Internal hazards

ISSUE TITLE: Need for systematic fire hazards assessment (IH 1) ISSUE CLARIFICATION:

Description of issue

This issue is also applicable to NPPs with LWR.

In order to ensure safety, an adequate degree of fire protection should be provided in nuclear power plants. A fire hazards analysis including consequences of fire fighting should be performed before initial fuel loading and be updated during operation to verify that the main safety functions to shut down the reactor, to remove residual heat, and to contain radioactive material are maintained against the consequences of a fire.

The fire hazards analysis has six separate purposes:

• identification of items important to safety and their locations in fire compartments;

• analysis of the anticipated fire growth and the consequences of the fire and fire fighting activities with respect to items important to safety;

• determination of the required resistance of fire barriers;

• determination of the type of fire detection and protection means to be provided;

• identification of cases where additional separation or fire protection is needed, especially for common mode failures, to ensure that items important to safety will remain functional during and following a credible fire;

• verification that the safety systems to shut down the reactor, to remove residual heat and to contain radioactive material are designed against the consequences of a fire.

Fires in nuclear power plants have demonstrated that fire can be a major risk contributor to the overall plant safety. Licensees are required to ensure that their plant operations are such that risk from fire is minimal.

Safety significance

Previous systematic fire hazards analyses have shown, for particular plants, that accidents could be initiated and safety functions impaired as a consequence of a fire.

Source of issue (check as appropriate)

• ____xx____ operational experience

• ____xx____ deviation from current standards and practices

• ____xx____ potential weakness identified by deterministic or probabilistic (PSA) analyses

MEASURES TAKEN BY MEMBER STATES:

Argentina

Standard AR. 3.2.3 establishes the safety criteria against fire (or events generated by it) and explosions resulting from fire, that may affect a nuclear power plant radiological or nuclear safety.

These criteria include the stages of design, commissioning and operation of the installations. The fulfilment of the criteria contained in the above mentioned standard is verified through inspections carried out by inspectors and analysts of the Regulatory Body.

On the other hand, CNA-I and CNE have specific procedures of fire protection. Such procedures contain the description of fire compartments; the composition, responsibilities and functions of the fire brigade; the detection and alarm systems; the extinction systems; the fire-fighting drills and other aspects related to the fight against fire of permanent application in the nuclear power plants.

The PSA of CNA-I and CNE foresees the core damage evaluation due to an eventual fire that may be initiated at a set of areas of the installation known as fire compartments. The analysis methodology chosen enables the calculation of a core damage probability associated with each of the fire compartments before mentioned, in the case such fire occurs. This methodology comprises a set of tasks such as:

• Establishment of a general procedure for the fire risk analysis.

• Determination of fire compartments, fire barriers and fire propagation routes

• Calculation of fire propagation probability to adjacent fire compartments.

• Preparation of a list of affected components at each fire compartment and calculation of the corresponding failure probability rate due to fire.

• Calculation of the core damage probability associated with each fire compartment where a fire occurs.

The following software tools are used for the execution:

• Fire Database NUREG/CR 4586.

• COMPBURN III A computer code for modelling compartment fires - NUREG/CR 4566.

• Database of Fire Compartments

The analysis of the results will enable the determination of the highest risk fire compartments for the installation, and the improvements to be carried out either in components or compartments, in order to reduce their failure probabilities in case of fire.

This methodology implies an identification of fire-induced failures of components as well as of the several fire propagation routes; therefore it advantageously substitutes the classic failure analysis of common cause due to fire.

Canada

Regulatory Body:

The CNSC expects that the nuclear industry meet the relevant requirements set out in CSA Standard N293-95, “Fire Protection for CANDU Nuclear Power Plants”.

CNSC staff position can be summarized as follows:

• Fire protection is a key element in nuclear safety.

• Relevant codes and standards are applicable and their implementation contributes to overall safety.

• Fire hazards assessments, as living documents, are a sure way of ensuring the continued integrity of fire protection defence-in-depth.

• To maintain the designed benefit of defence-in-depth, the CANDU separation philosophy must be maintained and monitored.

• The effectiveness of emergency response provisions and preventive programs must be regularly and continually verified.

• Implementation of backfits at operating plants is essential to nuclear and occupant safety.

CNSC staff intends to produce a position statement addressing this generic action item. Licensees are expected to satisfy the closure criteria given in that position statement.

Industry:

CANDU 6 plants are designed to satisfy the CSA Standard CAN/CSA-N293-M87, “Fire Protection of CANDU Nuclear Power Plants”. It requires applying defence-in-depth in fire protection design. The concept consists of (1) fire prevention, (2) fire detection and suppression, and (3) mitigation of the effects of fires. For the mitigation of the effects of fire, separation criteria are established and applied in the cable routing.

A fire hazard analysis is now performed during the design stage to confirm that the fire protection concept is adequately applied.

Safe shutdown is assured by ensuring that either two independent and separate groups of systems can perform all necessary safety functions. Group 2 systems are functionally and physically separated from Group 1 systems and the use of either Group 1 or Group 2 systems alone can safely shutdown the plant and maintain it so. The cables for Group 2 systems are physically separated from those of the Group 1 systems including those for power, control and instrumentation signals.

China

It’s licensing requirement to apply systematic fire hazards assessment in TQNPP safety review.

India

After the Narora fire incident extensive review was instituted for all the Indian NPPs. The basic objective was to ensure that fire, as a common cause, would not prevent achieving, maintaining and monitoring of

a) shutting down of the reactor b) core cooling

c) confining activity.

This detailed study resulted in recommendation in the areas of design provisions, operational (including maintenance) practices organisational arrangements, quality assurance, etc. AERB standard on fire protection was issued and this incorporated – current international standards. While all new stations incorporate the provisions, the older stations have been asked to come up with an action plan.

.Standard “Fire Protection System of Nuclear Facilities” and Safety Guide “Fire Protection in Pressurized Heavy Water Reactor based Nuclear Power Plants” published by AERB are being referred for matters connected with Fire Safety. Standard is applicable to all nuclear facilities including power plants and is mandatory in nature specifying requirements during design and operation. The Safety Guide addresses the design issues only with respect to PHWRs and fire hazard analysis is the key element to arrive at fire safety requirements. For new projects preparation of Fire hazard Analysis Report is essential. However, for old projects Fire hazard Analysis is being carried out and systems are being upgraded by retrofitting. Based on the Fire Hazard Analysis report following jobs have been completed. Power and control cables have been segregated. Fire retardant coating on the critical cables has been applied and fire seals to all critical cables ensured. Installation of fire dampers has been completed. Fire barriers between seal oil units, main oil tank, turbine oil tank, and diesel generator, class-II and class-III switch gears and fire water pumps have been installed. Supplementary control room has been set up where not existing and where not possible it has been ensured that essential equipment can be started from local control points/ breaker compartment. Additional DG firewater pump and sprinkler system to cover seal oil unit and oil piping has been installed.

Augmentation of detection and suppression system has been completed based on Fire hazard analysis.

Relocation of non-automatic sprinkler system valves for turbine building areas has been carried out for improved access. Based on the Fire Hazard Analysis report installation of fire dampers in Turbine

building ventilation system and upgradation of fire alarm system at MAPS has been completed. Cable route segregation was done at KAPS.

Korea, Republic of See SS 3

Romania

Cernavoda NPP unit 1 is designed in accordance with the basic design requirements on fire protection, i.e. the use of the safety systems separation on groups as a mean for protection to common cause failures due to fire. There is also, in addition to these aspects, a requirement for a fire hazard review of the plant to be done in accordance with the IAEA documents. The study is being developed under EU project with the information of the regulatory body. A future inclusion of the results of this study is required after the PSA level 1 completion by the end of 2002.

ADDITIONAL SOURCES:

• INTERNATIONAL ATOMIC ENERGY AGENCY, Protection against Internal Fires and Explosions in the Design of Nuclear Power Plants Safety Guide, IAEA Safety Standards Series No.

NS-G-1.7, IAEA, Vienna (2004).

• INTERNATIONAL ATOMIC ENERGY AGENCY, Fire Safety in the Operation of Nuclear Power Plants Safety Guide, IAEA Safety Standards Series No. NS-G-2.1, IAEA, Vienna (2000).

• INTERNATIONAL ATOMIC ENERGY AGENCY, Evaluation of Fire Hazard Analyses for Nuclear Power Plants: A Safety Practice, Safety Series No. 50-P-9, IAEA, Vienna (1995).

• INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of the Overall Fire Safety Arrangements at Nuclear Power Plants: A Safety Practice, Safety Series No. 50-P-11, IAEA, Vienna (1996).

• INTERNATIONAL ATOMIC ENERGY AGENCY, Preparation of Fire Hazard Analyses for Nuclear Power Plants, Safety Reports Series No. 8, IAEA, Vienna (1998).

• INTERNATIONAL ATOMIC ENERGY AGENCY, Treatment of Internal Fires in Probabilistic Safety Assessment for Nuclear Power Plants, Safety Reports Series No. 10, IAEA, Vienna (1998).

• INTERNATIONAL ATOMIC ENERGY AGENCY, Organization and Conduct of IAEA Fire Safety Reviews at Nuclear Power Plants, IAEA Services Series No. 2, IAEA, Vienna (1998).

• Canadian Standard CSA N293-95 “Fire Protection for CANDU Nuclear Power Plants”.

• Standard NFPA N-805 (proposed).

• National Canadian Building and Fire Codes.

• Strategic Policy for Cernavoda NPP Unit 2 licensing process, CNCAN 1997.

• FSAR Cernavoda Unit 1, 1995.

• Strategic Policy for Cernavoda NPP Unit 1 relicensing in May 2001, CNCAN March 2000.

• AERB, Standard for Fire ProtectionSystems of Nuclear Facilities, AERB/S/IRSD-1(1996).

• AERB, Fire Protection in Pressurised in Pressurised Heavy Water ReactorBased Nuclear Power Plants, AERB/SG/D-4(1999).

ISSUE TITLE: Adequacy of fire prevention and fire barriers (IH 2) ISSUE CLARIFICATION:

Description of issue

This issue is also applicable to NPPs with LWR.

In order to ensure safety, an adequate degree of fire protection should be provided in nuclear power plants. This should be achieved by a defence-in-depth concept including the prevention of fires from starting. In designing the plant, the amount of combustible materials and the fire load should be kept to a reasonably achievable minimum and operation or failure of any plant system should not cause fire. The on-site use and storage of combustible materials in areas adjacent to or containing items important to safety should be controlled.

In order to maintain the function of the safety systems to shutdown the reactor, to remove residual heat, and to contain radioactive material, they should be protected against the consequences of a fire.

The redundant parts of safety systems should be sufficiently segregated from each other so that a fire affecting one redundancy will not prevent the safety systems from performing the required safety functions. Fire barriers between redundant systems should be qualified to fulfil their protective functions considering the time specified with the fire hazards analyses and the presence of automatic fire suppression system.

Safety significance

Insufficient protection against common mode failures due to fire would impair defence in depth.

Safety functions could then be questionable, depending on the loss of redundant trains during DBA scenarios.

Source of issue (check as appropriate)

• ____xx____ operational experience

• ____xx____ deviation from current standards and practices

• ____xx____ potential weakness identified by deterministic or probabilistic (PSA) analyses

MEASURES TAKEN BY MEMBER STATES:

Argentina See also IH 1.

Canada

The fire barriers between fire zones are designed based on the results of the fire hazards analysis. The fire barriers are tested according to the CSA Standard or an equivalent standard. Some of the concerns on fire propagation due to transient combustible materials are explicitly addressed in the fire hazard analysis and are transferred to operating personnel as inputs for developing the plant-specific fire protection programs.

See IH1.

India

Detailed fire hazard analysis is done in critical area to estimate fire load. Maximum rise in temperature in case of imaginary fire and duration of fire is estimated. Based on the information designing of fire barriers are taken up. This Fire prevention measures include use of High ignition temperature lubricating oil, use of Fire resistance Low smoke cable and special type of insulation and house keeping. Grass should be cut before it becomes dry and cut grass removed. Areas of challenging decision making is whether to provide a manual big sized pipe to quickly empty turbine lubricating system main oil tank to reduce amount of combustible in case of adjacent fire as inadvertent actuation can be disastrous to the turbine bearing. Sharing of position of member states on this issue would be useful. Fire Barriers have been provided on the cable penetration on the wall and on the floor to prevent spread of fire through cable penetrations. At RAPS-1 during upgradation of Fire Safety system 211nos of fire barriers were identified. (Reactor bldg: 53,Turbine bldg: 115,Service bldg: 40, Auxiliary bldg: two and DG-6: 01 number). Job has already been completed. This coating has been applied on all power and control cables both at the equipment end and at the source end. For power cables this coating is applied for 2 meters length at every 6 meters intervals in horizontal run of the cable trays while this coating is applied in entire length of the cable in vertical run of cable trays. Fire retardant paint coatings (Fire breaks) are subjected to chimney test. During test, it is to be confirmed that fire will not propagate beyond the portion of the cable coating for duration of half an hour. Fire doors conforming to IS-3614 are provided as means to confine fire to the room where it is originated.

During up gradation of fire safety system eleven fire doors of three hours rating have been installed in various locations to segregate group A & B areas in RAPS-1. Proper design, selection and testing of fire barriers are important but their maintenance during operation, especially after modification is equally vital. The reason for spreading of fire to some vital areas during Narora fire incident was due to lack of quality assurance resulting in inadequate restoration of a few fire barriers after modification was carried out.

After detailed studies instituted at each NPPs some equipment were relocated. Example; hydrogen addition station for the turbine generator.

Korea, Republic of

Wolsung units 3 and 4, a fire protection program is established to meet the CAN/CSA-N293-M87(Fire Protection for CANDU NPP) and Korea fire protection laws. In accordance with that fire protection program, KEPCO are controlling the storage of combustible materials and handling the electric or hot work equipments. And, Wolsung units 3 and 4 are designed to use non-combustible materials, as far as practical. In case of fire, to minimize the release of the radioactive material and reduce the consequences of fire, they maintain the necessary safety function to shutdown the reactor in accordance with operation procedure. Fire area and fire barriers between redundant systems are installed in accordance with the fire hazard analyses and the fire suppression systems.

Pakistan

In accordance with NUSS Safety Guide and international practice, an adequate degree of fire protection is to be provided in NPPs. The objective is to prevent fires from starting i.e. fire prevention. One of the main concerns at KANUPP is that most of the redundant equipment, components and cable trains of safety important systems are not physically separated and not protected against fire spreading. Other concern is related to inadequate protection against oil fires.

Although, a lot of work has been undertaken by KANUPP in the past few years to improve fire detection and protection capabilities; however, PNRA observed that some deficiencies still exist, which has serious consequences on the plant safety. For example:

1. Redundant equipment, component and cable trains of safety and safety related systems are located without sufficient physical separation and are not protected against fire spreading. A fire could thus lead to loss of more than one redundancy of safety important systems.

2. Protections against oil fires are far below the satisfactory level.

KANUPP has been required to implement a comprehensive fire prevention and control program and carry out a fire PSA. Install fire barriers wherever required to:

• Segregate safety related cables as practical as possible.

• Improve habitability of control room or establish an Emergency Control Room (ECR).

Improve fire detection and suppression capability on potential fire hazard areas, especially in Turbine hall and around Primary Pumps in reactor building.

Romania Similar to IH 1

ADDITIONAL SOURCES:

• INTERNATIONAL ATOMIC ENERGY AGENCY, Protection against Internal Fires and Explosions in the Design of Nuclear Power Plants Safety Guide, IAEA Safety Standards Series No.

NS-G-1.7, IAEA, Vienna (2004).

• INTERNATIONAL ATOMIC ENERGY AGENCY, Fire Safety in the Operation of Nuclear Power Plants Safety Guide, IAEA Safety Standards Series No. NS-G-2.1, IAEA, Vienna (2000).

• INTERNATIONAL ATOMIC ENERGY AGENCY, Inspection of Fire Protection Measures and Fire Fighting Capability at Nuclear Power Plants: A Safety Practice, Safety Series No. 50-P-6, IAEA, Vienna (1994).

ISSUE TITLE: Adequacy of fire detection and extinguishing (IH 3) ISSUE CLARIFICATION:

Description of issue

This issue is also applicable to NPPs with LWR.

In order to ensure safety, an adequate degree of fire protection should be provided in nuclear power plants. This should be achieved by a defence in depth concept including fire detection and extinguishing. A nuclear power plant should have a sustained capability for early detection and effective extinguishing of a fire to protect items important to safety.

Fire protection and extinguishing systems of appropriate capacity, capability, and qualification should be provided to give timely alarm and or actuation so as to enable speedy extinguishing of the fire and to minimize the adverse effects of fires on personnel and on items important to safety.

In order to maintain the function of the safety systems to shutdown the reactor, to remove residual heat, and to contain radioactive material, they should be protected against the consequences of a fire.

The redundant parts of safety systems should be protected such that a fire affecting one redundancy

The redundant parts of safety systems should be protected such that a fire affecting one redundancy

Dans le document Generic Safety Issues for Nuclear Power Plants with Pressurized Heavy Water Reactors and Measures for their Resolution | IAEA (Page 160-180)