Information Notice 1997-11, Cement Erosion from Containment Subfoundations at Nuclear Power Plants

Cement Erosion from Containment Subfoundations at Nuclear Power Plants
	ML031050362
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	03/21/1997
From:	Martin T; Office of Nuclear Reactor Regulation
To:	;
References
	IN-97-011, NUDOCS 9703190136
	Download: ML031050362 (11)
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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 March 21, 1997 NRC INFORMATION NOTICE 97-11: 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

IN 97-11 March 21, 1997 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

97-10 Liner Plate Corrosion 03/13/97 All holders of OLs

in Concrete Containments or CPs for power

reactors

97-09 Inadequate Main Steam 03/12/97 All holders of OLs

Safety Valve (MSSV) or CPs for nuclear

Setpoints and Perform- power reactors

ance Issues Associated

with Long MSSV Inlet

Piping

97-08 Potential Failures 03/12/97 All holders of OLs

for General Electric or CPs for nuclear

Magne-Blast Circuit power reactors

Breaker Subcomponents

97-07 Problems Identified 03/06/97 All holders of OLs

During Generic Letter or CPs for nuclear

89-10 Closeout power reactors

Inspections

97-06 Weaknesses in Plant- 03/04/97 All holders of OLs

Specific Emergency or CPs for nuclear

Operating Procedures power reactors with

for Refilling the with once-through

Secondary Side of Dry steam generators

Once-Through Steam

Generators

91-85, Potential Failures of 02/27/97 All holders of OLs

Rev. 1 Thermostatic Control or CPs for nuclear

Valves or Diesel power reactors

Generator Jacket

Cooling Water

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

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NAME NHunemuller* AChaffee V T1Marti ?N I\^

DATE 12/16/96 02/19/97 03/l% /97 OFF C ARECORDPYl

IN 97-XX

February xx, 1997 containment structures compares favorably with the total predicted settlement, and