Federal Nuclear and Radiation Safety Supervision Authority

(Gosatomnadzor of Russia)

FEDERAL RULES AND REGULATIONS

IN THE FIELD OF ATOMIC ENERGY USE

Approved by Decree

of Gosatomnadzor of Russia (Federal Nuclear and Radiation Safety Supervision Authority)

dated December 31, 2002

No. 14

RULES FOR HYDROGEN EXPLOSION PROTECTION ASSURANCE AT NUCLEAR POWER PLANTS

NP-040-02

Effective

from September 1, 2003

Moscow 2002

Rules for hydrogen explosion protection assurance at nuclear power plants establish basic principles of explosion protection and requirements for explosion protection implemented in the course of design and operation for prevention and mitigation of design-basis and beyond design-basis accidents accompanied by explosion of hydrogen-containing mixtures.

The Rules are developed with due regard for the IAEA recommendations.

The Rules are applicable to power units of nuclear power plants with different types of reactors.

The Rules do not apply to explosion protection against external man-induced impacts, as well as against hydrogen and hydrogen-containing mixtures used in the systems and components for their normal operation.

First issue ^*

The regulatory document has passed legal examination at the Ministry of Justice of Russia (Letter of the Ministry of Justice of Russia No. 01/1093-YuD dated 04.02.2003). 

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^* The Rules are developed in the Research and Development Center of Gosatomnadzor of Russia for Nuclear and Radiation Safety with contributions from S. Antonov, V. Antoshin, I. Kaliberda, V. Slutsker, L. Soloviev, K. Tibenko (SEC NRS), Yu. Davydov (FSUE Atomenergoproekt), A. Yefimenko (Russian Research Center "Kurchatov Institute").

Proposals from the specialists of Gosatomnadzor of Russia, FSUE Atomenergoproekt, Russian Research Center "Kurchatov Institute", FSUE NIKIET, Main Department of the State Fire-Fighting Service of the Russian EMERCOM, Research and Development Center “Explosion Resistance” of Moscow State University of Civil Engineering (MSUCE), OKB “Gidropress” and FSUE "SPb AEP" were reviewed and taken into account in the course of development.

Contents

TERMS AND DEFINITIONS

1. PURPOSE AND SCOPE
2. BASIC PRINCIPLES OF HYDROGEN EXPLOSION PROTECTION ASSURANCE AT NUCLEAR POWER PLANTS

3. BASIC REQUIREMENTS FOR HYDROGEN EXPLOSION PROTECTION ASSURANCE AT NUCLEAR POWER PLANTS IMPLEMENTED IN THE COURSE OF DESIGN

4. BASIC REQUIREMENTS FOR HYDROGEN EXPLOSION PROTECTION ASSURANCE AT NUCLEAR POWER PLANTS IMPLEMENTED IN THE COURSE OF OPERATION 

TERMS AND DEFINITIONS

The following terms and definitions are used for the purposes of this document.

1. Explosion - a fast exothermic chemical conversion of explosion-hazardous medium accompanied by emission of energy and generation of compressed gases capable of work.

2. Containment - the set of building and other structural elements enclosing the space around the reactor facility or any other facility containing radioactive substances and forming the boundary as provided by the design in order to prevent releases of radioactive substances into the environment in the amounts exceeding the established limits.

3. Detonation - explosion of hydrogen containing mixture within a limited space with the reaction front spreading at supersonic velocity and creating high pressure and high dynamic head.

4. Deflagration - explosion of hydrogen containing mixture within a limited space with the reaction front spreading at subsonic velocity and creating moderate pressure and thermal loads (explosive burning).

1. PURPOSE AND SCOPE

1.1. Rules for hydrogen explosion protection assurance at nuclear power plants (hereinafter referred to as the Rules) establish basic principles and requirements for explosion protection to be implemented in the course of design and operation for prevention and mitigation of design-basis and beyond design-basis accidents accompanied by explosion of hydrogen-containing mixtures generated within the space enclosed by the containment.

1.2. The Rules apply to power units of nuclear power plants with various types of reactors.

1.3. The Rules do not establish requirements for the systems and elements where hydrogen is used in the course of normal operation.

1.4. The time limits and scope of work for bringing the existing power units of nuclear power plants into compliance with the Rules shall be determined in each particular case as per the procedure established by Gosatomnadzor of Russia.

2. BASIC PRINCIPLES OF HYDROGEN EXPLOSION PROTECTION ASSURANCE AT NUCLEAR POWER PLANTS

2.1. Hydrogen explosion protection at the nuclear power plant is deemed to be provided when:

a) generation of explosive hydrogen-containing mixtures in the systems, components and rooms within the space enclosed by the containment is prevented under normal operation of the nuclear power plant;

b) detonation and deflagration of hydrogen-containing mixtures in the rooms within the containment are eliminated in case of design-basis accidents;

c) detonation of hydrogen-containing mixtures is eliminated in case of beyond-design basis accidents, but deflagration is allowed provided that localizing safety systems perform functions according to the nuclear power plant design.

2.2. Hydrogen explosion protection shall be provided by prevention of explosive hydrogen-containing mixtures generation and mitigation of any possible consequences of explosion of these mixtures.

2.3. Prevention of hydrogen-containing mixtures generation under normal operation of the nuclear power plant shall be provided as follows:

a) maintenance of the nuclear power plant process in accordance with the operation limits and conditions established in the design;

b) leak-tightness of the process equipment eliminating ingress of hydrogen and other hydrogen-containing mixture components to the rooms inside the containment or minimizing it down to the level determined in the design;

c) operation of the systems (components) providing hydrogen explosion protection by reduction of explosive concentrations of hydrogen and other hydrogen-containing mixtures components within the containment volume;

d) concentration monitoring for hydrogen-containing mixtures.

2.4. Prevention of deflagration and detonation of hydrogen-containing mixtures shall be achieved by application of active and passive systems (components) controlling parameters and composition of hydrogen-containing mixture.

2.5. Abatement of thermal and mechanical impacts occurring in case of deflagration and detonation shall be achieved through the use of  engineering features.

3. BASIC REQUIREMENTS FOR HYDROGEN EXPLOSION PROTECTION ASSURANCE AT NUCLEAR POWER PLANTS IMPLEMENTED IN THE COURSE OF DESIGN

3.1. The following shall be determined in the design of the nuclear power plant:

a) potential processes and sources leading to hydrogen generation in the systems, elements and rooms within the containment with due regard for peculiarities of processes at the nuclear power plant under normal operation and in case of anticipated operational occurrences, including accidents (the list of potential hydrogen generating processes and sources is given in the Appendix);

b) composition of explosive hydrogen-containing mixtures in the rooms within the containment under normal operation and in case of any anticipated operational occurrences including accidents;

c) values and distribution of hydrogen concentration in the rooms within the containment under normal operation and in case of any anticipated operational occurrences including accidents;

d) points and hardware to monitor concentration of hydrogen and other components, as well as parameters of hydrogen-containing mixture in the rooms within the containment;

e) mechanical and thermal loads on the components of localizing safety systems (elements) resulting from possible explosion of hydrogen-containing mixtures during beyond design-basis accidents, as well as potential consequences of mechanical and thermal impact on the systems, components and rooms;

f) special-purpose structures for protection of systems, components and rooms within the containment against explosion of hydrogen-containing mixtures;

g) systems and components designed to perform their functions in case of explosion of hydrogen-containing mixtures.

3.2. The nuclear power plant design shall provide for the hydrogen explosion protection systems ^*, as well as measures taken to prevent accumulation of explosive hydrogen-containing mixtures in any interconnected volumes of the rooms or generation of local formations (dead zones) within isolated volumes of the rooms within the containment.

3.3. Substantiation of hydrogen explosion protection shall be made in the design and presented in the safety analysis report for the nuclear power plant. If calculation methods are applied substantiation of hydrogen explosion protection shall be performed through the use of certified software tools.

3.4. Engineering measures shall be applied in the nuclear power plant design to eliminate the sources of hydrogen-containing mixtures explosion initiation particularly resulting from electrical equipment operation.

3.5. Equipment and building structures in the rooms within the containment shall be made of structural materials or protected with special-purpose coatings eliminating hydrogen generation during normal operation and in case of any anticipated operational occurrences including accidents.

3.6. The limits and conditions for safe operation of the nuclear power plant with regard to hydrogen-containing mixture parameters shall be determined and substantiated in the nuclear power plant design.

3.7. The nuclear power plant design shall provide for the facilities measuring thermodynamic parameters of hydrogen-containing mixture with representation of necessary information in the main and emergency control rooms.

3.8. Number of points for monitoring of hydrogen-containing mixture parameters within the containment shall be selected and substantiated in the nuclear power plant design with due regard for the potential accumulation locations.

3.9. Conditions for actuation of the process interlocks based on the values of hydrogen-containing mixture parameters shall be determined and substantiated in the nuclear power plant design.

3.10. Measuring channels of the parameter monitoring system shall be checked in terms of metrology within the entire measurement range for parameters of hydrogen-containing mixture. The monitoring range for these parameters shall be determined and substantiated in the design.
 

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^* The hydrogen explosion protection systems include:

hydrogen-containing mixture combustion systems;
hydrogen-containing medium removal systems (including purification of the working medium and its discharge into the environment);
medium mixing systems;
systems of emergency and post-accident phlegmatization (dilution of hydrogen-containing mixture by injection of other gases (for example inert ones).

4. BASIC REQUIREMENTS FOR HYDROGEN EXPLOSION PROTECTION ASSURANCE AT NUCLEAR POWER PLANTS IMPLEMENTED IN THE COURSE OF OPERATION

4.1. Operation manuals shall be developed for hydrogen explosion protection systems and components

4.2. Operation manuals for hydrogen explosion protection systems and components shall specify the scope and frequency of maintenance, operability checks and scheduled repair of these systems and components. The results of inspections shall be presented in the form of a statement.

4.3. Monitoring of technical condition of the hydrogen explosion protection systems and components shall be performed in accordance with the requirements of operation manuals for hydrogen explosion protection systems and components.

4.4. Conditions for shutdown of hydrogen explosion protection systems and components for maintenance, operability checking and repair including the baseline minimum equipment for nuclear power plant safety assurance shall be determined.

4.5. Subsequent to repair of the systems and components providing hydrogen explosion protection they shall be checked for compliance with the design characteristics.

4.6. Hydrogen explosion protection systems and components shall be ready for operation from the beginning of reactor fueling, at all power levels including the minimum controlled power level and also within the period of scheduled preventive repair.

4.7. The operating organization shall monitor the useful operation time (service life) of the hydrogen explosion protection systems and components.

4.8. In the course of the nuclear power plant operation workers (personnel) shall be trained for operation of the hydrogen explosion protection systems and components and readiness of the personnel responsible for operation of the hydrogen explosion protection systems and components shall be controlled regularly.

Appendix

LIST OF POTENTIAL PROCESSES (SOURCES) LEADING TO HYDROGEN GENERATION^*

1. Under normal operation:

1.1. VVER type reactors:

• corrosion of structural materials;
• water radiolysis in the reactor core;
• water radiolysis in the spent fuel pool;
• release of hydrogen contained in the coolant in the course of repairs associated with loss of the primary circuit integrity.

1.2. RBMK type reactors:

• water radiolysis in the multiple forced circulation circuit and the control and protection system circuit in the course of the reactor power operation and during shutdown;
• water radiolysis in spent fuel pools;
• corrosion of structural materials.

1.3. BN type reactors:

• the process equipment assemblies where water is used as coolant (auxiliary heat exchangers, cooled blocks of pumps, gate valves, etc.);
• combination of sodium spillage or leakage and water ingress to the room;
• equipment cleaning from sodium;
• water radiolysis in the spent fuel pool and other systems where water might be exposed to intensive irradiation;
• interaction of sodium with oil under normal operation conditions and also with spirits or other liquids used for washing;
• contact of sodium with concrete.

1.4. For heat supply NPPs:

• coolant radiolysis in the reactor core;
• water radiolysis in the spent fuel pool;
• release of helium-hydrogen mixture from the reactor.

2. In case of accidents:

2.1. VVER, RBMK, BN type reactors:

• water and steam radiolysis in the core (for VVER and RBMK);
• water and steam radiolysis outside the core;
• discharge of hydrogen and oxygen contained in the reactor facility circuits before the accident;
• decomposition of ammonia contained in the coolant (for VVER);
• decomposition of hydrazine and ammonia dispensed into makeup water in case of any compensated leak (for VVER);
• decomposition of hydrazine contained in the hydroaccumulators and dispensed into safety systems from the tanks during accidents (for VVER);
• thermal dissociation of water (at temperatures exceeding 2000°C);
• zirconium-steam reaction;
• iron-steam reaction;
• steam-graphite reaction (for RBMK);
• corrosion of aluminum or zinc materials of heat insulation and structural components (for VVER and RBMK);
• corrosion of carbonic steel with damaged organic coating in boric acid solution (for VVER);
• interaction of uranium dioxide with water steam;
• nuclear fuel contact with concrete.

2.2. For heat supply NPPs:

• release of helium-hydrogen mixture from the reactor.

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^* The specific list for the nuclear power plant unit under development shall be determined in the design.