Reactor Physics Analysis of Commercial PWR VVER-1200 by using NECP-Bamboo1.0 and Bamboo-C 

(The following analysis has carried out for cycle 1. The same calculation has been carried out for cycle 2 of VVER1200 which is not represented here.)

Abstract: This research delves into the analysis of the core of the commercial pressurized water reactor (PWR) VVER-1200, employing NECP-Bamboo1.0 and Bamboo-C as instrumental tools. The primary objective is to scrutinize the core's behavior and performance, ensuring alignment with the intended design values through a process of meticulous verification. To achieve this, a well-structured two-step approach is implemented, enabling a comprehensive examination of the intricate hexagonal core geometry. The first step in this analytical journey involves lattice calculation, where sophisticated software packages such as LILAC and LOCUST come into play. These programs facilitate the calculation of diverse state parameters, including burnup (Bu), boron concentration (CB), effective fuel temperature (Tf), moderator temperature (Tm), and other significant variables. By establishing relationships between these state parameters and the few-group constants, the information is subsequently discretized and represented functionally. This process harnesses parameterization techniques to construct an extensive data library containing the essential few-group constants. The constructed data library, encapsulating the discretized relationships, is a valuable resource for conducting whole-core calculations using Bamboo-Core and Bamboo-Spark. These advanced computational tools play a pivotal role in evaluating the core's behavior during both the first and second cycles of the reactor. The obtained results are subjected to thorough comparison, employing a comprehensive set of benchmarks. Traditional two-step method simulations, along with the design data of Tianwan U7 and U8, provide a valuable reference for validating the accuracy and efficacy of the methodology employed in this study. The findings of the core calculation endeavor are highly promising, as they reveal an exceptional level of precision in examining the VVER-1200 hexagonal core. In particular, during the first cycle calculation, the identified maximum errors in key parameters are noteworthy. For instance, for NECP Bamboo1.0, the maximum errors for CBC, power distribution, and burnup are quantified as 44.44ppm, 2.58% (MOL), 2.17% (EOL), and 1.90%, respectively. Likewise, Bamboo-C demonstrates slightly higher deviations, with respective values of 74.8 ppm, 4.51% (MOL), 2.37% (EOL), and 3.28%. Despite these variations, the overall precision exhibited by the analysis serves as a testament to the efficacy and reliability of the NECP-Bamboo1.0 and Bamboo-C methodologies. As per design report, boron concentration at any stage may have a tolerance of ±106PPM. Therefore, both the codes are equally capable of accurate calculations within the prescribed tolerance. 

The Reflector Modeling of VVER 1200 Reactor

Burnable absorber 

A burnable absorber (BA), commonly referred to as a burnable poison, is incorporated into the reactor core to control excess reactivity during the early stages of the fuel cycle. Burnable absorbers are materials characterized by a high neutron absorption cross-section, enabling them to capture neutrons generated during the fission process. As reactor operation progresses, the absorber material is gradually depleted through neutron absorption, thereby reducing its reactivity suppression effect over time.

In this study, boron silicate (BSG) is utilized as the burnable absorber material. Owing to the strong neutron absorption capability of boron, boron silicate effectively suppresses excess reactivity at the beginning of the fuel cycle while contributing to a more uniform power distribution within the reactor core. The gradual depletion of boron during operation helps maintain reactor criticality and supports stable core performance throughout the fuel cycle.

Burnup of Identical Assemblies with grid and Without Grid

for Z33Z2 assembly with 3.3% enrichment (without grid) the maximum value for keff of Lattice and Locust is 1.1 where the minimum value is 1.03. The maximum Bias is 125.83 pcm. Figure 4-17 shows that for Z33Z2 assembly with 3.3% enrichment (with grid) the maximum value for Lattice and Locust is 1.08 where the minimum value is 1.0. The maximum Bias is 404.6 pcm. Figure 4-18 shows that for Z33Z9 assembly with 3.3% enrichment (without grid) the maximum value for Lattice and Locust is 1.15 where the minimum value is 1.03. The maximum Bias is 43.67 pcm. Figure 4-19 shows that for Z33Z9 assembly with 3.3% enrichment (with grid) the maximum value for Lattice and Locust is 1.11 where the minimum value is 1.0. The maximum Bias is 221.99 pcm. Figure 4-20 shows that for Z44B2 assembly with 4.4% enrichment (without grid) the maximum value for Lattice and Locust is 1.2 where the minimum value is 1.1. Figure 4-21 shows that for Z44B2 assembly with 4.4% enrichment (with grid) the maximum value for Lattice and Locust is 1.17 where the minimum value is 1.06. 

Modeling and Analysis of Fuel Lattices with Burnable Absorber

The VVER-1200 reactor employs several fuel assembly designs containing burnable absorbers (BAs) to control excess reactivity during the initial stages of the fuel cycle. In this study, gadolinium oxide (Gd₂O₃) is used as the burnable absorber material due to its exceptionally high neutron absorption cross-section. The incorporation of burnable absorbers helps reduce excess reactivity, improve power distribution, and enhance fuel cycle performance.

For Cycles 1 and 2, a total of five burnable absorber assembly types are considered: Z33Z2, Z33Z9, Z44B2, Z44A6, and Z40D2. Each assembly type differs in its lattice configuration and the number of burnable absorber rods incorporated within the fuel assembly. The utilization of these assembly types varies between operating cycles. The Z33Z2, Z33Z9, and Z44B2 assemblies are employed in both Cycle 1 and Cycle 2. 

Power Distributions

A comparison between NECP-Bamboo1.0 and Bamboo-C has been shown in the figure at the Beginning of Life (BOL) state. It should be noted that there is no available design value specifically for this state, which adds significance to the analysis. The maximum relative error recorded in this comparison stands at 7.61%. To obtain this data, measurements were taken at the control rod position (H12), which is located 337.5 cm above the core's bottom. At the time of measurement, the coolant temperature was registered at 297.4 degrees Celsius. Additionally, for the purpose of this analysis, a thermal power value of 3200 MW was considered. 

When the control rod position (H12), situated 337.5 cm above the bottom of the core. The coolant temperature at the time of measurement was recorded as 297.4 degrees Celsius. Moreover, for the purpose of this analysis, a thermal power value of 3200 MW was taken into consideration. The comparison presented in figure offers valuable insights into the performance of NECP-Bamboo1.0 in relation to the design value during the MOL state at 50 EFPD. The relative error serves as an indicator of the disparity between the calculated values of NECP-Bamboo1.0 and the expected design values. Assessing such differences is crucial for ensuring accurate and reliable calculations from the NECP-Bamboo1.0 model. The maximum relative error observed in this comparison is 2.58% in comparison with design values.

When the control rod position known as H12, located 337.5 cm above the core's bottom. The recorded coolant temperature during the measurement was 297.4 degrees Celsius. Additionally, for the purpose of this analysis, a thermal power value of 3200 MW was taken into account. The comparison presented in figure provides valuable insights into the performance of NECP-Bamboo1.0 when compared to the design value at the End of Life (EOL) state at 342.73 effective full power days (EFPD). The relative error serves as an indicator of the difference between the calculated values obtained from NECP-Bamboo1.0 and the expected design values. Evaluating such discrepancies is crucial to ensure the accuracy and reliability of calculations performed by the NECP-Bamboo1.0 model. The maximum relative error observed in this comparison is 2.17% when compared to the design values.

Power Distributions

To obtain this data at MOL, measurements were conducted at the control rod position referred to as H12, situated 337.5 cm above the bottom of the core. The recorded temperature of the coolant during the measurement process was 297.4 degrees Celsius. Additionally, a thermal power value of 3200 MW was taken into consideration for the purpose of this analysis. The comparison depicted in Figure 5-5 offers significant insights into the performance of Bamboo-C in relation to the design value at the Middle of Life (MOL) state, specifically at 50 effective full power days (EFPD). The relative error serves as a key metric indicating the disparity between the calculated values derived from Bamboo-C and the expected design values. Evaluating these discrepancies is crucial to ensure the accuracy and reliability of calculations carried out by the Bamboo-C model. When comparing the results, the maximum relative error observed in this comparison amounts to 4.51% in comparison to the design values.

In order to gather this information for EOL, measurements were conducted at the control rod position known as H12, which is located 337.5 cm above the bottom of the core. The coolant temperature recorded during the measurement process was 297.4 degrees Celsius. Furthermore, a thermal power value of 3200 MW was taken into account for the analysis. The comparison illustrated in Figure 5-6 provides valuable insights into the performance of Bamboo-C in relation to the design value at the End of Life (EOL) state, specifically at 50 effective full power days (EFPD). The relative error serves as a crucial parameter that indicates the difference between the calculated values obtained from Bamboo-C and the expected design values. Assessing these disparities is essential to ensure the accuracy and reliability of calculations performed by the Bamboo-C model. When examining the results, the maximum relative error observed in this comparison amounts to 2.37% in comparison to the design values.

Burnup Analysis

Burn Up calculations were performed using both NECP-Bamboo1.0 and Bamboo-C to assess their accuracy and reliability. The calculated values obtained from both models were then compared with the design value, serving as a benchmark for verification purposes within the context of the first cycle. The comparison between the calculated values and the design value aimed to evaluate the consistency and agreement between them. This verification process is crucial in ensuring the validity of the Burn Up calculations and the overall performance of NECP-Bamboo1.0 and Bamboo-C.

The comparison between NECP-Bamboo1.0 and Designed value is showed for Burn Up. In this state the maximum calculative value is 17.35 with a maximum relative error 1.90%. The comparison between Bamboo-C.0 and Designed value is showed for Burn Up. In this state the maximum calculative value is 17.62 with a maximum relative error 3.28%. The comparison between NECP-Bamboo1.0 and Bamboo-C is showed for Burn Up. In this state the maximum relative error is found to be 1.90%.

Fuel Temperature Distribution

One crucial safety measure to ensure the rejuvenation of a reactor involves considering the fuel element's safety system. It is essential to address the possibility of the component approaching or surpassing its melting point. Hence, the selection of an appropriate moderator or coolant that can effectively dissipate heat to the fuel becomes significant. Failure to do so could result in the accumulation of excessive heat on the fuel rod, leading to potentially hazardous thermal damage.

In terms of the comparison, calculations were carried out using both NECP-Bamboo1.0 and Bamboo-C. The diagram provided illustrates the results for fuel temperature at 0 effective full power days (EFPD). These calculations were performed at the control rod position known as H12, located 337.5 cm above the bottom of the core. Moreover, a thermal power value of 3200 MW was taken into account for this analysis. When analyzing the outcomes, the maximum relative error observed in this comparison between NECP-Bamboo1.0 and Bamboo-C amounts to 3.92%. This value represents the extent of the difference between the calculated values obtained from the two models. Understanding and assessing these disparities is essential to ensure accurate and reliable calculations in the context of NECP-Bamboo1.0 and Bamboo-C.

Regarding the comparison, calculations were performed using both NECP-Bamboo1.0 and Bamboo-C. The provided diagram illustrates the findings for fuel temperature at 342.73 effective full power days (EFPD) at the end of life (EOL) state. These calculations were conducted at the control rod position referred to as H12, situated 337.5 cm above the bottom of the core. Additionally, a thermal power value of 3200 MW was considered for this analysis. Upon examining the results, the maximum relative error observed in this comparison between NECP-Bamboo1.0 and Bamboo-C amounts to 2.49%. This value signifies the magnitude of the difference between the calculated values obtained from the two models. It is crucial to understand and evaluate these discrepancies to ensure accurate and reliable calculations within the context of NECP-Bamboo1.0 and Bamboo-C.

Moderator Temperature Distribution

Regarding the comparison, calculations were performed using both NECP-Bamboo1.0 and Bamboo-C. The provided diagram illustrates the results for moderator temperature at 0 effective full power days (EFPD) at the beginning of life (BOL). These calculations were conducted at the control rod position referred to as H12, situated 337.5 cm above the bottom of the core. Additionally, a thermal power value of 3200 MW was considered for this analysis.Upon analyzing the results, the maximum relative error observed in this comparison between NECP-Bamboo1.0 and Bamboo-C amounts to 1.25%. This value signifies the extent of the difference between the calculated values obtained from the two models. Understanding and evaluating these disparities is crucial to ensure accurate and reliable calculations within the context of NECP-Bamboo1.0 and Bamboo-C.

Regarding the comparison, calculations were conducted using both NECP-Bamboo1.0 and Bamboo-C. The provided diagram illustrates the results for moderator temperature at 342.73 effective full power days (EFPD) at the end of life (EOL). These calculations were performed at the control rod position referred to as H12, situated 337.5 cm above the bottom of the core. Additionally, a thermal power value of 3200 MW was considered for this analysis. Upon analyzing the results, the maximum relative error observed in this comparison between NECP-Bamboo1.0 and Bamboo-C amounts to 1.80%. This value signifies the magnitude of the difference between the calculated values obtained from the two models. Understanding and evaluating these disparities is crucial to ensure accurate and reliable calculations within the context of NECP-Bamboo1.0 and Bamboo-C.