Safety of Nuclear Reactors: Part A — Unsteady State Temperature History Mathematical Model

A nuclear reactor structure under abnormal operations of near meltdown will be exposed to a tremendous amount of heat flux in addition to the stress field applied under normal operation. Temperature encountered in such case is assumed to be beyond 1000°C. A mathematical model has been developed for the fire resistance calculation of a concrete-filled square steel column with respect to its temperature history. Effects due to nuclear radiation and mechanical vibrations will be explored in a later future model. The temperature rise in each element can be derived from its heat balance by applying the parabolic unsteady state, partial differential equation and numerical solution into the steel region. Calculation of the temperature of the elementary regions needs to satisfy the symmetry conditions and the relevant material properties. The developed mathematical model is capable to predict the temperature history in the column and on the surface with respect to time.

Fiber-Optic Transmitter for Nuclear Power Plants

A promising Fiber-Optic Differential Pressure (DP) Transmitter is under development in Flexible Maintenance System (FMS) Projects that supported by Ministry of Economic, Trade, and Industries of Japan. The object of FMS projects is to improve maintenance works at nuclear power plants with latest technology. The new DP Transmitter uses optic-fiber technology of Extrinsic Fabry-Perot Sensor and Fizeau White-Light Cross-Correlator. Validation tests were performed to evaluate the tolerance of the DP transmitter in Nuclear Power Plant conditions. General requirements of PWR are accuracy (repeatability and linearity) of within +/−0.5%, pressure-proof of maximum 17.16MPa, Irradiation of 100Gy, and temperature range of 10–50 degrees centigrade at normal condition. The test results show the new DP transmitter can be expected as the next generation instrumentation in Nuclear Power Plants.

Regulatory Issues of Digital I&C System in Lungmen Project

The Lungmen Nuclear Power Station (LNPS) is currently under construction in Taiwan, which consists of two advanced boiling water reactor (ABWR) units. The instrumentation and control (I&C) systems of the LNPS are based on the state-of-the-art modernized fully integrated digital design. This paper presents regulatory overviews, regulatory requirements, current major regulatory issues, as well as the areas of regulatory concerns and the lessons learned on the digital I&C systems in the Lungmen Project.

Thermal Analysis of a Marine Products Irradiator and Its Transportation Cask

Irradiation of sea-foods is carried out in a marine products irradiator. During the radiation processing, it is required to maintain the product temperature within very narrow temperature limits. A transient thermal analysis of the irradiator (when in use) was carried out to determine the chilled air temperature and velocity required to maintain the product temperature within the specified range. In order to transport the irradiator cask with its contents, it is enclosed in an outer enclosure. The transportation cask is required to satisfy regulations pertaining to temperature distribution in various constituents. A transient thermal analysis of the transportation cask was carried out to determine the temperature distribution under normal and accident conditions (800°C external fire).

Review of Practice for Deeply Embedded/Buried NPP Structures Subject to Seismic Loadings

Motivated by many design considerations, several conceptual designs for advanced reactors have proposed that the entire reactor building and a significant portion of the steam generator building will be either partially or completely embedded below grade. For the analysis of seismic events, the soil-structure interaction (SSI) effect and passive earth pressure for these types of deeply embedded structures will have a significant influence on the predicted seismic response. Sponsored by the US Nuclear Regulatory Commission (NRC), Brookhaven National Laboratory (BNL) is carrying out a research program to assess the significance of these proposed design features for advanced reactors, and to evaluate the existing analytical methods to determine their applicability and adequacy in capturing the seismic behavior of the proposed designs. This paper summarizes a literature review performed by BNL to determine the state of knowledge and practice for seismic analyses of deeply embedded and/or buried (DEB) nuclear containment type structures. Included in the paper is BNL’s review of the open literature of existing standards, tests, and practices that have been used in the design and analysis of DEB structures. The paper also provides BNL’s evaluation of available codes and guidelines with respect to seismic design practice of DEB structures. Based on BNL’s review, a discussion is provided to highlight the applicability of the existing technologies for seismic analyses of DEB structures and to identify gaps that may exist in knowledge and potential issues that may require better understanding and further research.

An Overview of the Direct Energy Conversion Proof of Principle Power Production Program

The United States Department of Energy, Nuclear Energy Research Initiative (NERI) Direct Energy Conversion Proof of Principle (DECPOP) project has as its goal the development of a direct energy conversion process suitable for commercial development. We define direct energy conversion as any fission process that returns usable energy without an intermediate thermal process. A prior Direct Energy Conversion (DEC) project [1] has been completed and indicates that a viable direct energy device is possible if several technological issues can be overcome. The DECPOP program is focusing on two of the issues: charged particle steering and high voltage hold-off. This paper reports on the progress of the DECPOP project. Two prototype concepts are under development: a Fission Electric Cell using magnetic insulation and a Fission Fragment Magnetic Collimator using magnetic fields to direct fission fragments to collectors. Included in this paper are a short project description, an abbreviated summary of the work completed to date, a description of ongoing and future project activities, and a discussion of the potential for future research and development.

Nuclear Instrumentation Systems in Prototype Fast Breeder Reactor

The nuclear instrumentation systems of the Prototype Fast Breeder Reactor (PFBR) primarily comprise of global Neutron Flux Monitoring, Failed Fuel Detection & Location, Radiation Monitoring and Post-Accident Monitoring. High temperature fission chambers are provided at in-vessel locations for monitoring neutron flux. Failed fuel detection and location is by monitoring the cover gas for fission gases and primary sodium for delayed neutrons. Signals of the core monitoring detectors are used to initiate SCRAM to protect the reactor from various postulated initiating events. Radiation levels in all potentially radioactive areas are monitored to act as an early warning system to keep the release of radioactivity to the environment and exposure to personnel well below the permissible limits. Fission Chambers and Gamma Ionisation Chambers are located in the reactor vault concrete for monitoring the neutron flux and gamma radiation levels during and after an accident.

The Application of the Welding Technique at Fillet Groove by the YAG-Laser Repair-Welding Robot for Underwater Environment

Generally, when we need repair welding due to the reduction of the thickness generated by corrosion in the inside of tanks, usually people enter and repair after the inner liquid is drained. However, the direction that performed repair work, without draining intension liquid may be desirable on work. Especially, for the radioactive waste (RW) tanks in operating nuclear plants, since there are danger that be accompanied by the risk of exposure, it is desired that to shorten their work time (abbreviation of drainage) and to use the robot system. As the welding repair method that can be performed underwater, there is underwater welding technology by YAG laser. So far, we developed the remote underwater YAG laser repair-welding robot. A repair welding work to the robot is performed as following steps: 1. Degradation area detection. 2. Crack removal and edge preparation. 3. Repair welding, and inspection. And we found that the application of the repair welding to use the robot at the base metal and butt joint. Furthermore, we will indicate the wide range application of the remote underwater YAG laser repair-welding robot to make sure the appropriate work of welding at fillet groove joint, in this time.

Expansive Development of a Decommissioning Program “Recycle Simulator” in Nuclear Power Station

A decommissioning program “RECYCLE SIMULATOR” should be put into practice in careful consideration of both recycle of non-radioactive wastes and reduce of radioactive wastes in the coming circulatory social system. Nevertheless current support systems for decommissioning planning mainly deal with decontamination, safety storage and dismantlement, so-called the prior part of the total decommissioning process. Authors emphasize the necessity of total planning of decommissioning including recycle or reuse of a large amount of demolition materials and are propelling the development of the multi expert system named “RECYCLE SIMULATOR”. This paper presents an algorithm of the recycling and reusing scenario of demolition materials and a summarized configuration. RECYCLE SIMULATOR for the demolished concrete was developed in 2000 and presented at 10th International Conference on Nuclear Engineering (icone10). Construction of a supporting multi expert system for the totally planning of decommissioning projects is objected by expansive development of the previous version. Main conclusions obtained from this paper are under this. (1) The previouslly developed expert system was advanced in its estimational function toward the satisfaction of decommissiong planners. (2) The applicability of the system was enlarged to all the radioactive and non-radioactive wastes, demolished metal and concrete products, in a corresponding site of decommissioning. (3) Finally decommissiong recycle simulator was completed in a harmonized unification.

Evaluation of Seismic Integrity for an Integral Reactor Assembly

The structural integrity of integral reactor assembly of 65Mwt thermal capacity is assessed by using the commercial finite element package ANSYS in order to evaluate the seismic safety margin. First of all, the modal analyses are performed using the various analysis models with/without the fluid coupling effect in order to validate a super element model and to evaluate the coupling effect on natural frequency. Based on the modal analysis results, the seismic analyses are performed using the ground response spectrum defined in Reg. Guide 1.60. Finally, time-history analyses are performed using the modal analysis results, the super element model and an inertia load approach. As a result, the reliable and efficient seismic analysis model for an integral reactor assembly is developed and it is found that an integral reactor assembly has the sufficient seismic safety margin.