ML20214W939
| ML20214W939 | |
| Person / Time | |
|---|---|
| Issue date: | 10/04/1984 |
| From: | Jerome Murphy NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Agrawal B, Baranowsky P, Burdick G NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| Shared Package | |
| ML20213E209 | List:
|
| References | |
| FOIA-87-113, FOIA-87-60 NUDOCS 8706160258 | |
| Download: ML20214W939 (11) | |
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October 4, IM 4 MEMORANDUM FOR:
B. Agrawal, DAE, RES P. Baranowsky, DRA0, RES A. Benjamin, SNL G. Burdick, DRA0, RES M. Cunningham, DRA0, RES DRA0, RES T. Eng,in, ORA 0, RES J. Mart C. Overbey, DRA0, RES F. Rowsome, NRR L. Soffer, DRA0, RES Joseph A. Murphy FROM:
Division of Risk Analysis and Operations, RES
SUBJECT:
IDCOR-NRC ISSUE PAPERS We have been advised that it will riot be necessary to prepare Issue Papers in the areas of ex-containment transport and consequences, characterization of plants and sequences, assessment of existing plants, and assessment of plants You were previously with modifications (Issue Papers 1.5.1 through 2.3.4).
assigned the responsibility for preparing one or more issue papers in these areas; please consider that assignment null and void.
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Jos ph A. Murphy Division of Risk Analysis and Operations Office of Nuclear Regulatory Research 0706160258 870610 PDR FOIA SHOLLYS7-60 PDR m
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a 1.2.2.
Rate and Maanitude of Combustible Gas Production Ex-vessel 4
This issue covers the production of hydrogen and carbon monoxide result-s 2
$j ing from reactions of hot core debris with concrete, and hydrogen from a
h core-coolant interactions in the reactor cavity, radiolysis of water and
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3) organic compounds,and corrosion.
It also cov.ers the release of flammable gases from the decomposition of organic materials. All these h
gases must be considered, together with the hydrogen released from
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in-vessel reactions (1.1.2) to assess possible early or late threats to
.yQ containment calculated in 1.2.3 and 1.2.4.
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Following vessel failure, unoxidized metal in the corium mixture RY can interact with water in the reactor cavity and produce signifi-6fjf cant quantities of hydrogen as the melt is quenched.
If the g4 f
reactor cavity is dry, or if the melt does not quench for some
.M other reason, interaction of the corium with the underlying con-gf crete will evolve large quantities of water and CO, which then 2
react with unoxidized metal in the melt, producing significant J
quantities of combustible CO and H.
In either case, the total 2
3s lif production of combustible gasjles following vessel failure can be
' equal to or greater than the production prior to failure.
In P.31 di addition, smaller amounts of hydrogen can be produced by radiclytic N
l.
decomposition of water and organic chemicals, and corrorinn of l
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Radiolysis of organic chemicals can also p:
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produce combustible hydrocarbons.
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MVJ The presence of combustible gases in sufficiently high concen 6g trations poses a threat to containment integrity and functionability of the essential equipment located in the contain-O.1 ment. The rate at which combustible gases will accumulate inside 7,',1 PWR containments and' Mark III BWR containments will determine the d,iQ probability of formation of inflammable or explosive mixtures whose presence can threaten safety related functions of the plant.
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EP.F - p h r t : "4th 4 ae-t e d ",a k I u r Hfrr-4,I.,_q,ccttW:c nts, t ha rato mt "Mch crycea sceumutates wfll constNte the-safety-determiMag
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A c to r, The rate and amount of ex-vessel combustible gas produc-h tion will depend on the mechanisms assumed and the accident scenar-kI b
ios.
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Subissues g.,
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-The presgence or absence of water in the reactor cavity, i
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-The effect of concrete composition (limestone vs. basaltic) on C0 m[
production, e
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-The quantity of unoxidized metal in the debris bed, ay
-The magnitude and distribution of radioactive materials to 3
g3 containment sumps.
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Acoroach" to R'esolution The CORCON-M002 code is being developed to study the interactions l
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of core debris with concrete and to determine the rate and l
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(Issue 1.2.9).
The code will include fh. ' ' -
effects of slurries and crusts and an overlying pool of water.
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With respect to hydrogen production during quenching of the core
- Ut IN debris, the principal uncertainty is the rate of production.
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Solution of that problem depends on the resolution of issues y
related to ex-vessel steam explosions (1.2.5)and debris coolability i
M (1.2.6).
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L There are no widely accepted methods of determining how much 33
$h unoxidized metal should be included in the core debris. Bounding l
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estimates can be made once accident progres11on issues (1.1.2, i
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I is 1.1.4,1.1.7) are resolved.
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The distribution of radionuclides in sump water will be determined i
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fy by reference of PBF tests and by thermal-hydraulic analysis of the i
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f release and spread of source term materials in the primary system.
l Iodine distribution will be determined in source term studies now l
g underway.
Y)4 xV Once these parameters are known reasonably well, the rates of I
f radiological decomposition of sump water can be estimated from existing theory.
Standards are available for the determination of
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{g the amount of hydrogen produced by corrosion of zine and aluminum, h
The aluminum rates are thought to be too high and the standard is
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being revised, but this source can be bracketed satisfactorily.
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gas generation from organic materials, we are able to use
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F61 thermal and radiological decomposition.
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St'atus of Understandino jnd Existing calculations of hydrogen production due to quenching of IB%
the molten core yield as much as 1000 pounds of hydrogen. Major h
l.Y uncertainties in these calculations include the initial temperature
!A i;e of the melt, the time required to quench and the quantity of 1
Y unoxidized metal in the melt.
The IDCOR methodology yields minimal p
y hydrogen production due to this mechanisms, because quench is
- r' calculated to occur over an interval of less than one minute.
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'TsX' Recent Sandia experiments indicate that even during a rapid quench,
- e as much as 30% of the available unoxdized metal will react to y,::
jij produce hydrogen.
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M Existing calculations using CORCON-M001 of core debris - concrete m
Li.h interaction have yielded as much as 1000 pounds of H and 12,000 2
- ry pounds of CO.
The major source of conservatism in these calcu-qM lations is the large quantity of unoxidized metal assumed to be if9 b,"j associated with the melt.
Recent IDCOR documents assert that the M
p reactor vessel will experience local failure rather than a gross Qj lgq melting of the lower head. This result would lead to a prediction l
of less unexidized metal in the melt.
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,Q The ability pf" predict generation of radiolytic gases is good as f'u long as the amount of activity and iodine released ' rem the core is
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Determination of these Quantities for severe accident is a
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'r necessary step in calculating the rates and extent of radiolysis.
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The current methods overpredict the hydrogen generated by corrosion jM of metallic surfaces.
In some instances the degree of A
S overprediction may be substantial. As in the case of radiolysis, a EN'i knowledge of specific accident related parameters is required.
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Although generation of combustible gases by decomposition of W) organic materials is.the least significant source of ex-vessel h
combustible gases, it cannot be ignored because some plants may wD contain significant amounts of organic materials.
Decomposition of fi(g these materials by the activity released into containment depends on plant specific materials and the environments associated with fr relevant scenarios which are usuatlly difficult to determine. The M,,
b9, general trend is to make very conservative assumptions which will 4!.]
overpredict the amount of gases generated.
Because the amount of 7R gases generated from organics is relatively small, this method is Q
considered acceptable.
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NRC Position Conservative estimates of the amount of metal in the core debris 3.,
will be used to estimate hydrogen production. The IDCOR results d
V indicating local failure of the reactor vessel lower head will be da h
accounted for in making these conservative estimates more reason-2 l
able.
The CORCON-M002 code or other correlations will be used to j
determine the release of H, C0 dr.d CO from core debris-concrete 2
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interactions.
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kb Sufficient information exists to bound the hydrogen production due P
i; to quenching the molten debris.
The rate of hydrogen production 4
. due to this mechanism is still an unresolved issue and will depend Mi on the outcome of issues 1.2.5 (steam explosions) and 1.2.6 (debris coolability).
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The NRC will base its estimates of radiolytic decomposition on the J
distribution of fission products, and iodine in particular, through 9
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the, containment and primary system.
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