ML20057F786
| ML20057F786 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 10/14/1993 |
| From: | Richard Anderson NORTHERN STATES POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9310190114 | |
| Download: ML20057F786 (2) | |
Text
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Northem States Power Company 414 Nicollet Mall Minneapohs, Minnesota 55401-1927 Telephone (612) 3345500 October 14, 1993 U S Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket Nos. 50-282 License Nos. DPR-42 50-306 DPR-60 Utilization of 8 w/o Gd in Prairie Island Fuel This letter is a followup to the FtR-NSP meetings that were held June 1992 and March 1993 to address utilization c. 8w/o Gadolinia (Gd) in Prairie Island (PI) fuel. In the March 1993 meeting, various concerns were expressed by the NRC. The purpose of this letter is to inform you of the actions that have been taken since the March 1993 meeting.
The table below is included to facilitate understanding the following discussion and to serve as a summary of the appropriate information.
SCHEDULED No of 8w/o Gd PI UNIT CYCLE START DATE / DURATION Assemblies 8 Lead Test 2
16 Dec '93 / 17 mon Assemblies (LTAs) 1 17 June '94 / 18 mon Full Reload The following significant actions have been taken since the March 1993 meeting:
1.
A detailed parametric study was performed by NSP to evaluate the potential effects of under-predicting Gd burnout. This study compared various aspects of two rore depletion scenarios:
Normal NSP modeling using approved methodology a.
b.
Normal NSP modeling except the Gd *.hermal absorption cross-section was increased by 10% to simulate a faster Gd burnout rate 2.
An outside consultant performed an independent design review of NSP's investigation of the potential impact of modeling Bw/o Gd incorrectly.
3.
Eight Lead Test Assemblies (LTAs) will be installed in the next core reload, which is PI 2 Cycle 16.
The parametric study and the independent design review addressed the operatiorsl and safety aspects of installation of Sw/o Gd in PI fuel, t sne
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s Northem States Power Company October 14, 1993 Page 2 Two potential operational problems that could be caused by under-predicting the Gd burnout rate are:
1.
The potential difference between predicted and measured core reactivity. (This difference would be observed between the predicted and measured boron letdown curves.)
2.
The potential difference between the predicted and " measured" assembly power. (This difference would be observed between predicted and-measured reaction rates of monitored locations and the comparison of inferred Fn and Fw with Tech Spec values.)
With regard to the potential core reactivity difference, it was concluded for 8w/o Gd that any variation between predicted and measured reactivity is not expected to be significantly larger than already experienced with Sw/o Gd. This
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conclusion was based on NSP's parametric study and on a stucy conducted by EPRI l
(Project 2803-2, Evaluation of Discrepancies in Assembly Cross Section Generator Codes, which has the resultc published in EPRI NP-6147).
The primary concern with regard to the potential assembly power difference is the potential inaccuracy in the calculated conversion coefficients that are used to convert measured fission rate to assembly power. It was concluded that potential modeling inadequacies of 8w/o Gd will have little impact on the conversion coefficients. The rationale for this conclusion is that the difference between conversion coefficients of Sw/o and 8w/o Gd is at most 3% and is virtually insensitive to assembly exposure (Gd depletion). The impact on the conversion factor in going from Sw/o to Bw/o is arguably much greater than any impact from modeling inadequacies of 8w/o.
Furthermore, the LTAs will provide the means by which these conclusions can be evaluated in that 2 of 8 LTAs are in monitored locations providing both:
1.
A measured to predicted boron letdown curve comparison 2.
A true measured to predicted reaction rate comparicon of monitored locations In addition, NSP's parametric study and the consultant's independent design review concluded that utilization of 8w/o Gd fuel will not present a safety problem.
It is believed that the above described actions address the concerns raised by the NRC. These actions plus NSP's previous successful experience in utilization of increased Gd concentrations (i.e. Iw/o, 4w/o, Sw/o, and 6w/o) provides assurance that Ow/o Gd fuel can be safely utilized in PI reloads. Thus plans are underway to incorporate a full reload of Bw/o Gd fuel in PI 1 Cycle 17' (fabrication of 8w/o Gd fuel is scheduled to commence on Nov 1, 1993).
Please contact us if you have any questions or comments on the above information.
My hone number is 61 337-2050.
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>r O Anderson Direct or Licensing and Management Issues c: Regional Administrator III, NRC Senior Resident Inspector, NRC NRR Project Manager, NRC J E Silberg
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