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[en] The CNSC (Canadian Nuclear Safety Commission) evaluates the safety performance of nuclear power plant (NPP) licensees and prepares an annual report on their safety performance referred to as the Regulatory Oversight Report, which is presented to the Commission and is subsequently published on the CNSC web page. Prior to 2017, the report was referred to as the Regulatory Oversight Report for Canadian NPPs. However, in 2017, the report was expanded to include the safety performance evaluation of waste management facilities located at NPP sites. The report has been renamed as the Regulatory Oversight Report for Canadian Nuclear Power Generating Sites. The CNSC evaluates how well licensees meet regulatory requirements and CNSC expectations for the performance of programmes in 14 safety and control areas (SCAs) that are grouped in accordance with their functional areas of management, facility and equipment, or core control processes. These SCAs are further divided into 71 specific areas that define the key components of the SCA. The functional areas, SCAs and the specific areas that are used in CNSC’s safety performance evaluation are presented. An example of safety performance ratings for Canadian NPPs is given. An example of a conclusion of a CNSC Regulatory Oversight Report for Canadian Nuclear Power Generating Sites is as follows: The evaluations of all findings for the SCAs show that, overall, NPP licensees made adequate provisions for the protection of health, safety and security of Canadians and the environment from the use of nuclear energy, and took the necessary measures to implement Canada’s international obligations.
[en] The water chemistry control in Nuclear Power Plants (NPPs) is important at least for the next reasons: structural materials integrity, plant radiation levels, deposits build-up and safety. One of the most important NPP systems is Primary Heat Transport System (PHTS) having in view its role in active zone cooling and heat transfer to steam generators. In PHTS the chemical control is directed to keep chemical parameters within specified limits in order to mitigate the corrosion of the key equipment and related piping, to control the corrosion rate and impurities concentration, such as corrosion and fission products and to minimize activity transport and heat transfer surfaces fouling. By operation in aqueous environment at high temperature and pressure, the structural materials from PHTS are covered with protective oxide films, which maintain the corrosion rate in admissible limits. A lot of potential factors exist, which can degrade the protective films and consequently intensify the corrosion processes. In order to minimize these adverse effects, an optimal water chemistry control and corrosion monitoring program were established. The understanding of the corrosion degradation phenomena that result in failure of some components from PHTS of CANDU NPP necessitates investigation of the structural materials corrosion processes in different conditions of water chemistry and temperature. Water chemistry management in Nuclear Power Plants can then be applied to mitigate the corrosive environments inherent in plant operation. The basis of chemistry control process consists of operational experience, laboratory tests, structural materials corrosion behaviour and the transport and deposition of impurities and corrosion products under operating conditions. To investigate the corrosion process of some structural materials from PHTS (Zr alloys) of CANDU 6 reactor corrosion experiments were performed in autoclaves assembled in by-pass loops of CANDU 6 reactor PHTS Cernavoda Unit#1 This paper presents the results obtained by in-situ monitoring of PHWR water chemistry effect on fuel cladding corrosion, Zircaloy-4. The optical metallographic and scanning electron microscopies, as well as XRD analysis have been used to evaluate the corrosion behaviour of the fuel cladding material, Zircaloy-4 coupons exposed in PHTS autoclaves system. The obtained results allowed us to establish the contribution of the water chemistry on the Zircaloy-4 corrosion behaviour. (author)
[en] This paper/presentation provides a regulatory perspective on the verification of licensees’ activities related to chemistry control. Verification activities include analyzing chemistry data provided by NPP licensees, performing inspections, and monitoring recent reportable events. The scope of these verification activities can be influenced by recent research in reactor chemistry. Despite these verification activities, chemistry-related incidents do occasionally occur. A brief summary of a sample of events related to chemistry control is provided, along with the follow-up action taken by the CNSC. Examples of the regulatory oversight of licensees’ reactor chemistry-related licensee activities are also provided. (author)
[en] Pressurized Heavy Water Reactor (PHWR), CANadian Deuterium-Uranium (CANDU), Operating Experience (OPEX) provides evidence that performing post-refurbishment Primary Heat Transport System (PHTS) Hot Conditioning (HC) with fuel in core presents a risk that the fuel bundles may become coated with iron-based, primarily magnetite and hematite, deposits during the evolution. This OPEX also provide evidence that these deposits remain on the fuel sheath for a period of approximately three to six months into the subsequent operation of the plant before the deposit material is redistributed into the PHTS coolant and removed from the system through the PHTS purification system. Such deposits, while present on the sheath, are thought to contribute to fuel sheath corrosion and impact fuel element heat transfer properties. OPG commissioned a series of laboratory testing to investigate the factors that contribute to the phenomena of fuel sheath deposit formation. These tests included comparative studies of HC evolutions, which emulated recent CANDU post-refurbishment OPEX in a laboratory setting. These investigations provided clarity on the parameters relevant to this adverse condition and on controls that can be implemented to minimize deposition on fuel bundle sheath surfaces. Sensitive parameters and associated controls include; (1) use of a “conventional” HC process as compared to a chelating-agent type HC, that use forms of Ethylenediaminetetraacetic Acid (e.g. Li2EDTA), (2) HC prior to reactor first approach-to-critical (i.e. no fuel heat), (3) maintenance of PHTS pH per current industry expert recommendations, and (4) careful control of other dissolved materials in the PHTS during PHT cold flush. OPEX observations suggest that the surface condition of fuel sheathing may also be a contributing factor related to the probability of deposition. This indicates that fuel sheaths that have been “polished” following tube production may be less susceptible to deposition of magnetite on sheath surfaces during HC. While OPG has considered this observation to be interesting, it was not further investigated, and thus requires validation. (author)
[en] In 2018, EDF operated a standardized fleet in France: 58 pressurized water reactors from one vendor and one licence through the 900 MW series (34 reactors); the 1300 MW series (20 reactors); and the 1450 MW series (4 reactors). In total, 75% of the fleet was built between 1979 and 1990, the oldest reactor is 40 years old and the average age of the fleet is 30 years. Thus, LTO programmes and plant life management have been key issues for years.The principles of asset management as mentioned in ISO55000:20141 are implemented in EDF processes, from strategic levels to working levels. If the main goals are shared inside the company, the nuclear operating branch is organized following several programmes (e.g.ageing management, obsolescence, maintenance and optimization, refurbishment for major components) and projects (e.g. periodic safety reviews, post Fukushima improvements) that are quite autonomous to contribute in maintaining or improving the value of the assets.
[en] The Dukovany nuclear power plant was put into operation in 1985-1987. These are 4 units of WWER-440 reactor type. The specific feature of the WWER-440 design is six reactor cooling loops, that means each reactor is connected to six circulating pumps and six steam generators (SGs). Equipment DEKOZ PG, as shown, was designed for the chemical decontamination of the SGs of the plant. It separates the primary part of SG from the remaining part of the reactor cooling loop, serves for filling and draining the decontamination solutions into and from SG separated section and ensures also their circulation. Used decontamination solutions are drained by compressed air from the SG into the liquid waste draining lines. The device does not allow the recovery of the used decontamination solutions.
[en] After the Fukushima accident, one of the highest priorities for CERNAVODA NPP was to investigate events that can lead to Spent Fuel Bay (SFB) loss of cooling and loss of coolant inventory. In CANDU plants, fuelling is performed on-power. Daily, fresh fuel bundles are loaded in core and spent fuel bundles are discharged from the core, transferred and stored in SFB. Due to the SFB limited storage capacity, bundles having 6 years or more of cooling time are transferred to the Dry Storage Facility. Thus, as per design, a maximum number of around 38 000 fuel bundles can be stored, at any time, in SFB. Following a loss of class III and class IV power sources (e.g. Station Blackout), the cooling and purification systems for SFB water become unavailable. Consequently, the bay water temperature increases up to the boiling conditions and, due to boiling and vaporization, the water inventory and level will decrease in time. The decrease of coolant level can leave uncovered a number of fuel bundles, degrading their cooling. The present paper reviews the analysis methodology and results for a typical event of Spent Fuel Bay loss of cooling. Methodologies used in the analysis and results presented are focused upon the CANDU fuel thermal-hydraulic behaviour during the event and upon its potential radiological hazard. (author)
[en] The Fukushima accident raised a concern on severe accident risk of a spent fuel pool (SFP), since the earthquake may breach the pool boundary and/or stop cooling the pool due to loss of AC power. Since then, a substantial effort has been made to analyse severe accidents which may occur in SFPs. In this context, the present study was intended to assess the severe accident risk of the SFP in a Nordic boiling water reactor (BWR). Two accident scenarios of risk importance, namely loss of cooling flow accident (LOF) and loss of coolant accident (LOCA) due to 0.01 m2 breach at the bottom of the pool, were simulated by two different MELCOR versions 1.8.6 and 2.2. The results show that the fuel degradation occurs at ~55 h and ~3 h for the LOF scenario and the LOCA scenario, respectively. Larger amount of H2 generation was predicted in the LOF (c.a. 1500 kg) than the LOCA (c.a. 400~450 kg). A sensitivity study on the breach size showed that a larger breach size led to earlier fuel degradation but less H2 generation. The comparison of the simulation results from the two MELCOR versions indicated that the transients of water level in the pool were similar, but the fuel degradation began earlier and more H2 was produced in MELCOR 2.2 simulation. (author)
[en] Automatic translation: When raising sheep for production lamb should follow the same requirements as well as before feeding cattle. It should be borne in mind that y lamb passes much more radionuclides, than in cattle, so before slaughtering animals is necessary feed for one to two months on clean feed. Wool can become surface contaminated radionuclides, but it is easily washed away ordinary detergents. Currently, sheep breeding is possible: c 4 and the zone without restrictions; in the 3rd zone on pastures with content of Cs 137 in the grass 600 Bq / kg. Pollution sheep wool is 8 9 times higher than meat.
[uk]При вирощуванні овець для виробництва баранини слід дотримуватися таких же самих вимог як і до годівлі худоби. Слід мати на увазі, що у баранину переходить набагато більше радіонуклідів, ніж у ВРХ, тому перед забоєм тварин необхідно годувати на протязі одного двох місяців на чистих кормах. Вовна може поверхнево забруднюватись радіонуклідами, але вона легко відмивається звичайними миючими засобами. В теперішній час ведення вівчарства можливе: в 4 й зоні без обмежень; в 3 й зоні на пасовищах з вмістом Cs 137 в траві 600 Бк/кг. Забруднення вовни овець у 8 9 разів вище, ніж м’яса.
[en] Automatic translation: Champignons are grown in the open ground. Make special lines deepened into the ground, at the bottom which are filled with rubble, slag. As a substrate use chopped straw and manure. In August plant grain and compost mycelium mushrooms. After 10 days the mycelium comes out on surface, and mushrooms bear fruit for 1.5-2 months.
[uk]Шампіньйони вирощують на відкритому ґрунті. Роблять спеціальні поглиблені у землю рядки, на дно яких насипають щебінь, шлак. У якості субстрату використовують подрібнену солому і гній. У серпні висаджують зерновий і компостний міцелій шампіньйонів. Через 10 днів міцелій виходить на поверхню, а гриби плодоносять протягом 1,5-2 місяців.