ASME NUCLEAR

ASME NUCLEAR

Forging a New Nuclear Safety Construct

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Introduction

The Great East Japan Earthquake and Tsunami inflicted major loss of life and destruction of property on the Nation of Japan, as well as substantial devastation of its environment. Emergency response capabilities were overtaxed and often overwhelmed. Furthermore, the extraordinary natural forces unleashed on the East Japan coastal areas led to a series of accident-initiating events that resulted in the inability to cool the reactor cores in three operating units of the Fukushima Dai-ichi Nuclear Plant, also referred to as Fukushima. Loss of core cooling in Units 1, 2, and 3 led to core degradation and fuel melting. Subsequently, continuing lack of core cooling led to loss of the reactor coolant pressure boundary, loss of containment integrity, and hydrogen explosions from zirconium cladding-water reactions, followed by large radioactivity releases to the environment from all three units. Radiological protection of the public necessitated evacuation of populated areas up to 30 km or nearly 19 miles from the plant.

Due to the current and expected absence of discernible radiation health effects, radiological protection of public health and safety appears to have been effective in Japan; however, the multi-unit nuclearplant accident at Fukushima continues to have serious impacts on socio-political, economic and energy-related issues in Japan, as well as globally, and has received extensive Government and media attention worldwide. The accident at the Fukushima plant has already affected energy portfolios by skewing the importance of nuclear electricity generation and its beneficial impacts on fuel diversification, climate change initiatives, and stability of electrical costs.

The ASME Presidential Task Force on Response to Japan Nuclear Power Events (ASME Task Force) is convinced that global and thoughtful solutions to the issues raised by the Fukushima Dai-ichi nuclear accident are essential to continue benefitting from use of nuclear power, to expand its use, and to address critical environmental and energy portfolio issues. The ASME Task Force is proposing an extended safety framework that would add complementary improvements to the existing nuclear safety infrastructure in a systematic manner, strengthening safety and accident response to external and internal events. The proposed improvements are focused on prevention or minimization of major impacts on public health, the environment, and socio-political-economic issues from large accidental releases of radioactivity. To achieve these objectives, the ASME Task Force supports development of a new safety construct for nuclear power generation, as described in this report, which enhances the existing safety framework using an all-risk approach.

The term "construct" denotes the conjunction of component parts that, working together, achieve a desired outcome. For nuclear power plants, the existing and evolving safety construct incorporates a set of elements, including plant design, physical systems, structures, and components, safety regulations, quality assurance, and procedures and practices for plant operation and maintenance, accident management, and emergency preparedness.

The term "all-risk," as used in this report, refers to consideration of all credible hazards in developing probabilistic risk assessments (PRAs), assessing defense-in-depth, and developing accident management strategies. Risk is the combination of the probability of an adverse event and its consequences. Protection of public health and safety and the environment are and will continue to be the most important consideration for nuclear safety. Complements to the existing and evolving safety construct would further strengthen the protection of public health and safety. The additional consequence of concern in the new safety construct is extensive disruption of society from a radioactivity release to the environment.

"All risks" should be considered to include rare yet credible events and potential accident scenarios that could threaten the safety of a nuclear power plant. Accident scenarios can be initiated by either internal or external hazards from natural or man-made causes, during all modes of plant operation.

Addressing rare yet credible events with extreme consequences should be limited by appropriate risk considerations. In this regard, it is important to rely on the rule of law, using what the Courts have determined is acceptable for nuclear power safety: "The level of adequate protection need not, and almost certainly will not, be the level of zero risk." [1]

Events that are not credible need not be considered. It is the intention of the ASME Task Force that very-low-probability events, such as extreme floods, large scale tornadoes, and other natural phenomena that are unprecedented but conceivable at a given site, should be considered. Of particular concern are initiating events that could lead to cliff-edge effects, whereby for a small incremental increase in severity, the consequences disproportionally increase. In those cases, systems and planned actions should be in place to provide core cooling and prevent a large release of radioactivity.

Organization: ASME International
Document Number: asme nuclear
Publish Date: 2012-06-14
Page Count: 112
Available Languages: EN
DOD Adopted: NO
ANSI Approved: NO
Most Recent Revision: YES
Current Version: YES
Status: Active

Publication Date: 06/14/2012 - Complete Document

Description :

Introduction

The Great East Japan Earthquake and Tsunami inflicted major loss of life and destruction of property on the Nation of Japan, as well as substantial devastation of its environment. Emergency response capabilities were overtaxed and often overwhelmed. Furthermore, the extraordinary natural forces unleashed on the East Japan coastal areas led to a series of accident-initiating events that resulted in the inability to cool the reactor cores in three operating units of the Fukushima Dai-ichi Nuclear Plant, also referred to as Fukushima. Loss of core cooling in Units 1, 2, and 3 led to core degradation and fuel melting. Subsequently, continuing lack of core cooling led to loss of the reactor coolant pressure boundary, loss of containment integrity, and hydrogen explosions from zirconium cladding-water reactions, followed by large radioactivity releases to the environment from all three units. Radiological protection of the public necessitated evacuation of populated areas up to 30 km or nearly 19 miles from the plant.

Due to the current and expected absence of discernible radiation health effects, radiological protection of public health and safety appears to have been effective in Japan; however, the multi-unit nuclearplant accident at Fukushima continues to have serious impacts on socio-political, economic and energy-related issues in Japan, as well as globally, and has received extensive Government and media attention worldwide. The accident at the Fukushima plant has already affected energy portfolios by skewing the importance of nuclear electricity generation and its beneficial impacts on fuel diversification, climate change initiatives, and stability of electrical costs.

The ASME Presidential Task Force on Response to Japan Nuclear Power Events (ASME Task Force) is convinced that global and thoughtful solutions to the issues raised by the Fukushima Dai-ichi nuclear accident are essential to continue benefitting from use of nuclear power, to expand its use, and to address critical environmental and energy portfolio issues. The ASME Task Force is proposing an extended safety framework that would add complementary improvements to the existing nuclear safety infrastructure in a systematic manner, strengthening safety and accident response to external and internal events. The proposed improvements are focused on prevention or minimization of major impacts on public health, the environment, and socio-political-economic issues from large accidental releases of radioactivity. To achieve these objectives, the ASME Task Force supports development of a new safety construct for nuclear power generation, as described in this report, which enhances the existing safety framework using an all-risk approach.

The term "construct" denotes the conjunction of component parts that, working together, achieve a desired outcome. For nuclear power plants, the existing and evolving safety construct incorporates a set of elements, including plant design, physical systems, structures, and components, safety regulations, quality assurance, and procedures and practices for plant operation and maintenance, accident management, and emergency preparedness.

The term "all-risk," as used in this report, refers to consideration of all credible hazards in developing probabilistic risk assessments (PRAs), assessing defense-in-depth, and developing accident management strategies. Risk is the combination of the probability of an adverse event and its consequences. Protection of public health and safety and the environment are and will continue to be the most important consideration for nuclear safety. Complements to the existing and evolving safety construct would further strengthen the protection of public health and safety. The additional consequence of concern in the new safety construct is extensive disruption of society from a radioactivity release to the environment.

"All risks" should be considered to include rare yet credible events and potential accident scenarios that could threaten the safety of a nuclear power plant. Accident scenarios can be initiated by either internal or external hazards from natural or man-made causes, during all modes of plant operation.

Addressing rare yet credible events with extreme consequences should be limited by appropriate risk considerations. In this regard, it is important to rely on the rule of law, using what the Courts have determined is acceptable for nuclear power safety: "The level of adequate protection need not, and almost certainly will not, be the level of zero risk." [1]

Events that are not credible need not be considered. It is the intention of the ASME Task Force that very-low-probability events, such as extreme floods, large scale tornadoes, and other natural phenomena that are unprecedented but conceivable at a given site, should be considered. Of particular concern are initiating events that could lead to cliff-edge effects, whereby for a small incremental increase in severity, the consequences disproportionally increase. In those cases, systems and planned actions should be in place to provide core cooling and prevent a large release of radioactivity.

Document Type : Complete Document

Language : English

Page Count : 112

Publication Date : 06/14/2012

Revision : 12

Status : Current

Title : Forging a New Nuclear Safety Construct

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