24-May-01 CANDU Safety - #10 - Design and Analysis Process.ppt Rev. Each system gives plant operators a chance to step in and stop an accident from progressing further.Safety is ongoing. The CANDU (Canada Deuterium Uranium) is a Canadian pressurized heavy-water reactor design used to generate electric power. Advantages . A CANDU-Based Fast Irradiation Reactor. Gentilly-2 and Other CANDU reactors; Emergency Electrical Power; Steam Line Accidents; Pressure Tube Ruptures; Pressure Relief Valves ; The Containment System; Citations from Official Documents; References; 1. The assumption is made that there would not be any evacuation of people or distribution of tablets despite the fact that the release of radioactive materials are assumed to continue for many days. The progression of a severe core damage accident in a CANDU reactor is analyzed using the MAAP4 CANDU code, which is the CANDU-version of the MAAP code. However, two well-informed nuclear critics who participated in the hearings, Dr. Gordon Edwards and Ralph Torrie, have argued that the probability of a dual failure could be about  100  times higher than the theoretical levels. The molten mass was then predicted to sink into the ground an additional   3   to   15   metres before coming to rest. … However, much of the core's radioactive material, which strictly speaking has escaped from containment, is prevented from reaching the environment because the ground acts as an effective filter. There are no simple answers to these and other questions and therefore an analysis of the consequences of a LOCA [LOSS OF COOLANT ACCIDENT]  involves a process of conservative assumptions in some cases and best engineering judgment based on extrapolations from available experimental information in others. ECCS . the fuel is small and the relatively long lifetime of prompt neutrons in the reactor precludes rapid changes in power levels • two fully capable safety shutdown systems, independent from each other and the reactor regulating system. In the absence of relevant Canadian information, the work done by N. C. Rasmussen, as described in the Reactor Safety Study (WASH-1400) issued in 1975 by the U.S. Nuclear Regulatory Commission is used. • CANDU reactors are exceptionally safe: the safety systems are independent from the rest of the generating station and each safety component has three backups. The task is overwhelming the AECB. However, the open literature describing these established methods is quite sparse, especially with regard to the unique advantages in operability and safety that arise from the computer-driven Reactor Regulating System (RRS). AECL and Ontario Power Generation Inc., in co-operation with Fauske and Associates Inc., have developed the MAAP4 CANDU code for severe core damage accident analysis in a CANDU reactor. Safety is designed in from the start. The unit at Pickering was improved upon to produce the CANDU-6 design, starting up in the early 1980s. ii) the quantity of radioactive gases which escape containment; iii) the weather conditions which prevail at the time of the accident. reactor rated at 450 MWe with two steam generators and two heat transport pumps connected in series. is composed of 380 fuel channels … Point Lepreau was the first CANDU 6 reactor to be licensed for operation, the first to achieve criticality and first to begin commercial operation. Thus, while this was considered the most likely sequence following a major core meltdown, it would not necessarily produce a dispersal of the bulk of the core's radioactive material into the environment. The purpose of the ECCS [EMERGENCY CORE COOLING SYSTEM]  is to remove the heat from the core as rapidly as possible. The reactor vessel may be built to withstand low pressure, therefore, the cost of the vessel is less. The most important of these are caesium, ruthenium, tellurium and the fission gases, iodine, krypton and xenon. Its four CANDU reactors are owned and operated by OPG. All Canadian nuclear reactors are of the CANDU type but the reactor has also been marketed abroad - until October 2011 AECL marketed and built 34 … In consequence, both prompt and latent cancers would be produced. Evidence to support the Edwards/Torrie position, which is available in the Pickering Safety Reports, indicates that there were in fact (if the commissioning period is included) six loss of regulation accidents within four years. The major advantage of this reactor is that the fuel need not be enriched. It is owned and operated by New Brunswick Power. Is it possible that the rewetting of some fuel channels will delay for an extended period of time the rewetting of others due to ''short-circuiting'' of the emergency coolant? The uncertainties in the quantity of radioactive gases and vapours which escape from the fuel include the uncertainties about the effectiveness of any ECCS [EMERGENCY CORE COOLING SYSTEM] . The purpose of the MoU is to advance the scientific and technical knowledge base for PHWRs and foster cooperation amongst research organisations that support PHWRs. The flaw consists of a potential for unanticipated sudden Loss of Coolant Accidents (“LOCAs”) arising from failures in so-called Feeder Pipes through two mechanisms – one of which has … The following text provides a general outline of one … AECL and Ontario Power Generation Inc., in co-operation with Fauske and Associates Inc., have developed the MAAP4 CANDU code for severe core damage accident analysis in a CANDU reactor. Flux Tilts — The flow of neutrons can vary beyond the specified limits in various sections of the reactor core, leading to … The closer to the reactor building (or within the building), the greater the probability of an individual's being exposed to intense radiation. The heat transport system (HTS) circulates the coolant through the reactor to remove the heat of fission from the fuel. Nor has any study on core meltdown accidents been done for the CANDU reactor. shutdown rods and "poison" injection), the theoretical probability per reactor might be considerably lower, perhaps in the order of 1 in 1,000,000,000 years [once in a billion years] . CANDU reactor design has inherent safety features as defences against severe accidents. For a given release of radioactive material from the plant, the predicted radiation dose to an individual at the plant exclusion boundary could easily vary by a factor of ten or more depending on the assumptions that are made with respect to the prevailing weather conditions and therefore the dilution of radioactive materials in the atmosphere. The two reactors were a success and led to the construction of the first multi-unit station in Pickering in 1971 with a capacity of 600 MWe. When modern nuclear power plants were being designed in Canada two decades ago. The AECB has concluded that operation of the Bruce A station during 1987 was only marginally satisfactory and that significant improvements were necessary. • The Pickering B Unit 7 reactor owned by Ontario Power Generation holds the world record for the longest, non-stop operation at 894 days. The philosophy must not change. Secondary menu. NRX operated for 45 years, being shut down permanently … if the [EMERGENCY CORE COOLING SYSTEM]failed to act, melting of metallic components of the core and eventually . Many Canadians are not prepared to accept assurances of safety that are not demonstrable and transparent. This paper presents a new concept for a CANDU-based fast irradiation reactor that is horizontal in orientation, with individual pressure tubes running the entire … The longer the neutron lifetime, the slower the reactor’s response to a reactivity insertion. In CANDU-6 type reactors, a multiple steam generator tube rupture (MSGTR) accident is characterized as a reactor building (RB) bypass scenario. The government announced, through its Regulatory Reform Strategy, that the Minister of Energy, Mines and Resources is to consider ways to increase the transparency and openness of the AECB, the composition of the Board, and the desirability of expanding the number of members to include representatives of industry, labour and the public. 0 17 Analysis Philosophy λ In past safety analysis performed for CANDU reactors, a conservative approach is used λ That is, the assumptions and methodology applied in a particular analysis is … It means that, on balance, the benefits of generating electricity with nuclear power plants outweigh the risks. i) the quantity of radioactive gases and vapours which escape from the fuel and into the reactor containment building; In the event of a LOCA [LOSS OF COOLANT ACCIDENT] , the normal cooling water would be lost from the main cooling system but core melting would normally be prevented by the action of the ECCS [EMERGENCY CORE COOLING SYSTEM] . This CANDU Textbook is suitable for students, educators, trainers and working professionals at a target level of senior undergraduate year university engineering and science. The resources needed to ensure that licensees are taking all possible measures to prevent accidents and for the AECB to take enforcement action when they do not are also currently insufficient. Chairman: Arthur Porter. Each year there are a variety of significant events at Canadian nuclear power plants with safety implications. All post-meltdown occurrences which threaten todamage or breach the containment structure can result in the release of substantial amounts of radioactive material to the environment. B. I I I I I I I I I I I I I I I I r • TABLE OF CONTENTS 1. … The paper begins with a review of the various definitions of DECs and how DECs fit within the concept of defence … 1. (This sequence of events is often referred to as the ''China Syndrome'', because the molten core heads in the general direction of China.). Effective regulation is essential to ensure such care is taken so that the clear benefits of nuclear power can be realized. 1.1 Overview Experts in health physics generally require formal training in radiation protection, environ-mental radioactivity, and shielding design. Despite its smaller size, the Pickering station powers up to 2.5 million households. The principles of "reduce, reuse, recycle" are followed throughout refurbishment to minimize the amount of disposable waste. - CANDU reactors use nuclear fuel in the form of natural uranium dioxide pellets, stacked in an array (bundle) of thin-walled tubes of zirconium alloy, E-DOCS #3399585 2 each about 12 mm in diameter and about 0.5 m in length, and called . These observations clearly indicate that a strong regulatory agency is essential to ensure industry meets its obligations to operate safely. Clearly, nuclear energy has been and can continue to be the source of substantial benefits to Canadians. A CANDU SMR has the potential to achieve lower capital costs relative to GW-class reactors, a shorter construction timeline of 35 months for the first unit (30 months for nth unit) and a 94% lifetime capacity factor. The Essential CANDU - a textbook on the CANDU nuclear power plant technology. Is it possible that the rewetting of some fuel channels will delay for an extended period of time the rewetting of others due to ''short-circuiting'' of the emergency coolant? Weather conditions can also be a significant variable. This issue is particularly important as twelve of Canada's largest reactors are close to Toronto. There is a fourth factor which would affect the radiation dose to people; protective actions such as evacuation of the affected populace or distribution of tablets of a stable iodine compound. Registration. This can lead to a loss of reactor control. Use of such tablets can greatly reduce the radiation dose resulting from inhalation of radioactive elements of iodine. The size and complexity of the task of ensuring and demonstrating the safety of nuclear power plants has not increased suddenly -- it has been building up for the last decade. By 1973 the other … In 1971 the first commercial CANDU reactor, Pickering A 1, began commercial operation. The assumption is made that there would not be any evacuation of people or distribution of tablets despite the fact that the release of radioactive materials are assumed to continue for many days. The design utilizes natural uranium fuel, computer-controlled operation, and on-line refueling. Will fuel bundle and fuel channel distortions under accident conditions interfere with cooling by the ECCS [EMERGENCY CORE COOLING SYSTEM]  to the point that additional gaseous fission products will be released from the uranium oxide fuel? This makes the calculation of consequences of potential accidents very difficult, research to simulate accident consequences is often incomplete, and, perhaps most significant, human errors are an unquantifiable element. addressing DECs for CANDU reactors, the set of fuel safety criteria that should be used for DECs remains to be formulated. Chapter 14 Nuclear Reactor Materials (pdf 1.2Mb) by Dr. Derek H. Lister and Dr. William G. Cook, as of 2017.04.12 When contacting the CNSC, please provide the title and date of the abstract. Interim Report on Nuclear Power, ~ commonly known as the Porter Commission Report ~, Chapter Six: Health, Environmental and Safety Concerns, Ontario Royal Commission on Electric Power Planning Waste minimization. This estimate is based on failure rates in the high pressure piping of the primary heat transport system being  10  times higher than has been assumed, and also on the fact that the availability of the Pickering ECCS [EMERGENCY CORE COOLING SYSTEM]  has been demonstrated to be  10  times lower than postulated by the designers. - The fuel bundles are inserted in horizontal fuel channels, each typically housing 12 fuel bundles. Use of such tablets can greatly reduce the radiation dose resulting from inhalation of radioactive elements of iodine. CANDU is a pressurized heavy water reactor (PHWR) that uses heavy water (deuterium oxide – D2O) as a moderator and coolant, and natural uranium as its fuel. Reactors accumulate in their initial training is designed as a multi-layered safety system first, and J … safety.! The reasons for CANDU reactors document, contact the CNSC time, in. Particularly serious because the iodine-131 could be ingested in the event of such a major would! 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