ML20210V103
| ML20210V103 | |
| Person / Time | |
|---|---|
| Issue date: | 09/26/1986 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20210V076 | List: |
| References | |
| NUDOCS 8610100503 | |
| Download: ML20210V103 (6) | |
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r Topical Report-Evaluation Report Identification: XN-75-27(P) Supplement 4 Report
Title:
Exxon Nuclear Neutronics Design Method for Pressurized Water Reactors Supplement 4 r
Peport Date:
December 1985 Originating Organization: Exxon Nuclear Company, Inc.
Reviewed By: Reactor Systems Branch /PWR-A 1.0 Introduction The Exxon Nuclear Company's (ENC) basic PWR methodology and associated verification are documented in " Exxon Nuclear Neutronics Design Methods for PWRs", XN-75-27 dated June 1975.
Improvements in methodology are documented in Supplement 1 dated September 1976 and Supplement 2 dated December 1977.
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1978 ENC began using gadolinia as a burnable absorber in PWRs. This devleopment and supporting measurements were documented in Supplement 3 dated
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November 1980 Due to the limited data base NRC recommended continued review of comparisons of calculated physics parameters with measured data and restricted the use of gadolinia bearing fuel' rods to those containing up to 4 w/o gadolinia when it approved Supplement 3 in August 1981.
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Since that time ENC has expanded the neutronics design base to encompass 56 cycles of ENC supplied fuel. These cycles have included improved water-to-fuel ratio designs fer 14x14 and 17x17 fuel assemblies, natural uranium axial blankets and expanded use of gadolinia with concentrations m to 8*0 w/o*
e610100503 e60926 DR TOPRP EMVE This supplement-(Supplement 4) to XN-75-27 provides an update of the ENC experience base with emphasis on the PWR gadolinia experience. The use of the transmission probability assembly code, CASMO-2E with MICBURN-2 is also discussed.
h 2.0 Sunoary of the Topical Report Gadolinia bearing.. fuel supplied by Exxon Nuclear Company has been used in 31 cycles at 9 PWRs. Over 3000 fuel rods in 451 assemblies have operated successfully with burnups up to 43,000 MWD /MTil. Extended fuel cycle desians with gadolinia' bearing rods of 8 w/o and a small number of 10 w/o rods have been used in the Tihange 1 reactor.
2.1 Results Using Standard ENC Methodology The ENC standard neutronics design methods have been compared with the measured results for 56 PWR cores. These include cores containing natural uranium axial blankets, cores with improved water-to-fuel ratio assembly designs, cores containing fixed (B-10) burnable absorber rods and cores containing gadolinia.
Comparisons between calculated and measured neutronics data for these cores show the following results: Hot zero power critical boron concentration, an average difference of 25 to 30 ppm with a maximum of 69 ppm. The het full power critical boron concentration as a function of exposure typically agrees with measured values within 30 ppm. On an assembly basis, the calculated relative power distributions differ from the measured value by 3% on the average with maximum differences of 7% in assemblies with relative powers greater than 1.0 and 14% in assemblies with relative power less than 1.0.
2.2 Results Using CASM0-2E and MICBURN-2 CASM0-2E and MICBURN-2 provide an alternate method for calculating the depletion of a fuel assembly and the generation of few group cross sections.
Use of these codes has several advantages: simplier input, fewer computer runs, more detailed modeling of the gadolinia and improved analytical results for higher (8 w/o) gadolinia concentrations. Comparison of power distributions, critical boron concentrations and control rod worths for both gadolinia bearing cores and non-gadolinia cores have results similar to those
.obtained using the current ENC methodology and compare well with measured data.
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<3.0 ~ Technical Evaluation We have ~ reviewed the :information presented with regard to the completeness with which it demonstrates that the previously approved ENC neutronic design
. methods can adequately. calculate the physics characteristics of reactor cores containing.various~ amounts of gadolinfa bearing fuel rods of different weight percents. Our review was based primarily on comparison of predicted and measured data from several operating pressurized water reactors. We have also reviewed the submittal on the use of CASM0-2E and MICBURN-2. Comparisons between predicted and measured data as well as comparison between the current methodology and the use of CASM0-2E and MICBURN-2 were the bases for most of our review.
3.1 Gadolinia Bearino Fuel Over 3,250 gadolinia bearing fuel rods have been used in nine operating PWRs.
Gadolinia concentrations have ranged from I w/o to 10 w/o with the majority being 4 w/o.
Fuel rods with 8 w/o gadolinia have been used in the Tihange 1 reactor and a small number -(32) of 10 w/o rods have also been used.
In
. general, agreement between measured and predicted neutronics parameters was very similar to that seen with non gadolinia bearing fuel.
In the Prairie Island units gadolinia has been used for a total of eleven cycles. Both I w/o and 4 w/o concentrations have been used to meet various cycle energy goals. Both startup test results and core follow results have shown good agreement between measured and predicted. Typically calculated and measured relative assembly powers for the gadolinia bearing assemblies agree within 2-3%.
Gadolinia has been used in the last three cyles of H. B. Robinson Unit 2.
Again the number of fuel rods per cycle was determined by the cycle energy goals. The majority of the rods contained 4 w/o gadolinia. Comparisons showed good agreement between measured and predicted values for critical boron concentrations, control rod worths, temperature coefficients and relative power distributions.
. 8 w/o and a small amount of 10 w/o gadolinia bearing fuel has been used in the Tihange-1 reactor. For the three cycles in which gadolinia bearing fuel has been used, agreement between measured and predicted values is good for the critical boron concentration and relative power distribution data presented.
Gadolinia bearing fuel has also been used in the Palisades, Biblis B, Unterweser and St. Lucie 1 reactors.
In general when we compared the gadolinia bearing fuel results with those using the entire ENC data base, the gadolinia bearing fuel results showed slightly greater differences (i.e., 29.4 vs 25 ppm for average difference of critical boron concentration). These comparisons were made for initial critical boron concentration, control rod worths, temperature coefficients and relative power distributions. These differences are not considered significant.
The ENC data base was compared with a larger data base for PWR for initial critical boron concentration and temperature coefficients. This comparison showed slightly greater average differences between predicted and measured data for the ENC data. Again this difference was not considered significant.
A qualitative compraison of relative power distribution differences could not be made, but based on available data the ENC data show less difference between measured and predicted values.
3.2 CASM0/MICBURN CASM0-2E is a multi group two-dimensional transmission probability code for burnup calculations on assemblies or pin cells. MICBURN is a multi group one-dimensional transmission probability code which calculates the microscopic burnup in an absorber rod containing initially homogeneously distributed gadolinia and generates effective cross sections as a function of a gadolinia number density to be used in a CASMO assembly depletion.
. CASMO assembly models were depleted for several PWR fuel types. Analogous PDQ and XPOSE models (current ENC methodology) were also depleted for the same models and comparisons were made. The CASM0 model yielded slightly higher k-infinity at BOL and slightly lower k-infinity after some burnup. The differences were small. Comparisons of relative pin powers as calculated by PDQ/XPOSE/XPIN, PD0/CASM0 and CASMO assembly models showed that on the average the CASMO model calculates relative pin powers within 1% of either PD0 model.
Comparisons were made of results from analytical models using CASMO with reactor measurements from four PWRs. The data included critical boron concentrations, control rod worths and power distributions. The differences between measurement and prediction were all less than one half the amount specified by the review / acceptance criteria. A similar comparison using standard ENC methodology yielded similar results.
4.0 Technical Position Based on our review of the report (Ref.1) and the additional information (Ref. 2) submitted by the licensee we conclude that the design methods as described in XN-75-27 and Supplements 1-4 are acceptable for calculating neutronic characteristics of PWR cores containing up to and including 8 w/o gadolinia bearing fuel rods. The data base for rods with greater than 8 w/o is too small to warrant approval for rods with greater than 8 w/o gadolinia. Since the comparisons using CASM0/MICBURN were limited we recommend continued review of comparisons of calculated physics parameters with measured data from future physics startup tests and operating reactor data.
References O' Leary, A.' H. et al., XN-75-27(P), Supplement 4, " Exxon Nuclear 1.
Neutronics Design Methods for Pressurized Water Reactors, Suplement 4,"
Exxon Nuclear Company, December 1985.
2.
Letter, G. N. Ward (ENC) to C. H. Berlinger, (NRC) July 11, 1986 with
.r enclosure " Answers to NRC Questions Regarding Exxon Nuclear Neutronics
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Design Methods. for Pressurized Water Reactors, XN-NF-75-27(P), Supplement 4.
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