ML060950570
| ML060950570 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee  |
| Issue date: | 03/22/2006 |
| From: | Morgan M NRC/NRR/ADRO/DLR/RLRC |
| To: | Office of Nuclear Reactor Regulation |
| morgan M NRR/NRC/DLR/RLRC, 415-2232 | |
| Shared Package | |
| ML060950189 | List:
|
| References | |
| %dam200611, TAC MC9668 | |
| Download: ML060950570 (5) | |
Text
AUDIT WORKSHEET GALL REPORT AMP PLANT: ______________________________
LRA AMP: __________________________ REVIEWER: ______________________
GALL AMP: XI.M22, Boraflex Monitoring DATE: __________________________
Program Auditable GALL Criteria Documentation of Audit Finding Element Program A. A Boraflex monitoring program for the actual Boraflex panels Consistent with GALL AMP: Yes No Description is implemented in the spent fuel racks to assure that no Document(s) used to confirm Criteria:
unexpected degradation of the Boraflex material would compromise the criticality analysis in support of the design of spent fuel storage racks. The applicable aging management program (AMP), based on manufacturers recommendations, Comment:
relies on periodic inspection, testing, monitoring, and analysis of the criticality design to assure that the required 5% subcriticality margin is maintained. The frequency of the inspection and testing depends on the condition of the Boraflex, with a maximum of five years. Certain accelerated samples are tested every two years. Results based on test coupons have been found to be unreliable in determining the degree to which the actual Boraflex panels have been degraded. Therefore, this AMP includes: (1) performing neutron attenuation testing, called blackness testing, to determine gap formation in Boraflex panels; (2) completing sampling and analysis for silica levels in the spent fuel pool water and trending the results by using the EPRI RACKLIFE predictive code or its equivalent on a monthly, quarterly, or annual basis (depending on Boraflex panel condition); and (3) measuring boron areal density by techniques such as the BADGER device. Corrective actions are initiated if the test results find that the 5% subcriticality margin cannot be maintained because of current or projected future Boraflex XI.M22 Boraflex Monitoring 1
Program Auditable GALL Criteria Documentation of Audit Finding Element degradation.
- 1. Scope of A. The AMP manages the effects of aging on sheets of neutron- Consistent with GALL AMP: Yes No Program absorbing materials affixed to spent fuel racks. For Boraflex Document(s) used to confirm Criteria:
panels, gamma irradiation and long-term exposure to the wet pool environment cause shrinkage resulting in gap formation, gradual degradation of the polymer matrix, and the release of silica to the spent fuel storage pool water. This results in the Comment:
loss of boron carbide in the neutron absorber sheets.
- 2. Preventive A. For Boraflex panels, monitoring silica levels in the storage Consistent with GALL AMP: Yes No Actions pool water, measuring gap formation by blackness testing, Document(s) used to confirm Criteria:
periodically measuring boron areal density, and applying predictive codes, are performed. These actions ensure that degradation of the neutron-absorbing material is identified and corrected so the spent fuel storage racks will be capable of Comment:
performing their intended functions during the period of extended operation, consistent with current licensing basis (CLB) design conditions.
- 3. Parameters A. The parameters monitored include physical conditions of the Consistent with GALL AMP: Yes No Monitored/ Boraflex panels, such as gap formation and decreased boron Document(s) used to confirm Criteria:
Inspected areal density, and the concentration of the silica in the spent fuel pool. These are conditions directly related to degradation of the Boraflex material. When Boraflex is subjected to gamma radiation and long-term exposure to the spent fuel pool Comment:
environment, the silicon polymer matrix becomes degraded and silica filler and boron carbide are released into the spent fuel pool water. As indicated in the Nuclear Regulatory Commission (NRC) Information Notice (IN) 95-38 and NRC Generic Letter (GL) 96-04, the loss of boron carbide (washout) from Boraflex is characterized by slow dissolution of silica from the surface of the Boraflex and a gradual thinning of the material. Because Boraflex contains about 25% silica, 25% polydimethyl siloxane polymer, and 50% boron carbide, sampling and analysis of the presence of silica in the spent fuel pool provide an indication of depletion of boron carbide from Boraflex; however, the degree XI.M22 Boraflex Monitoring 2
Program Auditable GALL Criteria Documentation of Audit Finding Element to which Boraflex has degraded is ascertained through measurement of the boron areal density.
- 4. Detection of A. The amount of boron carbide released from the Boraflex Consistent with GALL AMP: Yes No Aging Effects panel is determined through direct measurement of boron areal Document(s) used to confirm Criteria:
density and correlated with the levels of silica present with a predictive code. This is supplemented with detection of gaps through blackness testing and periodic verification of boron loss through areal density measurement techniques such as the Comment:
BADGER device.
- 5. Monitoring A. The periodic inspection measurements and analysis are to be Consistent with GALL AMP: Yes No and Trending compared to values of previous measurements and analysis to Document(s) used to confirm Criteria:
provide a continuing level of data for trend analysis.
Comment:
- 6. Acceptance A. The 5% subcriticality margin of the spent fuel racks is to be Consistent with GALL AMP: Yes No Criteria maintained for the period of extended operation. Document(s) used to confirm Criteria:
Comment:
- 7. Corrective A. Corrective actions are initiated if the test results find that the Consistent with GALL AMP: Yes No Actions 5% subcriticality margin cannot be maintained because of the Document(s) used to confirm Criteria:
current or projected future degradation. Corrective actions consist of providing additional neutron-absorbing capacity by Boral or boron steel inserts, or other options, which are available to maintain a subcriticality margin of 5%. As discussed Comment:
in the appendix to this report, the staff finds the requirements of 10 CFR Part 50, Appendix B, acceptable to address the corrective actions.
- 8. A. Site quality assurance (QA) procedures, site review and Consistent with GALL AMP: Yes No Confirmation approval processes, and administrative controls are Document(s) used to confirm Criteria:
Process implemented in accordance with the requirements of 10 CFR XI.M22 Boraflex Monitoring 3
Program Auditable GALL Criteria Documentation of Audit Finding Element Part 50, Appendix B. As discussed in the appendix to this report, the staff finds the requirements of 10 CFR Part 50, Appendix B, acceptable to address the confirmation process Comment:
and administrative controls.
- 9. A. See item 8, above. Consistent with GALL AMP: Yes No Administrative Document(s) used to confirm Criteria:
Controls Comment:
- 10. Operating A. The NRC IN 87-43 addresses the problems of development Consistent with GALL AMP: Yes No Experience of tears and gaps (average 1-2 in., with the largest 4 in.) in Document(s) used to confirm Criteria:
Boraflex sheets due to gamma radiation-induced shrinkage of the material. NRC INs 93-70 and 95-38 and NRC GL 96-04 address several cases of significant degradation of Boraflex test coupons due to accelerated dissolution of Boraflex caused by Comment:
pool water flow through panel enclosures and high accumulated gamma dose. Two spent fuel rack cells with about 12 years of service have only 40% of the Boraflex remaining. In such cases, the Boraflex may be replaced by boron steel inserts or by a completely new rack system using Boral. Experience with boron steel is limited; however, the application of Boral for use in the spent fuel storage racks predates the manufacturing and use of Boraflex. The experience with Boraflex panels indicates that coupon surveillance programs are not reliable. Therefore, during the period of extended operation, the measurement of boron areal density correlated, through a predictive code, with silica levels in the pool water is verified. These monitoring programs provide assurance that degradation of Boraflex sheets is monitored, so that appropriate actions can be taken in a timely manner if significant loss of neutron-absorbing capability is occurring. These monitoring programs ensure that the Boraflex sheets will maintain their integrity and will be effective in performing its intended function.
XI.M22 Boraflex Monitoring 4
EXCEPTIONS Item Program Elements LRA Exception Description Basis for Accepting Exception Documents Reviewed Number (Identifier, Para.# and/or Page #)
1.
2.
ENHANCEMENTS Item Program Elements LRA Enhancement Description Basis for Accepting Enhancement Documents Reviewed Number (Identifier, Para.# and/or Page #)
1.
2.
DOCUMENT REVIEWED DURING AUDIT Document Number Identifier (number) Title Revision and/or Date 1.
2.
3.
4.
.
XI.M22 Boraflex Monitoring 5