ML20217C212
| ML20217C212 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/07/1997 |
| From: | Etre M, Kupinski M, Lakshmipathiah NORTHEAST NUCLEAR ENERGY CO. |
| To: | |
| Shared Package | |
| ML20217C203 | List: |
| References | |
| S3-EV-9700574, S3-EV-9700574-R02, S3-EV-9700574-R2, NUDOCS 9804230245 | |
| Download: ML20217C212 (23) | |
Text
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Docket No. 50-423 B17115 l
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l Millstone Nuclear Station Unit No. 3 Safety Evaluation S3-EV-9700574, Rev.1 Containment Structure Porous Concrete Drainaae System l
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l April 1998 I'
9804230245 980416 DR ADOCK 05000423 PDR
Safsty Evcluntion Scrcon N'm (Sheet 1 of 3)
(Attachment 6 provides guidance)
Unit MP-3 Document No.S3-EV-9700574 Revision No. 2 Change No, t
A.
SUMMARY
INFORMATION (Completed by the Preparer) 1.
Description of the Proposed Change, Test or Experiment White residue precipitating out of the under-containment drainage effluent in the Engineered Safety Feature (ESF) building sumps has been observed since plant startup in 1986. The loss and precipitation of materials associated withwith the sub-containment porous concrete drainage system represents a change in the containment support and drainage system and is the basis for this safety evaluation.
l B. SCREENING QUESTIONS (Completed by the Preparer) l 1.
Will implementation of the proposed Change, Test or Experiment require a revision to l
the operating license or the technical specifications? (If"Yes,"NRC approvalis tequired -
l complete (a), go to Section D and sign as Preparer. If "No," complete (b) and go to Question 2) l Yes (OL or T/S change required) @ No a.
Reason OL or T/S change required and sections impacted:
l b.
Reason OL or T/S change not required and sections reviewed: The observed white residue was evaluated to be of no structural significance to the containment r
structure.
2.
Is the proposed Change, Test or Experiment fully bounded by the scope of a previously approve Safety Evaluation? (If 'Yes,"a new SEis not required -complete (a) and (b), attack p=!c=!; 2;p-^"cd SE, go to Section D and sign as Preparer. If *No,"go to Question 3 )
Yes (SE not required) % No a.
Identification of previously approved SE:
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3.
Is it obvious that the proposed Change, Test or Experiment requires a Safety Evaluation? (If 'Yes," a SE is required - complete (a) go to Section D and sign as Preparer. If "No," go to l
Question 4 3)
@ Yes (SE required)
No a.
Reason SE required:
l To assess the safety significance of the white residue with respect to containment structure inegrity and operability of safety systems inside containment and penetrating centainment.
RAC 12 Attachment 4 Level of Use
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Safety Evclur, tion Screen Form (Sheet 2 of 3) 4.
Does the proposed activity meet tLe cr* -ia of a Non-Intent Change to the Facility or procedures as described in the SAR? (d Yes,'a SEis not required -complete (a), go to Section D and sign as Preparer. If 'No,'go to Question 5)
Yes (SE not required)0 No Reason SE not required and SAR sections reviewed:
l a.
Will implementation of the proposed activity modify the Facility as described in the SAR?
5.
(If 'Yes," a SE is required - complete (a), go to Section D and sign as Preparer. If 'No ~ complete (b) and go to Question 6)
Yes (SE required) 0 No Reason SE required and SAR sections impacted:
a.
b.
Basis for 'No" and SAR sections reviewed: Proposed activity is for an evaluation of an existing condition.
Will implementation of the proposed activity modify procedures as describ5d in the i
6.
SAR? (If'Yes,'a SE is required - complete (a), go to Section D and sign as Preparer. If *No," complete (b) and go to Question 7)
Yes (SE required) 0 No l
a.
Reason SE required and SAR sections impacted:
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b.
Basis for 'No" and SAR sections reviewed: Only an evaluation of an existing change l
will be perfonned..
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l 7.
Will implementation of the proposed activity involve a Test or Experiment not described in the SAR? (If 'Yes,'a SE is required - complete (a) and go to Section D and sign as Preparer. If 'No,'
complete (b), go to Section D and sign as Preparer) l 0 Yes (SE required) 0 No a.
Reason SE required:
b.
Basis for 'No" and SAR sections reviewed: Only a safety evaluation of an existing change will be performed..
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C.
SUMMARY
(Completed by the Approver) l 1.
Is a revision to the technical specifications or operating license required" (Yes,if ouestion B.1 checked "Yes")
0 Yes 0 No 2.
Is a Design Engineering Screening Evaluation per the Design Change Manual Required? (Yes, ilproposed Change is an Intent Change to the Facility as described in the SAR)
Yes No Not Applicable g
b RAC 12 Attachment 4 b
Rev. 2 Ch 0 Levelof Use 4
4 Information 7
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Sr.fsty Evaluation Scrcon Form (Sheet 3 of 3) 3.
Is a new Safety Evaluation required? (Yes, if Question B.3 2 B.5, B.6 or B.7is checked "Yes")
@ Yes O No 4.
Is the proposed activity fully bounded by a previously approved Safety Evaluation? (Yes, if Question B.2 -3 is checked "Yes")
h O Yes @ No S.
Is a FSARCR per RAC 03 necessary? (Yes, if responses to Question B.5 or B.6 indicate proposed activity will cause the FSAR description to be incorrect)
O Yes @ No O Not Applicable lg 6.
Is the Quality Assurance Plan, Emergency Plan or Security Plan affected, requiring an evaluation per RAC 01? (Yes, if response to Question B.5, B.6, orb.7identi6es these portions of the SAR as being affected by the proposed activity)
O Yes @ No O Not Applicable l@
pg.g ////
1' 7/ff[
l D. APPROVAL 1
Preparer:
M. Kupinski/ M.S Etre-Dats: M7N[
Print and Sign" l
Reviewer 0
7h8 (iftequired)
K.Lakshmipathiah I\\
Man Date:
Print a1\\d Sign Il
[ l
~ ' ' '
7/W Approver C.G! adding Date:
~ Print and Sign I
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RAC 12 Attachment 4 Level of Use Information Rev. 2 Ch 0
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S;fsty Evcluntion Form (Sheet 1 of 19)
(Attachment 7 provides guidance)
Revision No. 2 Safety Evaluation Number S3-EV-97-00574 Revision No.
Activity Document Number Activity Document Title Millstone Unit-3 Containment Structure Porous Concrete Drainage System A.
SUMMARY
INFORMATION 1.
Descriotion of the Activity White residue precipitating out of the under-containment drainage effluent in the Engineered Safety Features Structure (ESP) sumps has been observed since plant startup in 1986 [1]. The loss and precipitation of materials associated with the sub-containment porous concrete drainage system represents a change i,n the containment support and drainage system and is the basis for this Safety Evaluation (SE).
The Millstone Unit-3's containment foundation substructure consists of two layers of porous concrete which were placed as a drainage system between the bedrock and the 10 ft. thick containment foundation concrete mat structure. The two porous concrete layers are separated from each other by a 2 inch thick protective layer of portland cement (PC) grout placed on top of the butyl rubber membrane. The substructure drainage system includes a 10 inch thick portland cement porous concrete layer placed directly on bedrock, and a 9-inch thick High Alumina Cement (HAC) porous concrete layer placed directly on top of the portland cement grout and below the containment mat. A system of G inch diameter PC porous wall concrete drain pipes is embedded in the HAC porous concrete layer to provide a flow path for the impounded water in the HAC porous concrete to drain into the ESF sumps located in the Emergency Safety Features (ESP) building.
The purpose of this SE is to assess the impact of the observed white residue and implied loss of materials with respect to licensing and design bases [2] and to determine if an Unreviewed Safety Question (USQ) exists. This SE summarizes the findings ofinvestigations, tests and monitoring programs conducted to determine the causes, effects and future implications of the change.
2.
Reason for the Activity The primary objective of the safety evaluation is to assess the significance of the observed white residue in the FSF sumps in accordance with the 10 CFIt 50.59 safety evaluation criteria.
3.
Safety Evaluation Summary Based on the investigations completed in April 1997 [3], the components of the white residue precipitating in the sumps can be understood as products of a dissolution mechanism, principally of calcium hydroxide (free lime) from the hydrated RAC 12 Attachment 5
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Levelof Use Rev. 2 Ch 0 information gjp njy 7 4/9/9811:15 AM wvv J
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Snfsty Ev lu::tian Form (Sheet 1 of 17)
(Attachment 7provides guidance)
Safety Evaluttion Number S3-EV-97-00574 Revision No. 2 Activity Document Number Revision No.
Activity Document Title Millstone Unit Containment Structure Porous Concrete Drainage System A.
SUMMARY
INFORMATION 1-Description of the Activity White residue precipitating out of the under-containment drainage effluent in the Engineered Safety Features Structure (ESF) sumps has been observed since plant startup in 1986 [1]. The loss and precipitation of materials associated with the sub-containment porous concrete drainage system represents a change in the containment support and drainage system and is the basis for this Safety Evalua' tion (SE).
The Millstone Unit-3's containment foundation substructure consists of two layers of porous concrete which were placed as a drainage system between the bedrock and the 10 ft. thick containment foundation concrete mat structure. The two porous concrete layers are separated from each other by a 2 inch thick protective layer of portland cement (PC) grout placed on top of the butyl rubber membrane. The substructure drainage system includes a 10-inch thick portland cement porous concrete layer placed directly on bedrock, and a 9-inch thick High Alumina Cement (HAC) porous concrete layer placed directly on top of the portland cement grout and below the containment mat. A system of 6 inch diameter PC porous wall concrete drain pipes is embedded in the HAC porous concrete layer to provide a flow path for the impounded water in the HAC porous concrete to drain into the ESF sumps located in the Emergency Safety Features (ESP) building.
The purpose of this SE is to assess the impact of the observed white residue and implied loss of materials with respect to licensing and design bases [2] and to determine if an Unreviewed Safety Question (USQ) exists. This SE summarizes the findings ofinvestigations, tests and monitoring programs conducted to determine the causes, effects and future implications of the change.
- 2. Reason for the Activity The primary objective of the safety evaluation is to assess the significance of the observed white residue in the ESF sumps in accordance with the 10 CFit 50.59 safety evaluation criteria.
3.
Safety Evaluation Summary Based on the investigations completed in April 1997 [3], the components of the white residue precipitating in the sumps can be understood as products of a dissolution mechanism, principally of calcium hydroxide (free lime) from the hydrated portland cement and oflime and alumina from the hydrated calcium aluminate cement. The dissolution of free lime is a common condition in plants having concrete RAC 12 Attachment 5 A
Levelof Use Rev. 2 Ch 2 Information S
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4/15/98 1:04 PM
Ssfsty Evcluntion Form (Sheet 2 of 17)
S3-EV-9700574 Rev.2 drainage systems [4] and does not deteriorate PC concrete or affect PC concrete strength. As a result of the investigation [3], the primary concern was with the integrity of the HAC porous concrete layer. It was recommended [3] that HAC cores be obtained to confirm any degradation mechanism and the residual compressive strength of the HAC porous concrete.
Several representative HAC porous concrete cores were extracted from the ESF foundation and subjected to (1) physical and chemical analyses to identify any degradation mechanism (s), and (2) confined compression strength testing to determine the actual compressive strength of the HAC porous concrete. The testing and analyses performed by CTL [ 5 ] included petrographic examinations, linear traverse measurements, x ray diffraction analyses, differential scanning calorimetry (DSC) and mercury intrusion porosimetry. The comprehensive examinations of the HAC porous concrete samples concluded that the HAC porous concrete has no evidence of structural degradation after 23 years of exposure. Three 6-inch dia. HAC cores from the ESF building foundation were subjected to instrumented confined compressive strength tests. The confined compressive strength tests concluded tlyat the HAC porous concrete has substantial compressive strength (2,700-3,000 psi) with negligible displacement (0.027 inches) [6] and, therefore, well exceeds the containment design loading conditions and criteria (215 psi) [9]. No settlement of the containment structure can occur under design basic loading since the average displacement is 0.001 inches at the limiting load of 215 psi.
Recently constructed reference HAC porous concrete mock-up samples representative of the original materials and construction processes were also subjected to chemical and physical and compressive strength testing. The compressive strength of the HAC cores from the ESF building is similar to the compressive strength obtained from the reference mock-up cores. This finding confirms that the structural properties of the HAC porous concrete have not been significantly affected after 23 years of exposure. No future structural degradation of the HAC porous concrete is expected under the existing chemical and environmental conditions [5].
The groundwater chemistry from both the portland cement porous concrete layer and the HAC porous concrete layer will be monitored periodically in the future to confirm the chemical and environmental conditions in the porous concrete layers [16].
In summary, this SE concludes that the change associated with the observed white residue in the sub-containment porous concrete drainage system ESF sumps is safe and not an USQ. This conclusion is based on the following:
3.1 Extraction of HAC Porous Concrete Cores HAC porous concrete cores were obtained to perform a realistic assessment of the actual conditions of the HAC porous concrete layer. The HAC porous concrete layer in the ESF building is continuous with the HAC porous concrete under the containment structure. The core samples from the ESF HAC porous concrete layer near the containment provide information representative of the HAC porous concrete layer below the containment structure basemat [7] as summarized below:
RAC 12 Attachment 5 Levelof Use Rev. 2 Ch 2 Information g
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Snfsty Evcluation Fcrm (Sheet 3 of 17)
S3-EY9700574 Rev.2 Prior to core boring, a technical evaluation was conducted to confirm that the HAC porous concrete core samples from the ESF building foundation are representative of the subcontainment HAC porous concrete conditions [7]. The technical evaluation considered the original as-constructed conditions, potential degradation mechanisms and the chemical and environmental conditions below the ESF building and the containment structure. The results of the assessment are summarized as follows:
- 1. The HAC porous concrete layer below the ESF mat and the containment mat is constructed as part of one uniform horizcmtal subcontainment drainage system. The location of the cores in the ESF building is in a section of the HAC porous concrete layer which is in essence a part of a containment pour which extends into the ESP building.
- 2. The construction processes and materials and the conditions in which the material was placed under both the containment mat and the ESF building mat were determined to be very similar. Therefore, the concrete characteristics of the 9-inch.
HAC porous concrete layer under the ESF building mat are representative of the material that existed under the reactor containment mat upon completion of the construction activities. A finite element heat transfer analysis was performed [17] and confirmed that the thermal conditions in the wet ESF and containment HAC porous concrete layers due to the heat of hydration from the placement of the portland cement concrete basemat during original construction were essentially similar. The peak temperature in the HAC porous concrete layer below the containment mat was calculated to be approximately 90-96 F, while the peak temperature in the HAC porous concrete layer below the ESF mat was calculated to be 85-90 F.
One minor difference in construction practice is that a PC mortar was used between the HAC porous concrete layer and the containment basemat, while an HAC mortar was used in the ESF building at the same location. However, the same PC mortar to HAC porous concrete exists also in the ESF building above the membranc. Based on the porosity of the HAC porous concrd! ' yer, both layers are exposed to the same chemical and environmental conditione. A s such, the ESF cores will provide representative information in regards to the condition of the PC mortar to HAC porous concrete materials and their interface for assessment of subcontainment conditions.
- 3. The potential degradation mechanisms for the HAC porous concrete were determined to be primarily conversion and high-pH dissolution [7 ]of the HAC paste.
Considering the continuous groundwater infiltration and the HAC porous concrete porosity, the HAC porous concrete layer below the ESF foundation and the containment mat has been submerged at a steady state temperature of approximately 65-68 F since original construction. Consequently, the potential for continued conversion of the HAC paste is considered to be the same under both the ESF and containment mat. Considering the chemical and environmental conditions in the HAC porous concrete layer, it is concluded that the post-construction conditions below the containment and the ESF building mat in the HAC porous concrete layer are relatively stagnant (low migration velocity) and quite homogenous for the majority of the porous concrete layer with the possible exception close to locations ofinleakage and the drainage pipes. Stagnation provides for diffusion and equilibration of the groundwater and its chemical content throughout the HAC porous concrete layer. Consequently, the RAC 12 Attachment 5 Levelof Use Rev. 2 Ch 2 Information 4/15/98 1:04 PM
S:fsty Evclustian Form (Sheet 4 of 17)
S3-EV-9700574 Rev.2 potential for high pH dissolution of the HAC paste is considered to be the same under both the ESF and containment mat.
Ilased on the evaluation [7], it is concluded that the as-constructed and post construction conditions in the ESF building HAC porous concrete layer and the IIAC porous layer under the containment structure are very similar and subject to the same post-construction chemical and environmental conditions. Therefore, the core samples from the ESF building foundation provide the materials properties information which is representative of the HAC porous concrete conditions below the containment basemat. The location of the samples was chosen to be away from the drainage pipes and the ESP sumps to the extent possible and as close as possible to containment to ensure that the most representative materials data is obtained for the assessment of the subcontainment HAC porous concrete layer.
3.2 Chemical and Physical Testing and Evaluation of Extracted Cores The HAC porous concrete cores were extre.cted intact and visually found to be in good condition. Chemical and physical testing including petrography, linear traverse measurements, differential scanning calorimetry, XRD and mercury porosimetry and evaluation of the cores has been completed [5,6]. In addition, a new set of mockup samples was made to establish the baseline properties for the original as-constructed HAC porous concrete.
The comprehensive testing and evaluation performed by CTL included the following materials and interface regions:
- a. The HAC porous concrete layer,
- b. The PC concrete basemat,
- c. The basemat concrete reinforcement,
- d. The HAC seal mortar,
- e. The PC mortar layer and interfaces,
- f. The PC porous concrete layer, The confined compressive strength testing was performed by Altran Corporation on both the reference mock-up samples representative of the as-constructed conditions and three 6-inch. diameter by 9-inch. long HAC porous concrete samples representative of the subcontainment conditions. The primary objectives of the test program were (1) to determine the compressive strength capacity of the in-situ HAC porous concrete, and (2) the potential effect of conversion and other degradation on the compressive strength capacity of HAC porous concrete.
The vertical basemat loading imposes a plane strain state of stress on the HAC porous concrete lab ' because of horizontal confinement. The horizontal confinement results from the very small aspect ratio of the HAC porous concrete layer [13]. To assess the compressive strength capacity of the HAC porous concrete in a confined plane strain state of stress, which exists in the HAC porous concrete layer by design, each HAC core was subjected to a confined compressive strength test. Ilecause of potential concerns that the HAC porous concrete might have significantly less strength RAC 12 Attachment 5 Levelof Use
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S3-EV-9700574 Rev.2 when wet than when dry, each HAC core was ultimately tested in a wet condition. The compressive strength tests were instrumented to measure lateral und axial displacement and potential specimen rotation for the full range of applied loading.
In summary, the comprehensive evaluations found no deterioration of the HAC porous concrete and confirmed substantial compressive strength capacity of the HAC porous concrete well in excess of design basis loading requirements. No significant build-up of deposits was observed in the HAC porous concrete voids thus assuring sufficient porosit3 to maintain drainage capability.
The significant findings from the chemical and physical tests and evaluations nre summarized below:
3.2.a High Alumina Cement Porous Concrete The HAC concrete layer is found to be in good condition after 23 years. The condition of the HAC porous concrete cement paste, porosity and aggregates is comparable to the recently constructed porous concrete mockup at Alden Research Laboratories which was undertaken to accurately replicate [5,11] the original porous concrete materials. The linear traverse measurements indicate that there is no significant difference in the distribution of paste coatings on aggregate particles between the mockup cores, representing the day zero conditions and the ESF cores representing the current day conditions. Therefore, conversion and reactions of the HAC paste with groundwater are not causing erosion or other microscopically observable changes in the HAC paste. There is some variation in paste, porosity and aggregate density from top to bottom which is attributable to placement during construction. The percentage of voids is about 10% greater in the bottom half of the cores than in the upper half of the cores. There is no evidence of chemical dissolution or erosion of the HAC paste.
Some conversion associated with the HAC paste is found. This conversion is expected to have been caused primarily by the heat of hydration associated with normal curing of both the porous concrete and the containment and ESF basemat.
Since the drainage system concrete temperature is constant around 65-68 degrees F, insignificant future conversion is expected. Voids in the HAC paste are coated with loosely attached crystalline deposits. Chemical reactions have occurred producing calcium carbosulfoaluminate, ettringite and other incidental phases. These deposits typically form a thin coating that does not substantially decrease the void space and, j
therefore, the drainage capability of the HAC porous concrete. Based on the concrete l
mix design, thermal history and exposure conditions and analyses, it is concluded that any conversion and subsequent chemical reactions have been mitigated by continued hydration and cold temperatures so that there should not be an overall significant loss of strength in the HAC porous concrete layer.
However, in order to quantify the effect of conversion and other degradation on the HAC porous concrete compressive strength, confined compressive strength tests were performed on three 6-inch diameter HAC porous concrete samples obtained from the ESF building foundation and mock-up samples representative of the original porous concrete materials properties. The average compressive strength capacity of the ESF HAC porous concrete cores was determined to be 2,850 psi with a corresponding deformation of approximately 0.027 inches. The compressive strength capacity of the RAC 12 Attachment 5 Levelof Use i"
Rev. 2 Ch 2 Information
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Snfsty Evcluation Form (Sheet 6 of 17)
S3-EV-9700574 Rev.2 IIAC porous concrete mock-up cores representing the HAC porous concrete properties during original construction was found to be similar to the ESF building samples with an average strength capacity of 2,650 psi. Therefore, it is concluded that the impact of conversion and other degradation, considering original construction and post-construction conditions over a 23 year period, on the HAC compressive strength capacity is structurally insignificant based on the compressive strength test results (5,8).
In summary, confined compressive strength tests of extracted core sampln f om the HAC porous concrete drainage system confirm that the HAC porous concrete layer has sufficient strength exceeding design load requirements with negligible settlement
[G). The compressive strength tests results confirm a displacement of approximately 0.001 inches under design loading ( 215 psi) conditions. Since there is sufficient strength without any structurally significant degradation mechanisms, no settlement or loss in strength is expected to occur in the future.
3.2.b Portland Cement Basenmt Concrete The portland cement basemat concrete is found to be in very good condition [5]. No unexpected chemical or physical degradation was observed based on microscopical examinations. Minor amounts ofincipient alkali silica reaction products were observed at some aggregates and were judged to be insignificant presently and likely not significant in the future. No reactions, distress, or leaching of constituents were observed at the interface between the concrete and the underlying HAC mortar.
Petrographic analyses confirm that the concrete mat is not a source of the white residue.
3.2.c Basemat Concrete Reinforcement During the Phase HI mock-up tests, a lack of boud was observed at the mating surface between the HAC mortar and the PC concrete. Since the bottom reinforcement of the ESF basemat has about 4-inches of clear cover and is lccated close to the HAC seal mortar grout, the most likely adverse effects due to the presence of HAC, as noted in the Phase HI tests, would be limited to the 4 inch PC concrete cover and the bottom rebar. To verify this aspect, several high density portland cement concrete core samples containing cut rebar were examined for possible eviJence of corrosion. The examination results are as follows:
Portions of steel rebar firmly embedded in the dense portland cement concrete do not exhibit evidence of corrosion or cracks associated with potential deterioration.
Itebar loosened during the coring operation does not exhibit corrosion. The reinforcement was observed to be tightly bonded to non-carbonated portland cement paste. Furthermore, the paste lining the rebar impression exhibits a high pH [5]. In summary, the examinations of the portland cement ESF concrete mat samples confirmed that there is no corrosion of the concrete reinforcement or bond degradation.
The construction of the ESF mat concrete and bottom rebar is similar in nature to the containment mat concrete and bottom rebar. Based on the examination results of the ESF core samples and the technical evaluation that the ESF mat materials and chemical and environmental conditions are representative of containment mat RAC 12 Attachment 5 Level of Use Rev. 2 Ch 2 Information g
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S fsty Evcluction Form (Sheet 7 of 17)
S3-EV-9700574 Rev.2 materials and conditions, it is our technical opinion that the containment concrete reinforcement has similarly not been subjected to corrosion degradation. No future degradation of the concrete reinforcement is expected under similar chemical and environmental subcontainment conditions.
3.2.d High Alumina Cement Seal Mortar The HAC seal mortar is in very good condition based on the petrographic examination of several ESF core samples. The mortar is well bonded to the overlying concrete basemat and the underlying HAC porous concrete. There is no evidence of chemical or physical degradation within this layer or at the interface with the basemat concrete layer [5]. While a thin layer of HAC seal mortar was used to seal the HAC porous concrete under the ESF mat, a layer of portland cement mortar was used to seal most of the HAC porous concrete under the containment basemat.
3.2.e Portland Cement Mortar Laver and Interface
~
The portland cement mortar underlying the HAC porous concrete is determined to be in very good condition based on the examination of several ESF core samples. It is not bonded to the HAC porous concrete. No degradation is observed at the HAC to PC mortar interface. Some dissolution of free lime is observed in a 2-3 mm layer of the portland cement grout at the HAC porous concrete and PC mortar interface. This confirms one source of free lime which is observed as a white precipitate in the ESF sumps. The dissolution of free lime does not affect the strength of the PC mortar [3].
The portland cement mortar is used in two locations under the containmt nt basemat. One layer of portland cement mortar is placed on top of the nwmbrane while the other layer of portland cement mortar is placed on top of the HAC porous concrete layer and below the containment mat. Since the chemical and environmental conditions under the ESF and containment mat are similar considering porous concrete porosity and groundwater chemistry, the portland cement mortar findings from the ESF core samples are considered applicable to the subcontainment mat conditions at the HAC porous concrete layer to portland cement mortar interface. No degradation is expected at the portland cement mortar to HAC porous concrete interface under the containment mat. The upper PC mortar layer may be another source of free lime to the drainage system.
The lack of bond between the HAC porous concrete and portland cement has been evaluated previously [9,10] and is not of structural concern.
3.2.f Portland Cement Porous Concrete Laver The portland cement porous concrete was reviewed in Reference [3] which concludes that it is not susceptible to structural degradation. A water sample from the portland cement porous concrete under the membrane was collected and analyzed. The pH and chemical composition indicate leaching of some calcium hydroxide from the portland cement paste in this layer. Such leaching is common in ordinary portland cement concrete and of no structural significance. The portland cement porous concrete layer can also be a possible source of free lime due to the normal interaction with the groundwater below the membrane.
RAC 12 Attachment 5 Level of Use b
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Safsty Evcluation Form (Sheet 8 of 17)
S3-EV-9700574 Rev 2 3.3.1 Effect on the Porous Concrete Capacity to Support the j
Containment Structure.
Compression strength tests confirm the HAC porous concrete strength (2,700-3,000 psi) [6] exceeds design requirements of 215 psi associated with SSE loading [9]. No structurally significant degradation was observed after 23 years of exposure below the containment foundation and no structural degradation is expected in the future under similar chemical and environmental conditions. [5]. Therefore, the HAC porous concrete has substantial compressive strength capacity to provide support to the containment structure for the design basis loading conditions.
3.3.2 Effect on the Containment StructuralIntentrity.
Compression strength capacity tests show that the HAC porous concrete has substantial strength with negligible displacement. Since there is no loss of strength and no change in HAC porous concrete compressibility, there is no e,ffect on the containment mat design basis. Therefore, the containment structural integrity will be maintained.
In addition, a worst case consequence assessment was completed [ 15 ] to evaluate the effects of postulated cement loss from the HAC porous concrete on the containment mat considering postulated uniform and non-uniform differential settlement. The finite element analysis was conducted for two extreme conditions of stiffness ranging from loose gravel to very stiff porous concrete (fc = 1,000 psi). For these limiting stiffness cases the elastic modulus of the porous concrete ranges from a lower bound value of approximately 15,000 ksf to an upper bound value of 250,000 kaf.
The first limiting cement loss distribution case assumes a uniform loss of cement in the porous concrete. The second limiting cement loss distribution represented a non-uniform condition assuming the containment mat is required to span across two 10 foot wide void regions 150 feet long the and simultaneously cantilever over a 4 foot wide settled region around the outer circumference of the mat. This scenario simulates postulated loss of cement around the subcontainment drainage pipes. For each scenario, ACI code evaluations were performed for the limiting design loading combinations. The results of the worst case assessment are as follows:
- 1. The design basis of the MP 3 containment is satisfied for the assumed wide variation of porous concrete stiffness ranging from loose gravel to very stiff concrete.
- 2. The design basis of the MP-3 containment is satisfied for the assumed conditions of non uniform differential settlement for either of the extreme values of porous concrete stiffness.
3.3.3 Effect on the Containment Structure Seismic Response.
The compressive strength tests conducted on the HAC porous concrete cores confirm no impact on the stiffness characteristics for the HAC porous concrete after 23 years of subcontainment exposure. Furthermore, the compressive strength capacity RAC 12 Attachment 5 Levelof Use j
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Snfsty Evtluation Fcrm (Sheet 9 of 17)
S3-EV-9700574 Rev.2 (2,700 3,000 psi) well exceeds the design basis loading of 215 psiincluding SSE.
Therefore, there is no impact on the design basis for the containment structure seismic response.
3.3.4 Effect on Containment Structure Settlement.
The evaluations completed in 1997 indicate that no structurally significant degradation of the HAC porous concrete has occurred after 23 years of exposure.
Compression strength tests show that the in situ HAC porous concrete has substantial strength (2,700-3,000 psi) with negligible displacement (0.027 inches) [6]. Negligible settlement of the containment structure (0.001 inches) will occur for the design loading conditions (215 psi) [9]. Since no active structural degradation is observed, this capacity is not expected to decrease in the future. Therefore, it is concluded that uniform or non-uniform differential settlement of the containment structure will not occur under design basis loading conditions.
)
3.3.5 Effect on the Sub-Containment Drainage.
Evaluation of extracted cores show negligible evidence of deterioration or clogging of the HAC porous concrete. The evaluations performed on the HAC porous concrete cores confirm that the voids are coated with loosely attached crystalline deposits and that these deposits do not substantially decrease the void space and therefore the drainage capability of the HAC porous concrete [ 5 ]. Therefore, sub-containment drainage is maintained.
4.
Aspects of the Activity Evaluated The observed precipitation of white residue occurring in the containment structure porous concrete drainage system is evaluated for possible adverse effects on containment structuralintegrity and safety systems functionality and operability.
This condition is evaluated for the following aspects:
- 1. Effect on the porous concrete capacity to support the containment structure.
J
- 2. Effect on the containment structuralintegrity.
- 3. Effect on the containment structure seismic response and seismic design basis.
i
- 4. Effect on containment structure settlement.
- 5. Effect on sub-containment drainage.
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S3-EV-9700574 Rev.2
- 5. References
[1] REF 91-52," Erosion of Cement from the Containment Basemat," Millstone Point Unit 3 Reportability Evaluation Form, April 1,1992.
[2] MNPS 3 FSAR, Sections 2 and 3
[3] CTL Project Report 050943, Rev.1," Investigation of Possible Deterioration of Porous Concrete - Millstone No. 3 Nuclear Reactor," Construction Technology Laboratories, Incorporated, April 17,1997.
[4] USNRC Information Notice 9711," Cement Erosion from Containment Subfoundations at Nuclear Power Plants," March 21,1997.
[5] CTL Project Report 050943, Rev. 0," Examination of Concrete Cores - Millstone III Subcontainment Porous Concrete," Construction Technology Laboratories, Incorporated, December 16,1997.
[6] Altran Report 97149-TR-00, Rev. O, " High Alumina Cement (HAC) Porous Concrete Core Tests," Altran Corporation, December,1997.
[7] NU Technical Position Paper, " Millstone Unit 3 Containment Basemat Project, ESFB Core Bore Samples," Northeast Utility System, May 29,1997.
[8] Letter Report, Dr. J. F. Young to Dr. A. Wong, " Assessment of Preliminary Findings on Cores taken from Millstone III," December 1,1997.
[9] NU Calculation 90-ENG-126303,"NRC Inspection Findings 50-245/96-04; 50-336/96-04;423/96-04 Letter Dated June 6,1990," Northeast Utility System, November, 1990.
[10] NU Docketed Letter, NRC Docket No. 50 423," Response to Request for Additional Information on Erosion of Cement from the Underlying Porous Concrete Drainage System, Millstone 3," Item B15985, November,1996.
[11] S&W Specification 03705.1015 001, Rev. O," Specification for Replicating ESF Building Slab and Sub-Containment Drainage System", Stone and Webster Engineering Corporation, September,1997.
[12] GEI Project Report 90199, " Porous Concrete Investigation - Millstone Unit 3," GEI Consultants, Incorporated, March 14,1997 RAC 12 Attachment 5 Level of Use R
Information
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S:faty Evcluntion Form (Sheet 11 of 17)
S3-EV-9700574 Rev.2 113] Letter Report, Dr. R. P. Kennedy to M. Kupinski," Assessment of High Alumina Cement (HAC) Porous Concrete Beneath Millstone III Containment Basemat,"
December 16,1997.
[14] E-Mail, Michael S. Kai (SAB) to P. Rieck, Date: 12/15/97,
Subject:
Containment Porous Concrete Draft SE - Reply.
[15] EQE Report Project No. 240020.01," Millstone Unit 3-Containment Mat Evaluation", EQE Calculation No. 240020-C-009 Rev. O dated September 29,1997.
[10] EP Memo MP-3 CON 98-13 from M.Kupinski to Distribution " Future Monitoring Requirements" dated March 17,1998.
[17] Altran Technical Report No.97149-TR-03" Thermal Analysis of the MP-3 Containment Foundation " dated November 1997.
[18] Millstone Unit-3 Maintenance Procedure MP-3710 FB Rev.0 " Monitoring and I
Cleaning of Sub-Containment Drain Piping".
B. UNREVIEWED SAFETY QUESTION DETERMINATION 1.
Malfunctions a.
Malfunctions Evaluated Malfunctions associated with safety related systems affected by changes in the porous concrete drainage system are:
1
- 1. Loss of structuralinteerity of the containment structure. Potential degradation of the porous concrete can cause uniform or non uniform settlements of the containment structure causing a loss in the containment basemat, liner and shell structural integrity. Extreme degradation can also reduce the stiffness characteristics of the porous concrete altering the containment structure seismic response.
- 2. Loss of operability of systems important to safety. Extreme degradation of the porous concrete can cause settlement of the containment structure causing the loss of operability of systems extending from the containment structure to surrounding structures. Changes in the seismic response of the containment structure can affect the seismic qualification of safety systems.
- 3. Loss of operability of the subcontainment drainare system. Degradation of the porous concrete and inflow of deposits / particulates could clog the voids or pores in the porous concrete layer and the porous concrete pipes. The subcontainment porous concrete drain pipes are not safety related by original design, since dewatering is not necessary to ensure the stability of the containment structure. The containment structure is designed for a hydrostatic head of groundwater at elevation 21 ft. and therefore the structural stability is assured by design. Also, by design no seismic RAC 12 Attachment 5 g
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S f;ty Evtlutticn Fcrm (Sheet 12 of 17)
S3-EV-9700574 Rev.2 category I dewatering system is required since significant amounts of groundwater are not expected.The waterproofing membrane is placed below and around the containment structure to protect the containment structure from the effects of groundwater and the steelliner from external hydrostatic pressure. If water penetrates the membrane, the porous concrete serves as a horizontal drain and a system of porous concrete drain pipes is provided to drain the impounded water below the containment structure to the ESF sumps. Changes in the drainage system may impact the intent of the original design to protect the containment structure from the effects of groundwater and the steelliner from external hydrostatic pressure.
By design, HAC was used for the porous concrete below containment and the ESF building to reduce the possibility of clogging of voids in the HAC porous concrete that normally occurs with portland cement.The chemical and physical testa conducted by CTL [5] on the HAC porous concrete cores extracted from the ESF building mat 4
verified indeed that the porosity and therefore the drainage capacity of the HAC porous concrete was not significantly affected after 23 years of exposure.The HAC j
porous concrete drainage capacity is expected to remain unaffected in the future under the existing chemical and environmental conditions.
However,since buildup of white residue has been observed in the the porous concrete drain pipes embedded in the HAC porous concrete, the porous concrete drainage piping will be inspected periodically to ensure continued operability in the future [18]. The analysis of the white residue from the ESF sumps indicates that the buildup in the pipes due to carbonation of free lime occurs mainly in the exit areas of the pipe where carbonated air has access [3]. Clogging of the pipes due to the white deposit buildup is a long-term process. Out of six drainage pipes, two appeared to be fully clogged while four pipes were partially clogged after 23 years of exposure and drainage. An evaluation of the subcontainment drainage system design confirmed that the porosity of the HAC porous concrete and the infiltration rate of the porous concrete pipe by far exceed the observed average inflow of groundwater. Even though full to partial clogging of the pipes was observed after 23 years, it was concluded that the subcontainment drainage sytem continued to effectively remove the low level of groundwater in-leakage into the ESF sumps. The periodic inspections of the exit areas
)
of the drain pipes and cleaning,when required, will therefore effectively ensure drain pipes operability in the future and compliance with the original design intent to provide for drainage of groundwater below containment into the ESF sumps.
In summary, since clogging of the HAC porous concrete is not expected and the periodic inspections of the subcontainment drain pipes will effectively ensure continued drainage piping operability, clogging due to deposition and/or infiltration of white residue will not result in a malfunction of the subcontainment drainage system.
b.
May the proposed activity increase the probability of occurrence of a Malfunction of Equipment important to Safety previously evaluated in the SAR?
Yes (activityinvolves an uSO) @ No Basis: Since there is no structural degradation occurring or expected to occur in the HAC porous concrete and the compression strength exceeds design requirements, and since potential clogging of the subcontainment drainage system will not result in a RAC 12 Attachment 5 Levelof Use Rev. 2 Ch 2 Information
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Scfaty Evelustion Form (Sheet 13 of 17)
S3-EV-9700574 Rev.2 drainage system malfunction, there is no effect on the probability of occurrence of a previously evaluated malfunction of equipment important to safety, May the proposed activity increase the Consequences of a Malfunction of c.
Equipment Important to Safety previously evaluated in the SAR?
Yes (activityinvolves an USO) @ No Basis: Since there is no structural degradation occurring or expected to occur in the HAC porous concrete and the compression strength exceeds design requirements, and since potential clogging of the subcontainment drainage system will not result in a drainage system malfunction, there is no effect on the consequences of previously 3
evaluated malfunctions of equipment important to safety.
{
i d.
May the proposed activity create the possibility of a Malfunction of a different type than any previously evaluated in the SAR?
Yes (activityinvolves an uso) @ No Basis: Since there is no structural degradation occurring or expected to occur in the HAC porous concrete and the compression strength exceeds design requirements, and since potential clogging of the subcontainment drainage system will not result in a drainage system malfunction, there is no effect on the possibility of a malfunction of a different type than previously evaluated.
2.
Accidents Accidents Evaluated The list of accidents ( Figure A.5 ) which are applicable to the containment basemat issue and were considered in the evaluation are:
L Steam Line Break ( Containment Integrity / Site Radiological Boundary Performance),
- 2. Feedwater Line Break ( Containment Integrity / Site Radiological Boundary Performance),
- 3. LOCA (Containment Integrity / Site Radiological Boundary Performance),
- 4. Failure of Small Lines Outside Containment ( Site Radiological Boundary Performance),
- a. May the proposed activity increase the probability of occurrence of Accidents previously evaluatedin the SAR?
i Yes (activityinvolves an uso)
No Basis: No structural degradation was observed nor is expected to occur in the HAC porous l
concrete in the future. The compression strength of the HAC porous concrete well exceeds the design loading requirements. No settlement of the containment structure can occur under design basis loading.
J RAC 12 Attachment 5 4
s Level of Use M
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S fsty Evtluttien Fcrm (sheet 14 of17)
S3-EV-9700574 Rev.2 May the proposed activity increase the Consequences of Accidents previously b.
evaluatedin the SAR?
D Yes (activityinvolves an uso) B No Basis: No structural degradation was observed nor is expected to occur in the HAC porous concrete in the future. The compression strength of the HAC porous concrete well exceeds the design loading requirements. No settlement of the containment structure can occur under design basis loading. Potential clogging of the subcontainment drainage pipes will not result in a malfunction of the subcontainment drainage system. It will therefore continue to protect the containment structure from the effects of groundwater and the steelliner from extemal hydrostatic pressure.
May the proposed activity create the possibility of an Accident of a different type c.
than previously evaluated in the SAR?
O Yes (activityinvolves an uso) @ No Basis: No structural degradation was observed nor is expected to occur in the HAC porous concrete in the future. The compression strength of the HAC porous concrete well exceeds the design loading requirements. No settlement of the containment structure can occur under design basis loading.
Does the proposed activity reduce the Margin of Safety as defiried in the basis 3.
forany technicalspecification?
O Yes (activityinvolves an USQ) % No Basis: Since there is no structural degradation occurring or expected to occur in the HAC porous concreto and the compression strength exceeds design loading requirements, the observed changes do not have an impact on the Margin of Safety for the containment structure, safety systems penetrating the containment structure and for safety systems inside containment as defined in the Technical Specifications.
4.
Does the proposed activity affect a liauid. solid or caseous radwaste system?
O Yes @ No (if'Yes." answer the following four questions andprovide the basis foryouranswers. If
'No.'go to C)
- a. Does the proposed activity meet the applicable seismic, quality group, quality assurance criteria and design provisions for controlling feleases of radioactive liquids in Regulatory Guide 1.1437 D Yes D No (activityinvolves an uso) D N/A Basis:
b.
Do the radiological contmis associated with the proposed activity meet the applicable criteria in Regulatory Guide 1.21 and Standard Review Plan Section 11.5, for process and effluent radiological monitoring and sampling systems?
O Yes D No (activityinvolves an usa) D N/A Basis:
RAC 12 Attachment 5 Level of Use 4
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Snfsty Evclustion Form (Sheet 15 of 17)
S3-EV-9700574 Rev.2 For systems involving potentially explosive mixtures, does the proposed activity c.
meet the applicable critena in Standard Review Plan Section 11.3, Subsection II, Item 67 0 Yes D No (activityinvolves an US0)
N/A Basis:
d.
Does the proposed activity cause (1) the radiological Consequences of unexpected and uncontrolled releases of radioactivity that is stored or transferred in a waste (3-system to be more than a small fraction of the 10CFR100 guidelines or (2) the radionuclide concentrations from liquid releases to be more than the maximum permissible concentrations specified in the 1993 version of 10CFR20, Appendix B, Table 11 column 2 at the nearest water supplies (see SRP 15.7.1, 2 & 3 for more details)?
Ocee the prepeted activity cauce the-radic!cgice! Centequence of unexpested and uncontrc!!cd re!cate cf r:dicactivity that i: etcred er transferred in v>
te system to be mere then eme!!'rection cf the 10CFR100 guide!!nce : more and
! cec then the radienuc!!de concentration cf 10CFR20, Appendig B, T b!c !!,
(1' Cc!umn 2 from liquid re!cace: et the nearect v/ ter supplies (see SRP 15.7 1,2 & 3 for-more deta!!:)?
O Yes (activityinvolves an uso)
No N/A Basis:
C. SAFETY DETERMINATION 1.
Qualitative Safety Determination a.
Is the proposed activity Safe?
Yes No Basis: The change associated with observed white residue in the ESF/ RSS cubicle sumps is reviewed against the 10 CFR 50.59 (a) criteria to determine whether the change constitutes an unreviewed safety question. Based on the detailed review in J
Section B, it is concluded that the change is safe and is not an unreviewed safety question (USQ) as summarized below:
- 1) The chemical and physicalinvestigations conclude that no structurally significant degradation has occurred or is expected for the HAC porous concrete in the future under the existing chemical and environmental subcontainment conditions.
Periodic sampling of groundwater from the HAC and PC porous concrete layers will be performed to verify the chemical and environmental conditions.
- 2) The HAC porous concrete has substantial compressive strength capacity which well exceeds the containment structure design loading requirements.
- 3) No settlement of the containment structure can occur under the design loading conditions.
- 4) The strength properties of the in-situ HAC porous concrete exceed the strength properties of the mockup samples representing the original HAC porous concrete properties.
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S3-EV-9700574 Rev.2
- 5) The observed deposits in the HAC porous concrete voids have not significantly impacted the porosity of the HAC porous concrete and, therefore, the drainage capability of the HAC porous concrete layer below containment. Periodic inspections of the subcontainment drain pipes will be performed to ensure the operability of the subcontainment drainage system.
Since no structurally significant degradation has occurred or is expected to occur in the HAC porous concrete layer under the existing chemical and environmental subcontainment conditions and the HAC porous concrete has substantial compressive strength which well exceeds the design loading conditions for the containment structure, and the subcontainment porous concrete drainage system is expected to remain operable the observed change will not affect:
(1) the probability of occurrence of an accident previously evaluated in the SAR, or (2) the probability of occurrence of a malfunction of equipment important to safety, or (3) the consequences of an accident, or (4) the consequences of a malfunction of equipment important to safety, or (5) the possibility of an accident of a different type than previously' analyzed, or (6) the possibility of a malfunction of a different type than any previously evaluated,or (7) the margin of safety as defined in the basis for any technical specifications.
The change associated with the white residue is considered safe, since it does not cause an increase in risk to public health and safety based on the following:
- 1. It will not increase the probability of an initiation of an accident, since the white residue observed in the ESF sumps is determined to be of no structural significance to the containment structure.
- 2. It will not increase the probability that operators will fail to mitigate an accident, since the llAC porous concrete strength capacity well exceeds the containment 1
structure design basis loading requirements and the subcontainment drainage system will remain operable. Furthermore, since no settlement can occur under design basis loading, all safety systems penetrating the containment structure are unaffected and therfore operable.
- 3. It will not increase the probability of failure of mitigating equipment, since the HAC porous concrete strength capacity well exceeds the containment structure design basis loading requirements and the subcontainment drainage system will remain operable. Furthermore, since no settlement can occur under design basis loading all safety system penetrating the containment structure are unaffected and therefore remain operable.
- 4. It will not increase the consequences of accidents which may result in radiological doses to the public, since the change was to determined to have no impact on the containment structural integrity.
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S3-EV-9700574 Rev.2
\\
2.
Detailed Safety Determination (IfISE and Change is an USQ)
Not required, since this is not a USQ and no ISE required.
Can the propoued activity increase the probability ofinitiation of an Accident?
a.
O Yes O No Basis:
b.
Can the proposed activity increase the probability that operators will fail to mitigate an accident?
O Yes O No Basis:
Can the proposed activity increase the probability that mitigating equipment will fail?
c.
O Yes O No Basis:
d.
Can the proposed activity increase the Consequences of an Accident?
O Yes O No Basis:
e.
Conclusion (based on the responses above, provide a conclusion for the detailed Safety Determination)
Not required since the change is not an USQ and safe.
D. APPROVAL pg g
s Preparer: Nuclear Materials Engr./DE M.Ku
. Etre D te 10/98 Discipline Print and Sign l
Reviewer:
b (if required) Nuclear Materials Engr.
.Lakshmipathiah 5!7O Date: 4/10/98 Discipline Print and Sign '
Concur O Do Not Concur (if do not concur, attach docume t tion of reasons) th f r Approver: Nuclear Materials Engr.
C. Gladding Dato 4/10/98 Discipline Print and Sign Q Concur O Do Not Concur (if do not concur, attach documentation of reasons)
PORC or ShC Meeting No.: M l2(,, Date: 4[13[9AApproval:
f
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Chairpe n RAC 12 Attachment 5 3
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Docket No. 50-423 B17115 Millstone Nuclear Station Unit No. 3 Construction Technology Laboratories (CTL) report Exmination of Concrete Cores Millstone Ill Subcontainment Porous Concrete
)
1 l
i April 1998 J