More deception by the NRC
If anyone who has been following the Oyster Creek license renewal process over the past couple of years isn't convinced by now that the process is rigged to ensure the Nuclear Regulatory Commission's desired outcome - license renewal - read the op-ed in today's Press by Dennis Zannoni, New Jersey's former chief nuclear engineer in the state Department of Environmental Protection's Bureau of Nuclear Engineering. Zannoni, a veteran employee who was intimately familiar with Oyster Creek's operations, was recently reassigned after an NRC official complained Zannoni had criticized the credentials of the members of an NRC advisory committee.
If the op-ed doesn't raise doubts in your mind about the wisdom of granting Oyster Creek a 20-year license renewal, a recent letter from Sandia National Laboratories, should. A manager for Sandia, which conducted an analysis of the plant drywell's ability to withstand stress, alleged that the NRC staff misrepresented the Sandia study, which an NRC advisory committee used to help justify its decision to conditionally approve Oyster Creek's relicensing. The letter was sent about a week after the decision was made. Had the representation not be made, Sandia's position on the drywell may have been substantially different.
Gov. Corzine, DEP commissioner Lisa Jackson and the region's federal legislators need to reopen the review of the drywell, based on Sandia's concerns.
The letter:
From: "Hessheimer, Michael"
To:
Date: 02/09/2007 12:57:53 PM
Subject: Comments on Buckling Limits for the Oyster Creek Drywell
Donnie,
I'd like to clarify a few points regarding our design analysis of the
Oyster Creek drywell shell documented in SAND-2007-0055 which were
discussed at the ACRS meeting on February 1. Our views on these issues
differ somewhat from the opinions presented by the licensee and the
Staff. In the event we are called upon to explain our views in the
future, I thought it was important to explain them to you first.
First, my comments below not withstanding, I would like to reiterate
that the fundamental conclusion in our report is still valid: Based on
our analysis of the 'best estimate' of the actual condition of the
degraded drywell shell during the extended license period, subject to
the assumptions stated in the report, the margins of safety for the
prescribed design loads satisfy the requirements of Subsection NE and
Code Case N-284 of the ASME B&PV code.
The emphasis by the licensee and others on determining the minimum
uniform thickness in the sandbed region at the various ACRS meetings has
tended to obscure this conclusion. We believe that it is important to
understand the subtle distinction that the minimum uniform thickness
across the entire sandbed region is not equivalent to the minimum
thickness anywhere across the sandbed region. The minimum uniform
thickness in the sandbed region should not be used to determine
compliance with the Code requirements. Since we cannot determine a
priori the location and extent of any future reduction in the shell wall
thickness, it is only meaningful and appropriate use the minimum uniform
thickness in the context of establishing a threshold for ongoing
surveillance, which might trigger a re-evaluation of the vessel. There
may be more appropriate threshold values on wall thickness which could
be established, however, we have not investigated this under the scope
of our current Work Order.
In the Staff's presentation to the ACRS on February 1, regarding the
stability or buckling limits, statements were made that the Sandia
analysis "did not include the effect of hoop tension in determining the
minimum shell thickness" in the sandbed region. The implication was
that we should have used an increased capacity reduction factor in
determining this value.
While we did not apply the increase in the capacity reduction factor due
to the presence of hoop tension (resulting from internal pressure)
allowed by ASME B&PV Code Case N-284, the theoretical buckling load
determined by the linear elastic finite element analysis, to which the
capacity reduction factor is applied, does, in fact, explicitly account
for the hoop tension which develops in the shell. This is evidenced by
the 'double-lobe' shape of the buckling mode in the sand bed region
illustrated in Figure 4.4 of our report. In the absence of hoop tension
in this area, we would expect a 'single-lobe' buckled shape to occur at
a lower theoretical buckling load. Therefore, we do not think it is
appropriate to take additional credit for the presence of hoop tension
(whether a result of internal pressure or arising from deformation of
the shell under the action of vertical loading).
We do not agree that the application of the increased capacity reduction
factor to our analysis, as presented to the ACRS by both the licensee
and the Staff, to determine the minimum uniform thickness in the sandbed
region is correct.
It may be helpful to offer a discussion of the provisions of Code Case
N-284 in the context of the current investigation to further explain the
basis for our position. The Code Case recognizes that constructed
shells exhibit lower buckling strengths, due to geometric and material
imperfections, than the theoretical capacity computed for idealized
geometries. The capacity reduction factors specified in the Code Case
reflects the important work by Dr. Miller and others to quantify this
effect for shells constructed within the tolerances specified by the
B&PV code. As he described at the ACRS meeting, the presence of
membrane tension may reduce the effect of initial geometric
imperfections and justify an increase in the capacity reduction factor,
i.e. allow a higher buckling load.
However, these empirically based reduction factors are presumed to be
conservative when used in conjunction with the analytic procedures (i.e.
by formula) described in N-284 without distinction for the complex
geometries and boundary conditions present in constructed vessels. The
capacity reduction factors in the Code Case does not distinguish between
determination of theoretical buckling via the prescribed analytic
methods or by more rigorous numerical (finite element) methods which
explicitly account for the biaxial stress state. (It is arguable
whether this presumption of conservatism for the reduction factors is
valid for shells which exhibit deformations from many years of
operational loading and environmentally induced degradation which may
further exacerbate the effect of initial imperfections.)
I hope this discussion clarifies some possible misunderstanding of
Sandia's analysis and the implications of the results. I've reviewed
these concerns with other members of our technical staff who are
recognized for their expertise in computational structural mechanics and
theyconcur with the positions stated. If you have any questions or
would like discuss any of these points further, please let me know.
-Mike
Michael F. Hessheimer, P.E.
Manager, Systems & Structures, Dept. 6764
Sandia National Laboratories
PO Box 5800
Albuquerque, New Mexico 87185-0744
e-mail: mfhessh@sandia.gov
If the op-ed doesn't raise doubts in your mind about the wisdom of granting Oyster Creek a 20-year license renewal, a recent letter from Sandia National Laboratories, should. A manager for Sandia, which conducted an analysis of the plant drywell's ability to withstand stress, alleged that the NRC staff misrepresented the Sandia study, which an NRC advisory committee used to help justify its decision to conditionally approve Oyster Creek's relicensing. The letter was sent about a week after the decision was made. Had the representation not be made, Sandia's position on the drywell may have been substantially different.
Gov. Corzine, DEP commissioner Lisa Jackson and the region's federal legislators need to reopen the review of the drywell, based on Sandia's concerns.
The letter:
From: "Hessheimer, Michael"
To:
Date: 02/09/2007 12:57:53 PM
Subject: Comments on Buckling Limits for the Oyster Creek Drywell
Donnie,
I'd like to clarify a few points regarding our design analysis of the
Oyster Creek drywell shell documented in SAND-2007-0055 which were
discussed at the ACRS meeting on February 1. Our views on these issues
differ somewhat from the opinions presented by the licensee and the
Staff. In the event we are called upon to explain our views in the
future, I thought it was important to explain them to you first.
First, my comments below not withstanding, I would like to reiterate
that the fundamental conclusion in our report is still valid: Based on
our analysis of the 'best estimate' of the actual condition of the
degraded drywell shell during the extended license period, subject to
the assumptions stated in the report, the margins of safety for the
prescribed design loads satisfy the requirements of Subsection NE and
Code Case N-284 of the ASME B&PV code.
The emphasis by the licensee and others on determining the minimum
uniform thickness in the sandbed region at the various ACRS meetings has
tended to obscure this conclusion. We believe that it is important to
understand the subtle distinction that the minimum uniform thickness
across the entire sandbed region is not equivalent to the minimum
thickness anywhere across the sandbed region. The minimum uniform
thickness in the sandbed region should not be used to determine
compliance with the Code requirements. Since we cannot determine a
priori the location and extent of any future reduction in the shell wall
thickness, it is only meaningful and appropriate use the minimum uniform
thickness in the context of establishing a threshold for ongoing
surveillance, which might trigger a re-evaluation of the vessel. There
may be more appropriate threshold values on wall thickness which could
be established, however, we have not investigated this under the scope
of our current Work Order.
In the Staff's presentation to the ACRS on February 1, regarding the
stability or buckling limits, statements were made that the Sandia
analysis "did not include the effect of hoop tension in determining the
minimum shell thickness" in the sandbed region. The implication was
that we should have used an increased capacity reduction factor in
determining this value.
While we did not apply the increase in the capacity reduction factor due
to the presence of hoop tension (resulting from internal pressure)
allowed by ASME B&PV Code Case N-284, the theoretical buckling load
determined by the linear elastic finite element analysis, to which the
capacity reduction factor is applied, does, in fact, explicitly account
for the hoop tension which develops in the shell. This is evidenced by
the 'double-lobe' shape of the buckling mode in the sand bed region
illustrated in Figure 4.4 of our report. In the absence of hoop tension
in this area, we would expect a 'single-lobe' buckled shape to occur at
a lower theoretical buckling load. Therefore, we do not think it is
appropriate to take additional credit for the presence of hoop tension
(whether a result of internal pressure or arising from deformation of
the shell under the action of vertical loading).
We do not agree that the application of the increased capacity reduction
factor to our analysis, as presented to the ACRS by both the licensee
and the Staff, to determine the minimum uniform thickness in the sandbed
region is correct.
It may be helpful to offer a discussion of the provisions of Code Case
N-284 in the context of the current investigation to further explain the
basis for our position. The Code Case recognizes that constructed
shells exhibit lower buckling strengths, due to geometric and material
imperfections, than the theoretical capacity computed for idealized
geometries. The capacity reduction factors specified in the Code Case
reflects the important work by Dr. Miller and others to quantify this
effect for shells constructed within the tolerances specified by the
B&PV code. As he described at the ACRS meeting, the presence of
membrane tension may reduce the effect of initial geometric
imperfections and justify an increase in the capacity reduction factor,
i.e. allow a higher buckling load.
However, these empirically based reduction factors are presumed to be
conservative when used in conjunction with the analytic procedures (i.e.
by formula) described in N-284 without distinction for the complex
geometries and boundary conditions present in constructed vessels. The
capacity reduction factors in the Code Case does not distinguish between
determination of theoretical buckling via the prescribed analytic
methods or by more rigorous numerical (finite element) methods which
explicitly account for the biaxial stress state. (It is arguable
whether this presumption of conservatism for the reduction factors is
valid for shells which exhibit deformations from many years of
operational loading and environmentally induced degradation which may
further exacerbate the effect of initial imperfections.)
I hope this discussion clarifies some possible misunderstanding of
Sandia's analysis and the implications of the results. I've reviewed
these concerns with other members of our technical staff who are
recognized for their expertise in computational structural mechanics and
theyconcur with the positions stated. If you have any questions or
would like discuss any of these points further, please let me know.
-Mike
Michael F. Hessheimer, P.E.
Manager, Systems & Structures, Dept. 6764
Sandia National Laboratories
PO Box 5800
Albuquerque, New Mexico 87185-0744
e-mail: mfhessh@sandia.gov
posted by Randy Bergmann at 2:59 PM
2 Comments:
The letter from Sandia explicitly stated that the shell is safe. Only an overpowering bias against nuclear power could lead to any of the wild accusations in the editorial blog comment. From the beginning of the Sandia letter: "Based on our analysis of the 'best estimate' of the actual condition of the degraded drywell shell during the extended license period, subject to the assumptions stated in the report, the margins of safety for the prescribed design loads satisfy the requirements of Subsection NE and the Code Case N-284 of the ASME B&PV code."
I couldn't find any evidence of deception on the part of the NRC. But Randy Bergmann sure seems to be full of it.
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