INVESTIGATION OF THE BUILDING LIQUID EFFLUENT PIPE WORK AS PART OF THE AGEING MANAGEMENT AT SAFARI-1

Transcription

1 INVESTIGATION OF THE BUILDING LIQUID EFFLUENT PIPE WORK AS PART OF THE AGEING MANAGEMENT AT SAFARI-1 N.F. Khathi and J.C. Mostert SAFARI-1 South African Nuclear Energy Corporation (Necsa), P.O. Box 582, Pretoria, South Africa ABSTRACT The SAFARI-1 research reactor has been operational since 1965; most Systems, Structures and Components (SSC) that are currently used were part of the original design. The SAFARI-1 Research Reactor has an ageing management programme that focuses on managing physical ageing of SSC important to safety and sustainability. One of the projects of the ageing management programme is an investigation of the facility s liquid effluent drainage systems. The overall drainage system consists of three different subsystems of collection areas, pipe work and storage facilities, all of which have to be inspected and evaluated. The purpose of the project is to provide a report on the status of the ageing drainage facilities with a particular focus on the state of the pipe work. The report will provide the bases for a further project in which repair and improvement actions will be instituted to bring the drainage facilities to an optimal operational state. One of the objectives of the project is to evaluate the potential impact of the ageing drainage systems on the environment. The evaluation intends to identify risks that the existing systems pose to the environment and to develop requirements for improvements and repairs to serve as a basis for recommendations for the next phase of the project that relate to the mitigation of these risks. This paper provides a brief overview of the project scope, a description of the drainage facilities, the ageing evaluation philosophy and processes that are applied in this particular case and finally, the environmental protection practices that will underpin the evaluation of the identified ageing related risks in the systems under investigation. The intention of the paper is to present SAFARI-1 s approach in bringing together a systematic ageing management programme and environmental management best practice in a real world application. 1. Introduction SAFARI-1 is a 20 MW tank-in-pool type material testing reactor that has been in operation since 1965[1]. The currently projected end of life of SAFARI-1 at the present rate of operation is provisionally set at the end of The design basis for the facility contains no information relating to the design life of the facility, but an assessment of, for example, the effect of neutron fluence on the fixed core structure, based on current operation, confirms that the soundness of this structure is predictable up to that date. Operation of the reactor beyond the currently projected end of life may follow one of two paths: Extension of the lifetime of the facility by a few years up to a decade or so, or Complete rejuvenation of the facility to operate for another years beyond Remedial actions have been identified to address lifetime extension aspects, this focus mainly on the former, as the latter possibility would entail substantial redesign of the facility and, in all likelihood, a substantial shutdown of two or more years to implement and commission the modernised facility. Many of the remedial actions, especially those involving instrumentation and information technology, involve technologies with a

2 maximum life span of years, hence the targeted lifetime extension of the current Ageing Management Programme is Operation beyond that time will need to be reviewed at a later date. The basic causes of ageing degradation of a SSC are the service conditions which support the activation of particular ageing mechanisms leading, unless properly managed, to loss of the SSC functionality. 2. Project scope This project entails inspecting the MA and LA piping at all levels of the building as well as those cast in the reactor basement floor and trenches leading to the inlet of Tanks R1 to R6 as well as the piping used to transfer MA and LA effluent to the Liquid Effluent Management Services. Inspection results will help determine if any pipes need to be repaired or replaced. 3. MA and LA Drainage facilities Four effluent systems are provided on the site. These are classed as Medium Active (MA) drains; Low Active (LA) drains; "trade"; and "sewage"[1]. Only the MA and LA systems will be discussed in this paper. The MA effluent originates from radioactive processes with a medium to high radioactivity content (Process water directly in contact with radio nuclides, e.g. water used for decontamination); it results mainly from the regeneration of the demineralisation columns and selective process wing drains. The MA effluent flows, by manual selection of valves, into one or both of two 27 m 3 rubber lined mild steel storage tanks (designated R1 and R2), located below ground level in concrete sumps to the south of the reactor building. MA effluent can overflow from R1 and or R2 tanks with an overflow line between the two tanks to prevent effluent build-up in the plant. The tanks are equipped with two diaphragm air pumps for circulation or mixing effluent, sampling of the effluent and also transferring effluent into the main MA line (51 mm stainless steel) to a nearby treatment facility. The MA effluent pipe system is exclusively for MA effluent and cannot transfer effluent into the LA system. SAFARI-1 also has the option, with special approval, to drain MA effluent directly to the treatment plant, thus bypassing the holding tanks. All MA drains consist of 304L stainless steel piping and are run in floor slabs, walls and the pool structure to provide the necessary shielding. All MA drain connections are either directly connected to items of equipment or are tightly closed with plugs. Located on the south side of the reactor building are two underground LA tanks of 114 m 3 capacity each, for storage of large quantities of LA effluent. LA effluent originates from radioactive processes with a low radioactivity content (Process water not directly in contact with radio nuclide, e.g. change room wash water). One of these tanks is normally on line to receive effluent from the plant and the other remains isolated until the other tank is full or awaiting release of effluent to the treatment facility. A shielded pump room just south of the tank cells contains two pumps, valves and piping which enable the tank contents to be circulated and sampled before transferring into the main LA line to the treatment facility. In addition, these two pumps, with the selection of valves, can be connected with a dedicated line and valve system to the MA holding tanks only for transferring LA effluent, to the MA tanks (R1 and R2).

3 All floor drains, emergency showers, wash hand basins and laboratory sinks in potentially contaminated areas drain into the LA system. Facilities around the pool structure and process equipment requiring LA waste discharge are also connected to this system. All floor drains are equipped with U type water traps of sufficient depth to provide a seal against the building ventilation pressure differential to atmosphere. All LA drains in the building are of close-grained cast iron. Located between the MA holding tanks and the LA holding tanks, are two 68 m 3 concrete basins for the storage of "potentially active" LA effluent. They are provided with two pumps in a shielded pump room just south of the tank cells, which also contains valves and piping which enable the tank contents to be circulated and sampled before transferring into the main LA line to the treatment facility. 4. SAFARI-1 Ageing Evaluation Philosophy Ageing Management is defined as engineering, operation, and maintenance strategy and actions to control degradation, obsolescence and wear out of SSCs within acceptable limits. The basic causes of ageing degradation of a SSC are the service conditions which support the activation of particular ageing mechanisms leading, unless properly managed, to loss of the SSC functionality. These service conditions can be categorized as normal operation, anticipated operational occurrences and environmental conditions. Some ageing that has been identified in many SSC at SAFARI-1 is technological obsolescence, where either whole technology (e.g. vacuum tubes vs solid state electronics) has become obsolete, or where suppliers/vendors of equipment have discontinued certain products (e.g. the primary pumps) to the point that even their support is discontinued and spares are not available. The management of ageing includes activities such as repair, refurbishment or replacement of SSCs, which are similar to other activities carried out at a research reactor during maintenance and testing or when a modification project takes place [2]. The objective of the Quality, Health, Safety and Environment (QHSE) system as applied to Ageing Management is to ensure that the facility meets the requirements for safety and compliance as derived from: The regulatory body s requirements; Design requirements and assumptions; The safety analysis report; The Operating Limits and Conditions; Administrative requirements of reactor management; Safety, Health, Environment and Quality Department (SHEQD) Instructions [3]. Corrosion is by far the biggest contributor to the record of ageing in RRs, and is not limited to old facilities. Corrosion on the concrete side of embedded pipes, components, and re-enforcing especially if the pool has been leaking, are problems that are often observed. Stainless steel is not immune to corrosion; there are many instances of (e.g.) incorrect welding procedures that have promoted rapid corrosion of SS components. The possibility of corroded pipes justifies the importance of inspecting the MA and LA pipes of SAFARI-1 s effluent systems. 5. Pipe inspections Inspection of MA and LA building pipe works is necessary for maintenance and the ageing management programme. These inspections cannot merely be viewed as part maintenance because normal maintenance provides for the possibility of fixing something when it breaks, while this piping system cannot be routinely fixed and are therefore prone to ageing related damage.

4 Inspections of the piping of the effluent systems will be conducted using a camera. The ideal camera should be able to fit into pipes with diameter ranging from 38 mm to 203 mm and it must be mounted on the end of a bendable extension rod that can be inserted into the pipes. The camera lens has to be protected from possible contamination and the camera cable will be cleaned when it is removed from be pipes to remove any possible contamination. In the past, CCTV camera equipment consisting of a camera, video recorder and a push rod was used to inspect pipes. The same technology will be used for these inspections For each pipe that will be inspected a video will be captured and the following will be noted: Date and time (start and end) of the inspection Diameter of the pipe The length of the pipe Condition of the pipe Any blockages that may be obstructing the camera Analysis of inspection results will assist with updating of all floor layout drawings and also help determine if there is a need for repair or replacement of any pipes. 6. Environmental Protection Practices Necsa is committed to the prevention of soil, water and air pollution through elimination or minimisation of waste, effluent and emissions [4]. This is in compliance to national legislation that advocates for protection of the environment and sustainable development. Pipe inspection is important for environmental protection because continuous use of corroded pipes will lead to leaks and therefore release of radioactivity to the environment. Therefore pipe inspections as part of maintenance and the ageing management programme are vital to ensure prevention of soil and water pollution. The pipe inspection is also important to ensure that there is no pipe leaking into another pipe and therefore increasing the volume of effluent sent to either the MA or LA tanks thereby increasing the volume of waste sent to the Liquid Effluent Management Services (LEMS). Environmental monitoring at Necsa consists of monitoring atmospheric releases through stack monitoring; water (surface and groundwater); soil and vegetation. The frequency of monitoring ranges from continuous, weekly, monthly, semi-annual and annual samples. This monitoring is essential to prove compliance to the licence issued by the National Nuclear Regulator. Most environmental monitoring at Necsa is mostly conducted by the corporate Environmental Management Department. SAFARI-1 is responsible for stack monitoring as well as effluent monitoring whilst the effluent is stored in the MA or LA tanks prior to release to the LEMS. To ensure protection of the environment water samples are taken from MA and LA tanks. These are analysed for gamma, alpha and beta emitting isotopes. When results are within limits and meet the Waste Acceptance Criteria the effluent is then released to LEMS for further treatment and final disposal. An environmental survey may also be conducted in the vicinity of SAFARI-1 to ensure that there is no localised pollution that may not be detected downstream where routine environmental samples are taken. 7. Conclusion Inspection of building pipe works is required for maintenance purposes and for the ageing management programme. Visual inspection of the MA and LA building pipe

5 work will inform management about the status of the pipes within SAFARI-1 and results will be useful for decision making concerning the extension of the life span of the reactor. Ensuring that MA and LA building pipe works are sound will also be beneficial for the environment because sound pipe works will lead to the protection of the environment from possible pollution. Acknowledgements Dr. JC Mostert Mr. H Stander Mr. BJ Steynberg References [1] Vlok JWH (2010); Ageing Management Plan for the SAFARI-1 Research Reactor; Necsa internal report; Pelindaba. [2] Vlok JWH (2010); SAFARI-1 Research Reactor Safety Analysis Report Chapter 10: Auxiliary systems; Necsa internal report; Pelindaba. [3] Vlok JWH (2009); Ageing Management Philosophy for the SAFARI-1 Research Reactor; Necsa internal report; Pelindaba. [4] Mackay MM (2010); Necsa Safety, Health and Environmental Policy; Necsa internal report; Pelindaba.