Information Notice 1995-38, Degradation of Boraflex Neutron Absorber in Spent Fuel Storage Racks

Degradation of Boraflex Neutron Absorber in Spent Fuel Storage Racks
	ML031060277
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:	09/08/1995
From:	Crutchfield D; Office of Nuclear Reactor Regulation
To:	;
References
	IN-95-038, NUDOCS 9509050009
	Download: ML031060277 (11)
	v • d • e

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UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001 September 8, 1995 NRC INFORMATION NOTICE 95-38: DEGRADATION OF BORAFLEX NEUTRON ABSORBER IN

SPENT FUEL STORAGE RACKS

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 to alert addressees to a potentially significant problem pertaining to

degradation of the Boraflex neutron absorber material in spent fuel storage

racks. 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

Degradation of Boraflex has been previously addressed by the NRC in

Information Notice (IN)87-43, "Gaps in Neutron-Absorbing Material in High- Density Spent Fuel Storage Racks," September 8, 1987, and IN 93-70,

"Degradation of Boraflex Neutron Absorber Coupons," September 10, 1993. The

Electric Power Research Institute (EPRI) has been studying the phenomenon of

Boraflex degradation for several years and recently issued EPRI report

TR-103300, "Guidelines for Boraflex Use in Spent-Fuel Storage Racks,"

December 1993, identifying two issues with respect to using Boraflex in spent

fuel storage racks. The first related to gamma radiation-induced shrinkage of

Boraflex and the potential to develop tears or gaps in the material. The

second concerned gradual long-term Boraflex degradation over the intended

service life of the racks as a result of gamma irradiation and exposure to the

spent fuel pool environment. This second issue has previously been observed

in degradation of Boraflex surveillance coupons at the Palisades plant

(IN 93-70), but further testing of the actual Palisades storage racks

indicated no similar degradation. Because of the relatively watertight

Boraflex panel enclosures in most spent fuel storage rack designs, this type

of degradation was typically not previously considered.

The potential exists for a gradual release of silica and boron carbide from

Boraflex following gamma irradiation and long-term exposure to the spent fuel

pool environment. When Boraflex is subjected to gamma radiation in the

aqueous environment of the pool, the silicon polymer matrix becomes degraded

and silica filler and boron carbide are released. Because Boraflex is

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iv> IN 95-38 September 8, 1995 polydimethyl siloxane

composed of approximately 25 percent silica, 25 percent of silica in the pool

polymer, and 50 percent boron carbide, the presence from Boraflex. The loss

provides an indication of depletion of boron carbide by slow dissolution

of boron carbide (washout) from Boraflex is characterized

a gradual thinning of the

of the silica from the surface of the Boraflex and Boraflex represents a

material. In a typical spent fuel pool, the irradiated and is the most

significant source of silica (several thousand kilograms) carbide loss will

boron

likely source of pool silica contamination. Thematrix of fuel and Boraflex in

result in an increase in the reactivity of the

the spent fuel pool.

that influence the rate

EPRI report TR-103300 has identified several factors water around the Boraflex

of silica release from Boraflex. The presence of

influencing the rate of silica

panels is perhaps the most significant factor rack designs, this rate

dissolution from Boraflex. Because of the different also increases with

will vary from plant to plant. The rate of dissolution

suggesting that Boraflex

higher pool temperature and gamma exposure, low and by not placing

degradation can be reduced by keeping pool temperatures cells at each refueling

freshly discharged fuel assemblies in the same storage

outage.

Description of Circumstances

racks installed in the spent

The South Texas Project, Unit 1, has fuel storage The pool contains two rack

fuel pool that use Boraflex as a neutron absorber. high reactivity fuel

types. The Region 1 racks are designed to receive panels in a removable

assemblies, including fresh fuel, and use Boraflex for low reactivity spent

stainless steel box. The Region 2 racks are designed between the cell

fuel assembly storage and contain fixed Boraflex panels that adequate negative

walls. The Boraflex panels were designed to ensure

pool were accidentally flooded with

reactivity would be maintained if the

unborated water.

during August 1994 on

Blackness (neutron absorption) testing was performed storage racks to determine

selected South Texas Project Unit I spent fuel pool size and location of any

the condition of the Boraflex and to determine the to gap development, which

gaps that may have developed. However, in additionthat the Boraflex had

is a known phenomenon, the results also indicated

boron content in several of

significantly degraded due to a decrease of thethat had been designated to

the storage cells tested. Of the eight cells cells exhibited large

receive an accelerated gamma dose in Region 1, fivefeet] in length) postulated

areas of degradation (0.9 to 1.4 meters [3 to 4.5 caused by pool water

to result from accelerated dissolution of the Boraflex

high accumulated gamma dose.

flow through the panel enclosures as well as the

Fort Calhoun Station. As

Similar Boraflex degradation was discovered at thestorage racks containing

part of their rerack project, the old spent fuel 1994 to determine the

Boraflex were removed and disassembled in December Boraflex racks which

condition of the Boraflex. Two cells from the removedwere inspected. Only

had experienced the highest gamma flux since 1983 panels from these cells

40 percent of the Boraflex remained in one of the loss of Boraflex. An

while another panel in the same cell exhibited no

s>< IN 95-38 September 8, 1995 subsequent

adjacent cell had a panel which had some Boraflex loss butboron-10 areal

attenuation and density tests confirmed that the average

The new Fort

density still exceeded the material minimum certifications.

Calhoun Station storage racks do not contain Boraflex.

Discussion

fuel storage racks

Because Boraflex is used in the South Texas Project spentBoraflex could result

for absorption of neutrons, a reduction in the amount of configuration, which

in an increase in the reactivity of the spent fuel pool criterion of k~ff no

may approach, or even exceed, the current NRC acceptance

greater than 0.95.

& Power

In response to the identified Boraflex problem, Houston Lighting restrictions to

Company, the licensee for the South Texas Project, developed1 for discharged

not use the substantially degraded storage cells in Region neutron

spent fuel. In addition, the licensee is developing a long-term

absorption panel management plan, as well as a dose-to-degradation

for use of the spent

correlation, which will aid in establishing restrictions criticality

fuel racks in both Units 1 and 2. The licensee also cited by at least

analyses that showed that the fuel will remain subcriticalboron concentration

5 percent, even with no Boraflex, as long as the soluble

is at least 2,500 ppm.

is normally borated

Although pressurized-water reactor spent fuel pool water requirements do not

to approximately 2,000 ppm of boron, current regulatory conditions. Many

allow credit for the soluble boron except under accident Because BWR

boiling-water reactor (BWR) storage racks also contain Boraflex. Boraflex

spent fuel pool water does not contain boron, any significant

margin.

degradation in a BWR pool may challenge the 5 percent subcritical

response. If

This information notice requires no specific action or writtenplease contact

you have any questions about the information in this notice, Office of

one of the technical contacts listed below or the appropriate

Nuclear Reactor Regulation (NRR) project manager.

n'Mis .Crut tor

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Laurence I. Kopp, NRR

(301) 415-2879 K. I. Parczewski, NRR

(301) 415-2705 Attachment:

List of Recently Issued NRC Information Notices

A~I.' fref

A,.Achment

IN 95-38 September 8, 1995 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

95-37 Inadequate Offsite Power 09/07/95 All holders of OLs or CPs

System Voltages during for nuclear power reactors.

Design-Basis Events

95-36 Potential Problems with 08/29/95 All holders of OLs or CPs

Post-Fire Emergency for nuclear power reactors.

Lighting

95-35 Degraded Ability of 08/28/95 All holders of OLs or CPs

Steam Generators to for pressurized water

Remove Decay Heat by reactors (PWRs).

Natural Circulation

95-34 Air Actuator and Supply 08/25/95 All holders of OLs or CPs

Air Regulator Problems in for nuclear power reactors.

Copes-Vulcan Pressurizer

Power-Operated Relief Valves

93-83, Potential Loss of Spent 08/24/95 All holders of OLs or CPs

Supp. 1 Fuel Pool Cooling After a for nuclear power reactors.

Loss-of-Coolant Accident

or a Loss of Offsite Power

95-33 Switchgear Fire and 08/23/95 All holders of OLs or CPs

Partial Loss of Offsite for nuclear power reactors.

Power at Waterford

Generating Station, Unit 3

95-10, Potential for Loss of 08/11/95 All holders of OLs or CPs

Supp. 2 Automatic Engineered for nuclear power reactors.

Safety Features Actuation

95-32 Thermo-Lag 330-1 Flame 08/10/95 All holders of OLs or CPs

Spread Test Results for nuclear power reactors.

95-31 Motor-Operated Valve 08/09/95 All holders of OLs or CPs

Failure Caused by Stem for nuclear power reactors.

Protector Pipe Inter- ference

OL = Operating License

CP - Construction Permit

IN 95-38

'V September 8, 1995 adjacent cell had a panel which had some Boraflex loss but subsequent

attenuation and density tests confirmed that the average boron-10'areal

density still exceeded the material minimum certifications. The new Fort

Calhoun Station storage racks do not contain Boraflex.

Discussion

Because Boraflex is used in the South Texas Project spent fuel storage racks

for absorption of neutrons, a reduction in the amount of Boraflex could result

in an increase in the reactivity of the spent fuel pool configuration, which

may approach, or even exceed, the current NRC acceptance criterion of kff no

greater than 0.95.

In response to the identified Boraflex problem, Houston Lighting & Power

Company, the licensee for the South Texas Project, developed restrictions to

not use the substantially degraded storage cells in Region 1 for discharged

spent fuel. In addition, the licensee is developing a long-term neutron

absorption panel management plan, as well as a dose-to-degradation

correlation, which will aid in establishing restrictions for use of the spent

fuel racks in both Units 1 and 2. The licensee also cited criticality

analyses that showed that the fuel will remain subcritical by at least

5 percent, even with no Boraflex, as long as the soluble boron concentration

is at least 2,500 ppm.

Although pressurized-water reactor spent fuel pool water is normally borated

to approximately 2,000 ppm of boron, current regulatory requirements do not

allow credit for the soluble boron except under accident conditions. Many

boiling-water reactor (BWR) storage racks also contain Boraflex. Because BWR

spent fuel pool water does not contain boron, any significant Boraflex

degradation in a BWR pool may challenge the 5 percent subcritical margin.

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.

orig /s/'d by DMCrutchfield

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Laurence I. Kopp, NRR

(301) 415-2879 K. I. Parczewski, NRR

(301) 415-2705 Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: 95-38.IN *See previous concurrence

To receive a copy of this docurnent, Indicate Inthe box: wCw a Copy without attachmentlenclosure 'E' = Copy with attachment/enclosure 'N' = No copy - ---- -

RXB:DSSA E EMCB:DE E OECB:DOPS E ADM:PUB N SC/EMCB:DE m

OFFICE

NAME

DATE

LIKopp*

06/27/95 JKIParczewski*

06/28/95 PCWen*

06/27/95 Tech Editor*

06/27/95 RAHermann*

06/29/95 OFFICE C/EMCB:DE IE S/SRXB:DSSA IE E CDSSA E SC/PECB:DRPM N

NAME JRStrosnider* EWWEiss* RCJones* GMHolahan* EFGoodwin*

DATE 107/03/955/95 07/07/95 08/02/95 08/03/9 OFFICE PECB:DRPM lE C/PECB:DRPM N D/DRP i 111 NAME RJKiessel* AEChaffee* DCrut efibld _

DATE 08/21/95 08/25/95 09/ Ir/95 OFFICIAL RECORD COPY

~ IN 95-XX

August xx, 1995 attenuation and density tests confirmed that the average boron-10 areal

density still exceeded the material minimum certifications. The new Fort

Calhoun Station storage racks do not contain Boraflex.

Discussion

Because Boraflex is used in the South Texas Project spent fuel storage racks

for absorption of neutrons, a reduction in the amount of Boraflex could result

In an increase in the reactivity of the spent fuel pool configuration, which

may approach, or even exceed, the current NRC acceptance criterion of keff no

greater than 0.95.

In response to the identified Boraflex problem, Houston Lighting & Power

Company, the licensee for the South Texas Project, developed restrictions to

not use the substantially degraded storage cells in Region 1 for discharged

spent fuel. In addition, the licensee is developing a long-term neutron

absorption panel management plan, as well as a dose-to-degradation

correlation, which will aid in establishing restrictions for use of the spent

fuel racks in both Units 1 and 2. The licensee also cited criticality

analyses that showed that the fuel will remain subcritical by at least 5 percent, even with no Boraflex, as long as the soluble boron concentration is

at least 2,500 ppm.

Although pressurized-water reactor spent fuel pool water is normally borated

to approximately 2,000 ppm of boron, current regulatory requirements do not

allow credit for the soluble boron except under accident conditions. Many

boiling-water reactor (BWR) storage racks also contain Boraflex. Because BWR

spent fuel pool water does not contain boron, any significant Boraflex

degradation in a BWR pool may challenge the 5-percent subcritical margin.

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.

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical contacts: Laurence I. Kopp, NRR

(301) 415-2879 K. I. Parczewski, NRR

(301) 415-2705 Attachment: List of Recently Issued NRC Information Notices

DOCUMENT NAME: G:\PETER\BORAFLEX.IN *See previous concurrence No copy

To receive a copy of this document, indicate In the box: wCw - Copy without attachment/enclosure E = Copy with attachment/enclosure "NF -

OFFICE SRXB:DSSA E EMCB:DE E OECB:DOPS E ADM:PUB N SC/EMCB:DE LE

NAME LIKopp* KIParczewski* PCWen* Tech Editor* RAHermann*

DATE 06/27/95 106/28/95 06/27/95 06/27/95 06/29/95 OFFICDE IC, E IE E/SRXB:DSSA I /DSSA l IE SC/PECB:DRPM N

NAME IJRStrosnider* EWWEiss* RCJones* GMHolahan* EFGoodwin*

E07/05/95 07/07/95 08/02/95 08/03/95 OFFICE PECB:DRPM E C/PECB:DRPM N D/DRPM L

NAME RJKessel* AEChaffee*i DCrutchfield

DATE 08/21/95 08/25/95 / /95 OFFICIAL RECORD COPY

+\ a\5b

IN 95-XX

August xx, 1995 the material minimum certifications. No other storage cells exhibited as

significant a loss of Boraflex. The new Fort Calhoun Station storage racks do

not contain Boraflex.

Discussion

Because Boraflex is used in the South Texas Project spent fuel storage racks

for nonproductive absorption of neutrons, a reduction in the amount of

Boraflex could result in an increase in the reactivity of the spent fuel pool

configuration, which may approach, or even exceed, the current NRC acceptance

criterion of ke no greater than 0.95. The NRC has established this

5-percent subcrgticality margin to comply with General Design Criterion 62,

"Prevention of Criticality in Fuel Storage and Handling."