SOME ASPECTS OF COOLANT CHEMISTRY SAFETY REGULATIONS AT RUSSIA S NPP WITH FAST REACTORS

Transcription

1 Federal Environmental, Industrial and Nuclear Supervision Service Scientific and Engineering Centre for Nuclear and Radiation Safety Scientific and Engineering Centre for Nuclear and Radiation Safety Member of SOME ASPECTS OF COOLANT CHEMISTRY SAFETY REGULATIONS AT RUSSIA S NPP WITH FAST REACTORS Nataliia Kharitonova, Rachet Sharafutdinov First IAEA Workshop on Challenges for Coolants in Fast Neutron Spectrum Systems: Chemistry and Materials Vienna, Austria, 5 7 July

2 Contents: 1. Introduction 2. Chemistry control of coolant for the first and second circuits of fast sodium reactors (BN) 3. General requirements for conduct of chemistry for fast reactors, used heavy liquid metal coolants (lead, lead-bismuth) 4. General proposals on the establishment of requirements for the chemical regime of liquid metal coolants at Russia's NPPs with fast neutron reactors 5. Conclusions 2

3 3 Current status of the nuclear power industry in Russia

4 Basic Regulatory Documents Russian Federal Rules and Regulations in the field of nuclear energy establish a number of requirements to chemistry at NPP for chemistry control. The basic safety requirements are reflected in the current regulatory documents that establish general requirements for the quality of coolants, including liquid metal for fast reactors: General Safety Rules of Nuclear Power Plants (NP ); Nuclear Safety Rules for Nuclear Plant Reactor Units (NP ); Requirements to the Content of Safety Analysis Report for Nuclear Power Plants with Reactors on Fast Neutrons (NP ); Rules for the Arrangement and Safe Operation of Equipment and Pipelines of Nuclear Power Plants" (NP ). 4

5 Federal norms and rules in the area of nuclear energy The requirements of normative documents for LMC are of a general nature and are limited to indications that: (1) in design of NPP should be established (in Safety Analysis Report should be reflected) the requirements to the chemical regimes in the systems and elements of NPP, which should be observed during operation of NPP in order to maintain the integrity of physical barriers to the spread of ionizing radiation and radioactive substances into the environment; (2) in Technical Specifications of the NPP unit must be established operational limits and conditions for safe operation relating to control of the chemical regime. 5

6 Chemistry control of sodium fast reactors (BN) (1/4) The Russian experience in the development of reactors on fast neutrons with sodium coolant (BN-350, BN-600, BN-800) has been recognized as successful worldwide. Unit 3 on Beloyarsk NPP (BN-600) with a capacity of 600 MW was put into operation in April 1980 and is in operation up to the present time, and its operation has been extended to In 2016, Unit 4 on Beloyarsk NPP with a fast neutron reactor (BN-800) was put into commercial operation (commercial fast reactor (800 MW (e)). 6

7 Chemistry control of sodium fast reactors (BN) Sodium has a low corrosive aggressiveness to construction materials, ensures their high corrosion resistance during the whole lifetime of the NPP unit by minimizing corrosion in all operating modes Technical requirements to the quality of sodium of reactor purity for BN type reactors (BN-600, BN-800) are currently established by standard OST Both on delivery and during operation are limited the mass concentrations of potassium, calcium, carbon, chlorides, nitrogen, iron, silicon, bismuth, barium, tin, oxygen, hydrogen in sodium and radionuclide 137 Cs (specific activity Is limited only by operation at the level of 185 M Bq / kg) 7

8 Chemistry control of sodium fast reactors (BN) Principles for conduct of primary and secondary chemistry for fast reactors (BN), used liquid metal sodium as a coolant: preventing the formation of sodium oxides and other compounds on the surface of primary equipment to avoid ingress of these compounds into the reactor core; minimising the construction materials corrosion in sodium to exclude a sodium contact with water and leaks of sodium; providing the sodium clean-up performance to remove oxides, hydrides, carbonates, etc. in the period of initial accumulation of coolant; providing the fire protection measures; using primary and secondary sodium purification systems effectively to remove impurities during the plant operation; ensuring the control of sodium and shielding gas quality; reducing the concentration of iodine and caesium radionuclides in sodium coolant. 8

9 Chemistry control of sodium fast reactors (BN) BN third water chemistry control programmes - protect the steam generators and other components of third circuit from corrosion-related damage and performance losses: minimising the deposits on heat exchange surfaces of steam generators, steam super heaters and on the flow-parts of the turbine; reducing flow-assisted corrosion and corrosion product input into the steam generator; maintaining turbine condenser reliability and leak-free; reducing impurity intrusion sources such as resin fines; using condensate purification systems to remove soluble and insoluble impurities; using chemical treatments; verifying high-quality makeup water. 9

10 Requirements for conduct of chemistry for fast reactors, used HLMC Heavy liquid metal coolants (HLMC) make significant corrosion and erosion impact on construction steel elements. Russian scientists have developed oxygen-based technology of structural steel surface passivation for this purpose*. This technology implies formation of protective oxide films on the steel surface and assurance of their integrity during plant operation by maintaining specified oxygen potential of coolant. Operation without purposeful supply of dissolved oxygen to the coolant spontaneous deoxidization of coolant takes place down to the level, at which corrosion protection of structural steels cannot be provided. *) P.M. Martynov, R.Sh. Askhadullin, Ju.I. Orlov. Current issues and the tasks of heavy liquid-metal coolant technology for nuclear power plants (lead, lead-bismuth). TZHMT-2013, Obninsk, September 23-26,

11 Principles for conduct of chemistry for fast reactors, used HLMC Main tasks of HLMC technology (lead, lead-bismuth), fundamentally important for ensuring the safety of reactor (1/2): ensuring the required purity of the coolant to maintain design limits and conditions specified in order to maintain the integrity of physical barriers in the path of ionizing radiation; excluding the slagging with lead oxides and corrosion products of structural materials of heat transfer surfaces of safety-important systems, as well as safety systems; providing the minimum corrosion of structural steels of equipment and pipelines in contact with lead coolant; providing the minimum deposits on the heat transfer surfaces of fuel rods, equipment and in pipelines of safety-important systems (including in gas systems); 11

12 Principles for conduct of chemistry for fast reactors, used HLMC Main tasks of HLMC technology (lead, lead-bismuth), fundamentally important for ensuring the safety of reactor (2/2): providing the instrumentation devices to control the process correctness, equipment and pipelines integrity; excluding the generation of hydrogen explosive concentrations in systems and equipment where the hydrogen accumulation is possible during operation. 12

13 Principles for conduct of chemistry for fast reactors, used HLMC The normative documents on the chemical regimes of HLMC should formulate the requirements for the technological procedures such : preparation of coolant (Pb-Bi or Pb) and filling of NPP circuits; preliminary passivation of reactor plant elements before their installation; passivation of the inner surface of the primary circuit of the reactor plant; coolant technology concerning repair and refueling procedures; coolant purification and removal of impurities from the circuit surfaces during normal operation; control of coolant oxidizing potential during operation of NPP with HLMC; purification of cover gas in the liquid metal circuit providing the instrumentation devices to control the process correctness, equipment and pipelines integrity; excluding the generation of hydrogen explosive concentrations in systems and equipment where the hydrogen accumulation is possible during operation. 13

14 Principles for conduct of chemistry for fast reactors, used HLMC Quality of the coolant is affected by the composition of the shielding gas (argon) in the gas cavity of the reactor before filling the primary circuit with a coolant and when operating the reactor. quality of argon is regulated by GOST Argon gaseous and liquid. Technical specifications. For the projected units with HLMC it is recommended to develop the quality standards for shielding gas. Criteria should be formulated that define the requirements for: means and methods for controlling the content of normalized impurities in a shielding gas; purification systems of shielding gas in the HLMC circuit. 14

15 General proposals on requirements for the chemical regime of LMC at Russia's NPPs with fast neutron reactors By analogy with the requirements for the NPP water chemistry (SSG-13, IAEA, Vienna (2011)) in normative documents for the LMC chemistry it is recommended to provide the requirements. LMC chemistry control should include the correct application of the appropriate chemistry regimes for safety systems and safety related systems; The control parameters selected should be the most important LMC chemistry parameters for monitoring the LMC chemistry regime and monitoring for the presence of deleterious impurities. In addition to control values, expected values may also be specified for internal use by plant staff in order to avoid a chemistry parameter inadvertently exceeding its limit value. 15

16 General proposals on requirements for the chemical regime of LMC at Russia's NPPs with fast neutron reactors By analogy with the requirements for the NPP water chemistry in normative documents for the LMC chemistry it is recommended to provide the following requirements. If a control parameter is outside its limit values, degradation of conditions for structures, systems and components may occur in the long term and may result in unavailability of safety systems. Thus, graded action levels may be specified in advance for control parameters; if deviations from these levels occur, corrective actions should be initiated progressively within an acceptable period of time and further corrective actions should continue to be applied until plant shutdown, if necessary; In addition, diagnostic parameters may be defined. 16

17 Conclusions The information is provided on the basic safety requirements reflected in the existing regulatory documents that establish general requirements for the quality of liquid metal coolants for fast reactors at NPP of the Russian Federation. The expediency is shown for optimization of LMT chemistry regulation in the part of chemical regime concept choice, as well as the basic principles and criteria for ensuring the safety of NPP by development, establishment and providing of the chemical regime. Reasonable practicality is shown to divide all LMC quality parameters (by analogy with water-chemistry) for control and diagnostic parameters. It is recommended to specify the graded action levels in advance for LMT coolant control parameters. If a parameter exceeds its limit, appropriate actions should be taken to recover its normal operating value within a specified time. 17

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