Analysis of ZPPR-15 experimental data for VTR software validation
Introduction
As part of the Versatile Test Reactor (VTR) program (Heidet et al., 2018), extensive validation work is being performed to demonstrate the fidelity of the Argonne Reactor Code (ARC) software package (Derstine, 1984, Just et al., 1971, Lee and Yang, 2012, Palmiotti et al., 1995, Smith, 2018, Lawrence, 1983, Smith et al., 2014, Toppel, 1983, Smith et al., 2017, Basehore and Todreas, 1980, Yang, 1993, Yang, 1989, Grudzinski and Moran, 2015) presently used for the core design studies. It is anticipated that this software will be also used for initial operations although additional software may be introduced at a later time to supplement or replace some components. The validation work was focused on accumulating reactor models that are consistent with the VTR and thus can be used to validate the accuracy of predictions made by the software used to design and operate the VTR.
The U.S. does not have any active experimental facilities that can neutronically mockup the VTR core design. However, in the past, the U.S. had extensive experimental facilities for fast reactor neutronics. In that regard, the ZPPR-15 experiments (McFarlane et al., 1989) carried out at ANL during the 1980s work best because the fuel form is closest to the VTR design, there is a considerable amount of processed data available for use, and existing staff are already familiar with the experimental machine and measurements. Because of previous collaborative work, many of the ZPPR-15 loadings of interest have already been processed into MCNP and preliminary ARC models, and a full uncertainty quantification has already been completed for many of the ZPPR-15 measurements.
This manuscript covers the recent analysis work on the ZPPR-15 experiments and compares it with the experimental results. With respect to the ARC software components, this manuscript focuses on validation of the MC2 (Lee and Yang, 2012), DIF3D (Derstine, 1984, Lawrence, 1983, Palmiotti et al., 1995, Smith et al., 2014), and GAMSOR (Smith et al., 2017) using the ZPPR-15 experimental data.
Section snippets
ZPPR-15 experimental data
The ZPPR-15 experiments (McFarlane et al., 1989) were mockups of a 330 MWe Integral Fast Reactor (IFR). The ZPPR-15 assembly consisted of a clean, two zone, approximately circular core surrounded by a depleted uranium (DU) blanket with sodium (Na) cooling and a stainless steel reflector. The ZPPR-15 program was conducted in four phases: A, B, C, and D. Each phase was marked by a particular composition of the reference assembly, with the last three being representative of the three stages of the
Analysis of critical cores
All selected measurements were analyzed for the discussed V&V activity. For each loading, the MC2 + DIF3D and, when available, the MCNP (Briesmeister et al., 2000) results were compared with the experimental measurements. Additionally, some commentary is provided on the suitability of each case for the VTR validation effort.
The analysis of critical cores is discussed in this section.
Using the UC cross section methodology of BuildZPRModel, keff values were calculated with DIF3D-VARIANT for all
Analysis of ZPPR-15 simulated control rod measurements
The ZPPR-15 measurements of control rod worth used 1 – 13 mockup control rods (CRs) or control rod positions (CRPs). CR/CRPs are not to be confused with the operational control rods used in ZPPR that consist of narrow stainless steel-clad blades of boron carbide inside stainless steel guide tubes and are referred to as poison safety rods or poison shim rods (PSRs). A CRP consisted of a 2 × 2 array of drawers filled with sodium plates over the entire 36 in. drawer length. With a few exceptions,
Analysis of void worth
Sodium voiding is a key concern in a sodium cooled fast spectrum reactor and thus was measured in all phases of ZPPR-15. The sodium cans were sealed, and the sodium in the cans was solid. It was not possible to change the density of the sodium in the cans, so it was not possible to perform experiments with reduced sodium density. Consequently, sodium void experiments in ZPPR-15 consisted of complete voiding of sodium in the void region. A sodium-voided zone was simulated in ZPPR by replacing
Analysis of neutron spectrum measurements
Neutron spectra were measured near the center of the core in ZPPR-15A loading 66 (see Fig. 10), ZPPR-15B loading 90 (see Fig. 11) and ZPPR-15D loading 186 (see Fig. 12). Neutron spectra also were measured at the center of the simulated shield as part of the ZPPR-15B shield experiment, specifically in ZPPR-15B loading 121 (SSNA configuration, see Fig. 13) and ZPPR-15B loading 126 (BCNA configuration, see Fig. 14). In the initial shield configuration, there was a large simulated stainless
Measured and calculated B-10(n,α) reaction Rates
The B-10(n,α) reaction rate was measured as part of the ZPPR-15B shield experiment. The measurements were performed by placing a flowing gas proportional counter into a drawer at six locations in the shield, radial reflector, blanket, and core of the ZPPR-15B BCNA shielding experiments. The counter was a cylindrical back-to-back (BTB) counter divided into two chambers. One chamber contained a rectangular deposit of enriched boron (96.5% B-10) on a stainless steel backing. The boron deposit was
Analysis of foil measurements
Several types of foils were irradiated in loadings 123 and 134 of ZPPR-15B and loading 203 of ZPPR-15D to measure spatial reaction rate distributions. The measurements in loadings 123 and 134 were performed only along the X-axis while in loading 203 measurements were made along the X, Y and Z axes. Since the ZPPR-15D reaction rate measurements are the most complete, only the analysis of these experiments will be discussed in the present manuscript. Additionally, the analysis of the ZPPR-15B
Analysis of axial expansion reactivity worth measurements
Axial expansion experiments were performed in ZPPR-15B and ZPPR-15D, and in each case a segmented drawer was constructed. The small gaps introduced between drawer segments simulated core axial expansion as closely as possible given the constraint that the core materials consisted of rigid plates of fixed sizes. The ZPPR-15B and ZPPR-15D experiments both had a base configuration with no gaps and one or multiple perturbed configurations where gaps between sections of each drawer were opened. Fig.
Analysis of Doppler sample reactivity worth measurements
Whole core Doppler reactivity worth measurements were not feasible in ZPPR, and instead Doppler sample reactivity worth measurements were performed in ZPPR-15A, ZPPR-15B, and ZPPR-15D. In the experiment, a Doppler sample was loaded into the Doppler mechanism which consisted of a heating element surrounded by an outer capsule. The temperature of the sample was measured with a thermocouple inserted into a small cylindrical cavity in the center of the sample. The difference between the measured
Analysis of TLD loadings
There are four ZPPR-15 experiments that considered TLD measurements: ZPPR-15B Loading 118, 122 and 133, and ZPPR-15D Loading 202. Problems with the gamma related solutions for EBR-II, ZPPR, and other reactors have led to the identification of mistakes in the processing of the ENDF cross section data. This requires a re-evaluation of the TLD work when the MC2 library work is complete and thus only the ZPPR-15D loading 202 TLD measurements were analyzed.
Conclusions
This manuscript covers the calculated and measured results of many different experimental measurements carried out in ZPPR-15. These experiments were identified to be particularly important for use as validation data of the reactivity coefficients generated by MC2 + DIF3D. Those reactivity coefficients are used in the safety analysis work in the VTR program. The projection of each experimental measurement to a given reactivity coefficient is beyond the scope of this manuscript. Thus, this
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The submitted document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne National Laboratory’s work was supported by the U.S. Department of Energy, Office of Nuclear Energy under contract DE-AC02-06CH11357. The work reported in this summary is the result of ongoing efforts supporting the Versatile Test Reactor.
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