S. Chandramouli

Testing and Qualification of Diverse Safety Rod and Its Drive Mechanism for PFBR

PFBR, India’s first commercial fast breeder reactor employing fast fission is a challenging project from technological point of view to meet the energy security of the country. It is currently under advanced stage of construction at Kalpakkam, India. PFBR is equipped with two independent, fast acting and diverse shutdown systems. A shutdown system comprises of sensors, logic circuits, drive mechanisms and neutron absorbing rods. The absorber rods of the second shutdown system of PFBR are called as Diverse Safety rods (DSR) and their drive mechanisms are called as Diverse Safety Rod Drive Mechanisms (DSRDM). DSR are normally parked above active core by DSRDM. On receiving scram signal, Electromagnet of DSRDM is de-energised and it facilitates fast shutdown of the reactor by dropping the DSR in to the active core. For the prototype development of DSR and DSRDM, three phases of testing namely individual component testing, integrated functional testing in room temperature and endurance testing at high temperature sodium were planned and are being done. The electromagnet of DSRDM operates at high temperature sodium environment continuously. It has been separately tested at room temperature, in furnace and in sodium. Specimens simulating the contact conditions between Electromagnet and armature of DSR have been tested to rule out self welding possibility. The Dashpot provided to decelerate the DSR at the end of its free fall has been initially tested in water and then in sodium. The prototype of DSR has been tested in flowing water to determine the pressure drop and drop time. The functional testing of the integrated prototype DSRDM and DSR in aligned and misaligned conditions in air/water has been completed. The performance testing of the integrated system in sodium has been done in three campaigns. Based on the performance testing in the first two campaigns of sodium testing, design modifications and manufacturing quality improvement were done. Methods of drop time measurement based on ultrasonics and acoustics were also developed along with the first two campaigns. During the third campaign of sodium testing, the performance of the system has been verified with 30 mm misalignment at various temperatures. The third campaign has qualified the system for 10 years of operation in reactor. This paper describes the test setup for all the above mentioned testing and also gives typical test results.Copyright

Experimental Qualification of Mechanical and Electrical Sub-systems of a Complex Mechanism Against Fatigue Failure

Absorber rod drive mechanisms (ARDM) play an important role in ensuring safety of a reactor by rapid insertion of an absorber rod during abnormal conditions. Various components/sub-systems of ARDMs, both mechanical and electrical, are subjected to different cyclic loadings during service life. Thus, qualifying these systems against fatigue is an important step for gaining confidence in their safe operation for the design life. ASME in Sec. III, Div. 1, Appendices (Para II—1500) provides guidelines for the experimental evaluation of the capability of components to withstand cyclic loading. These rules are developed for static components like pressure vessels. Since no such rules are available for moving components like mechanisms, the same were adopted for the ARDMs, with an understanding that the effect of inertia loads of a moving component are to be accounted in the experiments. In application of these rules to a complex mechanisms such as ARDM, various special cases arise which are not addressed explicitly in the code. The paper describes the intelligent adoption of the fatigue life rules given in ASME to various special cases and their extension to electrical systems. The paper also outlines the experiments carried out for qualifying the ARDM against fatigue.

Vibration Measurements on PFBR Fuel Subassemblies

Prototype Fast Breeder Reactor (PFBR) is a 500 MWe liquid metal cooled fast breeder reactor, which is in the final stage of construction. The core of PFBR consists of 1,758 subassemblies supported at the bottom on the grid plate sleeves. Liquid sodium is used as the coolant and flow through the maximum rated fuel subassembly is 36 kg/s. The coolant flows axially from the bottom of the subassembly to top and it is in highly turbulent regime. This turbulent flow can excite flow-induced vibration of fuel subassembly which can cause failure of the fuel pin clad tubes from fatigue, wear and vibration induced fretting. Excessive vibration of fuel subassembly can also results in reactivity noise, fatigue or rattling. Flow induced vibration studies of dummy fuel subassemblies in water were conducted in subassembly test facility and the design was qualified for PFBR. However it is planned to measure the amplitude and frequency of vibration during pre-commissioning tests of PFBR. Measurements are planned during the isothermal run of PFBR at 200 °C with dummy subassemblies loaded in the core. Since measurement has to be carried out in high temperature sodium environment, conventional contact type sensors such as accelerometers, strain gages etc. cannot be employed for vibration measurement. Non-contact measurement technique using ultrasound waves was planned to be developed for vibration measurement. Extensive experiments were carried out in various test facilities and ultrasonic vibration measurement technique was established and demonstrated. Based on the experimental results, a device named SONAR was designed and developed for PFBR. The SONAR device is equipped with ultrasonic sensors, which focuses on subassembly crown region, and is capable of movement in Z-axis (up and down) and in Theta-axis (rotation). The movement of the subassembly is detected from the train of ultrasonic pulses and echoes from the target subassembly. Time signal and frequency spectra of vibration are extracted from the ultrasonic signals using signal processing technique implemented in LabVIEW platform. This paper discusses the details of the FIV measurements on PFBR fuel subassemblies, details of ultrasonic technique and SONAR device, its testing and results and conclusion.

Tribological behaviour of AFNOR grade Z6 NCT DV 25-15 precipitation hardening austenitic stainless steel with NiCr-B coating in high temperature liquid sodium

The sliding wear and friction behaviour between AFNOR Grade Z6 NCT DV 25-15 precipitation hardening austenitic stainless steel and NiCr-B hardface coating was investigated in high purity liquid sodium at 823 K employing an indigenously developed reciprocating-type tribometer. The specimens for testing were in the form of pins and disc, with two pins in contact with both the surfaces of a disc specimen. The pin and disc specimens were made from precipitation hardened Z6 NCT DV 25-15 alloy and NiCr-B alloy deposited on 316L stainless steel substrate using Plasma Transferred Arc (PTA) welding process respectively. Testing was carried out at sliding speeds of 2 mm/s for a total sliding distance of 200 m under contact stress of 10 and 20 MPa respectively. The static friction coefficient (s) and dynamic friction coefficient (d) were estimated from the maximum value of friction force at the start of the movement and from the friction force measured during movement respectively. In both the tests d was found to be significantly lower than s. Weight loss measured for both the pins and disc at the end of the tests were negligible and this indicates that wear is very low in both the tests carried out at contact stress of 10 and

Experimental Evaluation of Wire Type Leak Detector Layout for Prototype Fast Breeder Reactor (PFBR)

Wire type leak detectors working on conductivity principle are used for detecting sodium leak in the secondary sodium circuits of FBRs. It is required to assess the performance of these detectors and confirm that they are meeting the requirements. A test facility by name LEENA was constructed at Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam to test the wire type leak detector lay out by simulating sodium leaks of different rates. This test facility consists of a sodium dump tank, a test vessel, interconnecting pipelines with valves, micro filter and test section with leak simulators. There are three different test sections in the test set up of length 1000 mm each. These test sections simulate piping of Prototype Fast Breeder Reactor (PFBR) secondary circuit and the leak detector layout in full scale. All test sections are provided with leak simulator. A leak simulator consists of a hole of size one mm drilled in the test section and closed with a tapered pin. The pin position is adjusted by a screw mechanism and there by the annular gap of flow area is varied for getting different leak rates. Test facility was commissioned and 20 experiments were attempted at 350°C to 550°C. Out of 20 experiments 11 experiments were successfully completed and 9 experiments were terminated in between due to the choke in the simulator hole. From the experimental data it is found that sodium leak rate of 200 g/h and above can be detected within 6 hours. A relationship between leak rate and detection time was established from the experimental results and found that sodium leak rate of 100g/h is likely to be detected in 11.4 hours. This paper deals with the details of wire type leak detector layout for the secondary sodium circuit of PFBR, performance requirement of leak detection system as per codes, description of test facility, experimental procedure and test results. Paper also reviews the experiment conducted in CEA, Cadrache and compares with results of present experimental study.Copyright