC GAS AND ELECTRIC COMPANY DIABLO CANYON NUCLEAR POWER STATION. UNITS I AND 2 DOCKET NOS. 50-275 AND 50-323
(2) In some cases, where material test data were available, actual material properties were used in lieu of code specified minimum properties to establish allowable stress limits to justify structural integrity where the calculated stress exceeded the limits of The American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code). Code allowable.
values were used in the original analysis.
Allowable stress values were established using the bases prescribed by Appendix IlI of Section III of the ASME Code so that the factors of safety used in the code are preserved. For this reason, we consider the use of actual material properties acceptable for the reevaluation.
(3) The responses to Hosgri earthquake loads or the double design earthquake loads (whichever was more limiting) were combined with the response due to normal operation and the response due to postulated loss-of-coolant-accident loads using the absolute summation method for response combination.
This is a conservative procedure which results in the reactor coolant system being designed for loads well in excess of those calculated for a seismic event alone without a pipe break. Even though the assumed seismic event is not expected to cause a pipe break in a seismically designed piping system, these loads are combined for design purposes to produce extra margin. A further conservative element is the requirement that the peak responses to these loads be combined on an absolute sum basis. This approach used by the applicant is conservative and, therefore, acceptable.
(4) A one-quarter scale model structural test was performed on the reactor vessel shoe and pad system to determine the load-carrying capacity of the
- assembly rather than using the usual methods to determine code allowable stresses.
The allowable load was limited to 80 percent of the ultimate load obtained from the test. This follows the practice permitted by Appendices 11 and F of Section III of the ASME Code and is, therefore, acceptable.
(5) In the reevaluation, upon the applicant's own initiative, low amplitude shock or vibration testing of systems and components as they are actually installed (in-situ testing) has been performed to experimentally validate the natural frequencies, mode shapes and damping values used in the seismic analysis.
This was done for selected components and supports such as tanks, heat exchangers, valves, piping systems and supports. Where significant differences were found, the analyses were revised to correspond to knowledge gained in the tests.
3-49
This procedure is not usually required. It represents an improvement in the accuracy of the seismic design methods. It has not resulted in any relaxation of requirements. It has, in a few instances, indicated a need for refinement of the analysis procedures and in very few instances required further strengthening of the supports. Therefore, we have found it acceptable.
(6) At our request the applicant performed a special study, not usually required, in which many piping systems, including the reactor coolant loops, were analyzed assuming single snubber failures. We are still reviewing this study as discussed further in Section 3.9.3.6 below.
As a general method, however, this study represents an improvement in the accuracy of our knowledge of the plant's seismic capabilities and is, therefore, acceptable.
Evaluation of Methods Several conservatisms are inherent in the usual procedures for the seismic design of nuclear power plant mechanical systems and components. They have been extensively discussed in various forums. The general methods used by the applicant in this reevaluation as described above contain few variations from the usual procedures as defined by our usual criteria. One is the higher damping value allowed for the reactor coolant loop analysis. As discussed above, this is based on tests and is normally acceptable for Westinghouse reactor coolant systems provided that similarity with the system that was tested is demonstrated.
Another is the use of actual material test strengths. As discussed above, the code safety factors have been retained in using these material test data to establish allowable stress levels. Finally, the in situ testing program and the piping snubber study represent improvements, relative to the normal case, in our knowledge of the plant's seismic capabilities.
In our review wehtve found that in the individual steps where there are variations from the usual procedures, those individual steps have remained conservative and have retained adequate safety margins. In the remainder of the analysis, the usual conservative elements apply. Accordingly, based on our review, we have concluded that the general methods of analysis described above are conservative and provide for adequate safety margins in the design of Category I mechanical systems and components. We therefore find them acceptable, subject to satisfactory demonstration of the similarity of the Diablo Canyon reactor coolant system to the reactor coolant system that was tested to justify the use of four percent damping.
3-50