2014 안전해석심포지움 July 17, 2014 코드 불확실도 평가 규제방향 한국원자력안전기술원 오덕연

KINS 2014 안전해석심포지움 Table of Contents Table of Contents I. 개요 II. 불확실도 관련 국제공동연구 III. PREMIUM 주요 연구 성과 IV. 불확실도 평가 규제방향 - 2/24 -

KINS 2014 안전해석심포지움  결정론적 안전해석 방법 IAEA Safety Standards No. SSG-2 Opt Computer Code Conservative Best-estimate System Availability Conservative PSA-based* Initial Condition Conservative data Realistic data w/uncertainty Realistic data * Component/system reliability data are often used I. 개요 - 3/24 -

KINS 2014 안전해석심포지움 인허가된 ECCS/LOCA 평가방법론  Conservative model (KINS Technical Guidance, KINS/GT-N007-1, or 10 CFR 50, App.K) Provide the model and calculation method whose conservatism is justified and approved for use KSNP CE EM and Westinghouse type WH EM  Best estimate model (KINS Technical Guidance, KINS/GT-N007-2, or Reg. Guide 1.157) Provide sufficient justification to show that the analytical technique realistically describes the behavior of the reactor system during a loss-of-coolant accident More broadly used in nuclear industries and regulations (e.g., KREM and WCOBRA/TRAC) I. 개요 - 4/24 -

KINS 2014 안전해석심포지움 I. 개요  대형냉각재상실사고에 대한 최적평가방법 Major trend in nuclear industries and regulations Increased regulatory demand for life extension, power uprating, and advanced reactor Independent BE calculation with uncertainty quantification for LBLOCA (KINS-REM)  최적평가방법론에서의 불확실도변수 정량화 Conventional method by expert judgment, code validation or reference documents Demand necessary to determine the uncertainty range by statistical or mathematical approach e.g., CIRCE (CEA), FFTBM (Pisa University), Data assimilation, and etc. - 5/24 -

KINS 2014 안전해석심포지움 II. 불확실도 관련 국제공동연구  BEMUSE (Best Estimate Method- Uncertainty and Sensitivity Evaluation) Program International research program supported by OECD/NEA/CSNI To evaluate the practicability, quality, and reliability of BE methods with uncertainty for LBLOCA Composed of 2 steps including 6 phases (LOFT L2-5 evaluation and Zion nuclear plant evaluation) from 2002 to 2010 Use of different codes and BE methodology for each participant Produce recommendations for BE methodology - 6/24 -

KINS 2014 안전해석심포지움 II. 불확실도 관련 국제공동연구  PREMIUM Program Post-BEMUSE Reflood Models Input Uncertainty Methods OECD/NEA/CSNI/WGAMA 가 승인한 국제공동연구 냉각재상실사고에 대한 불확실도 최적평가방법 연구인 BEMUSE 의 후속 프로그램으로 재관수 모델의 입력 불확실도 평가방법 연구 기간 : ~ 예정 ( 지연 중 ) 참여국 및 기관 : 10 개국 15 개 기관 참여 PhaseContentHostSchedule IDescription of methodsUPC II Definition (and recommendations) for influential input uncertainty parameters UNIPI III Quantification of input uncertainty ranges based on FEBA/SEFLEX data GRS IV Confirmation of the input uncertain parameter ranges based on PERICLES-2D data CEA and IRSN VConclusionsCSN /24 -

KINS 2014 안전해석심포지움 III. PREMIUM 주요 연구성과  FEBA 실험 Reflooding tests with possibility of maintaining constant flooding rates and constant back pressure The test section consists of a full-length 5 x 5 rod bundle of PWR fuel rod dimensions utilizing electrically heated rods with a cosine power profile approximated by axially 7 steps of different power density - 8/24 -

KINS 2014 안전해석심포지움 III. PREMIUM 주요 연구성과  불확실도 계산을 위한 FEBA 모델링 Heated part with 40 axial subvolumes, and rod bundle with 8 radial mesh points Test section including the heated part and housing were modeled Not use the specific model for the space grids The radiation has not been taken into account The initializing state was achieved when the heater surface temperatures reached at the temperature of experiment The rod bundle interphase friction model was applied in the hydraulic nodes of the heated part The default values and flags are used for hydrodynamic and heat transfer calculation - 9/24 -

KINS 2014 안전해석심포지움 III. PREMIUM 주요 연구성과  FEBA 불확실도 계산에 사용된 불확실도 변수 Two uncertainty parameters are considered, which determined in the Phase III process ‐ Based on RBHT PIRT, expert judgment and sensitivity analysis Uncertainty ranges for two parameters were obtained using CIRCE method ‐ Statistical method to get mean, standard deviation, type of distribution combining the differences between the experiment and code results, and derivatives of code response w.r.t. parameter Name of the parameter Physical model Type of PDF Features of the PDF Nominal value Constant value Dry/Wet Wall Criteria Normal ~ (Std.: ) TRACE blowing factor Interfacial Heat Transfer of Drop-Steam Normal ~ (Std.: ) /24 -

KINS 2014 안전해석심포지움 III. PREMIUM 주요 연구성과  FEBA 실험 불확실도 계산 124 uncertainty calculations for each six FEBA test were performed 2.5% and 97.5% percentiles for the cladding temperature and pressure drop were obtained - 11/24 -

KINS 2014 안전해석심포지움  FEBA-216 시험의 불확실도계산 결과 Max. cladding temperatures at each location are well covered, but earlier quenching time than experiment, because of very narrow band III. PREMIUM 주요 연구성과 - 12/24 -

KINS 2014 안전해석심포지움  FEBA 불확실도계산의 공통사항 In the reference calculation of most FEBA tests, predict well the cladding temperature behavior, but the earlier quenching The result of uncertainty calculation showed that the maximum cladding temperatures at 1135 mm and 2225 mm elevation except for FEBA 223 and 218 tests were well enveloped by lower and upper limits Both two tests had higher temperature prediction than experimental data Generally, the cladding temperature at 1135 mm had the wider uncertainty band than at 2225 mm. But the earlier quenching for all tests were predicted that uncertainty calculation did not envelope The pressure drop in the middle were under-predicted than the experiment III. PREMIUM 주요 연구성과 - 13/24 -

KINS 2014 안전해석심포지움 III. PREMIUM 주요 연구성과  PERICLES 실험 Reflood test to investigate 2D effects where the rod power is not identical from one assembly to the other ones Three different assemblies, denoted here by A, B and C Assemblies containing a vertical housing with a rectangular section Each assembly containing 7x17 full length heater rods - 14/24 -

KINS 2014 안전해석심포지움 III. PREMIUM 주요 연구성과  불확실도계산을 위한 PERICLES 주요 모 델링 Heated part with 42 subvolumes, the rod bundle with 42 axial nodes and 8 radial mesh points Modeled as two channels with cold (A,C) and hot (B) channels coupled with the crossflow junctions Specific model for the space grids was not used Fuel rod simulators are modeled as heat structures by averaged value of thermal conductivity for Boron Nitride at all sections. Also, the averaged multiplier of volumetric heat capacity for Nichrome V including the 10% uncertainty Initializing state achieved when the heater surface temperatures reached at the temperature of experiment - 15/24 -

KINS 2014 안전해석심포지움 III. PREMIUM 주요 연구성과  PERICLES 실험 불확실도 계산 Considered the same input parameters and the same pdf as those determined within Phase III using the FEBA tests 200 calculations for each six PERICLES test were performed, and 2.5% and 97.5% percentiles for the cladding temperature and pressure drop were obtained The maximum cladding temperature and quenching time were gotten for each run of all tests. Test No F nom (HA) W/cm 2 F nom (CA) W/cm 2 F xy GO(HA) g/cm 2 s GO(CA) g/cm 2 s T wi (HA) °C T wi (CA) °C DT °C P (bar) RE RE RE RE RE RE /24 -

KINS 2014 안전해석심포지움 III. PREMIUM 주요 연구성과  PERICLES RE0062 시험 (F xy =1) 불확실도계산 결과 Calculation result shows higher cladding temp. and earlier quenching time at 1828 mm than experimental data, not enveloped Calculation result over- predicts cladding temp. and quenching time is enveloped - 17/24 -

KINS 2014 안전해석심포지움  PERICLES RE0062 시험 주요 결과 Max. cladding temp. for 200 runs shows small deviation at 1828 mm, but more broadly scattered at 2998 mm Similar trend for quenching time III. PREMIUM 주요 연구성과 - 18/24 -

KINS 2014 안전해석심포지움  PERICLES RE0080 시험 (F xy ≠1) 불확실도계산 Comparatively well predict the cladding temp. and quenching time at 1828 mm in Assembly A, but higher prediction of cladding temp. in Assembly B Predict the cladding temp. higher at 2998 mm, but quenching time enveloped Slightly higher prediction of delta P in the middle III. PREMIUM 주요 연구성과 - 19/24 -

KINS 2014 안전해석심포지움  PERICLES RE0080 시험 주요평가 결과 Broader distribution for max. cladding temp. and quenching time at 2998 mm both in assembly A and B than at 1828 mm III. PREMIUM 주요 연구성과 - 20/24 -

KINS 2014 안전해석심포지움 III. PREMIUM 주요 연구성과  PREMIUM 주요 연구결과 Three possible reason for uncovering the experimental data  Insufficient number of uncertainty related to reflood phenomena  Narrow uncertainty ranges  Deficiency of reflood model in TH code Current general observation in Phase IV meeting  Extrapolate uncertainty results obtained with a given experiment (FEBA) to another experiment (PERICLES) is not justified if the experimental thermohydraulics conditions of both experiments are different  Using uncertainties found with a 1-D modeling to a 3-D modeling is also questionable, since the numerical schemes of both modelings are different  More generally, there is a scale-up problem between FEBA and PERICLES - 21/24 -

KINS 2014 안전해석심포지움 IV. 불확실도계산 규제 방향  BEMUSE 국제공동연구 Recommendation Code suitable to calculate the scenario under investigation Skill, experience and knowledge of the users about the suitable computer code as well as the used uncertainty method are important to reduce the user effect Increased number of calculations advisable in order to decrease the dispersion of the tolerance limits Important to include influential parameters and provide distributions of uncertainty input parameters through code validation with appropriate experimental data The method to select and quantify code model uncertainties could be studied -> PREMIUM program initiated - 22/24 -

KINS 2014 안전해석심포지움 IV. 불확실도계산 규제 방향  불확실도계산 규제방향 불확실도 정량화시 실험의 scaling, 초기 열수력 조건 등 발전소와 유사성 심층 검토 : Possibility of extrapolation to plant 불확실도 변수 정량화 방법론의 개선 가능성 KREM 방법론에서 data covering 에 대한 정량적 판단기준 필요  현재 PCT 관점의 covering 확인  전구간 피복재 온도, quenching time 등도 covering 되는지 검토 필요  Upper limit 뿐만 아니라 lower limit 에 대한 covering 여부 Calibrated calculation 비교  Reference 계산이 심하게 bias 되어 covering 안되는 경우 User effect ( 불확실도 변수 범위 포함 ) 의 최소화  충분한 실험 평가 및 민감도 해석 수행 요구 신형 원전 적용 및 모델 개선 등 코드의 변경시 기존 방법론과의 차이점 심층 검토  PIRT 통한 주요 불확실도 변수 선정의 타당성  실험 평가를 통한 불확실도 변수 범위 결정 - 23/24 -

KINS 2014 안전해석심포지움 IV. 불확실도계산 규제 방향  SPACE 코드 관련 최적방법론에 대한 규제방향 SPACE 코드의 냉각재상실사고 모사 적합성 기존 RELAP5/MOD3.3K 를 이용한 방법론과의 차이점 심층 검토 PIRT, 노딩, 실험평가 매트릭스 등의 타당성 불확실도 변수 선정과 변수 범위에 대한 타당성  파단 스펙트럼 등 새로 추가되었거나 범위가 변경된 경우 등 개별 열수력 모델에 대한 불확실도 범위 근거 및 타당성  SPACE 코드로 실험 평가 필요 여부  불확실도 관련연구 방향 KINS-REM 불확실도 변수 ( 모델 관련 ) 범위에 대한 재평가 다차원모델 관련 불확실도 변수 선정 개선된 방법론을 적용한 발전소 최적계산 및 불확실도 평가 - 24/24 -