Pre-test CFD analyses of experiments on the early phase of a MSL rupture
4.3 Proposal of cyclic material model for ABAQUS code
4.4 Status report and proposal of Finnish contribution to a forthcoming international project.
4.5 Justified proposal for optimally realistic experimental simulation of environment assisted thermal fatigue in feed water nozzle.
Applications
The project results will contribute to safety and plant life management (PLIM) in Finnish NPP’s. International experience indicates that pro-active management of fatigue normally pays back in reduced inspection and repair costs. In long run, quantitative mapping of fatigue damage and cracking probability will become an essential part of risk informed probabilistic PLIM.
Education of experts
The project will be realised in co-operation with VTT, HUT, Finnish industry and international networks. Thesis works (MS, Lic., PhD) will be continuously running. For 2007 we could name a few potential students (2/HUT, 2/VTT).
Liite 2a SAFIR2010 24.10.2006 RESEARCH PLAN for 2007/version 2
Water chemistry and oxidation in the primary circuit (WATCHEM) Vesikemia ja hapettuminen reaktoripiirin olosuhteissa
Duration 2007 – 2010
Project manager Timo Saario
Volume and funding 2007 1.1 person-years 167,785 k€
Funding sources (k€) 2007 VYR 67,785 k€, VTT 100 k€
1 person year = 10.5 person months.
Objectives
The project consists of four main objectives of which first three will be focused on during 2007.
The first objective is to study how different water chemistry conditions (e.g. normal vs elevated alkaline concentration and optional water chemistries) affect the oxidation rate of different fuel cladding materials. This information is obtained with experimental tests in relevant conditions. The results will be used in modelling in order to get estimates for the relevant parameters of the oxidation processes. Through this modelling approach the risks involved in application of new water chemistries can be estimated.
The second objective is to study the decontamination procedures available at the moment and options for chemistry conditions in these processes. This task consists of a thorough literature survey of the subject together with experimental tests in relevant conditions in which the different decontamination procedures are verified. With this approach a high enough competence level can be reached to enable selection of the best plant specific commercial decontamination practise.
The third objective is pre-oxidation of component and system surfaces, which can have a crucial effect on the corrosion rate and activity incorporation onto the surfaces. Knowledge on optimisation of pre-oxidation techniques is needed both when decontaminated components and/or system parts are taken back into use and when new systems are taken into use for the first time. This will be especially important when the Hot Functional Test (HFT) procedure of the EPR (OL3) is evaluated.
The fourth objective is to evaluate the effect of dissolved H2 on the stability of the oxide films on nickel-base alloys and their weldments during cool-down of a PWR. This knowledge will support the evaluations in the EAC-project within SAFIR2010 on the maximum H2
concentration to avoid the Low Temperature Crack Growth (LTCG) phenomena.
Background
The current and future power plants have plans to operate at higher power and/or longer than 12- month fuel cycles. These changes call for a higher pH in the primary coolant. This, on the other hand, sets new kinds of requirements for the corrosion resistance of fuel cladding materials. In the SAFIR 2003-2006 –programme fuel cladding oxidation studies were performed using three different cladding materials in normal PWR as well as in elevated Li coolants to check whether differences in oxidation processes can be observed. Results indicated that the higher alkaline concentration accelerates the oxidation rate of Zr alloys. In the proposed project, a comparison between alkaline solutions with different cations (Li vs. K) will be performed. The results from the earlier work as well as from the proposed project will be reported also in IAEA’s FUWAC – programme. This programme concentrates in studying the occurrence of Crud Induced Power Shift
(CIPS) phenomenon which is closely related to the oxide layer properties of fuel cladding materials.
Decontamination as a second objective in this project builds up new knowledge in Finland concerning the system decontamination at the plants. System decontamination procedures performed so far in Finland (Loviisa NPP 1994) have not been very successful. There are also international activities (IAEA –working group, EU FP6 project ANTIOXI) related to this subject in order to understand the possibilities to decrease the activity on primary circuit surfaces. One example of the main open questions in decontamination processes is the replacement of oxalic acid with some other chemical. This work benefits the plants in planning either a component or system decontamination in the future.
Preoxidation of system and component surfaces is a new subject which though will be of importance e.g. when deciding on the HFT procedure for OL3 power plant. In the future also larger system parts will be decontaminated and possibly re-preoxidised. In this subproject a new scientist training is planned to start in the form of a diploma thesis.
Specific Goals in 2007
1 Fuel cladding oxidation (Funding: VYR, NN, VTT)
In this subproject the effect of different water chemistries on fuel cladding material corrosion will be studied in relevant PWR conditions. The subproject consist of the following tasks:
− 1.1 EXPERIMENTAL: Effect of KOH water chemistry will be studied by performing a set of measurements in a water circulation autoclave using the Thin Layer Electrochemical Impedance Spectroscopy (TLEIS) method and ex situ analysis (FEGSEM/SEM) of the microstructures of the base materials and oxide films. These results will be compared with the corresponding results obtained earlier in different Li solutions within the SAFIR 2003- 2006 –programme.
− 1,2 MODELLING: The results obtained with the TLEIS technique will be used as input in modelling using the Mixed Conduction Model in order to find out the relevant parameters and their roles in describing the oxidation of the fuel cladding materials.
2 Decontamination
This subproject will include the following tasks:
− 2.1 LITERATURE STUDY: A thorough literature survey of available decontamination procedures and experiences from them both in real power plant as well as laboratory conditions
− 2.2 INTERNATIONAL WORKING GROUP: Participation to the IAEA coordinated working group dealing with decontamination procedures and processes in VVER 440s (Evaluation of crud deposition on fuel in WWER reactors: Investigation of crud deposition in primary circuit of WWER. (IAEA task in the frame of (RER/9/076)"STRENGTHENING SAFETY AND RELIABILITY OF NUCLEAR FUEL AND MATERIALS IN NUCLEAR POWER PLANTS" for the period 2006 to 2008.))
− 2.3 EXPERIMENTAL PLAN: Based on the working group propositions and the literature survey a plan will be made for the relevant laboratory experiments to study modifications to the current decontamination processes.
3 Preoxidation
This subproject includes the following task:
− 3.1 LITERATURE STUDY: A thorough literature survey of available data on preoxidation processes used when a new plant is taken into use (so-called Hot Functional
Test, HFT) or when taking intro use components which have been decontaminated using e.g. glass pebble blasting.
Deliverables
Goal Deliverable
1.1 A report of the effect of modified water chemistries on the oxidation of fuel cladding materials
1.2 A scientific publication on the fuel cladding behaviour under different alkaline water chemistries
2.1
3.1
A report on the literature study on decontamination procedures and their field success, including the experimental plan for decontamination investigations to be carried out in 2008.
A report on the literature study on preoxidation processes.
Applications
The risks (e.g. accelerated oxidation caused by elevated Li concentration and CIPS) on cladding material corrosion involved in application of new water chemistries can be better estimated based on the modelling work performed within this project.
Participation to the IAEA working group and the information gained there from on component decontamination will be used in planning future decontaminations at Finnish power plants.
Education of experts
Towards the second half of the year 2007 an MSc –thesis worker is planned to start. This work will concentrate on the fuel cladding oxidation.
Liite 2a SAFIR2010 22.01.2007 RESEARCH PLAN for 2007/version 2
Monitoring of the structural integrity of reactor circuit (RAKEMON) Rakenteiden eheyden monitorointi
Duration 2007 – 2010
Project manager Pentti Kauppinen
Volume and funding 2007 1.5 person-years 205,184 k€
Funding sources (k€) 2007 VYR 86,184 k€, VTT 119 k€
Objectives
The aim of this project is to develop techniques and monitoring systems that can be used to monitor the structural integrity of the primary circuit components. The aim is to develop measurement systems both for detection and analysis of macroscopic flaws and microscopic changes in the material that are often preceding the macroscopic failure. In 2007 the basics for the design of monitoring system will be studied.
It is also necessary to develop inspection techniques that can be applied to reactor circuit components where the access is restricted and decreasing the reliability of inspection. This kind of inspection items are e.g. welds with coarse grain size and nozzle welds where the difficult geometry is restricting the performance of inspection.
Background
Non-destructive testing techniques are used to monitor the condition of the structures of reactor circuit during the operation of nuclear power plants. The in-service inspections (ISI) are normally performed during the shutdown period but there is also increasing need to monitor the condition of components during service by on-line methods. The tendency worldwide and also in Finnish nuclear power plants is to improve the efficiency of in-service inspections by applying risk- informed methods to the selection of inspection items, methods and timing of in-service inspections. This kind of ISI-programme is supported by on-line monitoring techniques that are used to focus the inspections to areas where failures are most probable and/or consequences are most severe.
There is a specific need to improve the reliability of NDE-techniques used for the ISI of bimetallic welds and inspection items where access is limited. Ultrasonic simulation can be used to optimize the inspection techniques for these problematic inspection areas.
Specific Goals in 2007
1 Monitoring of the structural integrity of reactor circuit 1.1 Literature review of on-line monitoring NDE-techniques
The different techniques of non-destructive evaluation that can be applied to on-line monitoring of piping and components will be thoroughly reviewed in a literature wide scope review (including e.g. acoustic emission and leak monitoring). Special emphasis is put on techniques that can be used to monitor the whole through-thickness volume and large areas of the component and on the techniques that can be used without contact to the inspection item. The restrictions caused by the high temperature of primary circuit during operation and the effects of radiation dose on the transducer materials will be studied.
1.2 Data transfer and archive (will not be started in 2007)
The possibilities for data transfer from transducers placed on primary components to monitoring room or data storage locating outside the containment will be reviewed. Information concerning the existing instrumentation cabling used for temperature and vibration monitoring currently on site will be gathered from the utilities. Possibilities for wireless data transfer will be studied.
1.3 Selection of inspection items for pilot monitoring system
In cooperation with the utilities the inspection items that will be simulated in the pilot monitoring system will be specified. Most probably the work will be started with relatively simple inspection items and techniques for more challenging items will be developed later on in the project.
2 Inspection of items with limited access, difficult geometry or unfavourable grain structure 2.1 Inspection techniques for items with access limitations
Based on the experience gained in SAFIR-INTELI-project the simulation of inspection items will be continued and applied together with UT expertise. Typical difficult items from inspection point of view are e.g. nozzle welds. In technique development and qualification of inspection systems for these inspection items the results of ultrasonic modelling and simulation form an important element supporting e.g. the technical justification of the inspection system. A special question is the inspection of austenitic materials with coarse grain structure. Techniques for this problem area are searched.
2.2 Phased Array -techniques optimization for demanding inspection geometries (will not be started in 2007)
Recently promising results have been achieved by applying Phased Array-technique. In order to gain practical experience on the reliability of Phased Array-technique test measurements will be carried out and the technique optimised for example cases with demanding component geometry.
This work will also have a link to the international PINC-project launched by US-NRC and the results from this work will be reported.
3 Development of data archiving system for results (will not be started in 2007)
In non-destructive monitoring of components huge amount of experimental data will be collected.
The archiving of this data systematically in a data archiving system for possible subsequent analysis is necessary. The data archiving system developed for monitoring data can be also applied to store data from other material research activities. The basic structure of a data archiving system will be drafted.
4 Choice of fibre optical monitoring methods
The potential of using fibre optical monitoring technology in nuclear environments will be evaluated. International research networks will be utilized in the evaluation process.The focus will be on monitoring needs where traditional electrical sensors does not work well and on monitoring issues where on electrical sensing solution exist. The most suitable method(s) will be demonstrated later in the project.
Deliverables
Task Deliverable
1.1 Literature review on monitoring techniques (Research report)
1.3 Specification of inspection item for further development of monitoring system (Work report)
2.1 Report on ultrasonic modelling of inspection item with limited access (Research report)
3 Fibre optical monitoring in nuclear environments (Research report) Applications
The results of tasks 1.1 – 1.3 will be used in the design of the pilot monitoring system that will be constructed in the facilities of VTT.
The results of tasks 2.1 and 2.2 can be directly used to improve the reliability of in-service inspections of bimetallic welds and items where access is limited due to the difficult geometry of the item. Furthermore, the results of well-documented experimental data can be utilized in inspection qualification.
Education of experts