ML20128H427
| ML20128H427 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 10/03/1996 |
| From: | Huffman W NRC (Affiliation Not Assigned) |
| To: | NRC |
| References | |
| NUDOCS 9610090339 | |
| Download: ML20128H427 (29) | |
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UNITED STATES s
j NUCLEAR REGULATORY COMMISSION 2
WASHINGTON, D.C. 30e86-0001 October 3, 1996 APPLICANT: Westinghouse Electric Corporation PROJECT:
AP600
SUBJECT:
SUNiARY OF MEETING TO DISCUSS THE THERMAL-HYDRAULIC UNCERT RESOLUTION PROCESS FOR AP600 DESIGN The subject meeting was held on August 27, 1996, between representatives of Westinghouse and the Nuclear Regulatory Commission (NRC) at the NRC's Rockville, Maryland, office. The purpose of the meeting was to discuss the criteria used for determining which PRA scenarios are risk significant, low-margin cases and subject to more in-depth thermal-hydraulic (T/H) analyses.
Background information for this meeting was provided by Westinghouse letter NSD-NRC-96-4781 dated July 29, 1996, which supplemented the thermal-hydraulic (T/H) uncertainty resolution process outlined in Westinghouse letter NSD-NRC-96-4691 dated April 12, 1996.
!!ighlights of the meeting are summarized below:
The initial screening criterion used by Westinghouse to identify scenarios subject to additional T/H analyses is the occurrence of core uncovery.
t Westinghouse has identified the types of initiating events in conjunction with equipment unavailability that can lead to core uncovery.
For those scenarios where core uncovery is predicted to occur, further screening will be used to identify those risk significant, low margin cases.
4 To identify the risk significant, low margin cases, Westinghouse plans to expand the focused PRA event trees to more precisely address the contribution of system or equipment unavailability which has the potential to contribute to core damage frequency.. Westinghouse does not plan to expand the event tree success paths beyond 3 system failures in order to keep the trees manageable 4
i and because order of 10'ghe frequencies of scenarios with more than 3 failures are on the per year or less.
Westinghouse plans to quantify the frequency of the success paths (which is not normally done for PRAs). Those sequences where core uncovery occurs and the potential contribution of the sequence would be greater than 1 percent of the focused PRA core damage frequency (if the sequence were assumed to result in core damage in lieu of success) will be considered the low margin, high risk sequences.
These sequences will then ba subject to more in-depth T/H analyses using DBA computer codes. The success of the low margin, high j
risk sequences will be based on acceptable core cooling (no core damage),
defined as maintaining the peak cladding temperature below 2200*F assuming Appendix K criteria, except for large break LOCAs, where best estimate assumptions will be used.
gcWC 9610090339 961003 PDR ADOCK 0520 3
a
, October 3,1996 4
The NRC made the following observations:
The expanded event trees should explicitly identify which sequences result in core uncovery and which do not.
l Westinghouse should be prepared to clearly explain the basis for all sequences that it chooses not to analyze in detail, including why the
)
non-core uncovery cases are actually believed not to result in core uncovery.
The NRC contractor questioned the Westinghouse method of using a per-o centage of the focused PRA core damage frequency as a screening criteri-on for selecting success paths for closer T/H analyses in lieu of a
, frequency truncation criterion.
It was unclear if core-damage sequences in the focused PRA would be categorized as core-damage sequences in the baseline PRA and, if not, 4
how this difference would be explained.
In addition, it was also unclear how the unscreened (focused PRA low frequency cases) would be handled in the baseline PRA.
Westinghouse has still not provided its plan for addressing T/H uncer-tainties for long term cooling. Regardless of any event's short term behavior or frequency, nearly all success paths in the focused PRA lead to long term cooling. Westinghouse still needs to demonstrate that long term cooling can be maintained with a high degree of certainty.
l Westinghouse stated that they are proceeding with their detailed T/H analyses based on this plan. However, they were unable to provide an estimate as to when they expected to issue a T/H uncertainty report. Westinghouse also expressed a desire to refocus onto the ragulatory treatment of non-safety systems (RTNSS), which subsumes the T/H uncertainty issue.
, is the list of meeting attendees. Attachment 2 contains handouts provided by Westinghouse during the meeting to supplement the presentation and discussions.
original signed by:
William C. Huffman, Project Manager Standardization Project Directorate Division of Reactor Program Management Office Of Nuclear Reactor Regulation Docket No.52-003 Attachments: As stated cc w/ attachments:
See next page DISTRIBUTION:
See next page DDCUMENT NAME: A:8-27MTG. SUM (91 AP600 DISK) i Tm secebe e copy of ttdo document, andsete In the ben: 'C' = Copy without ettschment/ enclosure
- E" = Copy with attectwnent/ enclosure
- N" = No copy 0FFICE PM:PDST:DRPM SC:SRXBAS)A l D:PDST:DRPM l l
NAME WHuffman:sec3 eAlevig /k h TQuay4724t DATE 09)Q(j96 09/k. /AV
/
N/T/96 0FFICIAL RECORD COPY
e a
Q1SJRIBUTION w/ attachments.:
Doc 4et File PUBLIC PDST R/F TMartin BGrimes TQuay WHuffman TKenyon JSebrosky DTJackson JFlack, 0-10 E4 DMcPherson, 0-8 E2 BHardin, 0-10 E4 RJones, 0-8 E23
- NSaltos, 0-10 E4 RCaruso, 0-8 E2 GHsii, 0-8 E23 DISTRIBUTION w/o attachments:
i WRussell/FMiraglia, 0-12 G18 RZimmerman, 0-12 G18 AThadani, 0-12 G18 EJordan, T-4 D18 ACRS (11)
JMoore, 0-15 818 WDean, 0-17 G21 l
GHolahan, 0-8 E2 TCollins, 0-8 E23 i
0900G3
- _ = - -
Westinghouse Electric Corporation Docket No.52-003
~
cc: Mr. Nicholas J. Liparulo, Manager Mr. Frank A. Ross Nuclear Safety and Regulatory Analysis U.S. Department of Energy, NE-42 Nuclear and Advanced Technology Division Office of LWR Safety and Technology Westinghouse Electric Corporation 19901 Germantown Road P.O. Box 355 Germantown, MD 20874 Pittsburgh, PA 15230 i
Mr. Ronald Simard, Director Mr. B. A. McIntyre Advanced Reactor Program Advanced Plant Safety & Licensing Nuclear Energy Institute Westinghouse Electric Corporation 1776 Eye Street, N.W.
Energy Systems Business Unit Suite 300 Box 355 Washington, DC 20006-3706 J
Pittsburgh, PA 15230 Ms. Lynn Connor Mr. John C. Butler Doc-Search Associates Advanced Plant Safety & Licensing Post Office Box 34 Westinghouse Electric Corporation Cabin John, MD 20818 Energy Systems Business Unit Box 355 Mr. James E. Quinn, Projects Manager Pittsburgh, PA 15230 LMR and SBWR Programs GE Nuclear Energy Mr. M. D. Beaumont 175 Curtner Avenue, M/C 165 Nuclear and Advanced Technology Division San Jose, CA 95125 Westinghouse Electric Corporation One Montrose Metro Mr. Robert H. Buchholz 11921 Rockville Pike GE Nuclear Energy Suite 350 175 Curtner Avenue, MC-781 Rockville, MD 20852 San Jose, CA 95125 Mr. Sterling Franks Barton Z. Cowan, Esq.
U.S. Department of Energy Eckert Sesmans Cherin & Mellott NE-50 600 Grant Street 42nd Floor 19901 Germantown Road Pittsburgh, PA 15219 Germantown, MD 20874 Mr. Ed Rodwell, Manager Mr. S. M. Modro PWR Design Crrtification Nuclear Systems Analysis Technologies Electric Power Research Institute Lockheed Idaho Technologies Company 3412 Hillview Avenue Post Office Box 1625 Palo Alto, CA 94303 Idaho Falls, ID 83415 Mr. Charles Thompson, Nuclear Engineer AP600 Certification NE-50 19901 Germantown Road Germantown, MD 20874
Westinghouse Electric Corporation Docket No.52-003 cc: Mr. Nicholas J. Liparulo, Manager Mr. Frank A. Ross Nuclear Safety and Regulatory Analysis U.S. Department of Energy, NE-42 Nuclear and Advanced Technology Division Office of LWR Safety and Technology Westinghouse Electric Corporation 19901 Germantown Road P.O. Box 355 Germantown, MD 20874 Pittsburgh, PA 15230 Mr. Ronald Simard, Director Mr. B. A. McIntyre Advanced Reactor Program Advanced Plant Safety & Licensing Nuclear Energy Institute Westinghouse Electric Corporation 1776 Eye Street, N.W.
Energy Systems Business Unit Suite 300 Box 355 Washington, DC 20006-3706 Pittsburgh, PA 15270 Ms. Lynn Connor Mr. John C. Butler Doc-Search Associates Advanced Plant Safety & Licensing Post Office Box 34 Westinghouse Electric Corporation Cabin John, MD 20818 Energy Systems Business Unit Box 355 Mr. James E. Quinn, Projects Manager Pittsburgh, PA 15230 LMR and SBWR Programs GE Nuclear Energy Mr. M. D. Beaumont 175 Curtner Avenue, M/C 165 Nuclear and Advanced Technology Division San Jose, CA 95125 Westinghouse Electric Corporation One Montrose Metro Mr. Robert H. Buchholz 11921 Rockville Pike GE Nuclear Energy Suite 350 175 Curtner Avenue, MC-781 Rockville, MD 20852 San Jose, CA 95125 Mr. Sterling Franks Barton Z. Cowan, Esq.
U.S. Department of Energy Eckert Seamans Cherin & Mellott NE-50 600 Grant Street 42nd Floor 19901 Germantown Road Pittsburgh, PA 15219 Germantown, MD 20874 Mr. Ed Rodwell, Manager Mr. S. M. Modro PWR Design Certification Nuclear Systems Analysis Technologies Electric Power Research Institute Lockheed Idaho Technologies Company 3412 Hillview Avenue Post Office Box 1625 Palo Alto, CA 94303 Idaho Falls, ID 83415 Mr. Charles Thompson, Nuclear Engineer AP600 Certification NE-50 19901 Germantown Road Germantown, MD 20874
NEETING ON THERMAL-HYDRAULIC UNCERTAINTY ISSUE RES9LL' TION PLAN FOR THE AP600 AUGUST 27, 1996 MEETING ATTENDEES H8ME ORGANIZATION DEBRA OHKAWA WESTINGHOUSE CINDY HAAG WESTINGHOUSE LARRY HOCHREITER WESTINGHOUSE BRIAN MCINTYRE WESTINGHOUSE CHARLES THOMPSON DOE GARY HOLAHAN NRC TIM COLLINS NRC ALAN LEVIN NRC CONSTANTINE TZANOS ANL BILL HUFFMAN NRC Attachment I
1 HAND 0UTS PRESENTED AT THE AUGUST 27, 1996, NEETING ON THERMAL-HYDRAULIC UNCERTAINTY ISSUE RESOLUTION FOR THE AP600 9
4
t T/H UNCERTAINTY RESOLUTION PLAN D. K. Ohkawa L. E. Hochreiter August 27,1996
AGENDA 3
h Introduction Process Overview i
Types of Core Uncovery Expanded PRA Event Tree Methodology Risk-Significant, Low-Margin Scenarios T/H Analyses Summary NRC Feedback i
c:\\wp\\ap600\\thunomiB27%.mtg August 26,19%
1
G INTRODUCTION A 25-page write-up of the T/H uncertainty resolution process was sent to the NRC on July 29,1996 Process information Examples to illustrate and validate concepts Purpose of today's meeting is to discuss the plan, and to obtain NRC feedback c;\\wp\\ap600ishuncen\\82796.mtg August 26,1996 2
DEFINITION OF T/H UNCERTAINTY Passive nature of the safety-related systems in AP600 causes concern that uncertainties in predicting small changes in the system conditions could lead to different conclusions on success of core cooling Goal is to show that the consideration of T/H uncertainty does not significantly impact the PRA results Identify risk-significant scenarios Bound the uncertainty, rather than quantify it Use the Focused PRA to determine impact, so that active systems will not camouflage the importance of passive systems c:\\wp\\ap6(XNhuncert\\827%.mtg August 26,1996
PliOCESS OVERVIEW The T/H resolution process brings together information from the PRA and T/H analyses PRA directs attention to the most probable accident scenarios j
T/H analyses direct attention to accident scenarios that most greatly challenge core cooling c:\\wp\\ap6(KNhuncertW2796.mtg August 26,19%
4
FIGURE 1 T/H UNCERTAINTY RESOLUTION PROC,ESS PART 1 PARI 2 IDENTIFY TYPES OF CORE EXPAND EVENT UNCOVERY AND TREES AND WHICH INITIATING QUANTIFY EVENTS THEY SUCCESS PATHS APPLY TO I
l PART 3 IDENTIFY IMPACT ON FOCUSED PRA IF CORE UNCOVERY 15 COUNTED AS CORE DAMAGE PART 4 IDENTIFY RISK SIGNIFICANT SCENARIOS i
PART 5 j
IDENTIFY KEY T/H ASSUMPTIONS FOR RISK SIGNIFICANT, CORE UNCOVERY SCENARIOS
/
PART 6 FOR EACH RISK SIGNIFICANT CORE UNCOVERY SCENARIO, IS YES SUCCESS CRITERIA NOTRUMP/LOCTA PCT r
ARE PROVED TO BE
< 2200 DEG F RIGOROUS WITH BOUNDING KEY T/H ASSUMPTIONS?
NO y
OPTIONS ASSESS IMPACT OF ASSESS COUNTING SCENARIO AS ALTERNATIVE CORE DAMAGE IN THE OPTIONS BASELINE & FOCUSED PRA 5
TYPES OF CORE UNCOVERY s.
Purpose:
Find scenarios closest to the limits of acceptability, and thus ones most susceptible to T/H uncertainty having an impact on the conclusions of success versus core damage Core uncovery is used as screening criterion to fulfill purpose; acceptance criterion for core cooling remains at 2200 F PRA PIRTs were developed with focus on issues that have potential impact on minimum coolant inventory; the same challenges can be defined in terms of the equipment loss that causes them to occur I
c:\\wp\\ap600\\thuncert\\82796.mtg August 26,1996 6
FIGURE 2 TYPES OF CORE UNCOVERY Tme EARLY LATER LENG-TERM Pereoel UNCDVERY UNCOVERY RECIRCULATEM l
Controume -
to.. or to.. or c 1-
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O No Make-up Accumulator No Rapact Reduced No More DeFFicult Inventory Depletes Inventory Inventory Make-up to Achieve and Prolden +
If RCS Prior to Make-se Make-up Vhen Maantaan Detta P Pressure es Operator During Durmg ADSis for IRVST
> 700 p.10 Interventeon Blowdown Reftood Actuated Gravtty Injecison Intiating i
i l
I I
I Events NLOCA MLDCA ILOCA LLOCA NLDCA TBD Ewience DVI Line Break CMT Lme CMT Line SLDCA Core Uncovery SGTR Transeents s
7
EXPANDED PRA EVENT TREE METHdDOLOGY A single success path in the PRA represents many
=
combinations of equipment failures and successes Frequency of a single success path in current PRA /
Focused PRA is relatively large, and if treated as core damage, would have unacceptable impact on CDF and LRF
" Expanded" event trees allow differentiation between i
success scenarios that are grouped together in the PRA Baseline scenario accident analysis may show core uncovery 4
Other sets of functioning equipment, represented by the same success path, may not result in core uncovery cAwp\\ap60msbuncert\\827%.nng August 26,1996
Figure 4 MLOCA Event Tree in Focused PRA 1 or 2 1 OK 1 or 2 RECIRC 2,3'or 4 IRWST 0
2 CD 1 or 2 ADS-4 0
3 CD CMT 0 or 1 4 CD 1 or 2 5 OK NLOCA 1 or 2 RECIRC 1 or 2 IRWST 0
6 CD 2,3 or 4 Ace 0
7 CD 0
ADS-4 0
8 CD 0 or 1 9 CD OK = Successful Core Cooling CD = Core Damage c ar-24==
Page 9
w 24 1996
EXPANDED MLOCA EVEArr rgre W
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" RULES" FOR EVENT TREE EXPANSION 1.
Cannot redefine the definition of success 2.
Do not continue to expand beyond 3 system failures Maintains manageable event tree size j
Further differentiation cannot be risk important 3.
Arrange top events to minimize the number of paths j
4.
The top event options for expanding the event tree are summarized in Table B c;\\wp\\ap600\\thuncen\\82796.mtg August 26,19%
Table B Options for Expanding Esent Tree Success Paths Opnon Used?
Reason Break size No Break size and location are already used to define different initiating events. Although within an initiating event there remains some variability in the plant response depending on the Break location size and location of the break, there was no added value to Uf!IeFBFfs i or 2 CMTs does not make a significant n
Number of CMTs Yes difference in the course of the accident progression. However, the CMTs are highly reliable, and make an important contribution to the refinement of the frequency of a given accident scenario. That is, for a given scenario, the most likely condition is both CMTs available.
Number of stage I ADS lines No Stage 1 ADS lines are small, and do not significantly impact the course of the accident progression.
Number of stage 2/3 ADS Yes Stage 2 and 3 ADS lines can impact the ability to achieve l
lines IRWST gravity injection.
Number of stage 4 ADS lines Yes Stage 4 ADS lines can impact the ability to achieve IRWST gravity injection.
Number of accumulators Yes The number of accumulators is important to the core uncovery issues discussed in Section 3.1.
Number of IRWST lines No The ability to achieve IRWST gravity injection and longterm recirculation is most dependent on the number of open ADS lines and whether the containment is isolated. The number of s
j Number of recirculation lines lines open, as long as there is a pathway for injection, is not as crucial an element to successful core cooling.
Whether containment is fully Yes The containment back pressure that occurs when the isolated containment is isolated can impact the ability to achieve IRWST gravity injection. Also, containment isolation impacts the large release frequency calculation if the accident scenario is counted as core damage.
e m an Page 12 August 16, IM6
QUANTIFICATION OF SUCCESS PATHS, i
i I
Each success path is quantified individually i
For this application, non-minimal quantification is used and is acceptable for two reasons:
j The total success frequency is not desired or used I
Since the resulting success path frequencies overstate i
actual values, the impact of assigning a success path to failure is also overstated (i.e., this is a bounding i
approach) i l
1
)
i I
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l c:\\wp\\ap600\\thuncert\\827%.mtg August 26,1996 1
13
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1 RISK-SIGNIFICANT, LOW-MARGIN SCENARIOS Compile information from types of core uncovery (steli 1) and event tree expansion (step 2)
Identify PRA impact if the scenarios were not counted as success Tables for each type of core uncovery (step 3)
Summary (step 4)
" Risk significant" (for further T/H analyses) will be defined based on scenarios that influence the Focused PRA CDF or LRF by more than 1%
l l
i l
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c:\\wp\\ap600\\thuncert\\82796.mtg August 26,1996 l
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4
-a Table 3 No Rapid Make-up Inventory During Blowdown Event Equipment Assumptions Success Frequency if counted as core Path tper year) damage. increase to CI CMT Ace ADS-4 ADS rnema4 PR A 2.3 A CDF A LRF MLOCA Yes 2
0 4
4 17 9E-9 IE-8 7E 10 '"
2 0
4
<4 18 2E-9 2
0 2.3 54 19 3E-Il 1
0 2.3.4 14 32 2E-Il No 2
0 2.3.4 54 52 2E-Il 2E Il 2E 11 I
O 2.3.4 14 58 *
< 4E-12 CMT Lme
. i a en1 AMil
_IU L.1 1 1\\l1111 RM 1
- nL L,i in n t-Notes
(!)
LRF for scenarios with containment isolation is estimated at 6% of core damage.
(2)
Event tree is not decomposed to separate 0 versus I accumulator on this success path. The secoario with no accumulators i', a swall part of the path frequency.
l l
c w w ab Page 15 i
August 26,1996 l
l
s Table X (PARTIAL) SUMM ARY OF CORE UNCOVERY SCENARIOS THAT ARE SUCCESS IN FOCUSED PRA (Sorted by Contribution to CDF)
Event Equipment Assumptions Type of Core if counted as core Uncovery damage, increase to CI CMT Acc ADS-4 ADS 2,3 r - ioni ACDF A LRF LLOCA Yes 2
1 4
23,4 4
9E-7 6E-8 NLOCA Yes 0
2 4
54 i
FE-8 SE-9 NLOCA Yes 2
0 4
54 5
SE 8 3E 9 MLOCA Yes 0
2 23.4 54 2B 2E-8 IE-9 MLOCA Yes 2
0 4
54 3
IE-8 7E-10 DVI Line Yes 0
1 4
54 1
6E-9 4E-10 LLOCA No 2
1 4
14 4
1E-9 IE-9 MLOCA Yes 0
1 23,4 54 2A 2E-10 9E-12 NLOCA No 0
1,2 23,4 54 1
IE-10 1E-10 NLOCA No 2
0
' 2,3,1
$4 5
9E-Il 9E-Il MLOCA No 0
2 23,4 54 2B 3E-Il 3E-Il MLOCA No 0
I 23.4 54 2A
< 3E-Il
< 3E.11 MLOCA No 2
0 23,4 54 3
2E-Il 2E-Il DVI Line No 0
1 23.4 54 1
IE Il IE-Il inE liti idh EnF IIVI,IR cwma Page 16 Augwa 26,1996
T/H ANALYSES T/H analyses, with nominal assumptions, are currently being performed for MAAP4 benchmarking l
Further analyses, with more conservative assumptions, will be performed for Thermal-Hydraulic Uncertainty Resolution l
Outcome of PRA exercise will determine scenarios; they will fit within three areas:
Large-break LOCA Small-break LOCA Long term cooling c:\\wp\\ap600\\thuncen\\82796.mtg August 26,1996 17
T/H ANALYSIS METHODOLOGY Large-break LOCA i
WCOBRA/ TRAC calculation will be performed The uncertainties derived from the baseline best-estimate will be applied to this case to determine if the PCT < 2200 F
~
Ample validation exists for WCOBRA/ TRAC for Large-break LOCA Small-break LOCA NOTRUMP cases will be performed to determine if the PCT
< 2200 F The Appendix K version of NOTRUMP will be used to address the uncertainties Ample validation exists for NOTRUMP core uncovery / level swell Long term cooling WCOBRA/ TRAC cases will be analyzed to' determine if the PCT < 2200 F WCOBRA/ TRAC will be used with Appendix K assumptions on increased decay heat and maximum line resistances c-\\wp\\ap600Wiuncert\\82796.mtg August 26,1996 18
4 UNCERTAINTY TREATMENT
}
Large-break LOCA f
Uncertainties will have been quantified as part of the best-estimate analysis and can be applied to PRA case 1
(1 accumulator)
Small-break LOCA Appendix K
assumptions will be used to address
]
uncertainties.
Best-estimate LBLOCA and BE SBLOCA have shown this to be conservative.
Use of higher decay heat penalizes system depressurization.
Long term cooling WCOBRA/ TRAC with the Appendix K assumptions will i
address uncertainties.
Use of higher decay heat is conservative since it will pressurize the RCS and reduce DVI now.
4 c:\\wp\\ap600\\thuncert\\827%.mtg August 26,1996 19
SUMMARY
OF T/H ANALYSES The conservative design basis criteria (PCT < 2200 F) is used for determining acceptability of a given sequence 1
An approach exists which will address the analysis l
uncertainties for each transient type such that the sequence results (i.e., acceptable or not acceptable) can be determined with confidence i
The results from this approach will be documented and submitted to the NRC 1
l l
c:\\wp\\ap60(Athuncen 32796.mtg August 26,1996 20
SUMMARY
OF T/H UNCERTAINTY RESOLUTION The details of a process plan to resolve outstanding T/H uncertainty issues have been provided Scenarios are chosen based on:
Risk significance (Impacts Focused PRA CDF or LRF by at least 1%)
Low margin (Potential that the consideration of T/H uncertainty could impact the conclusion of success versus core damage)
Conservative analyses performed to bound T/H uncertainties c:\\wp\\ap@hhuncen\\827%.mtg i
August 26,1996 21