ML19327A652
| ML19327A652 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 08/10/1989 |
| From: | Lauben G NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Hodges M Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19327A642 | List:
|
| References | |
| TAC-73427, NUDOCS 8908140174 | |
| Download: ML19327A652 (12) | |
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UNITS 0 STAfss NUCLE AR REGULATORY COMMISSION
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NEMORANDUM FOR:
K. Wayne Hodges. Chief Reactor Systems $ ranch Division of Engineering & Systems Technology
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Office of Nuclear Reactor Regulation i
i FRON:
G. N. Lauben, Section Leader i
Accident Management Section
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Reacter 8 Plant $ystems tranch Office of Nuclear Regulatory Research j
$URJECT:
Co mENTS ON A DPV CONCERNING EARLY BLOWOOWN CLA00!NG
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RUPTURE DURING A LARGE BREAK LOCA t
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Per your request, I have reviewed certain aspects of the DPV on Containment
' Isolation Valves at Zion.
In particular, I addressed the issues raised with
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respect to cladding rupture of hiph burnup high pressure fuel early in blowdown prior to containment iso ation (about 7 seconds). The cessents are enciesed.
If you have any questions, please contact me on x23573.
I
- 2. @.k S. N. Lauben, Section Leader f
Accident Managenent Section Reactor & Plant Systems Branch I
Office of Nuclear
- Regulatory Research
Enclosures:
As stated cc: R.B.A Licciarde i
A. Thadani 9
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Comments on a DPV Concerning Early Blowdown i
Cladding Rupture During a Large Break LOCA in a DPV (reference 1) Bob Licciardo has postulated that PWR fuel rods with high burnop and high internal pressure could sustain cladding rupture within a few seconds of a large break LOCA prior to containment isolation. This is further postulated to lead to large off-site releases. Following is some information which may be helpful in addressing some of the issues in the DPV.
seven issues in the OPV are first addressed, then some preliminary j
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observations are made.
The DPV issues are referenced by page nuu6er and a guete er susunary of the issue.
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!ssue 1 (p. 31)
' Appendix K evaluation is not designed to report the i
l oorliest rupture tnat can occur" (Also on pp. 3 4 and 3 5)
While Appendix K does not specifically require sesrching for the earliest rupture, early ruptures would always be the worst with respect to 50.46 limits if they were calculated to occur.
Vendor analyses in the past have shown that l
because of the extensive cladding swelling prior to rupture, the resultant low transient gap conductance severely limits blowdown heat removal. As a
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l consequence, vendor evaluation model calculations showed that the 2200*F PCT was always exceeded. Therefore, the vendors would always need to reduce the peak power to avoid early blowdown cladding ruptures.
Vendor steady state i
fuel themel performance and subsequent LOCA analyses showed that the peak linear heat generation rate (PLNGR) was always low enough to avoid early bloedown swelling and rupture for high burnup pins. These studies were done about 13 to 15 years ago with Appendix K evaluation models which are no longer used. I do not know if analyses with high burnup pins have been done with j
i recently approved fuel performance and LOCA models. The older analyses always l
showed that low burnup post densification pins were always most limiting, in E
fact, because the PLNGR was highest and gap conductance was very low. High l
burnup pins are lowest in PLHGR although the pin pressure is highest.
The con 61 nation of high cladding temperature and higher internal pressure are needed to cause cladding rupture.
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!ssue 2 (p. 3 2)
"This shows that on infringement of DNBR at 1/10 second, average clad temperature increase very rapidly from a nomal operating value j
of 720'F to at'least 1350'F, and then to 1750'F, over a total period of seven i
socor.ds."
j l
i 1750'F is indeed a very high early blowdown peak cladding temperature (PCT),
but virtually impossible for a high burnup pin with a much lower PLHGR.
If a high burnup pin reached 1750'F, at 7 seconds it would aest likely rupture.
l More realistic, LOCA analyses have been performed as part of the Code scaling, j
Applicability, and Uncertainty program in Ris. A best estimate analysis was l
perfomed 'and ende uncertainties evaluated for a large break LOCA (reference i
!).
In order to accomplish this, sensitivity studies were perfomed which l
varied gap conductance, peaking factors and several other variables. The f
plant used was a Westinghouse 4-loop 3411 Mt plant with 17x17 fuel and a loi burnup of only 16000 MWD /NTU which resuited in a PLHGR of 3.35 kw/ft.
The l
blowdown peak for the nominal CSAU case was 1103'F (see figure 1). Based on j
over 250 clad temperature calculations and using Monte Carlo stapling j
techniques, it was detemined that the 95th percentile blowdown PCT was 1447'F.
It has been detemined that 15:15 pins (as used at Zion) with burnups greater l
than 40,000 MWD /MTU have PLHGRs no greater than 5.17 kw/f t.
Using the CSAU calculated sensitivity of blowdown PCT to LNGR, the value of 1447'F can be j
extrapolated to approximately 1265'F for the 5.17 kw/ft PLHGR high burnup 15i15 I
pin. This illustrates that the 1750'F blowdown PCT calculated by Westinghouse is quite conservative, especially for a high burnup pin.
I believe that this f
Westinghouse calculation is probably at least 10 years old.
e issue 3 (p. 3-2)
"Enhibit 10 also shows that W fuels require a design limit j
of 15 on cladding strain as a design limit, and 1.75 as a damage limit. The work of this section 3 will show how both of these limits can be exceeded inside the seven seconds on infringement of DNBR during the course of a LOCA, As exhibit 10 states, these design values are for nominal operatten or overpower conditions, gt LOCA. Also, DN8R infringement has never been t
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I considered the operant criterion for fuel failure during a LOCA. Although, I l
as told that this is not as clear as it should be in the standard review plan er any applicable reg. guides.
Incidentally, PBF LOCA test do not show DNB
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occurring until 3-4 seconds for a very severe LBLOCA (reference 3).
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Issue 4 (p. 3 3)
".... there is a need for empirical tests to deter:aine swelling and burst (rvpture) characteristics under these same synamic i
conditions."
f The results of the P5F LOCA tests satisfy this condition and will be discussed as part of Issu' 7.
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!ssue 5 (p. 3 3)
" Reference inforsetton shows that internal clad pressure i
under nomally operating conditions is of the order of 1400 psig for new fuel f f
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and expected to increase to 2250 psig at the end of the 3rd cycle (for the fue1).*
It is~ not known what reference information is being invoked here. GAPCON calculations show the following results.
TABLE 1 GAPCON Pin Pressuit Calculations Code Fuel PLHGR Burnup Pressure kw/ft MWD /MTU (psig)
GAPCON 15x15 15 0
1700 GAPCON 15x15 10 50,000 2700 GAPCON 15x15 5
50,000 2500 GAPCON 17x17 15 0
1900 GAPCON 17x17 10 50,000 3300 e
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The reference 4. SAPCON calculations were performed 9 to 10 years ago. The PAD
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3.4 model (reference 5) was approved by the NRC for design and safety analysis i
in May 1988. Proprietary calculations done with PAD 3.4 showed substantially j
lower pressures at comparable burnups and PLNGRs.
It is well known that the GAPC0N fission gas release nosel is very conservative. The PAD calculations were done at an arbitrarily high PLNGR and would show an even lower pressure j
at the reduced kw/ft.
Issue 6 (p. 3 3)
"It is proposed that 1sunedtately, on a LOCA as clad
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temperature inc'reases to 1350'F gap pressure will increase by 205, to 1800 l
psig..... At 7 seconds into the event, clad temperature has increased further to 1750'F.... From this, it can be proposed that gap pressure for the complete rod can increase by 365 over its normal operating value to 2100 f
psig."
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i The basis for concluding that pin pressure increases during an LSLOCA blowdown I-is not known and contrary to the evidence. A series of 31arge break LOCA simulations (reference 3) (LOC-3, LOC S. and LOC-6) were performed in PBF with
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well instrumented Zircaloy clad UD, fuel elements pre-pressurized to simulate
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low and high burnup PWR fuel. P8F blowdowns are quite severe compared to postulated PWR LBLOCA blowdowns.
In PBF, the pressure decrease and rate of mass loss is very rapid. No good reverse flow blowdown heat transfer is evident as is the case in LOFT results or PWR analysis.
Figure 2 (reference 6)showsthefuelrodpressureforrod3intestLOC-3. Also, shown are FAAP-76 calculations using two different plastic deformation models. Clearly, pressure jgg3gg throughout the transient. Figure 31s a plot showing l
measured pressure decrease for Rod 11 in Test LOC-6. A FRAP-T6 l
characterization calculation was done for a postulated L8LOCA in Zion (reference 7)whichalsoshowedapressuredecreasethroughoutthetransient.
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Issue 7 (p. 3 5) - Concern is expressed about the relevance of electrically heated rods used in defining the swelling and rupture curves in NUREG-0630.
l It is suggested that the TREAT data shown in NUREG 0630 (reference 6) would be more realistic. Also, on pp. 4 3 and 4-4, this concern is restated.
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Comparison of measured and calculated fuel rod plenum Figure 2.
pressure ve'rsus time for Rotf 3 of P8F test LOC-3.
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It is clear that TREAT data is anomalous compared to the electrically heated
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rods and is attributed to difficulties in obtaining accurate temperature datt in the burst region. A better source of in. reactor data is the PBF series j
discussed previously.
Figure 4 is a plot from NUREG 0030 (reference 8, J
exhibit 16).
Included are data points with temperature uncertainty for the g ruptured rods in the PBF LOC series of tests, and the FRF data from TREAT.
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1s clear that the more recent PBF data is very consistent with the NUREG-0630 curves.
Observations Regarding LSLOCA Blowdown Rupture of High Burnup Fuel Rods.
The main contributors to fuel cladding rupture are high pressure drop across the cladding and high cladding temperature. Early post-DN8 cladding temperatures are determined to a very large degree by pre-accident stored l
energy which is a function of local peak power (PLHSR), pre. accident gap conductance, effective U0, thermal conductivity, blowdown heat transfer, and critical flow model. TheCSAUstudy(reference 2)confirmedthisassessment.
Of these variables, only PLH6R is controllable by plant operators, and then only to a limited degree. High burnup, third cycle fuel is always placed in low power regions. Pin pressure is determined by pre-pressurization and fission gas release. As shown in reference 3 and 6, pin pressure does not exhibit a direct functional relationship to blowdown cladding temperature.
As noted earlier, the CSAU 17x17 95th percentile PCT of 1447'F (reference 2)
The could be approximately extrapolated to 1265'F for a high burnup 15x15 pin.
15x15 PCT calculated at 13.26 Lw/f t (reference 7) was 1543'F. The Zion hot pin l
did not rupture in reference 7.
The reference 7 calculation extrapolated to 5.17 kw/ft would result in a PCT of about 1187'F. Therefore, 1065'F determined l
l previously appears to be a good high side estimate of blow %wn PCT for a high l
burnup 15x15 pin.
In both reference 7 and reference 2, this blowdown peak occurred between 5 and g seconds.
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M model and 015E. correlation of rgture tagerature as a functlen of eneineerlag i
hoop stress and ra y rate,i e4b PS F LStoCA 4c34,c379 3.
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i PAD 3.4 calculations for a 15x15 pin were not perfomed in reference 5, but by extrapolating 1717 PAD analyses and the v61ues in Table 1, it is estimated that the pre accident 15x15 pin pressure at end of cycle 3 would be about 1800 psi. Based on the pressure decrease calculated for the !!x15 pin in the first 5 seconds in reference 7, it is estimated that the pin pressure at 5 seconds for a high burnup 15 15 pin wot1d be 1520 psi. The system pressure at that time was determined to be g20 psi. The pressure drop across the clad is therefore 600 psi and the engineering hoop stress is estimated to be 4.7 KP51, As shown in Fipwre 3, this is well below the NURES-0630 curves and even below i
the TREAT data. Therefore, it is not expected that av high burnup pins which l
have low LNGRs would experience any early blowdown ruptures, i
Itshouldbenoted,however,thatthisisbasedonextrapolations,andsurely'f direct calculations based on actual condition would be preferable. Also,if./
indeed high burnups are expected in the future with higher I,H6R, this issue should be revisited.
In fact, when significant changes in fuel design models and blowdown LOCA models are proposed, this issue shov1d also be addressed, j
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1
7 REFERENCES 1.
R.B.A. Licciardo, An Evaluation of the Criterion for and the Calculation
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of Offsite Doses Deriving from Open Containment Purge Valves During a f
LOCA a Zion Units 142, July 20, 1989.
J Z.
N. Zuber, et.al., Quantifying Reactor Safety Margins:
)
Application of Code Scaling, App 11f. ability, and Uncertainty Evaluation Methodology to a Large treak Loss of Coolant Accident NURES/CR 5249
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(Draft)DraftDate: August 1, 1989
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3.
J.M. Broughton, et.al., P8F LOCA Test LOC-6, Fuel Behavior Report,
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NUREG/CR-3184, April 1983.
4.
D.L. Acey, J.C. Vogelwede, A Comparative Analysis of LWR Fuel Designs,
)
NUREG-0559, July 1980.
l i
i 5.
R. A. Weiner, et.al., leproved Fuel Performance Models for Westinghouse l
Fuel Rod Design and Safety Evaluations, WCAP-10851 P-A, August 1988.
t 6.
L.J. Stefken, Developmental Assessment of'FRAP-T6 Interim Report No.
l EGG.CDAP-5439, May 1981.
7.
L.J. Stefkon, (Personnel communication to G.N. Lauben) Calculation of
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Response of Fuel Rod in Zion Reactor During Large Break LOCA, July 18, 1989.
l 8.
D.A. Powers, R.0. Meer, Cladding snelling and Rupture Models for LOCA Analysis, NUREG-0630, April 1980.
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ENCLOSURE 2 s.
i' August 8,1989
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k MJTE TDs Ashok Thadani
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i SLE0ECT: !YV CDmNJPG CaJTAltitN1 LEO.ATICN WU.CS AT Z1CN Fur your request in SAD Cfi-54, I tuvo revienM the opplicability of Feg.
i Cuidos, SFP's and BTP's cited in trn DFV. Ttu following are my conwnts en j
i the subject.
i 1te major refertnce within the EFV that is within the eft.B scope is Branch Technical Fosition CSD 6-4.
This DlP Is refermiced in SFP section 6.0.4 f
Centainmmt Itclation Systan. Etwner, the focus of the DFV only addresses f
the contents of DTP. To present a complete picture of the staf f's position, !
believe it is worttwhile to note the elements of SFF 6.0.4 and how the BTP CSB f
f 6-4 is referenced, f
i SFP 6.0.4, AGIFTRE CRITERIA does provide some guidance in this regard.
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Specific criteria necessary to meet the relevet requirements of the j
i i-regulations for purge valves is provided in subsection n.
First of all, the l
l guidance for closure time states l
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For lines which provide an open path from the contaiment to the l
stvirons; e.g., tre containment purge and vent lines, isolation valve closure times "on tte order ofi 5 seconds or less may be i
t nEnug.
tbte that tre intent trust be tal.cn as a goal but does not preclude cicatre
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time's greater than 5 seconds.
It also refers to BTP 6-4 for furttur guidence.
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0)t= final reference in the ETF is made which is relevant to the isste at hand.
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't inwt is ttw reference to tte need to perform dose analysis. Subsectiori n
.y 51 et es.;
...rugardino tte sire of tte purge system used during normal plant
. operation ' wx! tte justif.1 cation by acceptable dose consequence.
arialysis, may te waived if tte applicalt ccmnits to limit the use of the purge system to less trun 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> per year while the plant is in the startup, power, hot staridby and hot strtifown modes of ~
l operations.
i There added rvferences more properly reflect the staf f view on purging.
It t
does not indicate that the staff during the development of the SFF believed ttut ttn consequences of purging at the time of e LOCA would rwsult in the
.. y impact asserted in the DFV.
1 Beyond trese connents, I believe that t'w DFV cited the correct sections of l.
l the BTP.
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Jotri A. Kudrick i
Secticn Chief, SFt.B
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