Information Notice 1997-11, Cement Erosion from Containment Subfoundations at Nuclear Power Plants
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UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
March 21, 1997
CEMENT EROSION FROM CONTAINMENT
SUBFOUNDATIONS AT NUCLEAR POWER PLANTS
Addressees
All holders of operating licenses or construction permits for nuclear power reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert
addressees to intormation regarding the possible erosion of cement from porous concrete
subfoundations below the reactor building basemats at some reactor sites. It is expected that
recipients will review the information for applicability to their facilities and consider actions, as
appropriate, to monitor similar phenomena at their plants. However, suggestions contained in
this information notice are not NRC requirements; therefore, no specific action or written
response is required.
Background
The containment structure at Millstone Nuclear Power Station Unit 3 (MNPS-3) has a
3.05-meter [10-footJ-thick reinforced-concrete basemat founded on rock. Between the
foundation rock surface and the underside of the basemat are several layers of different
materials. These layers consist of (1) a 25.4-cm [10-inch]-thick leveling layer of porous
concrete made of coarse aggregates and Portland cement, (2) a 0.16-cm [1/16th-inch]-thick
butyl rubber waterproofing membrane, (3) a 5.08-cm [2-inch]-thick Portland cement mortar
seal, (4) a second layer of 22.86-cm [9-inch]-thick porous concrete made of coarse
aggregates and calcium aluminate (high-alumina) cement, and (5) a thin mortar seal
(consisting of calcium aluminate cement and sand) on the top of the upper layer of the
porous concrete. In the upper porous concrete layer, 15-cm [6-inch]-diameter porous
concrete pipes are installed to collect and drain ground water which may seep down along
the periphery of the containment wall. The collected water drains into two sumps inside the
Engineered Safety Features (ESF) Building.
The MNPS-3 licensee, Northeast Nuclear Energy Company (NNECO), identified the issue of
cement erosion from the porous concrete drainage system in 1987 upon examination of the
accumulated sludge in the two lower drain sumps in the ESF Building. The licensee's efforts
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IN 97-11 March 21, 1997 to follow up on and resolve this concern are documented in NRC Inspection Reports
50-423/94-11 (accession number 9406060281) and 50-423/96-04 (accession number
9606180450), dated May 27, 1994, and June 6, 1996, respectively. The main concern is the
adequacy of the eroded porous media to transfer the containment loads to the bedrock. The
unexpected erosion of the high-alumina cement also gave rise to another concern regarding
a potential for interaction between the concrete of the foundation basemat that contains
Portland cement and the high-alumina cement of the subfoundation in the presence of
underground water.
To address these concerns, the licensee performed strength tests on cores obtained from
mockup tests that simulated accelerated degradation of the porous concrete. The licensee
concluded that the load-bearing capacity of the porous concrete has not been compromised.
The licensee is continuing to investigate the effects of continuous water flow on the time- dependent degradation of porous concrete. In response to a staff question on settlement of
the containment structure, NNECO has stated that, to date, no detectable movement of the
containment structure has been observed. Furthermore, NNECO has reported that the loss
of cement as a result of erosion from porous concrete is not significant.
On the basis of a review of all the available information, it appears that there is no immediate
safety concern at MNPS-3 because only an insignificant amount of cement is estimated to
have possibly eroded from the porous concrete subfoundation since the plant was built in
1975, and because no adverse consequences of the cement erosion are either predicted or
have been observed at the plant.
Discussion
To address the question of whether there are other nuclear power plant sites at which these
types of conditions could exist, the staff reviewed the updated Final Safety Analysis Reports
(UFSARs) of 24 plants selected on the basis of (1) the unique practice of the constructor or
the architect and engineers (A&Es) and (2) a sampling of A&Es. The staff found that
12 reactor units had subfoundation layers of porous concrete: MNPS-3, North Anna Units 1 and 2, Surry Units I and 2, Nine Mile Point Unit 2 (NMP-2), Maine Yankee, FitzPatrick, Beaver Valley Units 1 and 2, Haddam Neck, and Perry. Of these 12 plants, 3 have
surveillance programs for monitoring cement erosion -
MNPS-3, NMP-2, and Maine Yankee.
Maine Yankee Inspection Report 50-309/95-08 (accession number 9505240167), dated
May 16, 1995, shows that the containment sump has been under surveillance since 1970 and
that no sign of cement slurry has been found. The NMP-2 licensee has replied verbally that
no calcium aluminate has been found in the sump water sample and that its surveillance
findings will be documented in due course. The staff has obtained the following information
from the licensees of the remaining nine plants regarding the conditions at their plants:
o
Virginia Electric & Power Company (VEPCO), the licensee of North Anna Units 1 and 2 and Surry Units 1 and 2, reported on November 5, 1996, that Type II, low-alkali, Portland cement (and not calcium aluminate cement) was used in the porous concrete
at North Anna and Surry sites.
IN 97-11 March 21, 1997 At North Anna Unit 2, water samples taken recently from the basemat sump and from
two domestic water wells at the plant site showed virtually no aluminum (less than
1 ppm) in the three locations. Insignificant amounts of calcium and sulfate were
noticed at the mat sump. No detectable settlement of the containment basemat was
noticed at North Anna Units 1 and 2.
At Surry Units 1 and 2, an external subsurface drainage system operates continuously
to control groundwater level. The Unit 1 valve pit area for the internal drainage
system was dry; the Unit 2 area had a few centimeters of standing water apparently
leaking in through a side wall. A minimum amount of leachate was observed in this
area. The settlement of the containment structures of both units at Surry were found
to be less than 0.32 cm [1/8 inch], which is within the design values (1.27 cm
[1/2 inch]) for settlement.
o
The Haddam Neck plant (HNP) licensee, Northeast Utilities Services Company, reported on October 31, 1996, that Type II, low-alkali, Portland cement (and not
calcium aluminate cement) was used in the porous concrete mix. For the last
10 years at HNP, no slurry was found in the drainage water from the external
containment sump during the monthly survey done for radiological concerns. Reactor
building settlement is not monitored; however, recent inspections inside the
containment found no evidence of containment settlement and no indications of
degradation of the concrete slab.
o
The Perry nuclear power plant licensee, Cleveland Electric Illuminating Company, reported on November 4, 1996, that no cement slurry has been noted in the drainage
and there has been no evidence of pea gravel in the drainage pipes or manholes.
The licensee has, however, reported that dissolved calcium carbonate is being caried
to the drainage pipes and the sumps, where it is solidifying as a fine particulate which
hardens into hard scale. According to NRC Region IlIl Inspection Report 50440/96-04 (accession number 9609030241) dated August 21, 1996, the licensee also discovered
an accumulation of mineral deposits that clogged the pores of the porous concrete
pipes and developed an effective method of clearing the clogged pipes. The licensee
plans to clear the remaining pipes. No containment structure settlement has been
observed at Perry.
o
The Beaver Valley Power Station (BVPS) Units 1 and 2 licensee, Duquesne Light
Company (DIC), reported on November 7, 1996, that neither of the two units has
experienced drainage from the porous concrete layers below the basemat.
DLC
further claims that such drainage is not expected at BVPS because of the plant's
containment design features and the waterproof membrane that envelops the porous
concrete layer, the containment mat foundation, and the exterior wall up to the plant
grade level. DLC has reported that the total observed settlement of the BVPS
IN 97-11 March 21, 1997 containment structures compares favorably with the total predicted settlement, and
that it has not noted any unusual conditions that were related to the porous concrete
layers at BVPS Units 1 and 2.
o
The James A. FitzPatrick nuclear power plant licensee, New York Power Authority
(NYPA), reported on November 8, 1996, that the porous concrete subfoundation slab
of 15.24-cm [6-inch] (minimum) thickness was constructed using Type II Portland
cement. This slab, laid between the basemat and the rock, is surrounded by
engineered backfill. On top of the backfill, a 30.48-cm 112-inch]-diameter porous
concrete drainage pipe leading to a sump was laid with its invert level about
1.22 meters [4 feet] above the top of the porous concrete slab. Any ground water
seeping down along the sides of the reactor building collects in the sump and is
pumped into the drainage system. NYPA has not observed any cementitious slurry in
the water samples being regularly collected from the drainage sump. NYPA has also
reported that the containment structure has not settled.
On the basis uf this information and also on the basis of the staffs preliminary assessments
of MNPS-3 and NMP-2, the staff finds that there is no immediate generic or plant-specific
safety concern related to the porous concrete subfoundations below the containment
basemat at nuclear power plants. However, the NRC staff is continuing to evaluate the
potential long-term impact of erosion of high-alumina cement at MNPS-3.
This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate project manager.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: R. Pichumani, NRR
(301) 415-2734 E-mail: rxp@nrc.gov
H. Ashar, NRR
(301) 415-2851 E-mail: hga@nrc.gov
Attachment: List of Recently Issued Information Notices
Attachment
March 21, 1997 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
Information
Date of
Notice No.
Subject
Issuance
Issued to
97-10
Liner Plate Corrosion
in Concrete Containments
03/13/97
All holders of OLs
or CPs for power
reactors
97-09
Inadequate Main Steam
Safety Valve (MSSV)
Setpoints and Perform- ance Issues Associated
with Long MSSV Inlet
Piping
03/12/97
All holders of OLs
or CPs for nuclear
power reactors
97-08
97-07
97-06
91-85, Rev. 1
Potential Failures
for General Electric
Magne-Blast Circuit
Breaker Subcomponents
Problems Identified
During Generic Letter
89-10 Closeout
Inspections
Weaknesses in Plant-
Specific Emergency
Operating Procedures
for Refilling the
Secondary Side of Dry
Once-Through Steam
Generators
Potential Failures of
Thermostatic Control
Valves or Diesel
Generator Jacket
Cooling Water
03/12/97
03/06/97
03/04/97
02/27/97
All holders of OLs
or CPs for nuclear
power reactors
All holders of OLs
or CPs for nuclear
power reactors
All holders of OLs
or CPs for nuclear
power reactors with
with once-through
All holders of OLs
or CPs for nuclear
power reactors
OL = Operating License
CP = Construction Permit
IN 97-11 March 21, 1997 containment structures compares favorably with the total predicted settlement, and
that it has not noted any unusual conditions that were related to the porous concrete
layers at BVPS Units 1 and 2.
o
The James A. FitzPatrick nuclear power plant licensee, New York Power Authority
(NYPA), reported on November 8, 1996, that the porous concrete subfoundation slab
of 15.24-cm [6-inch] (minimum) thickness was constructed using Type II Portland
cement. This slab, laid between the basemat and the rock, is surrounded by
engineered backfill. On top of the backfill, a 30.48-cm [12-inch]-diameter porous
concrete drainage pipe leading to a sump was laid with its invert level about
1.22 meters [4 feet] above the top of the porous concrete slab. Any ground water
seeping down along the sides of the reactor building collects in the sump and is
pumped into the drainage system. NYPA has not observed any cementitious slurry in
the water samples being regularly collected from the drainage sump. NYPA has also
reported that the containment structure has not settled.
On the basis of this information and also on the basis of the staff's preliminary assessments
of MNPS-3 and NMP-2, the staff finds that there is no immediate generic or plant-specific
safety concern related to the porous concrete subfoundations below the containment
basemat at nuclear power plants. However, the NRC staff is continuing to evaluate the
potential long-term impact of erosion of high-alumina cement at MNPS-3.
This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate project manager.
original signed by M.M. Slosson
hvThomas T. Martin, Director
'i
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: R. Pichumani, NRR
(301) 415-2734 E-mail: rxp@nrc.gov
H. Ashar, NRR
(301) 415-2851 E-mail: hga@nrc.gov
Attachment: List of Recently Issued Information Notices *SEE PREVIOUS
CONCURRENCES
Tech Editor has reviewed and concurred on 12/13/96 DOCUMENT NAME: 97-11.11N
To receive a copy of tfis document, kidicate hI the box: TC
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ettachmentienclosure 'E' - Copy w/attachmentlenclosure 'N' -
No copy
OFFICE
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IN 97-XX
February xx, 1997 containment structures compares favorably with the total predicted settlement, and
that it has not noted any unusual conditions that were related to the porous concrete
layers at BVPS Units 1 and 2.
o
The James A. FitzPatrick nuclear power plant licensee, New York Power Authority
(NYPA), reported on November 8, 1996, that the porous concrete subfoundation slab
of 15.24-cm [6-inch] (minimum) thickness was constructed using Type II Portland
cement. This slab, laid between the basemat and the rock, is surrounded by
engineered backfill. On top of the backfill, a 30.48-cm [12-inch]-diameter porous
concrete drainage pipe leading to a sump was laid with its invert level about
1.22 meters [4 feet] above the top of the porous concrete slab. Any ground water
seeping down along the sides of the reactor building collects in the sump and is
pumped into the drainage system. NYPA has not observed any cementitious slurry in
the water samples being regularly collected from the drainage sump. NYPA has also
reported that the containment structure has not settled.
On the basis of this information and also on the basis of the staffs preliminary assessments
of MNPS-3 and NMP-2, the staff finds that there is no immediate generic or plant-specific
safety concern related to the porous concrete subfoundations below the containment
basemat at nuclear power plants. However, the NRC staff is continuing to evaluate the
potential long-term impact of erosion of high-alumina cement at MNPS-3.
This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate project manager.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: R. Pichumani, NRR
(301) 415-2734 E-mail: rxpenrc.gov
H. Ashar, NRR
(301) 415-2851 E-mail: hga@nrc.gov
Attachment: List of Recently Issued Information Notices *SEE PREVIOUS
CONCURRENCES
OFC
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DOCUMENT NAME: G:\\NKH\\CMNTERSN.IN1
IN 97-XX
January xx, 1997 containment structures compares favorably with the total predicted settlement, and
that it has not noted any unusual conditions that were related to the porous concrete
layers at BVPS Units 1 and 2.
o
The James A. FitzPatrick nuclear power plant licensee, New York Power Authority
(NYPA), reported on November 8, 1996, that the porous concrete subfoundation slab
of 15.24-cm [6-inch] (minimum) thickness was constructed using Type II Portland
cement. This slab, laid between the basemat and the rock, is surrounded by
engineered backfill. On top of the backfill, a 30.48-cm [12-inchl-diameter porous
concrete drainage pipe leading to a sump was laid with its invert level about
1.22 meters [4 feet] above the top of the porous concrete slab. Any ground water
seeping down along the sides of the reactor building collects in the sump and is
pumped into the drainage system. NYPA has not observed any cementitious slurry in
the water samples being regularly collected from the drainage sump. NYPA has also
reported that the containment structure has not settled.
On the basis of this information and also on the basis of the staffs preliminary assessments
of MNPS-3 and NMP-2, the staff finds that there is no immediate generic or plant-specific
safety concern related to the porous concrete subfoundations below the containment
basemat at nuclear power plants. However, the NRC staff is continuing to evaluate the
potential long-term impact of erosion of high-alumina cement at MNPS-3.
This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate project manager.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: R. Pichumani, NRR
(301) 415-2734 E-mail: rxp@nrc.gov
H. Ashar, NRR
(301) 415-2851 E-mail: hga@nrc.gov
Attachment: List of Recently Issued Information Notices *SEE PREVIOUS
CONCURRENCES
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IN 97-XX
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Page 4 of
containment structures compares favorably with the total predicted settlement, and
that it has not noted any unusual conditions that were related to the porous concrete
layers at BVPS Units 1 and 2.
o
The James A. FitzPatrick nuclear power plant licensee, New York Power Authority
(NYPA), reported on November 8, 1996, that the porous concrete subfoundation slab
of 15.24-cm [6-inch] (minimum) thickness was constructed using Type II Portland
cement. This slab, laid between the basemat and the rock, is surrounded by
engineered backfill. On top of the backfill, a 30.48-cm [12-inchl-diameter porous
concrete drainage pipe leading to a sump was laid with its invert level about
1.22 meters [4 feet] above the top of the porous concrete slab. Any ground water
seeping down along the sides of the reactor building collects in the sump and is
pumped into the drainage system. NYPA has not observed any cementitious slurry in
the water samples being regularly collected from the drainage sump. NYPA has also
reported that the containment structure has not settled.
On the basis of this information and also on the basis of the staffs preliminary assessments
of MNPS-3 and NMP-2, the staff finds that there is no immediate generic or. plant-specific
safety concern related to the porous concrete subfoundations below the containment
basemat at nuclear power plants. However, the NRC staff is continuing to evaluate the
potential long-term impact of erosion of high-alumina cement at MNPS-3.
This information notice requires no specific agion or written response. If you have any
questions about the information in this notipb, please contact one of the technical contacts
listed below or the appropriate project m nager.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: R. Pichu
ni, NRR
(301) 4
-2734 E-mai
rxpenrc.gov
H. A ar, NRR
(30
415-2851 E ail: hgaenrc.gov
Attachment: List of R
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IN 96-XX
December xx, 1996 o
The James A. FitzPatrick nuclear power plant licensee, New York Power
Authority (NYPA). reported on November 8, 1996, that the porous concrete
subfoundation slab of 15.24-cm [6-inch) (minimum) thickness was
constructed using Type II Portland cement. This slab, laid between the
basemat and the rock, is surrounded by engineered backfill. On top of
the backfill, a 30.48-cm [12-inch]-diameter porous concrete drainage
pipe leading to a sump was laid with its invert level about 1.22 meters
[4 feet] above the top of the porous concrete slab. Any ground water
seeping down along the sides of the reactor building collects in the
sump and is pumped into the drainage system. NYPA has not observed any
cementitious slurry in the water samples being regularly collected from
the drainage sump.
NYPA has also reported that the containment
structure has not settled.
On the basis of this information and also on the basis of the staff's
preliminary assessments of MNPS-3 and NMP-2, the staff finds that there is no
immediate generic or plant-specific safety concern related to the porous
concrete subfoundations below the containment basemat at nuclear power plants.
However, the NRC staff is evaluating the potential long-term impact of erosion
of calcium aluminate cement at MNPS-3. Should the staff's evaluation indicate
adverse effects of the erosion of cement from the porous concrete
subfoundation, the staff will issue a suitable generic communication.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate project manager.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: R. Pichumani, ECGB/DE/NRR
H. Ashar, ECGB/DE/NRR
(301) 415-2734
(301) 415-2851 E-mail: rxp@nrc.gov
E-mail: hga@nrc.gov
Attachment: List of Recently Issued Information Notices
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IN 96-XX
December xx, 1996 a
The James A. FitzPatrick nuclear power plant licensee, New York Power
Authority (NYPA), reported on November 8. 1996. that the porous concrete
subfoundation slab of 15.24-cm [6-inch] (minimum) thickness was
constructed using Type II Portland cement.
This slab, laid between the
basemat and the rock, is surrounded by engineered backfill.
On top of
the backfill, a 30.48-cm [12-inch]-diameter porous concrete drainage
pipe leading to a sump was laid with its invert level about 1.22 meters
[4 feet] above the top of the porous concrete slab. Any ground water
seeping down along the sides of the reactor building collects in the
sump and is pumped into the drainage system. NYPA has not observed any
cementitious slurry in the water samples being regularly collected from
the drainage sump.
NYPA has also reported that the containment
structure has not settled.
On the basis of this information and also on the basis of the staff's
preliminary assessments of MNPS-3 and NMP-2, the staff finds that there is no
immediate generic or plant-specific safety concern related to the porous
concrete subfoundations below the containment basemat at nuclear power plants.
However, the NRC staff is continuing to evaluate the potential long-term
impact of erosion of High-alumina cement at MNPS-3.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate project manager.
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: R. Pichumani, ECGB/DE/NRR
H. Ashar. ECGB/DE/NRR
(301) 415-2734
(301) 415-2851 E-mail: rxp@nrc.gov
E-mail: hga@nrc.gov
Attachment: List of Recently Issued Information Notices
OFC
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