Information Notice 1987-43, Gaps in Neutron-Absorbing Material in High-Density Spent Fuel Storage Racks
Q->I SSINS No.: 6835 IN 87-43 UNITED STATES NUCLEAR REGULATORY
COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
D.C. 20555 September
8, 1987 NRC INFORMATION
NOTICENO.
87-43: GAPS IN NEUTRON-ABSORBING
MATERIAL ,IN HIGH-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:
1. List of Plants Using Boraflex Structures
in the Spent Fuel Pool 2. List of Recently Issued NRC Information
Notices Attachment
1 IN 87-43 September
8, 1987 LIST OF PLANTS WITH BORAFLEX STRUCTURES
IN THE SPENT FUEL POOL 1. Arkansas 1,2 2. Beaver Valley 1 3. Diablo Canyon 1,2 4. Calvert Cliffs 2 5. Farley 1,2 6. Fermi 2*7. Ft. Calhoun 8. Ginna 9. Grand Gulf 1,2*10. McGuire 1,2 11. Millstone
1,2,3 12. Nine Ni. Pt. 1,2 13. North Anna 1,2 14. Oconee 1,2,3 15. Oyster Creek*16. Peach Bottom 2.3 17. Pilgrim 18. Pt. Beach 1,2 19. Pr. Island 1,2 20. Quad Cities 1,2*21. Rancho Seco*22. River Bend 23. Robinson 2 24. Summer*25. Trojan 26. Turkey Pt. 3,4 27. Waterford
3 28. Seabrook 1,2 29. Watts Bar 1,2 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.._ --Noti c No.87-42 87-41 87-40 87-39 87-38 87-37 87-36 87-35 Subfect Diesel Generator
Fuse Contacts Failures of Certain Brown Boveri Electric Circuit Breakers Backseating
Valves Routinely to Prevent Packing Leakage Control of Hot Particle Contamination
at Nuclear Power Plants Inadequate
or Inadvertent
Blocking of Valve Movement Compliance
with the General License Provisions
of 10 CFR Part 31 Significant
Unexpected
Erosion of Feedwater
Lines Reactor Trip Breaker.u1etinghouse
Modal OSm4I6_Failed to Open on Manual Initiation
from the Control Room uasu or Issuance Issued to 9/4/87 All nuclear power reactor facilities
holding an OL or CP.8/31/87 All nuclear power reactor facilities
holding an OL or CP.8/31/87 All nuclear power reactor facilities
holding an OL or CP.8/21/87 All nuclear power reactor facilities
and spent.fuel
storage facilities
holding an NRC license or CP.8/17/87 All nuclear power reactor facilities
holding an OL or CP.8/10/87 All persons specifi-cally licensed to manufacture
or to Initially
transfer devices containing
radioactive
material to general licensees, as defined in 10 CFR Part 31.8/4/87 All nuclear power reactor facilities
holding an OL or CP.7/30/87 All nuclear power--mactui fEacz11 ties -holdthg an OL or CP eploying W DS-416 reactor trip Breakers.OL a Operating
License UNITED STATES CP a Construction
Permit NUCLEAR REGULATORY
COMMISSION
WASHINGTON, D.C. 20555 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE. $300 FIRST CLSS MAIL POSTAGE
- FEES PAID USNIIC PERMIT No. 0-67 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:NRR
4 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