Resolution of Generic Safety Issues: Task CH3: Containment (Rev. 1) ( NUREG-0933, Main Report with Supplements 1–35 )
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The Chernobyl accident, with its absence of effective containment, has focused attention on the strengths and performance limits of the substantial containments for U.S. LWRs. It has led to added recognition of the significance of ongoing work on the issue of whether U.S. containments that were built using criteria based on DBAs have adequate margins available to prevent the release of large quantities of fission products during severe accidents. Challenges include phenomena such as increased pressures from an uncontrolled hydrogen combustion or release of large quantities of noncondensible gases from core-concrete interactions. Venting the containment in case of certain severe accidents could be an effective way to preserve the long-term containment functional integrity and reduce the uncontrolled release of radioactive material. This task, outlined in Chapter 3 of NUREG-1251,1174 summarizes the activities already in place in the areas of containment integrity and containment venting.
ITEM CH3.1: CONTAINMENT PERFORMANCE DURING SEVERE ACCIDENTS
This item consists of one recommendation that is evaluated below.
ITEM CH3.1A: CONTAINMENT PERFORMANCE
DESCRIPTION
This issue called for the staff to determine whether the Chernobyl containment failure indicates that changes in U.S. containment or reactor design and operation requirements are warranted. In addressing this issue, the staff is expected to reflect Chernobyl experience, where relevant, in containment reviews under the Commission's Severe Accident Policy.
An existing set of tasks relating to adequate containment performance was underway in the U.S. before the Chernobyl accident. These tasks (IPE, the development of accident management strategies, containment performance, and NUREG-1150)1081 are related to determining whether the existing design and operation of U.S. commercial reactors provide an adequate level of safety or whether changes in regulatory guidance are required. The Chernobyl accident adds to the information base only indirectly because of differences in reactor types and containment (or confinement) approaches.
In pursuing this issue, the staff is expected to increase its knowledge, certainty, and understanding of safety issues in order to increase its confidence in assessing levels of safety. Therefore, the issue considered is to be a licensing issue.
CONCLUSION
Efforts to address this issue were underway, as noted in SECY-87-297. No separate projects or assessments were envisaged.
As a part of the improvements to NUREG-0933, the NRC staff clarified in SECY-11-0101, "Summary of Activities Related to Generic Issues Program," dated July 26, 2011,1967that the Generic Issues Program will not pursue any further actions toward resolution of licensing and regulatory impact issues. Because licensing and regulatory impact issues are not safety issues by the classification guidance in the legacy Generic Issues Program, these issues do not meet at least one of the Generic Issues Program screening criteria and do not warrant further processing in accordance with Management Directive 6.4, "Generic Issues Program," dated November 17, 2009.1858 Therefore, this issue will not be pursued any further in the Generic Issues Program.
ITEM CH3.2: FILTERED VENTING
This item consists of one recommendation that is evaluated below.
ITEM CH3:2A: FILTERED VENTING
The issue called for the staff to determine whether U.S. containments should be backfitted with filtered vents to mitigate the consequences of severe accidents as is being proposed and implemented in Europe. The Chernobyl accident heightened interest in this issue, though the issue itself has no specific Chernobyl counterpart. The purpose of this issue is to develop information to be used in assessing filtered vents proposed for U.S. reactors and to advise the Commission on whether such systems should be required for specific categories of U.S. reactors. The staff will assess the filtered venting technology emerging from European research and applications for potential U.S. reactor severe accident improvements. This work is a non-distinguishable part of the development of accident management strategies and containment performance assessments.
In pursuing this issue, the staff is expected to increase its knowledge, certainty, and understanding of safety issues in order to increase its confidence in assessing levels of safety. Therefore, the issue considered is to be a licensing issue.
CONCLUSION
As reported in the Supplement to NUREG-0933 published in 1989, venting was being studied by INEL under staff contracts. This study required an assessment of European research and applications and keeping abreast of relevant literature and participation in international evaluation activities. One such activity was the Nuclear Energy Senior Group of Experts on Severe Accidents meeting on Filtered Containment Venting Systems held in May 1988 in Paris and the preparation of a "white paper" on the technology and related issues. No separate projects or assessments arising from Chernobyl were envisaged.
As a part of the improvements to NUREG-0933, the NRC staff clarified in SECY-11-0101, "Summary of Activities Related to Generic Issues Program," dated July 26, 2011,1967 that the Generic Issues Program will not pursue any further actions toward resolution of licensing and regulatory impact issues. Because licensing and regulatory impact issues are not safety issues by the classification guidance in the legacy Generic Issues Program, these issues do not meet at least one of the Generic Issues Program screening criteria and do not warrant further processing in accordance with Management Directive 6.4, "Generic Issues Program," dated November 17, 2009.1858 Therefore, this issue will not be pursued any further in the Generic Issues Program.
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