ML20056E126
| ML20056E126 | |
| Person / Time | |
|---|---|
| Issue date: | 06/29/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20056C577 | List: |
| References | |
| NUDOCS 9308200060 | |
| Download: ML20056E126 (6) | |
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ENCLOSURE Safety Evaluation by the Office of Nuclear Reactor Reaulation Topical Report CENPD-382-P "Methodoloav for Core Desians Containina Erbium Burnable Absorbers" ABB Combustion Engineerina. Inc.
1 INTRODUCTION In a meeting with the U.S. Nuclear Regulatory Commission (NRC) on January 12, 1989. ABB-Combustion Engineering Nuclear Power (CE) described its development program to qualify the use of erbium (Er) as a burnable absorber in nuclear power plants.
A preliminary program schedule was transmitted to the NRC on February 10, 1989 and was amended on April 10, 1989.
In a letter of November 2,1990 (Ref.1), CE submitted the Topical Report CENPD-382-P, " Methodology for Core Designs Containing Erbium Burnable Absorbers, Part 1: Materials Properties and Behavior" (Ref. 2) for the NRC to review.
In a meeting on December 3,1990 (Ref. 3), CE gave a presentation on the material properties and the fuel performance aspects of erbia (erbium oxide, Er 0 ) mixed 23 integrally with urania (uranium oxide U0 ).
In a letter of February 25, 1992 2
(Ref. 4), CE submitted Supplement 1-P, "Part 11: Physics Properties, Methods and Performance Verification" (Ref. 5), for review. On May 20, 1992, CE j
submitted supporting information on the physics properties and methods verification program to the NRC staff (Ref. 6).
The staff discussed the status of the review in a telephone call on January 6,1993, and transmitted a request for adoitional information (RAI) in a letter of January 7,1993 (Ref. 7).
CE submitted responses in letters of January 11 (Ref. 8) and January 26, 1993 (Ref. 9).
In a conference call on February 23, 1993, the staff and CE discussed the remaining issues and agreed on the case-specific analyses to be performed by CE, as discussed in the attached technical evaluation report (TER).
9308200060 930629 PDR TOPRP Er1VC-E C-PDR
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EVALVAT10fl CE proposed to use erbium-bearing UO (urania-erbia) fuel rods to replace 2
either gadolinium or boron, as an integral burnable absorber, in both CE type 14x14 and 16x16 fuel lattices for their future 18-and 24-month fuel cycle designs.
Erbium and gadolinium are both rare earth (lanthanides) elements, are physically and chemically very similar, and the proposed thermal-mechanical performance analysis of urania-erbia fuel pellets is similar to the
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reviewed and approved CE orania-gadolinia fuel design methodology (Ref. 10),
j as discussed in Section 2.1 below.
fleutronically, natural erbium and natural l
baron have equivalent thermal energy neutron capture cross sections and can be treated as dilute neutron absorbers, using the approved CE physics design methods (Ref.11), as discussed in Section 2.2.
2.1 Fuel Thermal-Mechanical Analyses i
The !JRC staff obtained technical assistance from Pacific florthwest Laboratory (P!4L) to review the physical material properties and thermal-mechanical fuel performance behavior of erbium-bearing U0 fuel pellets which were addressed 2
in Part I of Topical Report CEf1PD-382-P. The staff has adopted the findings recommended in the attached Pf1L technical evaluation report (TER), as discussed below and summarized in our conclusions.
CE has fabricated test fuel pellets with erbia concentrations up to a maximum of [a proprietary number] weight percent (wt%) and has measured the specific thermal material properties of urania-erbia as discussed in Section 2.2 of the topical report.
As discussed in the TER, much of the sample CE calculational results furnished in the topical report was performed for a nominal fuel rod design which iepresents their currently expected erbium content.
However, the independent f4RC audit code calculations and evaluations discussed in the TER cover the erbia wt% range up to the maximum proposed content.
This is considered acceptable since CE has also committed (Ref. 9) to analyze both urania-erbia and urania-only fuel rods to verify the limiting rods for each reload application.
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1 2.2 Neutronic Analyses The NRC staff reviewed the verification of neutronic (physics) properties, methods, and in-reactor performance for Erbium-bearing fuel rods described in Part II of the topical report, designated as CENPD-382-P, Supplement 1-P.
The addition of small amounts of erbia to urania fuel rods affects the neutronic properties of the fuel rods because of the neutron capture by the principal erbium isotopes.
Natural erbium has a distinct double-peaked resonance capture (from Er-167) at 0.5 electron-volts (ev) while the natural boron thermal capture decreases linearly (1/v) with neutron energy.
This thermal erbium resonance allows effective moderator temperature coefficient (MTC) control at beginning-of-life (BOL) conditions.
The erbium-thulium (Tm) depletion chain is represented in sufficient detail to track all important isotopes with significant neutron capture.
CE represents these important isotopes in a library of 85 energy groups for use in CE's approved two-dimensional (2D) assembly lattice physics code (DIT).
Explicit treatment of self-shielded resonance cross-sections is used for Er-166, Er-167. Er-168 and for Tm-169.
A minimum of 5 mesh intervals is used in the fuel pellet region for urania-erbium rod analysis, to model the spatial-energy neutron flux.
DIT supplies lattice-averaged two-group microscopic cross-section tablesets to CE's approved three-dimensional (30) core simulator (ROCS).
ROCS tracks concentrations of Er-166, Er-167 and Er-168 explicitly, with a lumped residual macroscopic cross-section to represent the remainder of the erbium depletion chain.
CE verified the application of CE-approved neutronic models to erbium analysis by (1) comparison with benchmorking measurements made in 1991 at the Rensselaer Polytechnic Institute (RPI) reactor critical facility (RCF),
(2) comparison with operating experience from TRIGA low-enriched uranium (LEU) cores with erbium, and (3) evaluation of the lead test assembly (LTA) programs for two pressurized water reactors (PWRs).
At RPI, CE used the RCF to measure the BOL erbium reactivity worths, local power distributions, and low-temperature MTCs for lattice configurations similar to the standard ABB-CE 16x16 type design.
Comparisons of calculated with measured erbium worths
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4 indicated a slight overestimate [a proprietary amount] of the BOL reactivity worth.
The TRIGA analysis was used to verify MTC results in the operating temperature range.
The LTA programs were conducted, during the period from 1991-1993, at Calvert Cliffs Unit 2, for Cycle 9 operation with the CE 14x14 type fuel lattice design and at San Onofre Nuclear Generating Station Unit 2 i
for Cycle 6 operation with the CE 16x16 type design.
CE used the two LTA programs to verify the rate of erbium reactivity worth depletion and the radial distributions of global box power for both 14x14 and 16x16 lattice type core designs.
These measurements indicated that the erbium depletion rate may also be slightly overestimated by [a proprietary amount].
The staff finds these verification analyses acceptable because they were performed with approved CE methodologics, which have been qualified for similar fuel lattice designs.
Note that application to other PWR lattice types (15x5,17x17) or to boiling water lattice designs would require further benchmarking analysis and confirmation by LTA programs.
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CONCLUSIONS The staff has reviewed the urania-erbia evaluation methodology described in Topical Report CENPD-382-P, as modified by the CE responses to the NRC RAI, and finds it acceptable for reload licensing applications of both CE 14x14 and 16x16 PWR lattice type core designs.
This approval applies only for assemblies using the range of erbium concentrations and numbers of urania-i erbia fuel rods that have been qualified in the topical report.
The 85 energy group library is to be used with a minimum of five mesh intervals in the fuel pellet region to properly represent the erbium resonance region.
Licensees referencing this topical report should also observe the limitations on urania-l erbia melting temperature and on radial peaking factors resulting from the linear heat generation rate margin to rod internal pressure limits, as described in Sections 2.4. and 3.1.1 of the attached TER, concerning Part I of the topical report.
CE has also committed to analyze both urania-only fuel rods and urania-erbia fuel rods for each reload license application.
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4 REFEREf4CES l
(1)
Letter from S. A. Toelle (CE) to D. H. Lanham (NRC), LD-90-086, November 2, 1990.
(2)
CENPD-382-P, " Methodology for Core Designs Containing Frbium Burnable Absorbers, Part 1 - Material Properties and Behavior," ABB Combustion Engineering Nuclear Power, Windsor, Connecticut, October 1990.
l (3)
Letter from 5. A. Toelle (Ct to R. C. Jor.es (NRC), " Erbium Burnable Absorber ABB CENP/NRC Meeting - December 3, 1990'," LD-90-095, December 18, 1990.
(4)
Letter from S. A. Teelle (CE) to Document Control Desk (NRC),
" Transmittal of Physics Methods and Performance Verification for Core Designs Containing Erbium Burnable Absorbers," LD-92-032, February 25, j
1992.
(5)
CENPD-382-P, Supplement 1-P, " Methodology for Core Designs Containing Erbium Burnable Absorbers, Part II - Physics Properties, Methods and Performance Verification." ABB Combustion Engineering Nuclear Fuel, Windsor, Connet-
't, February 1992 (6)
Letter from S. A. Toelle (CE) to L. E. Phillips (NRC), "NRC/C-E Meeting on the Use of Erbium as a Burnable Absorber." LD-92-074, June 4,1992.
(7)
Letter from R. C. Jones (NRC) to S. A. Toelle (CE), " Request for Additional Information on Topical Report CENPD-382-P, ' Methodology for Core Designs Containing Erbium Burnable Absorbers'," January 7,1993.
(8) letter from S. A. Toelle (CE) to E. D. Kendrick (NRC), " Transmittal of Requested Additional Information," LD-93-001, January 11, 1993.
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(9)
Letter from S. A. Toelle (CE) to R. C. Jones (NRC), " Transmittal of Requested Additional Information," LD-93-010, January 26, 1993.
l (10) CENPD-275-P, Rev.1-P-A, "C-E Methodology for Core Designs Containing Gadolinia-Urania Burnable Absorbers," January 1988.
(11)
CENPD-266-P-A, "The ROCS & DIT Computer Codes for Nuclear Design," April 1983.
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