A decade''s experience in chemistry maintenance of once through steam generator of fast breeder test reactor

The steam generator of fast breeder test reactor (FBTR) at Kalpakkam (India) is a once through Steam Generator (OTSG) which requires the feed water at high purity level. Therefore, for maintaining feed water chemistry, all volatile treatment (AVT) is adopted along with a full-flow deep bed Condensate Polishing Unit (CPU) in the steam water system. Operational difficulties such as premature termination of operation cycle of the CPU, enhanced impurity pickup resulting in increased load for CPU, early silica breakthrough, etc. were observed on occasions. This paper describes the modifications carried out in the steam water circuit to overcome these problems. A decade's experience in operating the CPU and maintaining the feed water quality is also discussed.     

DEMO divertor maintenance

This paper presents a DEMO divertor segmentation and maintenance scheme together with maintenance time estimations. As far as it is known, it is the first such study for DEMO, and the work was coordinated by EFDA. The approach of the study was that DEMO divertor and its handling shall be very similar to that of ITER, therefore ITER divertor segmentation and maintenance schemes were used as starting point. The maintenance scheme for both ITER and DEMO is the following: the divertor is segmented into cassettes. For maintenance 3 divertor ports are used through which all equipment and cassettes are inserted and removed. A toroidal rail based machine transports the element toroidally in front of the port, from where a radial tractor is used that move it between cask and VV. The main difference between DEMO and ITER is the increase in major radius from 6.2 to 7.5 m, and the cassette segmentation changed from 6.66° to 11.25°. These two factors increase the cassette weight from 12 to 25 tons. Therefore the cantilevered radial transportation of ITER cassettes was not adapted, but instead, the first design of a new, bottom supported radial machine is proposed. For the entire blanket maintenance 70 days were calculated instead of the 179 days in ITER. It was also concluded, that if in-vessel toroidal machine is used for blanket maintenance, there are no real possibilities for parallel blanket/divertor replacement.     

Operational experience with forced cooled superconducting magnets

Force-cooled concept has been chosen for ITER superconducting magnet to get reliable coil insulation using vacuum-pressure impregnation (VPI) technology. However 17 breakdowns occurred during operation of six magnets of this type or their single coil tests at operating voltage < 3 kV, while ITER needs 12 kV. All the breakdowns started on electric, cryogenic and diagnostic communications (ECDCs) by the high voltage induced at fast current variations in magnets concurrently with vacuum deterioration, but never on the coils, though sometimes the latter were damaged too. It suggests that simple wrap insulation currently employed on ECDCs and planned to be used in ITER is unacceptable. Upgrade of the ECDC insulation to the same level as on the coils is evidently needed. This could be done by covering each one from ECDCs with vacuum-tight grounded stainless steel casings filled up with solid insulator using VPI-technology. Such an insulation will be insensitive to in-cryostat conditions, excluding helium leaks and considerably simplifying the tests thus allowing saving time and cost. However it is not accepted in ITER design yet. So guarantee of breakdown prevention is not available.     

Operating experience with a power-generating unit with a BN-600 reactor

Beloyarsk Nuclear Power Plant. Main Science Center of the Russian Federation — Physics and Power Engineering Institute. OKBM. Translated from Atomnaya énergiya, Vol. 80, No. 5, pp. 330–337, May, 1996.     

Initial operating experience with the A1200 fragment separator

A beam analysis device, the A1200, has been constructed at the National Superconducting Cyclotron Laboratory (NSCL) for routine cyclotron beam analysis, and separation of radioactive beams produced from projectile fragmentation. It has been in operation since October 1990. The A1200 begins the NSCL beamlines following the K1200 cyclotron, and hence can transport radioactive ions to any experimental device. Some details of the mechanical and optical designs are presented, along with a discussion of the initial operation.     

Operating experience with pressurised components of German light-water reactors

Operating experience of pressurised components is reported on the basis of 19 light-water reactors operating in Germany. The design basis and materials have demonstrated their worth. Licenses are not limited in time, and the major regulatory effort is directed to continuous improvement in plant safety. Technical issues for long-term operation as evaluation of operating experience, plant monitoring, replacement of components are addressed. The basic safety concept as the design basis for the pressurised components is illustrated by some of its details. The main results from the analysis of operating experience are mentioned. Plant monitoring and inspections are important measures to ensure the integrity of the components and to maintain the safety level of the plant. The expansion of the monitoring system may allow a reduction in the scope of inspections.     

Operational experience and safety experiments with the AVR power station

The AVR 15 MWe experimental nuclear power station in Jülich, which has been in operation since 1967, is the first power station with a pebble-bed high-temperature reactor. Succeeding HTR plants, in particular the smaller HTR-Module and HTR-100 facilities, have been developed on the basis of the AVR concept and experience gained during many years' operation.Operating results to date have confirmed the pebble-bed concept. Despite utilization of the plant for experimental purposes, mean time availability since 1967 has amounted to 67.5%. The inherent safety properties have been demonstrated in overall plant tests. In the current experimental programme, further experiments with the power plant will realistically demonstrate that the loss of coolant accident neither endangers the environment nor the plant itself.     

Review of experience with water reactor fuels 1968–1973

This review of water reactor fuel performance from 1968 to 1973 shows that defect levels in Zircaloy-clad UO₂ fuels have, at times, been up to 1 in 3 bundles/reactor yr or ～1 in 100 pins. Among the consequences of such events, are considerable efforts by manufacturers, designers and operators to understand the mechanisms of defection. As a result it has been possible to feed back the operating experience to give improvement in defect level to ～1 in 200 bundles/reactor yr or between 1 in 10³ and 1 in 10⁴ fuel pins. The various types of defects and limiting features of Zircaloy clad fuel have been classified and fitted to well established reliability technology. There is justification for establishing a statistical data bank on water reactor fuel performance, to establish models and confirm acceptable defect levels, similar to those available on reactor plant. Few defects can yet be described as ‘life limiting’ in that incore lifetime is currently decided on economic grounds. Some potential life-limiting features have been identified during the review which should be the subject of further work to improve the long term performance of water reactor fuel.     

Implementation of maintenance rule for structures

The maintenance rule, 10 CFR 50.65, ‘Requirements for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants’, was published by the Nuclear Regulatory Commission (NRC) in the Federal Register (56 FR 31324) on July 10, 1991. The rule became effective on July 10, 1996, giving nuclear power plant licensees 5 years to implement it. During 1994–1995, NRC staff visited nine nuclear power plant sites to observe licensees’ preparations for implementation of the rule. The teams found that most of the licensees had not established goals, or performance criteria for monitoring structures at their sites. The licensees contended that the structures were inherently reliable and required no monitoring under the maintenance rule. On the basis of earlier site visits performed by NRC staff to assess the condition of structures, the NRC staff could not accept this contention, and clarified its position in Revision 1 of Regulatory Guide 1.160, ‘Monitoring the Effectiveness of Maintenance at Nuclear Power Plants’. This paper discusses the applicability of the maintenance rule criteria for structures and its usefulness in ensuring that the structures, systems, and components within the scope of the maintenance rule are capable of fulfilling their intended functions. Also discussed are the aspects of maintenance rule efforts that could be useful for license renewal applications.     

ARIES-AT maintenance system definition and analysis

A fusion power plant must have a high availability to be competitive in the electrical generation market. Attaining high plant availability is difficult because the fusion power core has a limited service lifetime. Moreover, the core components are radioactive and very large. To assess these issues, the maintainability of the ARIES fusion power core is analyzed and integrated into the early power core design process, which results in a maintainability approach capable of attaining a relatively short refurbishment time. The developed timelines are presented for the scheduled maintenance of the power core. The short core refurbishment time coupled, with evolutionary improvements in the maintainability of the reactor plant equipment and the balance-of-plant equipment, infer an attractive plant availability in the range of 90%.     

In-cell maintenance by manipulator arm with 3D workspace information recreated by laser rangefinder

We developed a remote control system for maintenance of in-cell type fuel fabrication equipment. The system display recreated three-dimensional information of the workspace from data obtained by laser rangefinder and conventional cameras. It has allowed us to operate a manipulator arm remotely with several control modes. In order to evaluate the effectiveness and usefulness of developed system, we implemented remote handling experiments using mock up equipment. Performance was compared for remote operation conducted using several different display and operation modes. We confirmed that the system is able to maintain in-cell fuel fabrication equipment in each display and operation mode. Times required to complete the remote operations were collected and compared in each mode. It was observed that integration of 3D information from the laser rangefinder reduced operation time and reinforced visual information during remote operation.