The objective of this series of workshops is to enhance knowledge in the characterization of Prestressed Concrete Containment Vessels (PCCVs) and to assess the current practices and state of the art with respect to the calculation of response to severe accident conditions. The Round Robin is an opportunity to improve knowledge in the following areas: (1) local containment behavior under beyond design basis pressures, (2) characterization of leakage behavior as a function of pressure and temperature, and (3) probabilistic aspects of containment response.
The Round Robin Analysis on Containment Performance involves the assessment of the ultimate load capacity of a Prestressed Concrete Containment Vessel (PCCV) structure. This will be done in two stages.
The first stage of the Round Robin Analysis will examine local effects in the containment model. The local effects being proposed for consideration include:
- the behavior of tendon forces as a function of containment dilation,
- the friction models used to represent slippage of prestressing cables,
- the steel-concrete interaction surrounding penetrations,
- the failure mechanisms in the liner,
- and the use of nominal design parameters versus in-situ material properties and boundary conditions.
This stage will be principally based on the data of 1:4 scale model containment tests carried out at Sandia National Laboratories (SNL) between July of 2000 and November of 2001.
The second stage will focus on characterization of leakage behavior of containment vessels as a function of pressure and temperature. This stage will involve predicting leak rate as a probabilistic function of pressure and temperature in an effort to determine the significance and applicability of standard assumptions used when assessing containment structures, and to recast containment analysis conclusions into a containment performance framework.
Summary of Prior Efforts
The AERB, in conjunction with the US Nuclear Regulatory Commission (USNRC) and SNL, is interested in initiating collaboration in research and development on concrete containment structure designs. As part of this effort, the AERB and USNRC are sponsoring the Round Robin Analyses as part of the Standard Problem Exercise (SPE) #3 effort.
This effort is related to the USNRC-sponsored Containment Integrity Programs at SNL. These programs investigated the behavior of light water reactor (LWR) containment buildings under loadings that exceed the design basis or so-called “severe” accident loads. A combination of experimental and analytical studies was employed in these programs. Initially, over-pressurization tests of several scale model containment buildings were conducted under the programs: “Concrete Containment Experiments,” and “Experiments on Containment Models under Extreme Loading Conditions.”
Separate tests of typical containment penetrations were conducted under the “Integrity of Containment Penetrations under Severe Accidents Loads” program. Tests of electrical penetration assemblies (EPAs), a personnel airlock, bellows, a pressure-unseating equipment hatch, and the seals and gaskets used in penetrations were included in this program.
In 1990-1991, a cooperative program on containment integrity under severe accident conditions between the NRC and the Nuclear Power Engineering Corporation (NUPEC) of Japan was begun. Testing and analyses of a steel containment vessel (SCV) model representative of a BWR, Mk-II containment and a PCCV model, as used in some large, dry PWR containments, were funded.
Efforts were also made to assess the seismic capacity of containment structures. SNL performed pre- and post-test analyses of shaking table tests of a 1:10-scale prestressed concrete containment model and a 1:8-scale reinforced concrete containment model. These models were constructed and the tests were conducted by NUPEC at their Tadotsu Engineering Laboratory. The insights gained from analyzing the response of these test models were used to estimate the seismic capacities of typical US containments. The effects of aging-related degradation on containment capacity to resist severe accident pressures were also investigated.
Research into the integrity of containment structures for nuclear power plants has been conducted in both internal and international Round Robin Analyses. While the contributions of each of these efforts to the understanding of the role of containment in ensuring the safe operation on nuclear power plants is important, the most comprehensive experimental effort has been conducted at SNL, primarily under the sponsorship of the USNRC. NUREG CR 6906, “Containment Integrity Research at Sandia National Laboratories: An Overview,” summarizes the major results of the experimental efforts, the observations and insights gained from the analytical efforts for more than 25 years of Containment Integrity Research at SNL. Prior to pressure testing the scale models, a number of regulatory and research organizations were invited to participate in a pre-test Round Robin analysis to perform predictive modeling of the response of scale models to over pressurization. Seventeen organizations responded and agreed to participate in the pre-test Round Robin analysis activities. The purpose of the Containment Integrity Research at SNL was to provide a forum for researchers in the area to apply current state-of-the art analysis methodologies to predicting capacity of steel, reinforced and pre-stressed concrete containment vessels.
The SPE#3 is meant to progress from all of these efforts. The first phase, examination of local effects, will focus on examining those local effects which did not garner sufficient attention or study in the previous Round Robin Analyses due to limitations in scope. Of further interest is the characterization of leak rate as a function of pressure and temperature both in a deterministic and probabilistic design space.