ML19220C913
| ML19220C913 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/03/1979 |
| From: | Ahearne J NRC COMMISSION (OCM) |
| To: | Case E, Jennifer Davis, Gilinsky V NRC COMMISSION (OCM), NRC OFFICE OF INSPECTION & ENFORCEMENT (IE), Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7905160056 | |
| Download: ML19220C913 (6) | |
Text
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April 3,1979
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MEMORAi,DUM FOR:
Commissioner Gilinsky Edson Case, NRP, John Davis, I&E l
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.I FROM:
John Ahearned e
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SUBJECT:
SUGGESTED ACTIONS IN RESPONSE TO THE THREE MILE ISLAND ACCIDENT The follcuing suggestions have been nade to me concerning actions the NRC should take in response to the Three Mile Island accident.
I am forwarding then to you for your consideration.
1.
In addition to the items mentioned in IE Bulletin 79-05 of April 1,1979, the licensees of all operating E5'.4 power reactor facilities should be requested to review environmental qualification of equipment for:
(a)
Possible damage from a steem jet should the rupture disc on the quench tan'< fails.
(b)
Possible component failure due to a steam envirorment in the containment.
2.
A file of the following information should be kept off-site (of TMI) so that a record '..-ill be available in the event of an accident which destroys these records at TMI:
(a) Computer line printouts.
(b) Reactimeter cutputs.
(c) Any written statements taken by accident investigators.
I would also appreciate your comments on the enclosed "Possible Series of Events at Three Mile Island."
cc:
Chairman Hendrie Commissioner Kennedy Commissioner Bradford
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April 2,1979 Possible Series of Events at Three Mile Island i
1.
Operator t;crking on demineralizer in condensate system somehou caused loss '." uction for condensate pumps.
(Possibly he valved de-mineralizer rc, ins into the condensate flow, thereby clo;;ing suction strainers of the pumps.) Loss of condensate flow trips of f main feed pumps on low suction.
[ Auxiliary pumps should come on in 30 seconds.
Why did they not come on for 12 minutes?]
2.
Standing ',;ater in steem generator (SG) boils off.
Main SG iso-lation valves close to isolate SG from turbine.
lif t to release generator pressure.
[Open relief valves '..ould allow radiation into containment if there were any primary to secondary leaks in the SG.
One of the two SGs was leaking and therefore isolated.]
3.
Temperature increase in primary coolant loop causes a pressure increase.
Reactor screms on high pressure.
4.
Relief valves on pressurizer open due to high pressure, releasing large stea-flou tc que ch tan'; '.hich is designed for smaller transients Excess pressure blc.;5 possibl', H, He, other noble gases) to containment. quench tank rupture disc
[There are three pressurizer relief valves, two spring loaded with set pressure release points and one POR'l (power operated relief valve) which can be manually operated.
There is a man-ually ocerable isolation valve bet'..een the pressurizer and the PO??!.
In the Davis-3 esse incident of September 1977, the POR'!
stuck in the open po:ition.
Did it do so here?]
5.
Steam jet wets power cables to pressurizer heater.
Loss of adjust pressurizer pressure. pressurizer heater control and therefore of abil
[ Moisture and radiation damage may eventually degrade performance of other ccmponents (e.g., breakdown of insula tion on control cables), particularly in light of large radiation fields observed at top of containment.]
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6.
Primary pressure drops (particularly if PORV is stuck open and before isolation valve is closed). At 1C0 psi, high pressure injec-tion (HPI) autcmatically activates.
HPI slo.ts pressure drop but does not stop it.
Af ter seven minutes, HPI is turned off,
[Why was HPI shut off? Two possibilities:
(a) The safety features actuating system (SFAS) closes the makeup water valve and the fresh water return valve. The SFAS ray have been blocked (and thereby the HPI advertently or inad-vertently shut off) in an attempt to add makeup water or to protect the primary coolant pump seals.
(b)
If PORY is open and its isolation valve not closed, primary pressure would deep bilow saturation level quite rapidly
(~ 5 to 10 ninu tes).
Steam formation ticuld force water and perhaps steam into the pressurizer, causing an increased level reading.
Operator may h2ce interpreted this (errone-ously) as increased primary pressure and shut off HPI. Tnis occurred during 10/77 Davis-Besse incident.]
7.
Auxiliary feed pumps for SG actuated (about 12 minutes af ter start of incident).
Surge of cold water in se:cndary causes a surge of cooling c f primary.
Lar;e primary pressure drcp causes saturation, voiding cf pressurizer, shutoff of primarj coolant pumps.
Steam blccks primary coolant icop.
8.
Insufficient cooling.
Fuel damage and hydrogen generation.
Hydrogen (and He, r.able gases) bubble forms in top of pressure vessel.
Combination of gas and steam may cause partially uncovered core.
Re-duced water level over core allous streaming of radiation to top of contai n...ent.
9.
HPI and makeup feed pumps actuated in an attempt to break up steam blockage of primary coolant flo,,.
No natural cir:ulation, so primary coolant pumps won't work.
PORV (or isolation valve) opened intermittently to relieve pressurizer pressure, thereby releasing further steam, gas, and radiation to the containment.
10.
At about 2300 psi, r;aking water pumps overccme primary coolant loop blockage.
Primary reactor coolant pump s actuated.
Water level above core no.t several feet and heat is being removed via the one operating primary-secondary loop.
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April 2,1979 Comparison to September,1977 Davis-Sesse Incident Similarities 1.
Loss of steam generator feed water.
2.
Pressure relief through quench tank.
3.
Disabling of HPI.
Dissinilarities 1.
SG auxiliary feed pumps not actuated for 12 minutes at Three flile Island (vs. 40 seconds at Davis-3 esse).
Thus loss of cooling capability was more severe.
2.
Primary cooling loop blockage by steam at TMI.
Natural circu-lation not lost at D-B.
3.
fiuch more severe unco tering of core at TMI.
This resulted in hydrogen bubble, high radiation level at top of containment.
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