Information Notice 1993-70, Degradation of Boraflex Neutron Absorber Coupons

Degradation of Boraflex Neutron Absorber Coupons

ML031070107
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:	09/10/1993
From:	Grimes B Office of Nuclear Reactor Regulation
To:
References
-nr IN-93-070, NUDOCS 9309070206
Download: ML031070107 (9)

I UNITED STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON

D.C. 20555 September

10, 1993 NRC INFORMATION

NOTICE 93-70: DEGRADATION

OF BORAFLEX NEUTRON ABSORBER COUPONS

Addressees

All holders of operating

licenses or construction

permits for nuclear power reactors.PurDose The U.S. Nuclear Regulatory

Commission (NRC) is issuing this information

notice to alert recipients

to a potentially

significant

problem pertaining

to degradation

of Boraflex neutron absorber coupons. It is expected that recipients

will review the information

for applicability

to their facilities

and consider actions, as appropriate, to avoid similar problems.

However, suggestions

contained

in this information

notice are not NRC requirements;

therefore, no specific action or written response is required.Background

Palisades

has high-density

fuel storage racks installed

in the spent fuelpool that use Boraflex, a proprietary

neutron absorbing

material that was manufactured

by Brand Industrial

Services, Incorporated (BISCO). The storage racks are supplied by Westinghouse.

The Boraflex is attached to the walls of each canister and is held in place by a stainless

steel wrapper, which is spot welded to the walls.The licensee has a surveillance

program using Boraflex coupons to indicate the status of the Boraflex contained

in the high density storage racks in the spent fuel pool. Recently observed degradation

of several of these coupons, which may be due to exposure to high level gamma radiation

in conjunction

with interaction

with pool water, raised questions

about the integrity

of the Boraflex contained

in the storage racks. Significant

loss of Boraflex in the high-density

fuel racks could result in loss of the subcriticality

margin in the spent fuel pool. 'Through a commitment

to the NRC, Palisades

was required to test and inspect the Boraflex coupons after 5 years of use. The tests include opening the coupons for visual observation, neutron attenuation

determination, and a Boraflex hardness test.DescriDtion

of Circumstances

During a period from August 17 through 19, 1993, 5 of the existing 10 Boraflex coupons were removed from the spent fuel pool, 4 being full-length

coupons 9309070206 Phi tE funt 3- O7G O1~

IN 93-70 September

10, 1993 and 1 a short-set

coupon (see Figure 1). During removal of the full-length

coupons a powdery substance

and a grey debris cloud were observed emanating from the coupons. Further investigation

of the full-length

coupons revealed that one coupon had lost an estimated

90 percent of its Boraflex, two others 50 percent, and one 38 percent. Investigation

of the short-set

coupon showed that it had retained 100 percent of its Boraflex.

The licensee has determined

that the Boraflex in the 4 full-length

coupons and the short-set

coupon came from different

lots of material.A principal

difference

between the short-set

and the full-length

coupons is their geometrical

design. The short-set

coupon consists of eight compartments

encapsulating

the Boraflex with pool water accessing

only the edges of the coupons. However, in the full-length

coupon Boraflex is sandwiched

axially over the entire length of coupon and bolted between two 0.51-mm [0.020-inch]

stainless

steel metal strips. The licensee postulated

that a much larger area of the full-length

coupon was exposed to the pool water environment

and flow.In addition, the full-length

coupon has a 12.7-mm [0.5-inch]

hole through the metal strip on the top portion of the coupon, which contributes

to the pool water flow around the Boraflex.

The licensee has no immediate

plans for removal or testing of the remaining

five coupons in the spent fuel pool, but does intend to conduct neutron "blackness" testing in the spring of 1994.The licensee also had initiated

measurements

of the silica content of the spent fuel pool water. No increase in silica above normal 1-4 ppm levels have been observed except in instances

when the pool boron concentration

was increased.

Because silica filler material is a constituent

of Boraflex, the presence of silica in the water may be an indication

of degradation

of the Boraflex in the fuel pool.Discussion

Potential

degradation

mechanisms

for Boraflex include (1) gamma flux, which changes the material characteristics

of the base polymer, and (2) chemical environment, namely the accessibility

of water to the Boraflex.

The licensee has not drawn firm conclusions

as to (1) the root cause of the observed degradation

of Boraflex in the coupons, or (2) the correlation

of the behavior of Boraflex in the coupons to that in the storage racks.Degradation

of the Boraflex in fuel storage racks could reduce the subcriticality

margin in the spent fuel pool. The design basis assumes a 5 percent subcriticality

margin on the basis of lowest pool temperature, no boron concentration

in the pool water, and minimum spacing between fuel assemblies.

In its preliminary

analysis, the licensee assumed no boron in the pool water and a complete loss of Boraflex from the fuel storage racks. This reduced the subcriticality

margin from greater than 5 percent to about 2 percent. However, the licensee used the burnup for the currently

stored fuel in the criticality

calculation.

This is higher than the design burnup value, implying less reactive fuel in the fuel pool than assumed in the design calcul ation.The licensee took several compensatory

measures, including

(1) making the operating

staff aware not to dilute the spent fuel pool, (2) increasing

the

IN 93-70 September

10, 1993 spent fuel pool chemistry

sampling frequency

to daily, and (3) keeping the boron concentration

in the spent fuel pool above 1800 ppm, which exceeds the technical

specification

requirement

for boron concentration.

With these precautions

a subcriticality

margin greater than 5 percent would be maintained.

Degradation

of Boraflex has been previously

addressed

by NRC in Information

Notice 87-43, "Gaps in Neutron-Absorbing

Material in High-Density

Spent Fuel Storage Racks," September

8, 1987. The Electric Power Research Institute, which has been studying this phenomenon

for several years, has recently published

an interim report, "Boraflex

Test Results and Evaluation," TR-101986, February 1993.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

Office of Nuclear Reactor Regulation (NRR) project manager.(~/'Bran Grimes, Director Division of Operating

Reactor Support Office of Nuclear Regulatory

Regulation

Technical

contacts:

Kombiz Salehi, RIII (708) 790-5782 K. I Parczewski, NRR (301) 504-2705 Larry Kopp, NRR (301) 504-2879 Vern Hodge, NRR (301) 504-1861 Attachments:

1. Figure 1, Palisades

Boraflex Coupon Types 2. List of Recently Issued NRC Information

Notices

IN 93-70.- tSeptember

10, 1993 spent fuel pool chemistry

sampling frequency

to daily, and (3) keeping the boron concentration

in the spent fuel pool above 1800 ppm, which exceeds the technical

specification

requirement

for boron concentration.

With these precautions

a subcriticality

margin greater than 5 percent would be maintained.

Degradation

of Boraflex has been previously

addressed

by NRC in Information

Notice 87-43, "Gaps in Neutron-Absorbing

Material in High-Density

Spent Fuel Storage Racks," September

8, 1987. The Electric Power Research Institute, which has been studying this phenomenon

for several years, has recently published

an interim report, "Boraflex

Test Results and Evaluation," TR-101986, February 1993.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

Office of Nuclear Reactor Regulation (NRR) project manager.Original signed Uy Maian K. Grime$Brian K. Grimes, Director Division of Operating

Reactor Support Office of Nuclear Regulatory

Regulation

Technical

contacts:

Kombiz Salehi, RIII (708) 790-5782 K. I Parczewski, NRR (301) 504-2705 Larry Kopp, NRR (301) 504-2879 Vern Hodge, NRR (301) 504-1861 Attachments:

1. Figure 1, Palisades

Boraflex Coupon Types 2. List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCE

OFFICE OGCB:DORS:NRR

DRS:RIII DD:DRS:RIII

SRXB:DSSA:NRR

C:SRXB:DSSA:NRR

NAME *CVHodge *KSalehi *WLForney

• LIKopp *RCJones DATE 09/02/93 09/02/93 09/02/93 09/03/93 09/03/93 Tech Ed D:DSSA EMCB:DE:NRR

EMCB:DE:NRR

C:EMCB:DE:NRR

C:OEAB:DORS

• DGable *ACThadani

• JStrosnider

• KlParczewski

• RAHermann

• AEChaffee

09/01/93 09/04/93 01J0 M22 09/03/93 09/03/93 09/03/93 11 _ _ _ _ ,_C:OGCB:DORS:NRR

• GHMarcus

j I 09/03/93 09/7 /93 DOCUMENI NAME: 93-/U.IN

K>IN 93-xx I September

xx, 1993 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

Office of !Nuclear Reactor Regulation (NRR) project manager. I Brian K. Grimes, Director Division of Operating

Reactor Supi Office of Nuclear Regulatory

Regul 0ort at on Technical

Contact: Kombiz Salehi, (708) 790-5782 RIII K. I Parczewski, NRR (301) 504-2705 Larry Kopp, NRR (301) 504-2879 Vern Hodge, NRR (301) 504-1861 Attachments:

1. Figure 1, Palisades

Boraflex Coupon Types 2. List of Recently Issued NRC Information

Notices*SEE PREVIOUS CONCURRENCE

... ..... -..' at .-law. 1 OFFICE OGCB:DORS:NRR

DRS: RI I¢ .RP DD DR4:RIIIr SRXB:DSSA:NRR

L/C:SRXB:DSSA:NRRL

NAME CVHodge KSalehi WLForney LIKop RC ones, DATE O /l2/93 CO/72/93 £ /O2I93 7/3 /93 /3 /93*Tech Ed D:DSS r EMCB:DE:NRR

_MCB:DE:NRS

C: 7 U D NRR IOEAB:DORS

ACThada i Strosnider

XParczewski

RAHermann

j 0aef ffee/9 / /9 /3 /93 '1 /,3/93 § /3 /93 ___________

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GHMarcus OI M BKGrimes q/13 /93 / /93 DOCUMENT NAME: PALN0902.CVH

4Adr of ads? >.4 A 42XsK 4-ct-M etO 4 vJ IN 93-xx September

xx, 1993 The licensee took several compensatory

measures, including

(1) making the operating

staff aware to not dilute the spent fuel pool, (2) increasing

the spent fuel pool chemistry

sampling frequency

to daily, and (3) keeping the boron concentration

in the spent fuel pool above 1800 ppm, which exceeds the technical

specification

requirement

for boron concentration.

Degradation

of Boraflex has been previously

addressed

by NRC in Information

Notice 87-43, "Gaps in Neutron-Absorbing

Material in High-Density

Spent Fuel Storage Racks," September

8, 1987. The Electric Power Research Institute, who has been studying this phenomenon

for several years, has recently published

an interim report, "Boraflex

Test Results and Evaluation," TR-101986, February 1993.This information

notice requires no specific action or written response.

If you have any questions

about the information

in this notice, please contact the technical

contact listed below or the appropriate

Office of Nuclear Reactor Regulation (NRR) project manager.Brian K. Grimes, Director Division of Operating

Reactor Support Office of Nuclear Regulatory

Regulation

Technical

Contact: Kombiz Salehi, RIII (708)790-5782 K. I Parczewski, NRR Larry Kopp, NRR Vern Hodge, NRR (301) 504-2705 (301) 504-2879 (301) 504-1861 Attachments:

1. Figure 1, Palisades

Boraflex Coupon Types 2. List of Recently Issued NRC Information

Notices rnmriIDDrrr

• CFF DDVITNIC.3c LL. VUL J UVIRUURAJW

OFFICE lOGCB:DORS:NRR

DRS:RIII D:DRS:RIII

SRXB:DSSA:NRR

C:SRXB:DSSA:NRR

NAME CVHodge Ug KSalehi TOMartin LIKopp RCJones DATE Oq/ol0/93

/ /93 / /93 /93 /93 Tech Ed D:DSSA EMCB:DE:NRR

EMCB:DE:ND

C:EMCB:DE:NRR

C:OEAB:DORS

q j ACTHADANI

JStrosnider

KIParczews'ki

RAHermann

AEChaffee____ /93 /_/93 /_/93 9 /l/93 /L/93 / /93 C:OGCB:DORS:NRR

D:DORS:NRR

GHMarcus [BKGrimes/ /93 J / /93 DOCUMENT NAME: PALNOFIG.CVH

K-I Attachment

1 IN 93-70 September

10, 1993 Figure 1_Palisades

Boraflex a Coupon Types a Bodfes mate w boned bloom two I 3 Shoet M Paf kn*Q Ii..I I 3i i 3_..I: I --I 39r Ia le i ! 2 I I I4 i..4 I.I I E Li

Axtachment

2 IN 93-70 September

10, 1993 Page 1 of I LIST OF RECENTLY ISSUED NRC INFORMATION

NOTICES Information

Date of Notice No. Subject Issuance Issued to 93-69 93-68 92-16, Supp. 2 93-67 93-66 93-65 93-64 93-63 Radiography

Events at Operating

Power Reactors Failure of Pump Shaft Coupling Caused by Temper Embrittlement

during Manufacture

Loss of Flow from the Residual Heat Removal Pump during Refueling Cavity Draindown Bursting of High Pressure Coolant Injection

Steam Line Rupture Discs Injures Plant Personnel Switchover

to Hot-Leg Injection

Following A Loss-of-Coolant

Accident in Pres-surized Water Reactors Reactor Trips Caused by Breaker Testing with Fault Protection

Bypassed Periodic Testing and Preventive

Maintenance

of Molded Case Circuit Breakers Improper Use of Soluble Weld Purge Dam Material 09/02/93 09/01/93 08/23/93 08/16/93 08/16/93 08/13/93 All holders of OLs or CPs for nuclear power reactors and all radiography

licensees.

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.All holders of OLs or CPs for pressurized

water reactors.Al 1 for holders of OLs or CPs nuclear power reactors.08/12/93 08/11/93 All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.* OL = Operating

License CP = Construction

Permit