Fundamentals of CANDU Reactor Physics

Nuclear Engineering and Technology for the 21st Century - Monograph Series Jovica Riznic, Series Editor With more than 75 years of combined working experience in the area of reactor physics and safety, the intention of the authors of this monograph is to provide a practical book on reactor physics, particularly for the safe operation of aged CANDU reactors, with minimal mathematics or equations. The book gives a glimpse of first principles and their engineering application in reactor physics, for those who are interested in or are working in the Canadian nuclear industry. The book is also ideal as a reference for physicists, operators, regulatory staff, and for those who need to interact with reactor physicists at CANDU sites, nuclear laboratories, institutes, universities, or engineering companies. This book assumes prior knowledge of nuclear physics offered at the secondary level. As very few equations appear in the monograph, it is not considered suitable for specialists whose focus is only on calculations or on the development of software on reactor physics. Such readers should refer to the books listed in the bibliography at the end of the monograph.

Short.Term Reactivity & Power Control: Reactor Regulating System (RRS)

For CANDU reactors, the control of the long-term reactivity and of the power is carried out by on-power refuelling, while the control of the short-term reactivity and of power is done by the RRS. The RRS is part of the overall plant-control system that maintains the reactor power at a specified level, or, when required, manoeuvres the reactor power between specified setpoints. The reactor power setpoint can be entered by the operator (in the reactor-leading mode) or it can be calculated automatically by the Steam Generator (SG) pressure-control program (in the turbine-leading mode). The RRS consists of the following main components:

244Cm contributions to the alpha source term of CANDU reactors

In this report the expected rate of buildup of 244Cm in a CANDU neutron flux is evaluated and used to explain cases of high 244Cm in alpha-active samples from Bruce and Pickering Units. It is demonstrated that 244Cm is enriched on the surface of irradiated pressure tubes where it is associated with Zr/Nb activation products. It is further shown, using 94Nb as a fluence monitor, that the 244Cm/(239Pu + 240Pu) ratio for Bruce and Pickering irradiated pressure tube deposits exhibits a power law = 0.0042 (Fluence)3.1982. For non-pressure tube samples, such as feeder pipes, steam generator deposits and PHTS cruds, it is observed that Zr/Nb activation products are also associated with elevated 244Cm activities. Thus, based on the data presented in this report, the inference is that all CANDU Units may be expected to exhibit significant levels of 244Cm activity on PHTS surfaces, both in and out-of-core, with 244Cm/(239Pu + 240Pu) ratios significantly greater than one.

CANDU-Like Features in Emerging Small Modular Reactor Designs

Several small modular reactor (SMR) designs are emerging, but only the CANDU Small Modular Reactor and a couple of Indian designs incorporate the familiar features of the larger CANDU-reactors. This paper shows that while the CANDU concept did not seem to receive wider attention among SMR designers, it has influenced a few. The paper discusses how the CANDU operating experience can aid in the construction and operation of some SMRs. For example, the concept of passive reactor shutdown by draining the moderator, which was utilized in the early Pickering A units, is adopted in the Copenhagen Atomics Waste Burner; a molten slat (LiF-ThF$ _4 $) heavy-water moderated reactor. The heavy-water and lithium in this salt produce tritium and can benefit from the CANDU experience in handling tritium. The online refueling of CANDU reactors, their large heat sinks and seamless configuration are also reflected in SMR designs.

Characterization Of A Lanthanum Bromide Detector For Eye Lens Dosimetry At The Candu Nuclear Power Plants Based On Direct Measurements Of The Gamma-Ray Spectra

Gamma-ray spectra were measured using a LaBr$_{3}$(Ce) spectrometer during the outage periods, aiming at quantifying the gamma source term of radiation workers’ exposure, at the CANDU nuclear power reactors, for the purposes of eye lens dosimetry. The spectra were measured inside the boiler rooms, of the Bruce Power and Ontario Power Generation (OPG) CANDU nuclear power plants, where workers are exposed to relatively high dose rates radiation fields during the maintenance work. Prior to measurements at the CANDU reactors, the pulse shaping parameters of the gamma spectrometer were optimised for high rates gamma fields, up to an input rates of 120 kcps, in order to accomplish a high output rate with a reasonable energy resolution. In parallel, the response of the LaBr$_{3}$(Ce) detector was characterized by experiments and Monte Carlo simulations. The gamma spectra measured at the CANDU reactors were reported in terms of the gamma-ray fluence rate spectrum. In all measured data, $^{60}$Co and $^{95}$Nb were main contributors of the gamma fields. The measured spectra have been used to calculate the dosimetric quantities of interest: personal dose equivalents H$_{p}$(10) and H$_{p}$(0.07) and eye lens absorbed dose.

Short Range Ordering (SRO) Reaction in Ni-base Alloy X-750

The short range ordering (SRO) reaction of the X-750 Ni-base alloy used as a garter spring material for CANDU reactors was systematically investigated through differential scanning calorimeter (DSC) analysis. Water quenching (WQ) after solution annealing (SA) and 20% cold rolled (CR) X-750 were prepared and these samples were subjected to ordering treatment at 475 ^oC for up to 2,160 hours. The WQ and CR specimens showed an exothermic reaction due to the release of entropy formed by the WQ and CR processes, respectively, whereas the ordered WQ and CR specimens exhibited endothermic reactions. The exothermic reaction from the WQ and CR specimens means the SRO reaction occurred. In the WQ specimen, two exothermic reactions at 577 ^oC and 671 ^oC were observed, which corresponds to SRO formation of Ni₂Cr and CrFe, respectively. The critical temperature and thermal activation energy for these specimens were measured by varying the heating rate. The lattice variation with ordering time at 475 ^oC up to 2,160 hours was measured by XRD using CuKa X-ray. A 0.03-0.09% lattice contraction of the (200) plane occurred, depending on prior treatment condition. We discuss whether a lattice contraction due to SRO reaction may cause voids, providing formation sites for He bubbles in the X-750 garter spring exposed to the operating environment of the CANDU reactor.

A Novel Assessment of Delayed Neutron Detector Data in CANDU Reactors

A common opportunity for nuclear power plant operators is ensuring that routinely collected data are fully leveraged. Exploiting data analytics can enable improvements in anomaly detection and condition monitoring by identifying previously unseen data trends and correlations without major financial investment. One such opportunity is in facilitating the detection of fuel defects by augmenting the delayed neutron (DN) monitoring system deployed in the majority of Canada deuterium uranium (CANDU) reactors. In this paper, we demonstrate using archive data that the detection of fuel defects can be accelerated using this system in combination with the use of a deeper historical dataset and the introduction of a smoothing algorithm. The current defect identification process relies on the analysis of data of high variance and is subject to the judgment of a domain expert, resulting in variable defect identification periods. The proposed approaches seek to mitigate this and alleviate the variable identification time. Initial results presented here show that for an initial batch of 30 defects, identification periods can be meaningfully reduced compared to the current process, with defects potentially visible on an average of 11.4 days earlier. By shortening this identification period, fuel containing defects can be scheduled for earlier removal, reducing the risk of statutory shutdown obligations, protecting personnel, and promoting industry best practice. Exploring a historical dataset identifies previously undocumented trends and we discuss the potential to produce correlations with other reactor parameters. The application of this knowledge can lead to opportunities in the use of machine learning algorithms and, ultimately, more accurate predictions.