Information Notice 1987-43, Gaps in Neutron-Absorbing Material in High-Density Spent Fuel Storage Racks
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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
,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
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.
/
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Attachment 2
September 8, 1987
LIST OF RECENTLY ISSUED
INFORMATION NOTICES 1987
Tnfnrwmtinn
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--
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
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
8/31/87
All nuclear power
reactor facilities
8/31/87
All nuclear power
reactor facilities
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
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
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
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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: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