Modeling of deposition and erosion of CRUD on fuel surfaces under sub-cooled nucleate boiling in PWR

Seungjin Seo,Nakkyu Chae,Samuel Park,Richard I. Foster,Sungyeol Choi Korean Nuclear Society 2023 Nuclear Engineering and Technology Vol.55 No.7

Simulating the Corrosion-Related Unidentified Deposit (CRUD) on the surface of fuel assemblies is necessary to predict the axial offset anomaly and the localized corrosion induced by the CRUD during the operation of nuclear power plants. A new CRUD model was developed to predict the formation of the CRUD deposits, considering the deposition and erosion mechanisms. The heat transfer and capillary flow within the CRUD were also considered to evaluate the boiling amount within the CRUD layer. This model predicted a CRUD deposit thickness of 44 ㎛ during a one-cycle operation of the Seabrook nuclear power plant. The CRUD deposition tended to accelerate and decelerate during the simulation, by being related to boiling mechanism on the deposits surface. Additionally, during a three-cycle operation corresponding to the refueling period, the CRUD deposition was saturated at a thickness of 80 ㎛, which was in good agreement with the suggested thickness for CRUD buildupin pressurized water reactors. Surface boiling on the thin CRUD deposits enhanced the acceleration of the deposition, even when the wick boiling properties were not favorable for CRUD deposition. To ensure the certainty of the simulation results, sensitivity analyses were conducted for the porosity, chimney density, and the constants employed in the proposed model of the CRUD.

Modeling heat transfer through corrosion product deposits on fuel rods in pressurized water reactors

Yeo, D.Y.,NO, H.C. Elsevier 2019 Nuclear engineering and design Vol.342 No.-

<P><B>Abstract</B></P> <P>CRUD is the corrosion product deposit found on a fuel rod surface of pressurized water reactors (PWRs). Problematic phenomena caused by CRUD – CRUD Induced Power Shift (CIPS) and CRUD Induced Localized Corrosion (CILC) – are closely related to the heat transfer mechanism of CRUD. However, heat transfer regimes of CRUD are still not well clarified. Therefore, the heat transfer regimes of CRUD were investigated using existing database from the CRUD heat transfer experiment. As a result, it was found that there are three heat transfer regimes: (i) liquid-saturated regime, (ii) wick-boiling regime, and (iii) film-boiling regime. In addition, the boiling curves from the experiment were categorized according to their heat transfer regimes so that models for CRUD can be validated with appropriate database for the heat transfer regime where they are concerned. After obtaining the categorized databases, the model for the film boiling of CRUD was suggested. Unlike the conventional approaches that use capillary force as a unique source of the liquid supply in pores, the model we present in this paper adopted the disjoining force as an additional liquid supply term. This assumption was validated with the previous heat pipe experiment; the root-mean-square error (RMSE) for the prediction of the vapor film thickness was notably reduced from 790% to 18.7% by including the disjoining force to the supply term. The supply term considering the disjoining force was also applied to a model for the CRUD film boiling. The model estimates the wall superheat by balancing the supply term and the hydraulic resistance terms from fluid flows within CRUD. The model we present in this paper successfully predicted the wall superheat during the film boiling; the RMSE was 19% when the predicted wall superheats were compared with ones from the database categorized as film boiling. Finally, it was found from the sensitivity study using the model we present in this paper that the heat transfer performance of CRUD during the film boiling is highly sensitive to the pore radius.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Liquid-saturated regime, wick-boiling regime, and film-boiling regime are heat transfer regimes of CRUD. </LI> <LI> Vapor film exist within the CRUD during the heat transfer regime beyond the wick-boiling regime. </LI> <LI> Disjoining force becomes dominant during film boiling when heat flux is large. </LI> <LI> Heat transfer rate during film boiling is highly sensitive to pore radius. </LI> </UL> </P>

파울링된 피복관 표면의 가압 경수로 운전환경에서의 미포화 비등 열전달 성능평가를 위한 실험장치 구축 연구

김지용,이윤주,함준혁,김지현,방인철 한국유체기계학회 2022 한국유체기계학회 논문집 Vol.25 No.5

The CRUD (Chalk River Unidentified Deposit or Corrosion Related Unidentified Deposit) is a fouling deposit of metal or metal oxide on the nuclear fuel cladding under PWR (Pressurized Water Reactor) operating conditions and causing the several operational and safety-related problems. The major concerns related to the CRUD are AOA (Axial Offset Anomaly) caused by the accumulation of the boron species inside the porous CRUD from the primary reactor coolant and CILC (CRUD Induced Localized Corrosion) caused by locally increased cladding surface temperature due to the additional thermal resistance of the CRUD layer. The growth of CRUD and the CRUD-related problems are known to be governed by the sub-cooled nucleate boiling phenomena inside the upper part of the reactor core, especially on the hot fuel assembly and hot fuel pin. In the current study, the experimental facility called DISNY (crud DeposItion Simulator for Nuclear energY) was proposed as a testbed to simulate the CRUD growth and to investigate the sub-cooled nucleate boiling heat transfer performance of the CRUD deposited cladding surface under prototypical PWR operating conditions.

The DISNY facility for sub-cooled flow boiling performance analysis of CRUD deposited zirconium alloy cladding under pressurized water reactor condition: Design, construction, and operation

김지용,이윤주,김지현,방인철 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.9

The CRUD on the fuel cladding under the pressurized water reactor (PWR) operating condition causes several issues. The CRUD can act as thermal resistance and increases the local cladding temperature which accelerate the corrosion process. The hideout of boron inside the CRUD results in axial offset anomaly and reduces the plant's shutdown margin. Recently, there are efforts to revise the acceptance criteria of emergency core cooling systems (ECCS), and additionally require the modeling of the thermal resistance effect of the CRUD during the performance analysis. There is an urgent need for the evaluation of the effect of the CRUD deposition on the cladding heat transfer under PWR operating conditions, but the experimental database is very limited. The experimental facility called DISNY was designed and constructed to analyze the CRUD-related multi-physical phenomena, and the performance analysis of the constructed DISNY facility was conducted. The thermal-hydraulic and water chemistry conditions to simulate the CRUD growth under PWR operating conditions were established. The design characteristics and feasibility of the DISNY facility were validated by the MARS-KS code analysis and separate performance tests. In the current study, detailed design features, design validation results, and future utilization plans of the proposed DISNY facility are presented.

A Study on the Crystalline Boron Analysis in CRUD in Spent Fuel Cladding Using EPMA X-ray Images

정양홍,백승제,진영관 한국부식방식학회 2020 Corrosion Science and Technology Vol.19 No.1

Chalk River Unidentified Deposits (CRUDs) were collected from the Korean pressurized water reactor (PWR)plant (A, B, and C) where the axial offset anomaly (AOA) occurred. AOA, also known as a CRUD-inducedpower shift, is one of the key issues in maintaining stable PWR plant operations. CRUDs were sampledfrom spent nuclear fuel rods and analyzed using an electron probe micro-analyzer (EPMA). This paper describesthe characteristics of boron-deposits from the CRUDs sampled from twice-burnt assemblies from the KoreanPWR. The primary coolant of a PWR contains boron and lithium. It is known that boron deposition occursin a thick CRUD layer under substantial sub-cooled nucleate boiling (SNB). The results of this study aresummarized as follows. Boron was not found at the locations where the existence was confirmed in simulatedCRUDs, in other words, the cladding and CRUD boundaries. Nevertheless, we clearly observed the presenceof boron and confirmed that boron existed as a lump in crystalline form. In addition, the study confirmedthat CRUD existed in a crystal form with a unique size of about 10 μm.

미립화 및 분무장치 2 : 수력학적 캐비테이션을 모의 크러드 침전층 제거 실험

김성만 ( Seong Man Kim ),이승원 ( Seung Won Lee ),박성대 ( Seong Dae Park ),방인철 ( In Cheol Bang ) 한국액체미립화학회 2012 한국액체미립화학회 학술강연회 논문집 Vol.2012 No.-

Axial Offset Anomaly (AOA) referring to an unexpected neutron flux depression is also known as Crud Induced Power Shift (CIPS). Fuel assemblies removed from an AOA core has shown a thick porous deposition layer of crud on fuel clad surface. Hydrodynamic cavitation generates shock pressure of a few tens MPa due to bubble collapse like the cavitation generated by Ultrasonics. It is well known that the cavitation can erode the metal surface. The idea of the current study is that such energetic cavitation bubble collapses could help to remove the crud from the fuel assembly. Therefore, the current study first investigates effects of hydrodynamic cavitation occurred from a single hole orifice fundamentally. The orifice can be easily occurred the cavitation. In addition to common cavitation, effect of swirl was measured and quantified using sensitive film. The purpose of this study is to optimize the effect of cavitation erosion. For investigate the cavitation effect, effect of cavitation was measured by film. The film was discolored by the pressure with a measurement range of its own. It is individual to reflect the value stored pressure as the disposable film. For investigate of removal effect, CRUD was coated by nanoparticle. CRUD consists primarily of magnetite, nickel ferrite, cobalt ferrite, and so on. For only checking the cavitation effects in this work, however, specimens made of SS316L, alloy of Cr, Ni and Fe are simply deposited by silicon carbide nanoparticles since the nanoparticles with the CRUD porous layer. It shows a CRUD-like deposition structure. Weight change of sample was measured the through each coated sample for analyzing the removal effect on each cavitation number. The result of pressure in two flows, higher pressure level is observed in case of using swirl flow. The samples were exposed to cavitation during the same time, and it was compared the result between using only orifice and using both orifice and line static mixer. Maximum shock pressure was recorded at swirl flow caused by line static mixer.

Analysis of CRUD Flake Applied to Abnormal High Beam Current by Shielded-EPMA

( Y. H. Jung ),( S. J. Baik ),( S. B. Ahn ) 한국부식방식학회 2018 Corrosion Science and Technology Vol.17 No.6

CRUD specimens, scraped from twice-burned fuel cladding in the Korean Nuclear Power Plant, were analyzed using Shielded-EPMA. The principal elements of the CRUD were identified as Ni and Fe, at an approximate ratio of 1.3 Ni/Fe. To investigate the morphology and composition of the pure metallic materials in the CRUD, coolant impurities must be removed. This can be accomplished by increasing the EPMA current to an abnormally high intensity until the impurities are melted. Normally, EPMA applications are performed at conditions of 20 kV voltage and 20 nA current. But in our study, the applied current was increased up to 1200 nA, over time increments ranging from 5 to 30 seconds. This technique was performed by opening an adjustable aperture for the gun alignment. Results showed impurities contained in the CRUD material disappeared and pure metal materials, e.g., Ni and Fe, remained. This method presents an innovative way to analyze CRUD.

Hydrodynamic cavitation characteristics of an orifice system and its effects on CRUD-like SiC deposition

Kim, Seong Man,Bang, In Cheol Elsevier 2016 Annals of nuclear energy Vol.96 No.-

<P><B>Abstract</B></P> <P>In a nuclear power plant, chalk river unidentified deposit (CRUD) is known as a deposit that is composed of corrosion and oxidation materials. It has a porous structure, which combines with boron that is injected into the coolant for controlling power levels. The buildup of corrosion products on the fuel cladding surface has proven to be particularly significant for both BWRs and PWRs. The high temperature of the cladding surface attracts impurities and chemical additives in the reactor coolant that deposit on the fuel rod surface in a process. The deposits on a fuel rod, known as CRUD, can be tenacious, insulative compounds capable of increasing the local clad temperature and accelerating clad corrosion—sometimes to the point of fuel failure.</P> <P>The deposition of CRUD on fuel cladding surfaces causes uneven heating of the reactor core. The situation is exacerbated by boron, which is added to the coolant to control power levels. However, boron becomes concentrated and is deposited within thick CRUD deposits. Ultrasonic mechanisms were developed but they have limitations for decontamination. In this experiment, a decontamination test was conducted using a sample sheet that was composed of SiC/water nanofluids. In addition, it was exposed to swirl flow and common flow for checking enhanced cavitation. It is measured by a pressure film, as shock pressure is associated with cavitation number. As a pressure film is wetted easily in water, it was injected into a holder. In the experiment, the maximum shock pressure was obtained during swirl flow at a low cavitation number. This indicates that pressure was concentrated on the pressure film. Consequently, cavitation can get rid of CRUD layers partially.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CRUD-like SiC deposition was prepared for examining the erosion test in the cavitation field. </LI> <LI> We investigated the comparison between swirl flow and common flow on cavitation. </LI> <LI> Magnitude of shock pressure was investigated at low cavitation number. </LI> </UL> </P>

초음파 핵연료 세정장비의 시스템 구성과 제거된 크러드의 정량적 무게 측정법

신중철(Jung Cheol Shin),이학윤(Hak Yun Lee),성운학(Un Hak Seong),주영종(Yeong Jong Joo),김용찬(Yong Chan Kim),한욱진(Wook Jin Han) 한국압력기기공학회 2024 한국압력기기공학회 논문집 Vol.20 No.1

Crud is a corrosion deposit that forms in equipments and piping of nuclear reactor’s primary systems. When crud circulates through the reactor’s primary system coolant and adheres to the surface of the nuclear fuel cladding tube, it can lead to the Axial Offset Anomaly (AOA) phenomenon. This occurrence is known to potentially reduce the output of a nuclear power plant or to necessitate an early shutdown. Consequently, worldwide nuclear power plants have employed ultrasonic cleaning methods since 2000 to mitigate crud deposition, ensuring stable operation and economic efficiency. This paper details the system configuration of ultrasonic nuclear fuel cleaning equipment, outlining the function of each component. The objective is to contribute to the local domestic production of ultrasonic nuclear fuel cleaning equipment. Additionally, the paper introduces a method for accurately measuring the weight of removed crud, a crucial factor in assessing cleaning effectiveness and providing input data for the BOA code used in core safety evaluations. Accurate measurement of highly radioactive filters containing crud is essential, and weighing them underwater is a common practice. However, the buoyancy effect during underwater weighing may lead to an overestimation of the collected crud’s weight. To address this issue, the paper proposes a formula correcting for buoyancy errors, enhancing measurement accuracy. This improved weight measurement method, accounting for buoyancy effects in water, is expected to facilitate the quantitative assessment of filter weights generated during chemical decontamination and system operations in nuclear power plants.

Analysis of activated colloidal crud in advanced and modular reactor under pump coastdown with kinetic corrosion

Mehboob Khurram,Al-Zahrani Yahya A. 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.12

The analysis of rapid flow transients in Reactor Coolant Pumps (RCP) is essential for a reactor safety study. An accurate and precise analysis of the RCP coastdown is necessary for the reactor design. The coastdown of RCP affects the coolant temperature and the colloidal crud in the primary coolant. A realistic and kinetic model has been used to investigate the behavior of activated colloidal crud in the primary coolant and steam generator that solves the pump speed analytically. The analytic solution of the non-dimensional flow rate has been determined by the energy ratio b. The kinetic energy of the coolant fluid and the kinetic energy stored in the rotating parts of a pump are two essential parameters in the form of b. Under normal operation, the pump's speed and moment of inertia are constant. However, in a coastdown situation, kinetic damping in the interval has been implemented. A dynamic model ACCP-SMART has been developed for System Integrated Modular and Advanced Reactor (SMART) to investigate the corrosion due to activated colloidal crud. The Fickian diffusion model has been implemented as the reference corrosion model for the constituent component of the primary loop of the SMART reactor. The activated colloidal crud activity in the primary coolant and steam generator of the SMART reactor has been studied for different equilibrium corrosion rates, linear increase in corrosion rate, and dynamic RCP coastdown situation energy ratio b. The coolant specific activity of SMART reactor equilibrium corrosion (4.0 mg s1 ) has been found 9.63 103 mCi cm3 , 3.53 103 mC cm3 , 2.39 102 mC cm3 , 8.10 103 mC cm3 , 6.77 103 mC cm3 , 4.95 104 mC cm3 , 1.19 103 mC cm3 , and 7.87 104 mC cm3 for 24Na, 54Mn, 56Mn, 59Fe, 58Co, 60Co, 99Mo, and 51Cr which are 14.95%, 5.48%, 37.08%, 12.57%, 10.51%, 0.77%, 18.50%, and 0.12% respectively. For linear and exponential coastdown with a constant corrosion rate, the total coolant and steam generator activity approaches a higher saturation value than the normal values. The coolant and steam generator activity changes considerably with kinetic corrosion rate, equilibrium corrosion, growth of corrosion rate (DC/Dt), and RCP coastdown situations. The effect of the RCP coastdown on the specific activity of the steam generators is smeared by linearly rising corrosion rates, equilibrium corrosion, and rapid coasting down of the RCP. However, the time taken to reach the saturation activity is also influenced by the slope of corrosion rate, coastdown situation, equilibrium corrosion rate, and energy ratio b.