Main Results of Phase IV BEMUSE Project: Simulation of LBLOCA in an NPP

Phase IV of BEMUSE Program is a necessary step for a subsequent uncertainty analysis. It includes the simulation of the reference scenario and a sensitivity study. The scenario is a LBLOCA and the reference plant is Zion 1 NPP, a 4 loop PWR unit. Thirteen participants coming from ten different countries have taken part in the exercise. The BEMUSE (Best Estimate Methods plus Uncertainty and Sensitivity Evaluation) Programhas been promoted by theWorking Group on AccidentManagement and Analysis (WGAMA) and endorsed by the Committee on the Safety of Nuclear Installations (CSNI). The paper presents the results of the calculations performed by participants and emphasizes its usefulness for future uncertainty evaluation, to be performed in next phase. The objectives of the activity are basically to simulate the LBLOCA reproducing the phenomena associated to the scenario and also to build a common, well-known, basis for the future comparison of uncertainty evaluation results among different methodologies and codes. The sensitivity calculations performed by participants are also presented. They allow studying the influence of different parameters such as material properties or initial and boundary conditions, upon the behaviour of the most relevant parameters related to the scenario

Simulation of a LBLOCA in ZION Nuclear Power Plant - BEMUSE Phase IV Report

The main goals of the BEMUSE program are: ² To evaluate the practicability, quality and reliability of best{estimate methods including uncertainty evaluations in applications relevant to nuclear reactor safety; ² To develop common understanding; ² To promote/facilitate their use by the regulatory bodies and the industry The scope of Phase IV of the BEMUSE programme is the simulation of a LB{LOCA in a Nuclear Power Plant using experience gained in the previous Phase II. Calculation results will be the basis for uncertainty evaluation, to be performed in next phase. The objectives of the activity are: ² To simulate a LB{LOCA reproducing the phenomena associated to the scenario. ² To have a common, well-documented basis for the execution of the uncertainty evaluation step in Phase V. Task speci¯cation The activity followed the example of Phase II. The selection of the plant has been a quite important issue. Some other options were considered. The group made the decision of using Zion plant and CSNI approved the choice. Zion Station was a 4 loop dual-reactor nuclear power plant of Westinghouse design. An input deck of the plant existed for TRACE and RELAP5 codes. NRC provided the input decks of Zion plant for TRACE and RELAP5 codes and the coordina- tors prepared a specification that enabled the users of di®erent computer codes to produce their own Zion input decks. For this purpose, along with plant parameters, the main features of the LBLOCA scenario were specified in order to assure common initial and boundary conditions. Similarly to the activity performed in Phase II, a list of sensitivity calculations was proposed to study the influence of di®erent parameters such as material properties, initial and boundary conditions upon the behaviour of key parameters of the scenario. Main Results Results can be summarized as follows: ² All participants managed to simulate the scenario and predict the main parameters with credible consistency. ² Maximum values of PCT predicted by participants are quite close one each other. ² PCT time trends and timing of complete core rewet still show some disagreements. ² A database, including comparative tables and plots has been produced. This database is suitable for providing the explanations needed for the following phases. More in detail and related to steady state achievement, participants managed to reproduce the pressure vs. length reference curve and to match the more significant parameters for the scenario simulation. Discrepancies in steady state appeared only in some other parameters like those related to the secondary system which are not that much influent. Related to the reference case, the core thermal behaviour is the most interesting aspect to report. Cladding temperature time trends produced show a consistent behaviour. The spread of results for the PCT is about the same order of magnitude than that of Phase II (roughly 260-280 K). The major di®erences between results come with the re°ooding behaviour and mainly its duration. In this case the report correlates this point with some code e®ect. Conclusions Phase IV results are a step forward that contributes to the general goals of BEMUSE project. At the time when this Phase IV Report is written, all participants are developing a Phase V analysis based on the reference calculations produced in Phase IV. The coordinators want to emphasize this point as a proof of how participants accept the usefulness of Phase IV. It is clear that dispersion bands exist but it is also clear that the e®ort of explaining the reasons of such dispersion is a valuable outcome from this phase. The outcome of BEMUSE Phase IV is also helpful to understand the nuances existing inside the user e®ect and also to clarify the di®erences between user e®ect and code e®ect. Assumptions made by the user due to the lack of information are not part of the traditional user e®ect and this report is useful to deal with them. Participants, in average, have found or corroborrated the most in°uential parameters regarding the their in°uence on PCT and tREFLOOD. The sensitivity study performed in Phase IV has also pointed out that the user and code e®ects can appear not only in obtaining a reference case value, but also when analyzing variations on the reference case. Sensitivity calculation results are a good guidance for developing Phase V uncertainty evaluation. BEMUSE Phase IV is a reference good enough to start with Phase V development

Main Results of phase IV BEMUSE project: Simulation of LBLOCA in an NPP

Phase IV of BEMUSE Program is a necessary step for a subsequent uncertainty analysis. It includes the simulation of the reference scenario and a sensitivity study. The scenario is a LBLOCA and the reference plant is Zion 1 NPP, a 4 loop PWR unit. Thirteen participants coming from ten different countries have taken part in the exercise. The BEMUSE (Best Estimate Methods plus Uncertainty and Sensitivity Evaluation) Program has been promoted by the Working Group on Accident Management and Analysis (WGAMA) and endorsed by the Committee on the Safety of Nuclear Installations (CSNI). The paper presents the results of the calculations performed by participants and emphasizes its usefulness for future uncertainty evaluation, to be performed in next phase. The objectives of the activity are basically to simulate the LBLOCA reproducing the phenomena associated to the scenario and also to build a common, well-known, basis for the future comparison of uncertainty evaluation results among different methodologies and codes. The sensitivity calculations performed by participants are also presented. They allow studying the influence of different parameters such as material properties or initial and boundary conditions, upon the behaviour of the most relevant parameters related to the scenario. © 2010 M. Pérez et al

Main Results of Phase IV BEMUSE Project. Simulation of LBLOCA in a NPP

Phase IV of BEMUSE Program is connected with previous phase II, being a necessary step for an uncertainty analysis: the simulation of the reference scenario and sensitivity analysis. Present phase analyses a LBLOCA scenario in Zion 1 NPP, a 4 loop PWR unit. Thirteen participants coming from ten different countries have taken part in the Phase IV of the program. The BEMUSE (Best Estimate Methods plus Uncertainty and Sensitivity Evaluation) Program has been promoted by the Working Group on Accident Management and Analysis (GAMA) and endorsed by the Committee on the Safety of Nuclear Installations (CSNI). The paper presents the results of the calculations performed by participants and emphasizes its usefulness for future uncertainty evaluation, to be performed in next phase. The objectives of the activity are basically to simulate the LBLOCA reproducing the phenomena associated to the scenario and also to build a common, well-known, basis for the future comparison of uncertainty evaluation results among different methodologies and codes. Following activities performed in phase II, a list of sensitivity calculations was proposed and performed by participants to study the influence of different parameters such as material properties or initial and boundary conditions, upon the behaviour of the most relevant parameters related to the scenario