ML19345B557
| ML19345B557 | |
| Person / Time | |
|---|---|
| Issue date: | 09/30/1980 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-1777, NUDOCS 8012020037 | |
| Download: ML19345B557 (6) | |
Text
AcRS.17 4)
E DATE ISSUED:
9/30/80 MINUTES OF THE le RO ACRS SUBCOMMITTEE MEETING ON CLASS 9 ACCIDENTS AUGUST 28, 1980 WASHINGTON, D.C.
The ACRS Subcommittee on Class 9 Accidents met on August 28, 1980 in Washington, D.C. to continue examination of the role of Class 9 Accidents in the licensing process and to consider hydrogen generation and control during degraded core accidents.
ACRS members present were W. Kerr - Subcommittee Chairman, S. Lawroski, C. Siess, J. C. Mark, and H. Etherington. ACRS consultants in attendance were R. Seale, S. Siegel, J.' Lee, R. Strehicw, G. Schott, and D. Gregory.
Presentations were made by Sulter - NRC/NRR, Fleishman - NRC/OSD, Medeiros -
NRC/OSD, Shapaker - NRC/NRR, Tinkler - NRC/NRR, Bowman - LLL, Hubbard - R&D Associates, Lau - TVA, and Miller - NSAC.
Attached are a list of documents provided to the Subcommittee and a copy of the meeting agenda.
Introductory Remarks by the Chairman Dr. Kerr noted that a number of questions currently exist regarding NRC's treatment of hydrogen. For example, (1) will a design basis or a probabilistic approach be taken in dealing with the problem; (2) will treatment of the hydrogen problem be conservative or realistic; (3) will the Staff's suggested approach to Class 9 Accidents be published prior _to rulemaking; (4) does the Staff have a safety goal for mitigation features; (5) how much' have TMI-mandated changes reduced the prob-ability of hydrogen-generating accidents; and (6) will single failure criteria be applied to mitigation features.
NRC Efforts on Hydrogen Generation and Control Mr. Butler, NRC/NRR, summarized NRC actions on hydrogen generation and control.
The Staff issued SECY 80-107, 80-107A, and 80-107B on hydrogen control. A draf t 8012020 o37
Class'9' Accidents Mtg
. August 8, 1980 interim rule has been prepared (SECY 80-399), to become effective in 1981. The -
rule requires inerting BWR Mark I and Mark II containments.(only two operating BWRs currently are not inerted - Vermont. Yankee and Hatch-2). Requirements
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for Mark IIIs and Ice Condensers are still being studied.
There will probably be no requirements for the "large dry" containments.
Short term programs' on' Ice Conden',er containments were described, including:
(1) efficacy' of igniters - LLL; (2) MARCH calculations-BCL; (3) alternate hydrogen control measures-Sandia; (4) strcugth of containments-Ames; and (5) TVA/ Westinghouse studies.
The 5'.aff position on Sequoyah is that full power operatio'n need not await the igniter system.
The Staff does not currently have a position on the specifics of hydrogen generation
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that must be dealt with, for example, the rate and amount of hydrogen generation, and the design approach (probabil.istic or design basis). The Staff does not expect to formulate a position prior to rulemaking.
i Interim Rule on Hydrogen Control Mr. Fleischman, NRC/NRR, described the proposed interim rule on hydrogen, the intent of which is to. insure protection up to 50% equivalent clad / water reaction with evolution expected to occur over several hours. The interim rule requires i
licensees to perform analyses of hydrogen up to 75% equivalent clad / water reaction with evolution over' periods of from of 0 to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. Dr. Kerr noted the interim rule gives only vague guidance to the licensees on what they are supposed to analyze.
Rulemaking on Hydrogen Control Mr. Medeiros, NRC/OSD, discussed long'tenn rulemaking on degraded cores and
-the Advance Notice of Rulemaking -(ANR), which will be released soon.
The ANR solicits comments on-hydrogen control measures and inerting.
Class 9 Accidents .cg August 8, 1980 Sequoyah Ignition System - TVA Experiments Mr.- Shapaker, NRC/NRR, discussed the Sequoyah containment ignit',on system. The system is currently installed.
It is planned that it be manually activated upon actuation of engineered safety features. The system makes use of 30 glow plugs; 18 in the lower compartment; 5 in the lower plenum of ice condenser; 3 in the upper plenum of the ice condenser; and 8 in the upper compartment.
It is powered by emergency power sources. -. Glow plug operating temperatures are *1700 F, which is about 500 F above the hydrogen ignition point.
Tests are being performed to characterize br'rogen combustion in the presence of steam and to determine the reliability of glow plugs for ignition.
A report on the-initial test phase is due October 1,1980. Longer-tenn work will study; (a) effect of hydrogen c'ombustion on eauipment, (b) effect of containment sprays; (c) possible installation of additional glow piugs; and (d) alternate hydrogen control measures.
TVA will submit to NRC plans for determining effect of hydrogen burning on essential components. TVA expects their hydrogen control studies to continue for 1 year.
Hydrogen Control Experiments - NRC Sponsored Programs Mr. Tinkler, NRC/NRR, described NRC programs on hydrogen control. LLL is testing the operation of the Sequoyah igniter systems in order to confirm TVA results. Also, LLL is surveying hydrogen monitors.
BCL is performing analyses of some aspects of the igniter system using MARCH.
MARCH does not treat details of hydrogen burning, rather, the burn parameters must be input to the code. Homogeneous mixtures are assumed. Mr. Tinkler charac-terized the MARCH code as a significant improvement over previous. ways of doing containment analyses, and said the code gives reasonably good results.
Sandia will.perfonn longer-term work on hydrogen contrui systems su. as water fog, hydride converters, Halon-1301, and ignition systems.
s Class. 9 Accidents Mtg - August 8,1980 There were some general comments made:
'Dr.: Strehlow ind'icated that turbulent flow in long air ducts could cause transition to detonation in hydrogen concentrations as low as 8%,
which may' be a serious concern.
'Dr. Gregory indicated that hydride converters are not likely to be feasible because they oxidize in air, thus losing their effectiveness.
' System pressure has ~little effect on flammability limits of hydrogen mixtures.
NRC-Soonsored LLL Program on Hydrogen Mr. Bowman, LLL, described the igniter. test program.
The program objective; are to (a) test Sequoyah igniters in various-air / steam / hydrogen mixtures, (b) survey hydrogen. detection devices; and (c) perform a literature survey on hydrogen com-bustion. A q'uick-look report is due October 30, 1980, with a final report in January 1981.
-There are 4' types of hydrogen monitors:
(1) catalytic, which measures increas-ing temperature of the catalyst; (2) semi-conductor, which measures change in current; (3) voluma expansion, which changes size with hydrogen absorbtion; and, (4) electrochemical, which measures the output of a battery. The volume expansion device is slow-response (aa 5 minutes)- whereas the.other three types are faster (3 to 30 seconds). The first two types function only up to *P4%
hydrogen, whereas the-latter two-are not so limited.
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MARCH Calculations on Sequoyah Mr. Cybulskis, BCL, summarized MARCH calculations on Sequoyah. The particular 1
accident sequence examined was a small break-LOCA with no ECCS. fpie results indicate the igniter system would prevent overpressurization of containment during the meltdown phase of'this seq'uence. For example, with a hydrogen -
concentration of 10 v/o and 1 sec. adiabatic burn, and with the burn occuring throughout the entire containment, the peak pressure is 43 psig.
(As a reference, 27% equivalent cl'ad reaction results in a hydrogen concentration of **10% in containment.) The code predicts containment failure upon melt-through of the pressure vessel.
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C1 ass 9-Accidents A gust 8, 1980 1
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CLASIX Calculations on Secuoyah.
Mr. Tinkler summarized analyses performed using CLASIX, a Westinghouse contain-ment code. A second code (LOTIC) is used to provide initial conditions to CLASIX. The calculations indicate the igniter systems would prevent over-pressurization for 70% clad oxidation. Assuming a small break LOCA w/o ECCS scenario and 70% equivalent clad. reaction, about 300,000 lbs of ice remain following completion of all hydrogen burns. Analyres, however, indicate pressure remains' within acceptable levels even wit 1 early loss of ice.
The analysec also indicate that peak pressure is sensi:ive to operability of the air circulation fans.-
Comments by R&D Associates Mr. Hubbard, R&D Associates (RDA), described the RDA assessment of the igniter system. He indicated (a) there is a concern with detonable pockets of hydrogen near the containmerit wall and (b) the uncertainties in hydrogen production and burning analyses are too large for him to have confidence in use of igniters.
Comments by TVA on Igniter System-Mr. Lau, TVA, summarized work on igniter 5.
The locations of the 30 igniters were influenced by the pre-existing emergency lighting circuits to which they are attached. A question was raised as to whether igniters should be located near points of likely release of hydrogen from the coolant system.
TVA is performing tests to determine glow plug reliability-and to characterize hydrogen combustion. A 7 foot diameter vessel is being used.
It was said that detonable mixtures are not expected in ice condenser containments if the air circulation fans are on. There are two air circulation fans, each with 40,000 cfm capacity.
Mr. Lau indicated that for concentrations of interest, steam has only a small effect on hydrogen ignition temperature.
Coments by EPRI on Hydrogen Mr. Miller, NSAC, described analyses of-the TMI-2 hydrogen burn, which indicated 25% to 50". clad / water ~ reaction.
Class 9 ~ Accidents Mtg
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August 8,1980 EPRI plans hydrogen tests in a 50-foot diameter (65,000 cu ft) ve:sel to investigate scale effects on combustion.
Initial tests will begii: in the summe r, - 1981 Summary Ccmments The follo<ing summary. remarks were made:
' Optimized ' placement of glow plugs is important.
Igniters should procably be placed close to likelf release points.
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'Dr. Strchlow, ACRS consultant, expressed concern with flame propagation through the air circulation ducts.
' Effects of high temperatures on components and potential-fires in foam insulation should be evaluated.
'The consultants felt, in general, that the igniter system is a good idea and that it should prove effective. -Dr. Lee,'however, indicated that consequences of. hydrogen burning in containment should be carefully studied since this is a new matter.
Future Meetings There are no meetings currently scheduled.
NOTE: For additional details, a complete transcript of the meeting is available in the NRC Public Document Room, 1717 H St., NW, Washington. 0C 20555 or from Alderson Reporting Company, Inc., 300 7th Street, S.W., Reporters Building, Washington, D.C. 20024 (202) 554-2345.
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