[en] The paper presents a retrospective assessment of the use of ASSET methodology in India since the first ASSET seminary organized by IAEA in collaboration with the Atomic Energy Regulatory Board, India (AERB) in May, 1994. The first ASSET seminar was organized to initiate the spread of idea among operating and research organizations and regulatory body personnel. The participants were carefully chosen from various fields and with different levels of experiences to generate teams with sufficiently wide spectrum of knowledge base. AERB took initiative in leading by example and formed ASSET teams to carry out the first ASSET reviews in India. These teams at the instance of AERB carried out ASSET review of three Safety Related Events, two at Nuclear Power Plants and one at Research Reactor. This paper describes the outcome of these ASSET studies and subsequent implementation of the recommendations. The initiative taken by the regulatory body has led to formation of ASSET teams by the utilities to carry out ASSET study on their own. The results of these studies are yet to be assessed by the regulatory body. The result of the ASSET experience reveals the fact that it has further potential in improving the safety performance and safety culture and brining in fresh enthusiasm among safety professionals of Indian Nuclear Utilities

[en] Indian nuclear power generation programme started with commissioning of twin unit BWRs at Tarapur way back in 1969. Today 14 units, mostly PHWRs, with total installed capacity of 2720 MW are in operation and eight units with installed capacity of 3880 MW are under various stages of construction. The new plants are built to current standards and employ the present day technology and hence easily meet the present day safety requirements. The old plants obviously cannot meet these requirements to the same extent since they were built to the standards that existed at the time of their construction. AERB therefore has instituted certain mechanisms/procedures to address the issue of re-licensing vintage plants. License Renewal, Periodic Safety Review (PSR) and Life Extension programmes are used as regulatory tools for authorizing continued operation of NPPs with high level of safety. The regulatory criteria evolve continuously based on operating experience, identified generic safety issues and new developments in technology. The licensing as well as re-licensing procedure in India is designed to respond to these evolving safety criteria. Technical assessment of components with respect to ageing, Review of the original design basis along with Final Safety Analysis Reports, Life assessment of irreplaceable equipment, structures and components and Plant specific PSAs and their relationship to the traditional deterministic methods are identified as key issues in the relicensing or safety upgradation process. This paper deals with the present approach and regulatory mechanisms being followed for life extension and safety upgradation in Indian NPPs. Also, the safety upgradation and license renewal of older Pressurized Heavy Water Reactors (PHWRs) and Life extension studies carried out in vintage Boiling Water Reactor (BWR) are described. (author)

[en] Atomic Energy Regulatory Board (AERB), the authority for licensing and monitoring safety in Indian Nuclear Power Plants (NPPs), makes use of insights gained from PSA together with the results of the other deterministic analyses in taking decisions regarding the acceptability of the safety of the NPPs. PSA provides an estimation of risks; it also gives information on a balanced design by revealing interaction between engineered features and weak areas in a design. For regulatory use, PSA needs to be carried out using standardized methodology and state of the art technology. PSA helps regulators in taking faster and consistent decisions. Keeping in mind the limitations associated with PSA study, AERB has decided to adopt risk-informed decision making in regulatory licensing process. This paper describes the AERB policy regarding PSA and gives an overview of the experience in this area. (author)

[en] The Indian nuclear power generation programme started with the commissioning of twin unit BWRs at Tarapur way back in 1969. Today 14 units, mostly PHWRs, with total installed capacity of 2720 MW are in operation and eight units with installed capacity of 3880 MW are under various stages of construction. The new plants are built to current standards and employ the present day technology and hence easily meet the present day safety requirements. The old plants obviously cannot meet these requirements to the same extent since they were built to the standards that existed at the time of their construction. The Atomic Energy Regulatory Board (AERB) therefore has instituted certain mechanisms and procedures to address the issue of relicensing vintage plants. Licence renewal, periodic safety review (PSR) and life extension programmes are used as regulatory tools for authorizing continued operation of nuclear power plants with a high level of safety. The regulatory criteria evolve continuously, based on operating experience, identified generic safety issues and new developments in technology. The licensing as well as relicensing procedure in India is designed to respond to these evolving safety criteria. The technical assessment of components with respect to ageing, review of the original design basis along with final safety analysis reports, life assessment of irreplaceable equipment, structures and components, and plant specific PSAs and their relationship to the traditional deterministic methods are identified as key issues in the relicensing or safety upgrading process. The paper deals with the present approach and regulatory mechanisms being followed for life extension and safety upgrading in Indian nuclear power plants. Also, the safety upgrading and licence renewal of older PHWRs and life extension studies carried out in vintage BWRs are described. (author)

[en] Subsequent to the accident at the Fukushima Daiichi nuclear plant extensive lessons has been learnt through special safety review conducted for enhancing safety of India NPPs as well as through the inputs received as a result of safety review by International agencies like IAEA and NEA. Results of those lessons learnt has been translated in to implementable actions/measures with the consensus of all stake holders and timely implement them through appropriate follow-up and enforcement measure was a gigantic task. With the implementation of the identified safety enhancement measures, Indian NPPs capability to deal with beyond design basis events and severe external events such as tsunamis, cyclones, floods etc. has improved. These safety enhancement measures have been provided in addition to the design features incorporated in the NPPs as per AERB’s requirement to withstand any design basis event, thereby improving the overall safety of the plant

[en] The use of state of art digital instrumentation and control (I and C) in safety and safety related systems (like reactor power regulation, reactor shutdown etc.) in nuclear power plants has gained importance due to the performance in terms of accuracy, computational capabilities and data archiving capability for future diagnosis. Added advantages in computer based systems are fault tolerance, self-testing, signal validation capability and process system diagnostics. But, uncertainty exists about the quality, reliability, performance and security of such software based nuclear instrumentation which poses new challenges for the nuclear industry and regulators in using them for safety and safety related systems. Therefore, it becomes mandatory to demonstrate that these systems are reliable, safe and secure. To obtain adequate confidence in licensing them for use in NPPs, digital I and C were deployed gradually from monitoring system to control system (i.e. non-safety, safety related and lastly safety systems). Based upon the experience over a decade, AERB safety guide AERB/SG/D-25 was prepared to prescribe the criteria and requirements to assess the qualitative reliability of digital I and C. The detail regulatory requirements for the use of FPGA and CPLD in nuclear applications are being worked out for addition in this document. This paper elaborates gradual deployment of digital I and C system in Indian NPPs. It covers the AERB approach for regulatory review and audit process for digital I and C as recommended in AERB safety guide AERB/SG/D-25. Further, aspects like Configuration Management (due to operation feedback, introduction of additional features and obsolescence), use of software developer tools and security of the digital I and C systems are mentioned. (author)

[en] Regulators have an important role to play in assisting organizations under their jurisdiction to develop positive safety cultures. It is therefore essential for the regulator to have a robust safety culture as an inherent strategy and communication of this strategy to the organizations it supervises. Atomic Energy Regulatory Board (AERB) emphasizes every utility to institute a good safety culture during various stages of a NPP. The regulatory requirement for establishing organisational safety culture within utility at different stages are delineated in the various AERB safety codes which are presented in the paper. Although the review and assessment of the safety culture is a part of AERB’s continual safety supervision through existing review mechanism, AERB do not use any specific indicators for safety culture assessment. However, establishing and nurturing a good safety culture within AERB helps in encouraging the utility to institute the same. At the induction level AERB provides training to its staffs for regulatory orientation which include a specific course on safety culture. Subsequently, the junior staffs are mentored by seniors while involving them in various regulatory processes and putting them as observers during regulatory decision making process. Further, AERB established a formal procedure for assessing and improving safety culture within its staff as a management system process. The paper describes as a case study the above safety culture assessment process established within AERB

[en] Achievement of high safety standard is essential for ensuring sustainability of nuclear power generation. Regulatory requirements for ensuring safety in design is very crucial so that due priority is given to safety during design of NPPs. These requirements need to be changed from time to time in order to refresh the concepts and goals of safety with evolution of technology accommodating innovations, experience from design, construction and operation as well as experience from major nuclear events in the world. Public expectations of safety, socio economic situations and demographic conditions plays a major role in framing safety goals. Large scale contamination of land and crops or relocation of public living in the vicinity of NPPs for indefinite time frame has become unacceptable. AERB recently published ‘Safety Code on Design of Light Water Reactor Based Nuclear Power Plants,’ stating mandatory requirements for design of light water based Nuclear Power Plants (NPP), intended to ensure the highest level of safety that can reasonably achieved. New requirements redefined the concept of ‘Defence in Depth’ by introducing ‘Design Extension Conditions’ (DEC) in National safety regulation. The code also specifies requirements with respect to public dose for Design Basis Accidents and Design Extension Conditions and provides regulatory approach in the area of beyond design basis including severe accidents as well as extreme/unexpected events. (author)

[en] Experimental studies have shown that there is heat transfer enhancement (HTE) for supercritical fluid near the pseudocritical temperature at relatively low heat flux to mass flux ratios. At very high values of heat flux, a peak in wall temperature appears due heat transfer deterioration (HTD). In the present research work R22 has been selected as working fluid as the simulant fluid for water. A supercritical Freon test facility is then designed and built. Two vertical tubular test sections of ID equal to 6 mm and 13.5 mm are employed. Experiments with vertically upward flow at 55 bar system pressure were carried out. Thermal camera is used to obtain wall temperatures at distances about 1-1.5 mm apart. Experiments were conducted with water before using R22 to validate experimental procedure. Initial experiments with R22 were conducted to demonstrate the reduction in peak heat transfer enhancement with increase in heat flux. Experiments are then conducted at several heat and mass flux values and inlet temperature. It is observed from experimental results that onset of HTD occurs when q/G more than 0.056 to 0.072 (kJ/kg). When the inlet temperature is lowered, the onset of HTD appears at relatively high q/G. The bulk fluid enthalpy and temperature at which onset of HTD appears also reduces when the inlet temperature was decreased. At the lower inlet temperature, two peaks in wall temperature were observed in the experimental results

[en] Achievement of high safety standard is essential for ensuring sustainability of nuclear power generation. Regulatory requirements for ensuring safety in design is very crucial so that due priority is given to safety during design of NPPs. These requirements need to be changed from time to time in order to refresh the concepts and goals of safety with evolution of technology accommodating innovations, experience from design, construction and operation as well as experience from major nuclear events in the world. Public expectations of safety, socio economic situations and demographic conditions plays a major role in framing safety goals. Large scale contamination of land and crops or relocation of public living in the vicinity of NPPs for indefinite time frame has become unacceptable. AERB recently published ‘Safety Code on Design of Light Water Reactor Based Nuclear Power Plants,’ stating mandatory requirements for design of light water based Nuclear Power Plants (NPP), intended to ensure the highest level of safety that can reasonably achieved. New requirements redefined the concept of ‘Defence in Depth’ by introducing ‘Design Extension Conditions’ (DEC) in National safety regulation. The code also specifies requirements with respect to public dose for Design Basis Accidents and Design Extension Conditions and provides regulatory approach in the area of beyond design basis including severe accidents as well as extreme/unexpected events. (author)