ML20137L506
| ML20137L506 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 04/02/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20137L479 | List: |
| References | |
| NUDOCS 9704070249 | |
| Download: ML20137L506 (5) | |
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1 UNITED STATES y
j NUCLEAR REGULATORY COMMISSION 2
WASHINGTON. D.C. 30666 4001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR _. REACTOR REGULATION RELATED TO AMENDMENT NO. 86 TO FACILITY OP/ RATING LICENSE NO. NPF-37, AMENDMENT NO. 86 TO FACILITY OPERATING LICENSE NO. NPF-66, AMENDMENT NO. 78 TO FACILITY OPERATING LICENSE NO. NPF-72, AND AMENDMENT NO. 78 TO FACILTTY OPERATING LICENSE NO. NPF-77 COMMONWEALTH EDISON COMPANY BYRON STATION. UNIT NOS. I AND 2 BRAIDWOOD STATION. UNIT NOS. I AND 2 DOCKET NOS. STN 50-454. STN 50-455. STN 50-456 AND STN 50-457
1.0 INTRODUCTION
By letter dated November 5,1996, Commonwealth Edison Company (Comed, the licensee) requested changes to the Byron Station, Units 1 and 2, and Braidwood Station, Units 1 and 2 Technical Specifications (TS) to allow credit to be taken for soluble boron in the spent fual storage pool water in maintaining an acceptable margin of subcriticality. Specifically, TS 3.9.11 " Water Level -
Storage Pool," TS 5.6.1.1, " Criticality," and TS 6.9.1.10, " Criticality Analysis of Byron and Braidwood Station Fuel Storage Racks" would be modified.
The proposed changes are temporary in nature and are requested to compensate for the degradation of the Boraflex panels in the spent fuel storage cells until long-term corrective actions for this problem are implemented. The proposed changes would be in effect until no later than December 31, 1997.
Additional information was provided in the licensee's submittal of February 27, 1997.
Subsequently, Comed submitted two additional letters related to the issue of an acceptable margin of subcriticality in the spent fuel storage pools. The first of these dated March 25, 1997, addressed the long-term resolution of this issue in response to Generic Letter (GL) 96-04, "Boraflex Degradation in Spent Fuel Pool Racks," dated June 26, 1996. Comed stated in this letter that it would submit in June 1997, license amendment requests for both the Byron and Braidwood Stations which would include a new criticality analysis using a methodology approved by the NRC. These forthcoming license amendment requests do not bear on the pending license amendments.
The second Comed letter dated March 30, 1997, discusses a modeling deficiency related to the configuration of Boral plates in those portions of the spent fuel racks used to store new fuel elements (i.e., Region 1). This modeling 9704070249 970402 PDR ADOCK 05000454
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- error did not account for the fact that the Boral plates which were added ^o the interior portions of the new fuel storage racks, were not present on the periphery of the Region 1 fuel racks.. Accordingly, certain peripheral cells, identified as Y cellt, actually contain Boral plates on only three sides; and the four corner cells in each Region I rack actually contain only two interior 3 oral plates as opposed to the Boral plates assumed on all four sides of the fuel cells in the original modeling of the Region 1 fuel racks. This incorrect modeling was contained in the criticality analysis submitted in Comed's letter dated November 5, 1996, cited above. The staff's evaluation of this supplemental information is presented below.
2.0 EVALUATION 2.1 Technical Evaluation The spent fuel storage pools (SFP) at Byron and Braidwood have fuel storage racks installed that use sheets of Boraflex for reactivity suppression.
Boraflex is constructed of an organic polymer with a silica filler and neutron absorbing boron carbide interspersed within the silica filler.
Boral plates have also been added to the Region I racks for additional reactivity suppression.
The results of recent neutron attenuation tests (blackness tests) performed at Braidwood and Byron during August and September 1996, respectively, indicate that at least some of the Boraflex sheets have degraded to an extent whereby it can not be stated with certainty that the TS 5.6.1.1 requirement for equal to 0.95 when flooded with unborated water will be meI. ) less than or maintaining the effective neutron multiplication factor (k,,in some limiting rack locations.
Comed is considering several long-term corrective actions to return the SFP to compliance with TS 5.6.1.1.
These actions include restricted storage (checkerboard) patterns, neutron absorber rods or inserts, reracking with non-Boraflex racks, dry cask storage, or partial credit for soluble boron.
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However, these corrective actions may require some time to implement. As l
discussed above, Comed will submit its proposed long-term corrective actions i
in June 1997 using the methodology of WCAP-14416-NP-A, " Westinghouse Spent j
Fuel Rack Criticality Analysis Methodology," Revision 1, November 1996.
In addition to the proposed TS revisions which would allow credit to be taken for soluble boron in the spent fuel storage pool water to maintain an j
acceptable margin cf subcriticality, Comed has implemented compensatory
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measures.
(1) Exrerimental data indicates that once silica reaches an equilibrium value, the rate of Boraflex dissolution is greatly reduced.
i However, when water purification systems are used to remove silica from the pool water, the solubility equilibrium becomes unbalanced and dissolution i
resumes. Therefore, Comed has imposed a restriction on the use of the reverse osmosis unit for silica removal to slow the rate of Boraflex dissolution.
(2) local indications at the SFP as well as alarus in the main control room are in place to indicate both high and low SFP water level. Therefore, any 1
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i level change that could be indicative of a dilution event would be quickly noticed to allow for prompt corrective actions.
(3) In order to preclude the possibility of a 3FP boron dilution event during the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> surveillance time interval, SFP lev 0 loss procedures will be revised to clearly state that the unborated water emers,ency makeup sources must be used only as a last resort.
Confirmation of the procedure revisions was provided in the licensee's letter of February 27, 1997. The compensatory measures and the proposed TS changes are temporary and would be in effect until December 31, 1997, at which time, i
long-term corrective actions for the Boraflex degradation problem are expected to be implemented. An additional compensatory measure in the form of administrative controls was added to the procedures of both stations as stated in Coned's letter dated March 30, 1997, to correct for the modeling errors discussed above. This administrative control on the placement of new fuel
- assemblies states in part that:
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"No assembly may be placed in a Region I rack location face adjacent to another assembly across a Region 1 rack to Region 1 rack interface."
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The net effect of this control on the placement of fuel assemblies is to limit j
the number of new fuel assemblies along each Region I to Region 1 interface to j
no more than eight fuel assemblies, four in each interfacing rack, as opposed to the 16 available positions.
Each of these fuel assemblies along the j
subject interfaces would also be limited to a diagonal (i.e., checkerboard) j placement as required in Figure 2 of Comed's letter dated March 30, 1997.
I TS 3.1.11, as revised, would address SFP boron concentration as well as water level.
The limiting condition for operation (LCO) would require the dissolved boron concentration of the water in the SFP to be maintained at greater than or equal to 2000 ppe. With the boron concentration requirement not met, all movement of fuel assemblies and crane operations with loads in the fuel storage areas would be suspended and action immediately taken to restore the boron concentration to within its limit. A surveillance requirement would also be added to require the SFP boron concentration to be verified at least once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. These proposed changes would include a footnote indicating that the requirements will be in effect until December 31, 1997.
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A proposed footnote to TS 5.6.1.1 also included a statement that until December 31, 1997, the spent fuel storage racks shall be maintained with a k
of less than or equal to 0.95 when flooded with water containing a alnnimum # 2000 ppe soluble boron.
F Comed performed additional criticality analyses and submitted the results in its March 30, 1997, letter. The licensee stated in this letter that these supplemental analyses verify that k,n remains less than 0.95 with 2000 ppe soluble boron and no Boral and no Boraflex present in the spent fuel pool.
Based on previous calculations reviewed by the staff for similar spent fuel pools, the reactivity equivalent of 2000 ppe of boron is at least 30 percent ak. This amount of negative reactivity is more than sufficient to maintain at least a 5 percent margin of subcriticality, even assuming all the Boraflex and i
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Boral is ineffective from a reactivity mitigation standpoint. This staff i
conclusion, therefore, remains valid even in light of the error in the modeling of the placement of Boral plates in the Region 1 periphery and corner cells. Since, in reality, an appreciable amount of Boraflex (and Boral) still remains, the requirement to maintain at least 2000 ppa of boron is conservative. The staff, therefore, concurs that the proposed temporary changes to TS 3.9.11 will compensate for the degradation of the Boraflex and maintain k,, less than or equal to 0.95, even for those cells whose Boral plateconflgurationswerepreviouslymodeledincorrectly.
In addition, the procedures and alarms in place allow for prompt corrective actions to preclude j
a SFP dilution event.
Further, the restriction on the use of the reverse osmosis unit for silica removal will slow the rate of future Boraflex degradation.
Finally, the additional administrative controls on the placement of new fuel assemblies adjacent to Region 1 to Region 1 interfaces as discussed above, which were recently incorporated into the Byron and Braidwood Station procedures, provide additional assurance that the reactivity of the Region I fuel racks will satisfy all NRC acceptance criteria. Therefore, the i
staff finds the proposed changes to 3.9.11 and 5.6.1.1 related to maintaining 2000 ppm of boron in the SFP are acceptable until long-term corrective actions are implemented.
A second part of the footnote to TS 5.6.1.1 and a proposed footnote to TS 6.9.1.10 referenced the Westinghouse document CAC-96-248, " Byron and Braidwood i
Spent Fuel Rack Criticality Analysis with Credit for Soluble Boron" which was i
submitted with this amendment reques).. However, this document is not based on the NRC-approved Westinghouse methodoiogy for soluble boron credit, as given in WCAP-14416-NP-A dated November 1996, and, therefore, may not be relied on as a basis for the proposed change.
2.2 Significant Hazards Consideration In the Federal Reaister notice issued on February 10, 1997 (62 FR 6016), the staff made no initial determination regarding a significant hazards 4
consideration. Accordingly, there is no need to reissue the initial notice.
3.0 SUPfiARY Basad on the safety evaluation above, the staff finds the proposed changes to TS 5.6.1.1 and TS 6.9.1.10 related to maintaining 2000 ppm in the SFPs for Byron and Braidwood in order to maintain subcriticality to be acceptable. The I
use of an unapproved methodology, CAC-96-248, is not acceptable.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Illinois State official was notified of the proposed issuance c' the amendments. The State official had no comments.
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5.0 ENVIRONMENTAL CONSIDERATION
Pursuant to 10 CFR 51.21, 51.32 and 51.35, an environmental assessment and finding of no significant impact has been prepared and published in the Federal Reaister on March 20, 1997 (62 FR 13403).
In that this environmental assessment and finding of no significant impact is unaffected by the supplemental information submitted by the licensee on March 30, 1997, there is no need to reissue this environmental assessment.
Accordingly, based upon the environmental assessment, the Commission has determined that the issuance of this amendment will not have a significant effect on the quality of the human environment.
6.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
Laurence Kopp M. David Lynch Date: April 2, 1997
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