[Federal Register Volume 70, Number 171 (Tuesday, September 6, 2005)]
[Rules and Regulations]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-17589]
Rules and Regulations
This section of the FEDERAL REGISTER contains regulatory documents
having general applicability and legal effect, most of which are keyed
to and codified in the Code of Federal Regulations, which is published
under 50 titles pursuant to 44 U.S.C. 1510.
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Federal Register / Vol. 70, No. 171 / Tuesday, September 6, 2005 /
Rules and Regulations
NUCLEAR REGULATORY COMMISSION
10 CFR Part 50
[Docket No. PRM-50-76]
Robert H. Leyse; Denial of Petition for Rulemaking
AGENCY: Nuclear Regulatory Commission.
ACTION: Petition for rulemaking; denial.
SUMMARY: The Nuclear Regulatory Commission (NRC) is denying a petition
for rulemaking submitted by Mr. Robert H. Leyse (PRM-50-76). The
petitioner requests that the NRC's regulations concerning the specified
evaluation models for emergency core cooling systems (ECCS) and
associated guidance documents be amended. The petitioner asserts that
amendments are necessary to correct technical deficiencies in the
correlations and data used for calculation of metal-water oxidation.
The petitioner states that the correlations and data do not consider
the complex thermal-hydraulic conditions present during a loss-of-
coolant accident (LOCA), including the potential for very high fluid
temperature. The Commission is denying Mr. Leyse's petition for
rulemaking (PRM-50-76). None of the specific technical issues raised by
the petitioner have shown safety-significant deficiencies in the
research, calculation methods, or data used to support ECCS performance
evaluations. NRC's technical safety analysis demonstrates that current
procedures for evaluating ECCS performance are based on sound science
and that no amendments to the NRC's regulations and guidance documents
ADDRESSES: The NRC is making the documents identified in the table
below available to interested persons through several means. Publicly
available documents related to this petition, including the petition
for rulemaking, public comments received, and the NRC's letter of
denial to the petitioner, may be viewed electronically on public
computers in the NRC's Public Document Room (PDR), O-1 F21, One White
Flint North, 11555 Rockville Pike, Rockville, Maryland 20852. The PDR
reproduction contractor will copy documents for a fee. Selected
documents, including comments, may be viewed and downloaded
electronically via the NRC rulemaking Web site at http://ruleforum.llnl.gov.
Publicly available documents created or received at the NRC after
November 1, 1999, are also available electronically at the NRC's
Electronic Reading Room at http://www.nrc.gov/reading-rm/adams.html.
From this site, the public can gain access into the NRC's Agencywide
Documents Access and Management System (ADAMS), which provides text and
image files of NRC's public documents. If you do not have access to
ADAMS or if you have problems in accessing the documents in ADAMS,
contact the PDR reference staff at (800) 387-4209 or (301) 415-4737 or
by e-mail to [email protected].
Document PDR Web ADAMS
Federal Register Notice-- X X ML022800472
Receipt of Petition for
Rulemaking (67 FR 51783; Aug.
Letter of Denial to the X X ML052220454
Penn State/US NRC ``Rod Bundle ML023040657
Test Facility and Reflood Heat
Petition for Rulemaking (PRM-50- X X ML022240009
Public Comments for PRM-50-76.. X X ML042740105
US NRC Office of Nuclear X X ML041210109
Research (RES) ``Technical
Safety Analysis of PRM-50-76,
A Petition for Rulemaking to
Amend Appendix K to 10 CFR
Part 50 and Regulatory Guide
US NRC, ``Updated Program Plan ....... ....... ML031810103
for High-Burnup Light-Water
Studies of Metal Water ....... ....... ML050550198
Reactions at High
Experimental and Theoretical
Studies of the Zirconium-Water
Reaction,'' L. Baker and L.C.
Just, ANL-6548 (May 1962).
PWR FLECHT (Full Length ....... ....... ML052230221
Emergency Cooling Heat
Transfer) Final Report,''
Zirconium Metal-Water Oxidation ....... ....... ML052230079
Kinetics IV. Reaction Rate
FOR FURTHER INFORMATION CONTACT: Timothy A. Reed, Office of Nuclear
Reactor Regulation, U.S. Nuclear Regulatory Commission, Washington, DC
20555-0001, telephone (301) 415-1462, e-mail [email protected].
The petition for rulemaking designated PRM-50-76 was received by
the NRC on May 1, 2002. A notice of receipt of the petition and request
for public comment was published in the Federal Register (FR) on August
9, 2002 (67 FR 51783). The notice of receipt requested comment on two
questions: (1) Are the petitioner's three concerns about ECCS cooling
valid, and if so, do these concerns constitute a significant safety
concern? (2) Are there actions available to the Commission other than
rulemaking that would effectively address the concerns raised by the
The petition, PRM-50-76, covers three broad issues: (1) Amending
Appendix K to Part 50 of the Commission's regulations, (2) amending
Regulatory Guide (RG) 1.157, and (3) the need for further analysis of
the 10 CFR Part 50, Appendix K, backup data.
Issue 1: Amending Appendix K to Part 50
The petitioner describes at length alleged technical deficiencies
in Appendix K Section I.A.5, ``Metal-Water Reaction Rate.'' The
petitioner claims that Section I.A.5 does not accurately describe the
extent of zirconium-water reactions that may occur during a LOCA. The
petitioner states that the
Baker-Just equation, which is used to calculate the metal-water
reaction in assessing ECCS performance, does not include any allowance
for the complex thermal-hydraulic conditions during a LOCA, including
the potential for very high bulk fluid temperatures within the cooling
channels of the zirconium-clad fuel elements.
The petitioner cites the abstract of an Argonne National Laboratory
(ANL) report (ANL-6548 ``Studies of Metal Water Reactions at High
Temperatures, III. Experimental and Theoretical Studies of the
Zirconium-Water Reaction,'' L. Baker and L.C. Just, May 1962) and
disputes the conclusions based on the petitioner's opinion that the
tests discussed in ANL-6548 do not accurately reflect the conditions
present during a LOCA. The petitioner makes the following points to
support his views:
The bulk water temperature was no greater than 315 [deg]C
The volume of water within the test apparatus was
substantially greater than the volume of zirconium specimens, creating
a vastly greater capacity to cool the heated zirconium particles of the
Baker and Just experiment than would exist under LOCA conditions.
Zirconium specimens were exposed to water only, while LOCA
conditions include steam and nonequilibrium water-steam mixtures that
reached higher bulk fluid temperatures.
A footnote in ANL-6548 states: ``This discussion is of a
preliminary nature: work in this area is continuing.'' Based on this
footnote, the petitioner concludes that it is not appropriate to apply
the Baker-Just equation as prescribed in Appendix K Section I.A.5 for
the calculation of energy release rates, hydrogen generation, and
cladding oxidation from the metal-water reaction.
Issue 2: Amending Regulatory Guide 1.157
The petitioner states that RG 1.157, which allows use of data from
NUREG-17 (ORNL/NUREG-17, ``Zirconium Metal-Water Oxidation Kinetics IV,
Reaction Rate Studies,'' by Cathcart et al., August 1977) for
calculating energy release rates, hydrogen generation, and cladding
oxidation for cladding temperatures greater than 1900 [deg]F, results
in flawed ECCS performance evaluations. The petitioner claims the
NUREG-17 data is based on very limited test conditions and consequently
the results should not be used for evaluating LOCA conditions.
In support of this contention, the petitioner describes the
following test conditions:
Zircaloy-4 specimens exposed only to steam, rather than
fluid conditions as present in a LOCA.
No documented heat transfer from the Zircaloy surface to
the slow-flowing steam.
Small-scale laboratory testing without conditions typical
of the complex thermal-hydraulic conditions that prevail during a LOCA.
An unexplained shift from the MaxiZWOK (testing apparatus
for investigations in the temperature range 1652 [deg]F to 1832 [deg]F)
to the MiniZWOK (a different testing apparatus for investigations in
the temperature range 1832 [deg]F to 2734 [deg]F).
The petitioner believes that the investigators' conclusions include
a statement that ``overlooks the very substantially greater mass
transfer coefficients that accompany the so-called appropriate heat
transfer coefficients.'' The petitioner concludes that ``it is those
very substantially greater mass transfer coefficients that led to the
temperature overshoot of the MaxiZWOK test at 1832 [deg]F, and that
would have led to very substantially greater temperature overshoots and
likely destruction of the Zircaloy tubing if MaxiZWOK had been operated
over the temperature range of the MiniZWOK runs.''
The petitioner contends that the NUREG-17 investigators do not
warrant their work, and specifically assume no responsibility for the
accuracy of their work, and therefore, that NUREG-17 is not applicable
to the regulation of nuclear power reactors in the United States of
America. To support this contention, the petitioner cites the following
statement on the introductory page of NUREG-17: This report was
prepared as an account of work sponsored by the United States
Government. Neither the United States nor the Energy Research and
Development Administration/United States Nuclear Regulatory Commission,
nor any of their employees, nor any of their contractors,
subcontractors, or their employees, makes any warranty, express or
implied, or assumes any legal liability or responsibility for the
accuracy, completeness or usefulness of any information, apparatus,
product or process disclosed, or represents that its use would not
infringe privately owned rights.''
Issue 3: Need for Further Analysis of Appendix K Backup Data
The petitioner states that the results of Zircaloy bundle test no.
9573, which was a test done for the Full Length Emergency Cooling Heat
Transfer (FLECHT) tests and documented in WCAP-7665 (``PWR FLECHT (Full
Length Emergency Cooling Heat Transfer) Final Report, Westinghouse
Report WCAP-7665, April 1971''), are applicable to the calculation of
the metal-water reaction and shows that the Baker-Just equation
(referenced in Section I.A.5 of Appendix K for calculating the metal-
water reaction) is not conservative. The petitioner states that the
data in WCAP-7665, which includes test run 9573, includes the complex
thermal-hydraulic conditions and Zircaloy-water reactions that
characterize the reflood portion of the LOCA transient. The petitioner
states that these conditions are not found in the narrow test
procedures of ANL-6548 or NUREG-17.
The petitioner states that a pertinent description of the
complexities of thermal-hydraulic conditions during reflood, including
negative heat transfer coefficients, is included in Section 3.2.3 of
WCAP-7665 and that this description applies to data collected with
FLECHT bundles with stainless steel cladding. The petitioner feels that
another FLECHT Zircaloy bundle test, run 8874, is also pertinent to
issues raised in this petition.
The petitioner cites Section 5.6 of WCAP-7665 and finds statements
comparing Zircaloy to stainless steel to be misleading because they
imply that stainless steel heat transfer coefficients may be used as a
conservative representation of Zircaloy behavior. The petitioner
believes that the differences in behavior for various test runs are
explained by the differences in the thermal-hydraulic conditions
leading to a different combination of heat transfer and mass transfer
factors, and are not due to inconsistency of the data, as implied by
The petitioner also finds WCAP-7665, Section 5.11, ``Materials
Evaluation,'' to be misleading in view of the total experience with
FLECHT run 9573. Finally, the petitioner notes that the same warning
language used in NUREG-17 is on the cover page of WCAP-7665.
The petitioner further identifies several aspects of the data
supporting the document entitled ``Acceptance Criteria for Emergency
Core Cooling Systems for Light-Water Cooled Nuclear Reactors-Opinion of
the Commission,'' (Docket No. RM50-1, December 28, 1973) and notes the
Commission concluded: ``It is apparent, however, that more experiments
with Zircaloy cladding are needed to overcome the impression left from
run 9573.'' The petitioner finds that there has been a lack of
appropriate response to the Commission's expressed wish for more
experiments, and believes that at the very least, run 9573 should have
been repeated. The petitioner emphasizes that although at least $1
billion had been expended on other analytical efforts, there has been
no reported analysis of FLECHT run 9573.
The petitioner states that the test programs discussed in the
petition were funded by Government agencies. He believes that most of
the programs were firmly controlled by those ``who were indoctrinated
in the methods of the tightly regimented Naval Reactors Program.'' The
petitioner finds that the ``biased reporting of WCAP-7665 may be traced
to these controls'' and believes that ``the lack of application of the
MaxiZWOK apparatus beyond 1832 [deg]F in NUREG-17 may likely be traced
to rigid restrictions by management at the NRC.'' The petitioner
further contends that while the Argonne work in ANL-6548 was likely
less impacted by these controls, the controls likely did inhibit
further analysis or reporting of FLECHT run 9573.
The petitioner notes that he has made several requests to the
Knolls Atomic Power Laboratory for report KAPL-1534 and that his
requests have been ignored.
Public Comments on the Petition
Six letters of public comment were received on the petition in
response to the request for public comment. Three of these letters were
from the petitioner. These letters are summarized below.
By letter dated September 11, 2002, the petitioner provided
comments that did not raise new issues. The petitioner stated that the
Baker-Just equation and the Cathcart-Pawel equation in NUREG-17 have
been grossly misapplied by the NRC. According to him, it is
fundamentally important that the determinations of LOCA transient
chemical kinetics include the geometry of the stationary Zircaloy
reactant in combination with the thermal-hydraulic conditions of the
flowing water/steam reactant. In addition, he repeated in his letter
that there are deficiencies in RG 1.157, since it references documents
such as NUREG-17 that do not consider the complex thermal-hydraulic
conditions during LOCAs, including the potential for very high fluid
temperatures. The petitioner also stated that the Commission should
provide a rational basis for regulation of ECCS performance and perform
additional experiments with Zircaloy cladding due to the cladding
failure reported in Westinghouse report WCAP-7665.
By letter dated October 23, 2002, Westinghouse Electric Company
submitted comments that opposed the proposed changes. Westinghouse
commented that runaway oxidation is prevented by the 2200 [deg]F peak
cladding temperature limit. Additionally, Westinghouse commented that
the Baker-Just correlation is known to be conservative, over-predicting
the zirconium-water reaction by as much as 30 percent at the limiting
temperature (2200 [deg]F). Westinghouse stated that the conditions of
FLECHT run 9573 (high power and high initial temperatures) were
extremely severe, intentionally beyond design basis for ECCS
performance. Westinghouse stated that the Cathcart-Pawel tests had
adequate steam flow so that the zirconium-water reaction rate was not
limited by the availability of steam, and as a result, the tests were
valid. Westinghouse commented that differences between ECCS test
conditions and reactor core fluid conditions during postulated LOCAs do
not prevent the current zirconium-water reaction database from being
applicable to ECCS analysis.
By letter dated October 25, 2002, the Nuclear Energy Institute
(NEI) submitted comments supporting the Westinghouse comments, stating
that extensive testing and analysis by the nuclear industry and
national laboratories indicate that the Cathcart-Pawel correlation test
is conservative. The NRC notes that the Cathcart-Pawel correlation is
intended to be a best estimate, and is not intended to conservatively
bound metal-water reaction rates. NEI commented that the test run,
FLECHT 9573, was intentionally performed under very severe, beyond
design-basis conditions, that post-test evaluations showed oxidation
was within the expected range, and that runaway oxidation did not occur
until the cladding temperature was well beyond 2300 [deg]F. NEI further
commented that the petitioner's concerns do not constitute a
significant safety concern and thus, there is no need to revise
Appendix K to Part 50 or RG 1.157.
By letter dated November 6, 2002, Strategic Teaming and Resource
Sharing (STARS), a group of six utilities, submitted comments opposing
the petition. These comments stated that within the range of test
parameters applicable to ECCS evaluation models, as specified in
Appendix K and RG 1.157, the regulations and guidance are valid and
conservative. STARS notes that all of the data referenced in the
petition was either available to the Commission and industry when the
regulations and guidance were created or was assessed later when the
test information became available.
On November 22, 2002, the petitioner submitted a reply to STARS but
raised no new issues. On December 14, 2002, the petitioner responded to
Westinghouse and NEI comments by discussing runaway oxidation in the
WCAP-12610 report and severe fouling of fuel cladding during a LOCA.
The petitioner stated that no allowance for higher temperatures due to
fouling was made in run 9573, and repeated his request for more
experiments with Zircaloy cladding.
NRC Requirements for ECCS Evaluations
Section 50.46 specifies the performance criteria against which the
ECCS must be evaluated. The criteria include the maximum peak cladding
temperature, the maximum cladding oxidation thickness, the maximum
total hydrogen generation, and requirements to assure a coolable core
geometry and abundant long-term cooling. This regulation also states
that the ECCS cooling performance following postulated LOCAs must be
calculated in accordance with either a realistic (also called a best-
estimate) evaluation model that accounts for uncertainty or a
conservative evaluation model that conforms with the required features
of appendix K to 10 CFR part 50. If a licensee elects to calculate ECCS
performance using an Appendix K evaluation model, then one important
feature of that model is the way the metal-water reaction is
calculated. For this calculation, Appendix K prescribes the use of the
Baker-Just equation from ANL report ANL-6548 (L. Baker, L.C. Just,
``Studies of Metal Water Reactions at High Temperatures, III.
Experimental and Theoretical Studies of the Zirconium-Water Reaction''
May 1962). The metal-water reaction, which is predicted to occur during
the LOCA and which is calculated using the Baker-Just equation, is the
subject of much of this petition. The Baker-Just equation calculates a
conservative rate of hydrogen generation and fuel cladding oxidation
during the LOCA transient. Additionally, for licensees electing to use
best-estimate calculations to evaluate ECCS performance, NRC RG 1.157
provides guidance for such evaluations. RG 1.157 allows the use of data
from NUREG-17 for the calculation of the metal-water reaction.
NRC Technical Evaluation
The NRC reviewed the petitioner's request and concluded that none
of the issues raised by the petitioner justified the initiation of
rulemaking. The NRC's response to the technical issues raised in PRM-
50-76 is based largely on a technical study by the Office of Nuclear
Regulatory Research (RES) ``Technical
Safety Analysis of PRM-50-76, A Petition for Rulemaking To Amend
appendix K to 10 CFR part 50 and Regulatory Guide 1.157.'' The NRC's
responses to the petitioner's issues are as follows:
Issue 1: Amending Appendix K to Part 50
The petitioner claims that the requirement to use the Baker-Just
equation in Section I.A.5 of Appendix K to 10 CFR Part 50, does not
accurately describe the extent of zirconium-water reaction that may
occur during a LOCA. He states that the Baker-Just equation does not
include any allowance for the complex thermal-hydraulic conditions
during a LOCA. The NRC disagrees with the petitioner's assertions.
In Section 3.1 of the petition, the petitioner discusses the
inapplicability of the Baker-Just equation for calculating zirconium-
water reaction rates during a LOCA. The NRC notes that it is important
to distinguish between the experiments performed by Baker and Just, and
the equation developed by them and adopted in Appendix K to Part 50.
Experiments run with 40-60 mil wires at temperatures at, or near, the
zirconium melting point (3400 [deg]F) for one or two seconds are not
typical of fuel rod cladding at temperatures in the range of 1800
[deg]F-2200 [deg]F for 50 to 400 seconds that are postulated to occur
in a design basis LOCA. In the Baker-Just report, only one data point
from their experiments (at 3366 [deg]F) is used in developing the
Baker-Just equation. This one data point was used to anchor the Baker-
Just equation at the melting point of zirconium. The remaining data
from Bostrum (``The High Temperature Oxidation of Zircaloy in Water,''
W. A. Bostrum, WAPD-104 March 1954) and Lemmon (``Studies Relating to
the Reaction Between Zirconium and Water at High Temperatures,'' A. W.
Lemmon, Jr., BMI-1154, January 1957), at more relevant zirconium
cladding conditions, were used by Baker and Just in the derivation of
their equation. The use of the single data point at the melting
temperature makes the Baker-Just equation very conservative. At the
time of the promulgation of Sec. 50.46, the Commission expected the
NRC staff to obtain new and better zirconium-water reaction data. The
petitioner also expressed concerns about the need for additional data.
The substantial work of Cathcart and Pawel was performed for the NRC in
response to the Commission's expectation.
The NRC compares the Baker-Just correlation to other correlations
in a technical study (ADAMS accession ML041210109). The comparisons
show the conservatism of the Baker-Just correlation in the temperature
range important for clad oxidation calculations for LOCAs. In the
discussion of Issue 3, comparisons of the Baker-Just correlation to
relevant data demonstrate the substantial conservatism of the Baker-
Just correlation. The petitioner expresses concern about the low water
temperature (no greater than 599 [deg]F) in the Baker-Just experiments.
This temperature corresponds to the saturation temperature at 1530
psia, which was the pressure for that particular experiment. While a
few degrees of liquid superheat may be possible under LOCA/ECCS
conditions, the degree of nonequilibrium required for higher liquid or
``bulk'' temperatures postulated by the petitioner is not possible.
The petitioner is also concerned about the large water volume
compared to the zirconium sample size with respect to the quench
capability of zirconium-clad fuel rods. As noted, these experiments
were atypical in that respect, but barely used in the formulation of
the Baker-Just correlation. Further, it should be noted that the Baker-
Just report was not intended to be a heat transfer study, but rather an
investigation of zirconium-water reaction kinetics at very high
One interesting feature of the Baker-Just report is the heat and
mass transfer analysis of an example case analyzed to examine the
processes limiting the reaction rate. In this severe case, a 0.21 cm
zirconium sphere at its melting point was dropped into water. Baker
andJust were concerned that the reaction could be limited by gas phase
diffusion of steam through a film of steam and hydrogen. This appears
to be similar to the petitioner's concern. As explained in the Baker-
Just report, water cannot stay in contact with the hot metal and a
vapor film immediately forms around the sphere. Figure 15 in that
report shows that vapor phase diffusion is the limiting steam transport
process for less than 0.2 seconds, during which a slight film of oxide
is forming on the surface of the sphere. After that, the parabolic rate
equation, (e.g., the Baker-Just equation) becomes limiting. The figure
also shows that the gas phase diffusion is far less temperature-
sensitive than the parabolic rate law. Certainly at lower temperatures
more typical of a LOCA, the parabolic law is even more limiting than
gas phase diffusion as long as the reaction is not steam starved.
Comparison of the Baker-Just equation to numerous data sets has
shown the equation to be conservative. A significant example of this
conservatism is discussed under Issue 3.
In summary, the NRC found no technical basis in the petition or in
NRC records for the assertion that the NRC requirement to use the
Baker-Just equation, along with other requirements of Appendix K, is
flawed and is a significant safety concern.
Issue 2: Amending Regulatory Guide 1.157
The petitioner stated that RG 1.157, which allows use of the data
and the Cathcart-Pawel equation presented in NUREG-17, results in
flawed evaluations of ECCS performance. The NRC disagrees with the
petitioner's assertions on this issue. In Section 3.2 of the petition,
the petitioner states that the limited test conditions described in
NUREG-17 preclude the use of the results for LOCA calculations. He
further states that Zircaloy-4 specimens were not exposed to LOCA fluid
conditions and that only steam was applied at very low velocities for
the main test series. The petitioner states that there was no
documented heat transfer from the Zircaloy surface to the slow-flowing
steam and that as a result the conditions of the small-scale laboratory
tests were not typical of the complex thermal-hydraulic conditions that
prevail during a LOCA.
The petitioner suggests that without liquid water, the tests are
invalid. The NRC disagrees. The presence of liquid water would
invalidate the tests. Accurate steady-flow measurement would be
extremely difficult. The droplets or liquid film would make it
difficult to achieve the relatively constant sample temperatures that
are necessary in these reaction kinetics tests. However, adequate steam
flow is a concern. If the flow is too low, the reaction becomes steam
starved. Otherwise, it is unnecessary to have steam flow typical of
LOCA/ECCS conditions. These are not heat transfer tests. Once a
reaction rate model is developed using data from experiments like
these, the model should be validated against transient tests under LOCA
conditions, as in the four Zircaloy tests described in WCAP-7665 and
the transient tests described in the Cathcart-Pawel report.
Calculations were performed to assure that there was adequate steam
flow for the MiniZWOK experiments used to derive the Cathcart-Pawel
correlation in NUREG-17. These calculations are described in the RES
An important argument for the absence of steam starvation is how
the isothermal Cathcart-Pawel experiments
described in NUREG-17 give consistent results that support the
parabolic/Arrhenius behavior. This is also discussed in the RES
Much of the petitioner's criticism of the Cathcart-Pawel work is
related to a comparison of MiniZWOK and MaxiZWOK experimental
conditions. MiniZWOK was used to develop a consistent set of data for
correlation development. Controlling sample temperature by adjusting
heater power (MiniZWOK) was much more successful than adjusting steam
flow (MaxiZWOK). As the petitioner notes, temperature overshoot was a
problem with MaxiZWOK and at high temperatures could have led to
temperature runaway. As noted previously, temperature control is
absolutely necessary in reaction kinetics experiments such as these.
The petitioner implies that the experimenters abandoned MaxiZWOK in
favor of MiniZWOK. Actually, the isothermal MiniZWOK experiments were
essentially complete before the MaxiZWOK experiments were begun.
Results from MaxiZWOK between 1652 [deg]F and 1832 [deg]F agreed well
with MiniZWOK data at the same temperatures. Cathcart and Pawel state
The very good agreement between these two data sets is regarded
as evidence that steam flow rate and steam insertion temperature do
not affect significantly the kinetics of the steam oxidation of
Zircaloy, at least in this temperature range.
Certainly, with steam velocities at least an order of magnitude
greater in MaxiZWOK than MiniZWOK, the potential for more rapid gas
phase diffusion of steam to the sample surface ``mass transfer'' is
greater for MaxiZWOK. But clearly this is not the limiting phenomenon.
This was demonstrated by the good agreement between MiniZWOK and
MaxiZWOK data and the good agreement of MiniZWOK data to parabolic/
Arrhenius behavior. There is no evidence to suggest that high ``mass
transfer coefficients'' in MaxiZWOK caused temperature overshoot in
MaxiZWOK at 1832[deg]F, as the petitioner proposes. It is true, as the
petitioner suggests, that ``[i]t is not possible to achieve an
isothermal rate of oxidation of Zircaloy-4 if the Zircaloy-4 is exposed
to LOCA fluid conditions at elevated conditions,'' but not for the
reasons postulated by the petitioner. Rather, large-break LOCA reflood
conditions are characterized by constantly decreasing power (decay
heat) and increasing heat transfer coefficients after a few seconds.
Under these conditions, isothermal conditions are impossible. WCAP-7665
showed that this kind of heat transfer and power behavior was universal
for all tests done under design basis conditions, and as a result,
these heat transfer tests did not exhibit isothermal cladding
The petitioner implies that Cathcart and Pawel's statement, that
scoping tests on the effect of steam pressure were in progress, is an
admission of inapplicability of their work. On the contrary, the
scoping work was completed and subsequent work by others has been
undertaken to examine pressure effects. The petitioner's notion that
the authors' statement about ongoing work applies to very low steam
velocities is also unsupported.
Work in this area did not end in 1977. The NRC, foreign partners,
and the industry have continued to conduct and evaluate experimental
and analytical programs on fuel cladding behavior. As in the case with
many other research activities and their link to the agency's
regulatory framework, an important objective of this work is the
confirmation of current Sec. 50.46 criteria and models and the
development of more realistic, performance-based, and contemporary
criteria and models. An important link to the current work is the
extensive research reported by Cathcart and Pawel.
The NRC disagrees with the petitioner's assertion that the
disclaimer in the introduction to NUREG-17 causes the technical work to
be inapplicable to reactor regulation. The disclaimer protects the
United States Government from potential litigation. It is not intended
to discredit the technical validity of the work documented in NUREG-17.
As such, the disclaimer is irrelevant to whether the NUREG-17 work is
an adequate basis for reactor regulation. That is a question that
should be decided solely on the technical merits of the work.
The NRC found no technical basis in the petition nor in NRC records
to support the assertion that the Regulatory Guide 1.157 conditions for
acceptance of the use of ORNL/NUREG-17 information result in flawed
evaluation of ECCS performance.
Issue 3: Need for Further Analysis of Appendix K Backup Data
In Section 3.4 of his petition, the petitioner quotes from the AEC
decision on the ECCS rulemaking [See Rulemaking Hearing, Acceptance
Criteria for Emergency Core Cooling Systems for Light-Water Cooled
Nuclear Power Reactors, RM-50-1, CLI-73-39, 6AEC1085, at 1124]: ``It is
apparent, however, that more experiments with Zircaloy cladding are
needed to overcome the impression left from run 9573.'' The petitioner
claims that such experiments have not been performed and are necessary.
The NRC disagrees.
Run 9573 refers to one of four Zircaloy clad FLECHT experiments
performed in 1969 and reported in WCAP-7665. The ``impression''
referred to by the AEC Commissioners in 1973 appears to be the fact
that run 9573 indicates lower ``measured'' heat transfer coefficients
than the other three Zircaloy clad tests reported in WCAP-7665 when
compared to the equivalent stainless steel tests. This is not a concern
about the zirconium-water reaction models. The AEC Commissioners
believed that this anomaly could be cleared up with more experiments on
Zircaloy cladding. Some of the anomaly can probably be explained by a
deficiency in the data reduction process. As will be discussed later,
additional Zircaloy clad tests were performed in the 1980s.
Regarding the data reduction process, heat transfer coefficients
are not directly measurable quantities. They must be calculated from
measured temperatures, known heat sources, and known thermal
properties. WCAP-7665 describes the heat transfer data reduction
process using the DATAR code. For these experiments, the decay heat
simulation was well known, as was the time of heater failure. However,
the heat source, due to the zirconium-water reaction, had to be
estimated in some way. The Baker-Just correlation was used for that
purpose. Because of its conservatism, the Baker-Just correlation
overestimates the amount of reaction and the associated heat generation
rate. At 21 locations on 19 rods among the four Zircaloy tests, post-
test oxide thickness measurements were made. Westinghouse applied the
Baker-Just correlation to each temperature transient measured at or
very near to each oxide thickness measurement. The comparison between
predicted and measured oxide thickness was presented in Figure B-12 of
WCAP-7665. The Baker-Just calculated oxide thickness is about 1.6 times
the measured value. Thus for this data set, the Baker-Just correlation
overpredicts the data by about 60 percent, which is quite conservative.
The NRC obtained tabular time/temperature data from Westinghouse
for 19 of the 21 locations analyzed by Westinghouse for the four
Zircaloy FLECHT tests. The Baker-Just correlation was applied to these
19 data sets as a check on the analysis in WCAP-7665. The RES technical
study clearly demonstrates that the analysis in WCAP-7665 is correct
and that the
Baker-Just correlation is conservative even under the severe conditions
of run 9573.
The petitioner asserts that a detailed thermal-hydraulic analysis
of run 9573, including evaluation of the heating from Zircaloy-water
reactions, was never performed. Contrary to that assertion, not only
was an evaluation of the heating from Zircaloy-water reaction performed
for run 9573, it was done for all four Zircaloy tests. Unfortunately,
using the conservative Baker-Just correlation to estimate the
zirconium-water heat release results is an overestimation of the
derived heat transfer coefficients. Thirty-five years later, it would
be difficult to replicate the DATAR code, substitute a better metal-
water model, and re-derive the heat transfer coefficients. The
difficulty would be in addition to the significant monetary expense of
conducting high-temperature Zircaloy tests and would have marginal
benefit in terms of increased understanding of large-break LOCA heat
transfer and metal-water reaction kinetics. The current programs being
conducted at Pennsylvania State University and Argonne National
Laboratory are far more cost-effective.
High-temperature tests similar to run 9573 would require rod bundle
powers well outside the range of operation of any current or proposed
pressurized water reactors (PWRs) and would produce very little useful
heat transfer information. Therefore, the NRC does not believe that
such tests are necessary.
The petitioner states that more experiments with Zircaloy cladding
have not been conducted on the scale necessary to overcome the
impression left from run 9573. The NRC disagrees. In fact additional
Zircaloy tests have been performed. In the early 1980s, the NRC
contracted with National Research Universal (NRU) at Chalk River,
Ontario, Canada to run a series of LOCA tests in the NRU reactor. More
than 50 tests were conducted to evaluate the thermal-hydraulic and
mechanical deformation behavior of a full-length 32-rod nuclear bundle
during the heatup, reflood, and quench phases of a large-break LOCA.
The NRC is reviewing the data from this program to determine its value
for assessing the current generation of codes such as TRAC-M (now
In assessing the need for further experiments like the Zircaloy-
clad FLECHT tests, it is important to understand the past and current
role of rod bundle reflood heat transfer tests. In the late 1960s, a
mechanistic understanding of reflood heat transfer did not exist. To
develop heat transfer models as expeditiously as possible, the Atomic
Energy Commission (AEC), Westinghouse, and Electric Power Research
Institute (EPRI), cooperatively developed the PWR FLECHT program. The
principal objective was to determine reflood heat transfer coefficients
as a function of key initial and boundary conditions, rod elevation,
and time after the beginning of reflood and to develop empirical
correlations based on that dependency. As long as a sufficiently large
matrix of tests was performed with full-scale rod bundles, there was no
great need for a comprehensive mechanistic understanding. The key
B. Peak power
C. Decay power
D. Flooding rate
E. Inlet subcooling
F. Initial temperature
G. Bundle size
H. Cladding material
I. Housing temperature
When nuclear plant behavior and design conditions are outside the
envelope defined by these test parameters or the design of the
experimental system, there is no basis for extrapolation, since the
derived heat transfer models are not necessarily based on the physical
models governing the reflood heat transfer processes. For the very
empirical process used in the early FLECHT experiments, limited effort
was expended obtaining data needed for development of mechanistic
physical models. It would have been impractical to obtain sufficient
Zircaloy heat transfer coefficient data for the empirical process used
with the early FLECHT experiments.
As the FLECHT program and other rod bundle reflood heat transfer
programs have progressed over the last 30 years, more information
appropriate for mechanistic model development has been obtained. As
better mechanistic models are developed, careful extrapolation has a
better chance of success, and the role of experiments like FLECHT has
shifted from model development to developmental assessment. In fact,
many of the FLECHT-SEASET experiments are used to assess the new code
models. As mentioned previously, the NRC is reviewing the NRU Zircaloy-
clad nuclear fuel bundle test results to establish their value for
further code assessment.
The NRC investigated each of the petitioner's key concerns. The NRC
concludes that Appendix K of 10 CFR Part 50 and the existing guidance
on best-estimate ECCS evaluation models are adequate to assess ECCS
performance for U.S. light water reactors (LWRs) using Zircaloy-clad
UO2 at burnup levels currently permitted by regulations.
This general conclusion is based on the following considerations:
The Baker-Just correlation using the current range of parameter
inputs is conservative and adequate to assess Appendix K ECCS
performance. Virtually every data set published since the Baker-Just
correlation was developed has clearly demonstrated the conservatism of
the correlation for the temperature range important to clad oxidation
calculations for LOCAs.
The parabolic/Arrhenius behavior of the Cathcart-Pawel isothermal
experiments confirmed that there was adequate availability of steam. An
NRC analysis confirms the ORNL/ANL assessment that the Cathcart-Pawel
isothermal experiments were not steam starved by at least two orders of
magnitude. Therefore, the experimental data is valid.
NRC has continued to study complex thermal hydraulic effects on
ECCS heat transfer processes during LOCA accident conditions consistent
with Commission direction. As part of that initiative, the NRC funded
more than 50 Zircaloy-clad nuclear fueled bundle reflood experiments at
the NRU reactor. These experiments evaluated fuel rod and heat transfer
behavior but did not include metallurgical examination to evaluate
oxidation behavior. The NRC is continuing to conduct and evaluate
experimental and analytical programs on fuel cladding behavior.
The petitioner did not take into account Westinghouse's
metallurgical analyses performed on the cladding for all four FLECHT
Zircaloy-clad experiments reported in WCAP-7665. The petitioner also
ignored the Westinghouse application of the Baker-Just correlation to
these experiments, which had the ``complex thermal hydraulic
phenomena'' deemed important by the petitioner. This application of the
correlation to the metallurgical data clearly demonstrates the
conservatism of the Baker-Just correlation for 21 typical temperature
transients. The NRC also applied the Baker-Just correlation to the
FLECHT Zircaloy experiments with nearly identical results, confirming
the WCAP-7665 results.
For the development of oxidation correlations, limited by oxygen
diffusion into the metal, well-characterized isothermal tests are more
important than the complex thermal hydraulics suggested by the
The petitioner's suggested use of complex thermal-hydraulic conditions
would be counter-productive in reaction kinetics tests because
temperature control is required to develop a consistent set of data for
correlation development. Isothermal tests allow this needed temperature
control. It is more appropriate to apply the developed correlations to
more prototypic transients (including complex thermal hydraulic
conditions) to verify that the proposed phenomena embodied in the
correlations are indeed limiting. This is what was done by Westinghouse
in WCAP-7665, by Cathcart and Pawel in NUREG-17 and by the NRC in its
technical safety analysis of PRM-50-76.
The NRC applied the Cathcart-Pawel oxygen uptake and
ZrO2 thickness equations to the four FLECHT Zircaloy
experiments, confirming the best-estimate behavior of the Cathcart-
Pawel equations for large-break LOCA reflood transients.
Cathcart and Pawel applied their oxide thickness equation, using
the BILD5 program, to 15 of their transient temperature experiments as
described in ORNL/NUREG-17. The results showed that the correlation,
based on numerous isothermal experiments, was conservative or best-
estimate when applied to this transient data set.
Petitioner's Public Comments
The petitioner submitted two public comment letters in which he
again asserted that the Baker-Just and Cathcart-Pawel equations are
grossly misapplied by the NRC. The first comment letter basically
repeated the arguments in the petition. No new technical information
was supplied. The second comment letter introduced the issue of severe
fouling, which was the subject of PRM-50-78 and addressed by the
staff's evaluation of that petition for rulemaking. Other issues
addressed in the second letter are related to the issues already
discussed in this document, and therefore, no further response is
Reasons for Denial
For the reasons cited in this document, the Commission is denying
the petition for rulemaking (PRM-50-76) submitted by Mr. Robert Leyse.
The NRC believes that the requested rulemaking would not make a
significant contribution to maintaining safety because current
regulations and regulatory guidance already adequately address the
evaluation of performance of the ECCS. No data or evidence was provided
by the petitioner or found in NRC records to suggest that the research,
calculation methods, or data used to support ECCS performance
evaluations were sufficiently flawed so as to create significant safety
problems. NRC's technical safety analysis demonstrates that current
procedures for evaluating performance of ECCS are based on sound
science and that no amendments to the NRC's regulations and guidance
documents are necessary. Additionally, the petitioner has not shown,
nor has the NRC found, the existence of any safety issues regarding
calculation methods or data used to support ECCS performance
evaluations that would compromise the secure use of licensed
radioactive material. The proposed revisions would not improve
efficiency, effectiveness, and realism because licensees and the NRC
would be required to generate additional information (as part of the
evaluation of ECCS performance) that has no safety value and does not
significantly improve realism.
Dated at Rockville, Maryland, this 26th day of August, 2005.
For the Nuclear Regulatory Commission.
Annette L. Vietti-Cook,
Secretary of the Commission.
[FR Doc. 05-17589 Filed 9-2-05; 8:45 am]
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