View source for Information Notice 1987-43, Gaps in Neutron-Absorbing Material in High-Density Spent Fuel Storage Racks

{{Adams
| number = ML031130349
| issue date = 09/08/1987
| title = Gaps in Neutron-Absorbing Material in High-Density Spent Fuel Storage Racks
| author name = Rossi C
| author affiliation = NRC/NRR
| addressee name = 
| addressee affiliation = 
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| license number = 
| contact person = 
| case reference number = -nr
| document report number = IN-87-043, NUDOCS 8709010085
| document type = NRC Information Notice
| page count = 7
}}
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                                                            I

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SSINS No.:   6835 IN 87-43 UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON D.C. 20555 September 8, 1987 NRC INFORMATION NOTICENO. 87-43:    GAPS IN NEUTRON-ABSORBING MATERIAL

,INHIGH-DENSITY SPENT FUEL STORAGE

RACKS

==Addressees==
:
      All nuclear power reactor facilities holding an operating license or a con- struction permit.

==Purpose==
:
      This notice is to alert recipients to a potentially significant problem per- taining to gaps identified in the neutron absorber component of the high- density spent fuel storage racks at Quad Cities Unit 1. The safety concern is

that certain gaps might excessively reduce the margin of nuclear subcriticality

in the fuel pool. The NRC expects that recipients will review this notice for

applicability to their facilities and consider actions, if appropriate, to

preclude a similar problem occurring at their facilities. However, suggestions

in-this notice do not constitute NRC requirements; therefore, no specific

action or written response is required..

==Description of Circumstances==
:
      On May 1, 1987, Commonwealth Edison Company (CECO), the licensee at Quad Cities

1 and 2, presented data to the NRC regarding gaps measured in Boraflex,.a

neutron-absorbing material used in the high-density fuel storage racks manufac- tured by the Joseph Oat Corporation (OAT). Boraflex is a trade name for a

boron carbide dispersion in an elastomeric silicone matrix manufactured by

Bisco Products, Inc. (BISCO). Data pertaining to the gap size and distribution

had been obtained by National Nuclear Corporation.(NNC) under.contract to CECO.

The licensee had retained Northeast Technology Corporation (NETCO) to interpret

the data. NETCO prefaced their assessment as preliminary, noting that avail- able data was limited, but concluded that the gap formation mechanism may be

related to large local stresses in the Boraflex from fabrication-induced re- straint within the rack and to tearing and shrinkage of the material..

The average gap size is 1-1/2 inches, with the largest 4 inches..   The gaps

occur in the.upper two-thirds of the cell length.        -
                     709010085

IN 87-43 September 8, 1987 These gaps are inferred from anomalies in "blackness" testing results by NNC.

The existence of a gap in the Quad Cities neutron absorber panel has been

confirmed by underwater neutron radiography conducted by Nusurtec, Inc.

CECO also discussed the effects these gaps might have on the approved safety

analysis for the spent fuel storage racks. CECO used conservative assumptions

for gap size, gap location, and fuel burnup. Considerable margin in k-eff

appears to be available before the licensing limit of 0.95 would be approached.

In July 1986, Wisconsin Electric Company, the licensee at Point Beach 1 and 2, reported to the NRC that test coupons of Boraflex material had shown consider- able degradation under high radiation. However, the licensee asserted that

this result did not represent the actual condition of Boraflex used in its

spent fuel storage racks because of differences in methods of encapsulation, sample geometry, and handling frequency. Additionally, the coupons had been

subjected to about 5 times more radiation than is associated with the average

fuel rack position. Subsequent examination of full-length panels disclosed

two results: in one panel examined for effects of the water environment but

exposed to negligible gamma radiation, there was no degradation of the Boraflex.

In another panel exposed to significant gamma radiation, 1-2 percent of the

surface showed a gray discoloration at the edges, similar to the degradation

of the coupons.

Discussion:
The concern is that separation of the neutron-absorbing material used in high

density fuel storage racks might compromise safety. Although Quad Cities

reports that its racks, even with gaps in the Boraflex as large as 4 inches, can meet the criticality criterion of k-eff less than or equal to 0.95, this

may not be the case for larger gaps or for other plants. A list of the 31 sites

using Boraflex is given in Attachment 1. Related information is given in

"Behavior of High-Density Spent-Fuel Storage Racks," EPRI NP-4724, Electric

Power Research Institute, August 1986.

Efforts to understand the gap formation have revealed several topics on which

information is needed. Accordingly, the material supplier (BISCO) and the

Electric Power Research Institute (EPRI) have undertaken research programs

to collect this information. Some of their objectives are described below.

The BISCO program  aims to establish with increased accuracy the relationship

between radiation  dose and size changes. The program also evaluates the

potential effects  of handling and restraint, during and subsequent to the fuel

rack fabrication,  on gap formation.

The EPRI program will correlate data from utilities' neutron absorber coupon

surveillance programs. EPRI will further examine data obtained from CECO, as

well as from BISCO and other sources, to improve the understanding of possible

or actual gap formation models, including the effects of rack fabrication

methods and irradiation damage mechanisms. The EPRI Program will also attempt

IN 87-43 September 8, 1987 to model the specific Quad Cities experience considering absorbed gamma dose as a

function of axial elevation, neutron absorbing sheet restraint, and fractional

change in length.

The effect of rack design and manufacturing methods on the consequences of

stress, temperature, and chemical environment to irradiated Boraflex is uncer- tain. Recent blackness test results at Turkey Point, who uses a Westinghouse

spent fuel storage rack, did not indicate the presence of gaps in the Boraflex.

The research programs are designed to evaluate each consequence and, In partic- ular, to improve the understanding of stress caused by method of attachment of

the Boraflex panel to the stainless steel wall of the cell. -
Together, these programs are designed to improve the industry understanding of

the safety implications of the observed gaps in the Boraflex neutron absorber

component of the OAT high-density spent-fuel storage racks at Quad Cities.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate regional office or this office.

hares E. Rossi, Director

_     _   -     -                         Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts:       Vern Hodge

(301) 492-8196 Albert D. Morrongiello

(309) 654-2227 Attachments:
                                                                               Attachment 1
1. List of Plants Using Boraflex                                               IN 87-43 Structures in the Spent Fuel Pool                                       September 8, 1987
2. List of Recently Issued NRC Information Notices LIST OF PLANTS WITH BORAFLEX

STRUCTURES IN THE SPENT FUEL POOL

1. Arkansas 1,2                         16.  Peach Bottom 2.3
                       2. Beaver Valley 1                      17.  Pilgrim

3. Diablo Canyon 1,2                    18.  Pt. Beach 1,2
                       4. Calvert Cliffs 2                     19.  Pr. Island 1,2
                       5. Farley 1,2                           20.  Quad Cities 1,2*
                       6. Fermi 2*                             21.  Rancho Seco*
                       7. Ft. Calhoun                          22.  River Bend

8. Ginna                                23.  Robinson 2
                       9. Grand Gulf 1,2*                      24.  Summer*
                      10. McGuire 1,2                          25.  Trojan

11. Millstone 1,2,3                      26.  Turkey Pt. 3,4
                      12. Nine Ni. Pt. 1,2                     27.  Waterford 3
                      13. North Anna 1,2                       28.  Seabrook 1,2
                      14. Oconee 1,2,3                         29.  Watts Bar 1,2
                      15. Oyster Creek*                        30.  Comanche Peak 1,2
                                                               31.   Harris

*Plants having spent fuel storage racks fabricated by Joseph Oat Corporation.

/                                                        \_J     Attachment 2 IN 87-43 September 8, 1987 LIST OF RECENTLY ISSUED

INFORMATION NOTICES 1987 Tnfnrwmtinn                                     n.._ --
                                                                                    uasu     or

Noti c  No.     Subfect                          Issuance        Issued to

87-42           Diesel Generator Fuse            9/4/87          All nuclear power

Contacts                                          reactor facilities

holding an OL or CP.

87-41          Failures of Certain Brown         8/31/87         All nuclear power

Boveri Electric Circuit                           reactor facilities

Breakers                                          holding an OL or CP.

87-40          Backseating Valves Routinely      8/31/87         All nuclear power

to Prevent Packing Leakage                        reactor facilities

holding an OL or CP.

87-39          Control of Hot Particle           8/21/87         All nuclear power

Contamination at Nuclear                          reactor facilities

Power Plants                                      and spent.fuel

storage facilities

holding an NRC

license or CP.

87-38          Inadequate or Inadvertent         8/17/87        All nuclear power

Blocking of Valve Movement                        reactor facilities

holding an OL or CP.

87-37          Compliance with the General       8/10/87        All persons specifi- License Provisions of                            cally licensed to

10 CFR Part 31                                   manufacture or to

Initially transfer

devices containing

radioactive material

to general licensees, as defined in 10 CFR

Part 31.

87-36          Significant Unexpected           8/4/87          All nuclear power

Erosion of Feedwater Lines                       reactor facilities

holding an OL or CP.

87-35          Reactor Trip Breaker.            7/30/87         All nuclear power

u1etinghouse Modal OSm4I6_                  - -mactui fEacz11 ties -
                                                  Failed to Open on Manual                         holdthg an OL or

Initiation from the Control                      CPeploying WDS-416 Room                                             reactor trip Breakers.

OL a Operating License

UNITED STATES            CPa Construction  Permit

FIRST CLSS MAIL

NUCLEAR REGULATORY COMMISSION                                                                                      POSTAGE

* FEES PAID

WASHINGTON, D.C. 20555                                                                                              USNIIC

PERMIT No. 0-67 OFFICIAL BUSINESS

PENALTY FOR PRIVATE USE. $300

IN 87-43 September 8, 1987 to model the specific Quad Cities experience considering absorbed gamma dose as a

function of axial elevation, neutron absorbing sheet restraint, and fractional

change in length.

The effect of rack design and manufacturing methods on the consequences of

stress, temperature, and chemical environment to irradiated Boraflex is uncer- tain. Recent blackness test results at Turkey Point, who uses a Westinghouse

spent fuel storage rack, did not indicate the presence of gaps in the Boraflex.

The research programs are designed to evaluate each consequence and, in partic- ular, to improve the understanding of stress caused by method of attachment of

the Boraflex panel to the stainless steel wall of the cell.

Together, these programs are designed to improve the industry understanding of

the safety implications of the observed gaps in the Boraflex neutron absorber

component of the OAT high-density spent-fuel storage racks at Quad Cities.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate regional office or this office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts:  Vern Hodge

(301) 492-8196 Albert D. Morrongiello

(309) 654-2227 Attachments:
1. List of Plants Using Boraflex

Structures in the Spent Fuel Pool

2. List of Recently Issued NRC Information Notices

*SEE PREVIOUS CONCURRENCES

0// /87
*OGCB:DOEA:NRR *AC/ECEB:DEST:NRR    *RI:QUAD       *PPMB:ARM *t/dGCB:DOEA:NRR

CVHodge        CMcCracken           AMorrongiello  TechEd    CHBerlinger

08/20/87       08/26/87             08/25/87       07/17/87 08/24/87

IN 87-XX

t 'August

xx, 1987 to model the specific Quad Cities experience utilizing absorbed gamma dose as a

function of axial elevation, fractional change in length and neutron absorbing

sheet restraint.

The effect of rack design and manufacturing methods on the consequences of

stress, temperature, and chemical environment to irradiated Boraflex is uncer- tain. Recent blackness test results at Turkey Point, who uses a Westinghouse

spent fuel storage rack, did not Indicate the presence of gaps in the Boraflex.

The research programs are designed to evaluate each consequence and, in partic- ular, to improve the understanding of stress caused by method of attachment or

entrapment of the Boraflex panel to the stainless steel wall of the cell.

Together, these programs are designed to improve the industry understanding of

the safety implications of the observed gaps in the Boraflex neutron absorber

component of the OAT high-density spent-fuel storage racks at Quad Cities. To

date, the NRC has not received information to prompt a more immediate address- ing of this issue.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate regional office or this office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts:     Vern Hodge

(301) 492-8196 Albert D. Morrongiello

(309) 654-2227 Attachments:
          1. List of Plants Using Boraflex

Structures in the Spent Fuel Pool

2. List of Recently Issued Information Notices

*SEE PREVIOUS CONCURRENCES

D/DOEA:NRR

_r~d~t-_(_CERossi

6           b0                                            On08//87 OGCB:DOEA:NRR    AC/ CEB:DEST:NRR      Rr:QUAD        *PPMB:ARM C/OGCB:DOEA:NRR4 CVHodge          CMcCracken           AMorrongiello   TechEd    CHBerlinger CP6
          084;0/87         o8/aIb/87            08/;S787        07/17/87  08Lpt/87

IN 87-XX

July xx, 1987 of maximum gap size, on which the determination of k-eff rests. MaJor uncer- tainties in this picture include isotropy of volume changes, damage mechanism, and influence of stress, temperature, and chemical environment.

Volume changes are assumed isotropic. If untrue, the presently estimated

maximum gap size would be significantly affected.

The radiation damage mechanism is uncertain. Crosslinking leads to shrinkage, whereas scissioning leads to increased friability of the material. In the

absence of low dose data, it is presently assumed that crosslinking damage is

proportional to dose; thus it is thought that crosslinking is about complete at

1-2 E 10 rads. The degraded Point Beach coupons were given a dose of this

magnitude, however the essentially nondegraded Point Beach panels and Quad

Cities panels and representative positions in spent fuel pool storage racks are

associated with doses from 3 to 6 times smaller than this range of values.

Stress, temperature, and chemical environment may influence the estimate of

maximum gap size and hence pool criticality. In particular, to improve the

understanding of stress, the EPRI program will determine the dependence of gap

formation on the method of attaching the Boraflex panel to the stainless steel

wall of the storage rack cell.

Together, these programs are designed to improve the industry's understanding

of the safety implications of the observed degradation of Boraflex.

No specific action or written response is required by this information notice.

If you have any questions about this matter, please contact the Regional

Administrator of the appropriate regional office or this office.

Charles E. Rossi, Director

Division of Operational Events Assessment

Office of Nuclear Reactor Regulation

Technical Contacts:   Vern Hodge

(301) 492-8196 Albert D. Morrongiello

(309) 654-2227 Attachments:
1. List of Potentially Affected Plants

2. List of Recently Issued Information Notices

OGCB:DOEA:NRR        RI:QUAD          PPMB:ARM C/OGCB:DOEA:NRR      D/DOEA:NRR

CYHodge              AMorrongiello   TechEd     CHBerlinger         CERossi

07/ /87              07/ /87         07/11/87 07/ /87               07/ /87}}

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