ML20135E666
| ML20135E666 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 12/06/1996 |
| From: | Wadley M NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-96-04, GL-96-4, NUDOCS 9612110405 | |
| Download: ML20135E666 (6) | |
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Northern States Power Company Prairie Island Nuclear Generating Plant 1717 Wakonade Dr. East i
Welch Minnesota 55089 December 6,1996 Generic Letter 96-04 l
U S Nuclear Regulatory Commission Attn: Document Control Desk i
Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos.50-282 License Nos.DPR-42 50 306 DPR-60 Supplemental Response to Generic Letter 96-04, Boraflex Dearadation in Spent Fuel Pool Storace Racks l
This letter provides supplemental information in response to Generic Letter 96-04:
l Boraflex Degradation in Spent Fuel Pool Storage Racks. Our original response to Generic Letter 96-04 was submitted to the NRC by letter dated October 23,1996.
Because of additional development work necessary to adapt the EPRI RACKLIFE computer program to the Prairie Island specific spent fuel pool conditions, we were unable to provide a full assessment of the physical condition of the Prairie Island Boraflex spent fuel racks in our October 23,1996 response.
The assessment of the Prairie Island spent fuel racks using the EPRI RACKLIFE program, while not complete, has provided sufficient preliminary information to allow for an updated response to Generic Letter 96-04. An assessment of the physical condition l
of the Boraflex in the Prairie island spent fuel racks is attached.
In this letter we have made new Nuclear Regulatory Commission commitments, l
indicated as the statements in italics. These commitments are in addition to the commitments made in our October 23,1996 response to Generic Letter 96-04.
ik Please contact Gene Eckholt (612-M3-1121) if you have any auestions related to our response to Generic Letter 96-04.
a11ow Michael D Wadley Plant Manager Prairie Island Nuclear Generating Plant 9612110405 961206 PDR ADOCK 0500o282 P
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V USNRC NORTHERN STATES POWER COMPANY December 6,1996 Page 2 l
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Regional Administrator - Region lil, NRC Senior Resident inspector, NRC NRR Project Manager, NRC l
J E Silberg j
l Attachments:
- 1. Affidavit
- 2. Supplemental Response to Generic Letter 96-04 t
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1 UNITED STATES NUCLEAR REGULATORY COMMISSION NORTHERN STATES POWER COMPANY PRAIRIE ISLAND NUCLEAR GENERATING PLANT DOCKET NO. 50-282 50-306 GENERIC LETTER 96-04, Boraflex Degradation in Spent Fuel Pool Storage Racks Northem States Power Company, a Minnesota corporation, with this letter is submitting information requested by NRC Generic Letter 96-04.
This letter contains no restricted or other defense information.
NORTHERN STATES POWER COMPANY BY mcl 00 &
Michael D Wadley
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Plant Manager Prairie Island Nuclear Generating Plant
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On this b ay of MBAL '
efore me a notary public in and for said County, personally.appetfred Michael D Wadley', Plant Manager, Prairie Island Nuclear Generating Plant; and bein0 irst duly sworn acknowledged that he is authorized to execute this document on behalf of f
Northem States Power Company, that he knows the contents thereof, and that to the best of his knowledge, information, and beli f the state ents made in it are true and that it is not interpos.ed for delay
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SUPPLEMENTAL RESPONSE TO GENERIC LETTER 96-04 Requested Action:
Provide an assessment of the physical condition of the Boraflex, including any deterioration, on the basis of current accumulated gamma exposure and possible water ingress to the Boraflex and state whether a subcritical margin of 5 percent can be maintained for the racks in unborated water.
l Response to the Reauested Action:
The Prairie Island Boraflex racks were put into use in late 1981 and were filled to near capacity by 1995. As a result, most of the individual spent fuel cells have a high accumulated gamma dose. A Boraflex coupon surveillance program was established when the racks were installed to monitor long term performance of the Boraflex material. At five year intervals, an irradiated Boraflex test coupon is removed from its location in the spent fuel pool and is sent for analysis of physical dimensions, hardness and B10 areal density. The last coupon was analyzed in 1994 and was found to not be significantly degraded, with the B10 areal density exceeding original specification.
Due to high levels of silica in the Prairie Island spent fuel pool relative to the rest of the industry, EPRI and the EPRI Boraflex Working Group shifted its focus from gap formation in Boraflex to the potential for Boraflex dissolution under long term exposure to spent fuel pool conditions. EPRI sponsored studies have shown that the combination of gamma exposure and water ingress into the Boraflex panel cavity significantly degrades the silica polymer matrix. The Prairie Island rack design allowed for a large amount of water ingress to alleviate the potential for cell wall bulging as a result of the Boraflex material offgassing. The Prairie Island sample coupons were not designed to allow for significant water ingress and are therefore not believed to be accurate indicators of rack Boraflex degradation.
The EPRI sponsored calculational model RACKLIFE is being used to estimate the condition of the Boraflex panels. The RACKLIFE model utilizes spent fuel pool chemistry parameters (including silica levels) and cell-by-cell exposure histories to estimate each Boraflex panel's potential for degradation. Additional modeling was necessary to attempt to simulate the Prairie Island spent fuel pool data. In our Octobsf 23,1996 response to Generic Letter 96-04 we anticipated the RACKLIFE analysis to be completed in November of 1996. Due to continuing difficulties with the modeling of the Prairie Island specific conditions, the assessment of the Prairie Island spent fuel racks using the EPRI RACKLIFE program has taken longer than originally expected.
However, even though the analysis has not been completed, preliminary information provided by the Prairie Island-specific RACKLIFE model, in combination with
information published in EPRI Interim Report TR-103300, " Guidelines for Boraflex Use in Spent-Fuel Storage Racks" (Dec 1993), indicates that some of the spent fuel pool 4
cells are outside their design basis and outside the requirements of Prairie Island Technical Specification 5.6.A.1.b, with a margin to criticality of less than 5% assuming no solubie boron in the spent fuel pool water. Per the requirements of 10 CFR Part j
50.72, Section 50.72(b)(1)(ii)(B), this condition was reported by phone to the NRC on November 26,1996.
In response to the Boraflex degradation identified by the EPRI RACKLIFE program, a safety evaluation was performed _to address the use of soluble boron in the spent fuel l
pool to offset the degradation of the Boraflex in the racks. That evaluation determined
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that the use of credit for soluble boron is an unreviewed safety question. A License Amendment Request, which requests approval of a criticality analysis for the Prairie Island spent fuel storage racks with no credit for Boraflex panels and instead utilizing credit for soluble boron, was submitted on July 28,1995. This License Amendment f
Request specifically addresses the unreviewed safety question related to the use of crt dit for soluble boron in spent fuel pool criticality analyses.
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As part of the developmental work for the July 28,1995 License Amendment Request, l
spent fuel pool criticality analyses were performed that show that 1850 ppm boron will maintained k.n < 0.95 under accident conditions with no credit for Boraflex or checkerboarding. Analyses crediting soluble boron using the existing checkerboarding i
requirements have not been performed, but that checkerboarding would provide additional margin. Until review of the July 28,1995 License Amendment Request is completed, administrative controls have been implemented to ensure that the spent fuel J
pool soluble boron concentration is maintained at a level adequate to ensure K.n for the spent fuel storage racks will remain less than 0.95. Those administrative controls conservatively require that the spent fuelpool boron concentration be maintained
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> 2000 ppm and that the spent fuel pool baron concentration will be conRrmed weekly.
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To ensure that adequate soluble boron is maintained in the spent fuel pool under all conditions, the following actions have been taken.
1 Procedures that provide for emergency makeup to the spent fuel pool have been i
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revised by temporary memo to state that non-borated emergency makeup l
sources shall only be used as a last resort. In addition, procedures that provide r
for normal and emergency makeup to the spent fuel pool have been revised by temporary memo to require boron sampling following makeup to verify acceptable baron levels remain. The relevant requirements of these temporary memos will be permanently incorporated into the procedures once the July 28, j
1995 License Amendment Request for soluble boron credit has been approved.
Operator spent fuel pool checks will be increased in frequency from once per day j
to once per shift to potentially decrease the time an unplanned dilution can go undetected.
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Dry boric acid has been placed in the immediate vicinity of the spent fuel poolin i
the event manual addition is required.
Spent fuelpool dilution sources have been tagged out to eliminate their use without adherence to the new administrative controls.
i Finally, as part of the original Prairie Island response to Generic Letter 96-04 a fuel management strategy has been established to ensure that fresh and other high i
reactivity assemblies (based on a combination of burnup and initial enrichment) will only l
be placed in spent fuel pool cells that are projected to have little or no boron carbide loss. The determination of boron carbide loss will be based on the RACKLIFE l
simulations.
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- While preliminary results from the RACKLIFE analysis indicate that some of the spent fuel pool cells are outside their design basis, additional developmental work is still required to fully quantify the extent of Boraflex degradation in the Prairie Island spent 4
i fuel storage racks. We expect the RACKLIFE analysis to be completed by January 15, i
1997, and a supplemental response to Generic Letter 96-04, including the Mnal results.
of the EPRI RACKLIFE ca!culations, will be submitted to the NRC at that time.
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