Darrell L. Knudson

Thermocouples for High-Temperature In-Pile Testing

Traditional methods for measuring in-pile temperatures degrade above 1100°C. Hence, the Idaho National Laboratory (INL) initiated a project to explore the use of specialized thermocouples for high temperature in-pile applications. Efforts to develop, fabricate, and evaluate specialized high-temperature thermocouples for in-pile applications suggest that several material combinations are viable. Tests show that several low-neutron cross-section candidate materials resist material interactions and remain ductile at high temperatures. In addition, results indicate that the candidate thermoelements have a thermoelectric response that is single-valued and repeatable with acceptable resolution. The selection of the thermocouple materials depends on desired peak temperature and accuracy requirements. For applications at or above 1600°C, tests indicate that thermocouples having doped molybdenum and Nb-1%Zr thermoelement wires, HfO2 insulation, and a Nb-1%Zr sheath could be used. INL has worked to optimize this thermocouple’s stability. With appropriate heat treatment and fabrication approaches, results indicate that thermal cycling effects on this thermocouple’s calibration is minimized. INL initiated a series of high-temperature (1200 to 1800°C) long-duration (up to 6 months) tests to assess the long-term stability of these thermocouples. Initial results indicate that the INL-developed thermocouple’s thermoelectric response is very stable. Typically, <20°C drift was observed in a 4000-h test at 1200°C. In comparison, commercially available types K and N thermocouples included in these 1200°C tests experienced drifts up to 110°C.

Options Extending the Applicability of High-Temperature Irradiation-Resistant Thermocouples

Abstract Several options have been identified that could further enhance the reliability and extend the applicability of high-temperature irradiation-resistant thermocouples (HTIR-TCs) developed by the Idaho National Laboratory (INL) for in-pile testing, allowing their use in temperature applications as high as 1800%C.The INL and the University of Idaho (UI) investigated these options with the ultimate objective of providing recommendations for alternate thermocouple designs that are optimized for various applications. This paper reports results from INL/UI investigations. Results are reported from tests completed to evaluate the ductility, resolution, transient response, and stability of thermocouples made from specially formulated alloys of molybdenum and niobium,not considered in initial HTIR-TC development. In addition, this paper reports insights gained by comparing the performance of HTIR-TCs fabricated with various heat Ntreatments and alternate geometries.

Comparison Measurements of Silicon Carbide Temperature Monitors

As part of a process initiated through the Advanced Test Reactor (ATR) National Scientific User Facility (NSUF) program to make Silicon Carbide (SiC) temperature monitors available for experiments, a capability was developed at the Idaho National Laboratory (INL) to complete post-irradiation evaluations of these monitors. INL selected the resistance measurement approach for detecting peak irradiation temperature from SiC temperature monitors. To demonstrate this new capability, comparison measurements were completed by INL and Oak Ridge National Laboratory (ORNL) on identical samples subjected to identical irradiation conditions. Results reported in this paper indicate that the resistance measurement approach yields similar peak irradiation temperatures if appropriate equipment is used and appropriate procedures are followed.

Linear variable differential transformer (LVDT)-based elongation measurements in Advanced Test Reactor high temperature irradiation testing

New materials are being considered for fuel, cladding and structures in next generation and existing nuclear reactors. These materials can undergo significant dimensional and physical changes during high temperature irradiations. Currently, such changes are determined by repeatedly irradiating a specimen for a specified period of time in the Advanced Test Reactor (ATR) and then removing it from the reactor for evaluation. The labor and time to remove, examine and return irradiated samples for each measurement make this approach very expensive. In addition, such techniques provide limited data and may disturb the phenomena of interest. To resolve these issues, an instrumented creep testing capability is being developed for specimens irradiated under pressurized water reactor coolant conditions in the ATR at the Idaho National Laboratory (INL). This paper reports the status of INL efforts to develop this testing capability. In addition to providing an overview of in-pile creep test capabilities available at other test reactors, this paper focuses on efforts to design and evaluate a prototype test rig in an autoclave at INLs High Temperature Test Laboratory.

Enhanced In-Pile Instrumentation at the Advanced Test Reactor

Many of the sensors deployed at materials and test reactors cannot withstand the high flux/high temperature test conditions often requested by users at U.S. test reactors, such as the Advanced Test Reactor (ATR) at the Idaho National Laboratory. To address this issue, an instrumentation development effort was initiated as part of the ATR National Scientific User Facility in 2007 to support the development and deployment of enhanced in-pile sensors. This paper provides an update on this effort. Specifically, this paper identifies the types of sensors currently available to support in-pile irradiations and those sensors currently available to ATR users. Accomplishments from new sensor technology deployment efforts are highlighted by describing new temperature and thermal conductivity sensors now available to ATR users. Efforts to deploy enhanced in-pile sensors for detecting elongation and real-time flux detectors are also reported, and recently-initiated research to evaluate the viability of advanced technologies to provide enhanced accuracy for measuring key parameters during irradiation testing are noted.

ATR NSUF Instrumentation Enhancement Efforts

Abstract A key component of the Advanced Test Reactor (ATR) National Scientific User Facility (NSUF) effort is to expand instrumentation available to users conducting irradiation tests in this unique facility. In particular, development of sensors capable of providing real-time measurements of key irradiation parameters is emphasized because of their potential to increase data fidelity and reduce posttest examination costs. This paper describes the strategy for identifying new instrumentation needed for ATR irradiations and the program underway to develop and evaluate new sensors to address these needs. Accomplishments from this program are illustrated by describing new sensors now available to users of the ATR NSUF. In addition, progress is reported on current research efforts to provide improved in-pile instrumentation to users.

IN-SITU CREEP TESTING CAPABILITY FOR THE ADVANCED TEST REACTOR

An instrumented creep testing capability is being developed for specimens irradiated in pressurized water reactor coolant conditions at the Advanced Test Reactor (ATR). A test rig has been developed such that samples will be subjected to stresses up to 350 MPa at temperatures up to 370°C in pile. Initial Idaho National Laboratory (INL) efforts to develop this creep testing capability for the ATR are summarized. In addition to providing an overview of in-pile creep test capabilities available at other test reactors, this paper reports efforts by the INL to evaluate a prototype test rig in an autoclave at INL’s High Temperature Test Laboratory. Data from autoclave tests with Type 304 stainless steel and copper specimens are reported.

Hot Wire Needle Probe for In-Reactor Thermal Conductivity Measurement

Thermal conductivity is a key property that must be known for proper design, test, and application of new fuels and structural materials in nuclear reactors. Thermal conductivity is highly dependent on the physical structure, chemical composition, and the state of the material. Typically, thermal conductivity changes that occur during irradiation are measured out-of-pile using a “cook and look” approach. Repeatedly removing samples from a test reactor to measurements is expensive, has the potential to disturb phenomena of interest, and only provides understanding of the samples end state when each measurement is made. There are also limited thermophysical property data for advanced fuels. Such data are needed for simulation design codes, the development of next generation reactors, and advanced fuels for existing nuclear plants. Being able to quickly characterize fuel thermal conductivity during irradiation can improve the fidelity of data, reduce costs of post-irradiation examinations, increase understanding of how fuels behave under irradiation, and confirm or improve existing thermal conductivity measurement techniques. This paper discusses efforts to develop and evaluate an in-pile thermal conductivity sensor based on a hot wire needle probe. Testing has been performed on samples with thermal conductivities ranging from 0.2 to 22 W/m·K at temperatures ranging from 20 °C to 600 °C. Thermal conductivity values measured using the needle probe match data found in the literature to within 5% for samples tested at room temperature, 6% for low thermal conductivity samples tested at high temperatures, and 10% for high thermal conductivity samples tested at high temperatures.

New Sensors for In-Pile Temperature Measurement at the Advanced Test Reactor National Scientific User Facility

Abstract The U.S. Department of Energy designated the Advanced Test Reactor (ATR) a National Scientific User Facility (NSUF) in April 2007 to support U.S. research in nuclear science and technology. As a user facility, the ATR is supporting new users from universities, laboratories, and industry, as they conduct basic and applied nuclear research and development to advance the nation’s energy security needs. A key component of the ATR NSUF effort is to develop and evaluate new in-pile instrumentation techniques that are capable of providing measurements of key parameters during irradiation. This paper describes the strategy for determining what instrumentation is needed and the program for developing new or enhanced sensors that can address these needs. Accomplishments from this program are illustrated by describing new sensors now available and under development for in-pile measurement of temperature at various irradiation locations in the ATR.

Extension wire for high temperature irradiation resistant thermocouples

In an effort to reduce production costs for the doped molybdenum/niobium alloy high temperature irradiation resistant thermocouples (HTIR-TCs) recently developed by the Idaho National Laboratory, a series of evaluations were completed to identify an optimum compensating extension cable. Results indicate that of those combinations tested, two inexpensive, commercially-available copper–nickel alloy wires approximate the low temperature (0 °C to 500 °C) thermoelectric output of KW–Mo (molybdenum doped with tungsten and potassium silicate) versus Nb–1%Zr in HTIR-TCs. For lower temperatures (0 °C to 150 °C), which is the region where a soft extension cable is most often located, results indicate that the thermocouple emf is best replicated by the Cu–3.5%Ni versus Cu–5%Ni combination. At higher temperatures (300 °C to 500 °C), data suggest that the Cu–5%Ni versus Cu–10%Ni combination may yield data closer to those obtained with KW–Mo versus Nb–1%Zr wires.