ML19246B087
| ML19246B087 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/13/1979 |
| From: | Johnston W Office of Nuclear Reactor Regulation |
| To: | Ross D Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7907120150 | |
| Download: ML19246B087 (4) | |
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APR 13 1970 liEliORAtlDUM FOR:
D. Ross, Deputy Director Division of Project l'anagement Office of ?!uclear Reactor Regulation FRCM:
W. V. Johnsten, Chief Fuel Behavior Research Branch Division of Reactor Safety Research Office of t;uclear Regulatory Research
SUBJECT:
FUEL EXPERTS MEETI::G ON CONDITIO:t 0F THE TMI CCRE A meeting of nuclear fuel experts was held on April 12 to update the estimates of the damage to the TMI core and to consider its effect on the desirability of moving to natural convectior ccoling of the core.
The Experts Group consisted of the folicwing pemons:
J. S. Tulenko, 3*J!;
R. DeMars, St.W; T. Kassner, ANL; R. A. Proebstic, GE; K. A. Jordan, W; R. Duncan, CE; T. Fernandez, EPRI; T. Euhl, ;RC R. Mayer, NRC; N. Johnston, i:RC,,
Chairman.
Additicnal attendees included L. Rub 1 stein, I'RC; C. Berlinger,
!RC; M. Tokar, NRC; R. Majors, ACRS Staff and T. !*ott, TEC.
Summary The group concluded that although the core is badly damaged, essentially all of the fuel has remained in the core and that the overall packing density of the settled portion is not expected to exceed 70'.'.
There fore, shutting off the RC pumps should not seriously tiseaten furtP - damage to the reactor.
It was further concluded that the thermoccu;.,;es (Tc's) located in the upper end fittings are the most important indicator of core condition during transition to natural ccavection cooling.
If feasible, the addition of a 7 spectrometer to monitor the activity of the loop ccolant for new fission products released.sthe transition to natural convection cooling will provide an indeperpent alert to possible difficulties.
4,g Two questions c.ere ccnsidered:
Is a pump trip likely to lead to an unsafe condition? and What signals will indicate undesirable conditions in the core?
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D. Ross PN i.1 ::G Sumnary of Core Status Summaries of amount of damage to the core based upon measurements or calculations of fission gas release, hydrogen produced by zircaloy oxidation, coolant analysis, coolant boil-off cates, incore and excore instrumentation were presented by J. Tulenko and R. "cyer. A relatively large pressure drop across the core is inferred by TH calculations.
If the pressure drop is real, bicckage must also exist in the peripheral assemblies (perhaps by ballo:ning).
The shift in lecction cnd m:gnitude of the high reading core Tc's following the pump trip on April 6 was believed to indicate either a change in the core flow path through more heavily damaged sections of the core to a redistribution of debris surrounding some of the thermocouple beads. An al ternate explanation for the change in Tc temperature distribution patterns was presented by T. "ott of TEC.
He suggested that the Tc temperature difference may be due to non uniform flow distributions caused by operation of a single pump rather than non uniformity within the damaged region of the core.
Due to this non uniform ficw distribution portions of the core may already be experiencing similar cooling to that expected during natural convection. Mott estimates smaller core pressure drop and suggests the B&'l estimates may include substantial external pressure drops.
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The group visualizes the core as consisting of a heavily damaged region resembling an inverted bell extending across nearly the full width of the top of the core and reaching dcun about five - six feet into the core at the center and a less damaged remainder of the core. In the heavily damaged region,100% oxidation of tre zircaloy and Idss of a regular geometry is expected.
ine guide tubes and poison rods are damaged similarly to the cladding. Spacer grids should be located at or near their original locations.
The important coolability ccnclusions are that although some settling may have taken place, the overall packing density of the settled parlian is not expected to be greater than 70%
and that 85% to 98% of the fuel and cladding from this region is believed to have remained in the " core" region including the upper end fitting.
The remainder of the core is less damaged although considerably oxidized.
The original flow gecmetry is probably retained although the rods may be twisted or warped and broken in a few places and the spacer grids may have collected scme loose debris.
The above conditions should not preclude satisfactory achievement of natural convection ficws.
'cl hat should be monitored to determine undesirabie chances in the core during the transition to natural convection ccoling? The temperature distribution of the core exit thermocouples are the most important 28287 5
D. Ross The group believes that all exit Tc'sS&N sugge
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condition monitoring signals.
should be continuously tracked and recorded.
No...are than 2 i
criteria for remaining in natural ccnvecticn cool ng:
There ware some Tc's above 300 F and at least 10 Tc's below Tsat.any Tc's to read above reservatio~ns among the group about allcuing so m There was d concern.
Tsat (as m ny as 39) and radiolysis tras an expresseinterior Tc's should be a lot of discussion but no concensus on how manyTc's in peripheral assc.bli m
paratitted to exceed Tsat.
i n and its exceed Tsat.
Ele following table sur..:.arizes the available instrumentat o possible application to monitoring core condition.
Basis Event-Core Overheating Criteria Cetector iot to exceed previous Limit no. in film boiling core damage; reverse
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- 1. Exit Tc's Limit no above 800 F procedure.
"o flow reversal Maintain positive ai across permitted.
- 2. RTD core.
Hot leg Cold leg Ambiguous signal since Void formaticn some local superheat
- 3. Ian chambers If +, record for future may be permitted.
7'and N interpretation, watch Tc's.
Same as abcVe.
If + indicates bubbles in
- 4. "oise detection core or icop, check Tc's, SG.
"ot direct indication
-e Branch should, system effec s of core condition, but t
If increasing review this, for gas bubble formation _-
- 5. System Pressure detection.
Same as above.
Same as above.
- 6. Pressurizer Level Additional Cetectica - Feasibility needs to be established.
Overheated core alert Increasing activity of Xe, I 2 for major error in 3',spectrosccpy procedure.
or coolant via sacpling line Core criticality and Baron, 09, H, chemistry control radiolysis and H M0 analysis on contant control.2 line monitor L'./ /j?s:~$^!. n J-W. V. Jchnston, Chief Fuel Sahavior Research 3 ranch o d 2, b; O Civision of Riactor Safety Research, RES
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.ss 4/13/79 l'ote to M. Aycock The attached should have the follcuing distribution and should also be telefaxed to Stallo at the site.
E. Case R. Mattson
'/. Stello, Jr.
R. Goyd D. Ross F. Schrceder D. Eisenhut D. Sunch/0. Crutchfield M. Aycock/F. Miraglia Team A/ Team 3 Staff D. Ross e
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