Integral Light Water Reactor Research Articles

Calorimetric Analysis to Infer Primary Circuit Flow in Integral and Pool-Type Reactors

Primary system flow rate is a key parameter for monitoring and controlling thermal power in a nuclear power plant. The existing fleet of large light water reactors uses direct measurements of primary flow rate with the application of venturi meters, orifice plates, and magnetic flowmeters in primary loop piping. Integral light water reactors and pool-type advanced reactor designs, however, have largely eliminated primary loop piping to improve the inherent safety characteristics of these reactors. Furthermore, longer operating cycles between maintenance opportunities (typically 4 to 40 years) limit the applicability of these direct measurement methods over the operating period. Methods to infer the primary flow rate based on other, easily measured parameters are needed to ensure the operability of integral and pool-type reactors. Calorimetric analysis across the intermediate heat exchanger was investigated for real-time inference of primary flow rate. Heat balance equations were applied to an experimental forced flow loop to evaluate the efficacy of this approach. When appropriate time delays and heat losses are accounted for, the primary flow rate was inferred with accuracy and 95% prediction variance of 1.57 and 4.80 % mean value, respectively.

Monitoring Pump Parameters in Small Modular Reactors Using Electric Motor Signatures

Abstract Small modular nuclear reactors (SMRs) are designed for long-term operation with minimum outages and for possible deployment in remote locations. To achieve this operational goal, the SMRs may require remote and continuous monitoring of performance parameters that contribute to operation and maintenance. This feature is also important in monitoring critical parameters during severe accidents and for postaccident recovery. Small integral light water reactors have in-vessel space constraints, and many of the traditional instrumentation are not practical in these systems. To investigate this issue, analytical and experimental researches were carried out using a flow test loop to characterize the relationship among process variables (flow rate and pressure) and pump motor signatures. The findings of this research are presented, with implications in relating electrical signatures to pump parameters. The relationship between the electrical signatures and the process variables is discussed with reference to the experimental results. The results of this work may be used for monitoring process variables in small modular reactor systems.

The Use of Flashing Drums and Microchannel Heat Exchangers to Generate Steam in Large Integral Light Water Reactors

Integral pressurized water reactors are innovative reactors in which all of the components typically associated with the nuclear steam supply system of a nuclear power station are located within the reactor pressure vessel. In order to facilitate this modification in large [~1000-MW(electric)] light water reactors (LWRs), compact heat exchangers such as microchannel heat exchangers must be used. Previous attempts at using microchannel heat exchangers were unsuccessful since they are prone to vapor locking and crud blockage when the primary coolant boils. Therefore, the authors propose the use of a flashing drum to facilitate boiling in conjunction with a primary microchannel heat exchanger for a large integral LWR. The integral inherently safe light water reactor (I2S-LWR) is used as a basis for the implementation of this novel concept. The high-temperature, high-pressure secondary water generated in the secondary loop through heating in the microchannel primary heat exchanger of the I2S-LWR is sent to a flashing drum where 99.9% pure vapor is extracted and sent to the turbines. This prevents boiling in the primary heat exchanger that in turn reduces crud deposition, flow instabilities, and the potential for channel blockage or vapor locking in the small channel sizes of microchannel heat exchangers. The benefits and disadvantages of this approach are presented in this paper. Unfortunately, this innovative approach to nuclear steam generation for integral LWRs is challenged by a potential decrease in thermodynamic efficiency. Therefore, a sensitivity study is presented that explores the impact of several design variables on the thermodynamic efficiency of the plant. As part of this study, a simple and a complex Rankine cycle were modeled in order to determine the impact that system design modifications can play in recovering thermodynamic efficiency lost by the steam drum. Both cycles utilize turbines, condensers, and condensate/recirculation pumps, while the complex Rankine cycle utilizes a four-stage turbine with subsequent separation and open feedwater heaters. The optimized efficiencies for the simple and complex Rankine cycles are 31% and 33%, respectively, indicating that additional system enhancements to the power conversion system could compensate for the inclusion of a flashing drum.

Instrumentation and control strategies for an integral pressurized water reactor

Abstract Several vendors have recently been actively pursuing the development of integral pressurized water reactors (iPWRs) that range in power levels from small to large reactors. Integral reactors have the features of minimum vessel penetrations, passive heat removal after reactor shutdown, and modular construction that allow fast plant integration and a secure fuel cycle. The features of an integral reactor limit the options for placing control and safety system instruments. The development of instrumentation and control (I&C) strategies for a large 1,000 MWe iPWR is described. Reactor system modeling—which includes reactor core dynamics, primary heat exchanger, and the steam flashing drum—is an important part of I&C development and validation, and thereby consolidates the overall implementation for a large iPWR. The results of simulation models, control development, and instrumentation features illustrate the systematic approach that is applicable to integral light water reactors.

A Perspective on Small Reactor Licensing and Implementation

A great deal of interest has developed recently in the implementation of small reactors in the United States and abroad. Small reactors may offer a significant number of advantages over larger reactors. The diversity of size, design, configuration, and construction features and their planned utilization for nonelectrical power applications as well as traditional power applications pose significant challenges to the current U.S. Nuclear Regulatory Commission (NRC) regulatory structure. The current structure is geared toward nontransportable, commercial, electrical power-producing, light water-cooled reactors utilizing traditional nuclear fuel designs. The NRC is currently engaged in a number of preapplication discussions concerning small reactor designs encompassing three distinctively different technologies. These are integral light water reactors, high-temperature gas-cooled reactors, and liquid metal-cooled reactors. Light water reactor technology-based power generation small reactors will fit best in the current NRC regulatory framework.In response to the anticipated licensing workload, the NRC has implemented organizational changes and has increased its focus in areas supporting the licensing of small reactors. Although the licensing of small reactors has to comply with the requirements imposed by the Atomic Energy Act and the National Environmental Policy Act, there are significant design differences among the various proposed small reactors and the currently licensed reactor designs that result in a number of issues that need to be resolved to properly comply with these statutory requirements. Given the diversity of small reactor designs, a regulatory structure that provides licensing flexibility combined with the required degree of safety assurance would be needed. This is likely to involve a risk-informed and technology-neutral regulatory approach.

Nuclear energy sources on the basis of integral reactors

This report deals with design features of nuclear plants on the basis of integral light water reactors (LWRs) of AST, ATEC and VPBER types developed by OKBM. Special attention is given to environmental safety of the power plants. Their significant advantages in terms of environmental impacts are shown compared with conventional plants using fossil fuels.