ML20133G591

Research Info Ltr 144, Effect of Hydrogen Gas on Downcomer Fluid Temps During TMI Accident. Forwards Cooldown Aspects of TMI-2 Accident, Based on Tg Theofanous Study of Fluid Mixing in Thermally Stratified Flows

ML20133G591
Person / Time
Site:	Three Mile Island
Issue date:	10/09/1985
From:	Minogue R NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20133E494	List: ML20133E489 ML20133G591
References
REF-GTECI-A-49, REF-GTECI-RV, TASK-A-49, TASK-OR RIL-144, NUDOCS 8510160039
Download: ML20133G591 (4)

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i MEMORANDUM FOR: Harold R. Denton, Director

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, ;-013 fiE~s7T& I FROM: Robert B. Minogue, Director R%m  :!a K Office of Nuclear Regulatory Research-

SUBJECT:

RESEARCH INFORMATION LETTER N0. 144, "THE EFFECT OF HYDR 0 GEN GAS ON 00WNCOMER FLUID TEMPERATURES DURING THE TMI ACCIDENT" This memorandum transmits research results on the effect of hydrogen gas on the downcomer fluid temperatures during the accident at Three Mile Island (TMI).

This work was performed by Professor T. G. Theofanous of Purdue University, as part of a study of fluid mixing in thermally stratified flows. Earlier models developed through this fluid mixing research program have received extensive use in NRR's pressurized thermal shock (PTS) study.

The purpose of the research described herein has been to predict the downcomer fluid temperatures for the portion of the TMI accident during which high pressure injection (HPI) flow was actuated. The Rogovin Report (Volume 2, Part 2) states that HPI actuation occurred at 200 minutes into the accident while the primary system pressure was in excess of 1000 psia. Since this was a high pressure transient with the potential for achieving low downcomer fluid temperatures, this research may interest you from a PTS standpoint.

Shortly after the TMI accident, Babcock and Wilcox (B&W) addressed this same subject. These early analyses examined HPI fluid flow into a steam filled cold leg. The presence of steam in the cold leg was attributed to vent valve fluctuations which expose the downcomer region to the steam filled upper plenum. These vent valves open when the primary system coolant approaches stagnant conditions. Such conditions are thought to have existed when HPI flow was initiated during the TMI accident. Steam condensation on the cold HPI fluid served to warm the fluid before reaching the downcomer. As a result, the B&W analyses predicted a minimum downcomer fluid temperature of approximately  ;

280 F.

During the TMI accident, large quantities of hydrogen were produced when the l zircaloy cladding, which encased the fuel, reacted with the surrounding water vapor. As a result, hydrogen may have been present in the loops during the 3 period of HPI actuation. The new analysis, presented as an enclosure to this memorandum, differs from the earlier B&W analyses in that it examines HPI fluid i flow into a cold leg filled with both steam and hydrogen. It shows that the

. presence of hydrogen inhibits the heating of the HPI fluid prior to entering i the downcomer region. As steam condenses on the cold HPI flow, a low pressure l region is created in the cold leg and upper downcomer. This low pressure region induces an increased flow of steam and hydrogen through the vent valves.

As the steam condenses, it warms the HPI fluid. However, the hydrogen does not condense and its concentration increases with time. This buildup of hydrogen 8510160039 DR 851009 p ADOCK 05000320  !

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8 05 Harold R. Denton 1 in the cold leg ,orevents further steam condensation on the HPI fluid. As a result, this beneficial warming mechanism is shut off. Because the actual conditions (volumes present, timing of events, lower plenum obstructions) during the TMI accident have not been definitively established, Professor Theofanous has performed parametric analyses. His results indicate that the downcomer fluid temperatures may have been less than 200*F. These analyses also indicate that certain sections of the reactor vessel may have been in direct contact with HPI fluid having temperatures of less tnan 100 F because of fluid deflection off of the thermal shield support clips.

It is recommended that the Office of Nuclear Reactor Regulation (NRR) review the effect of this new research on current activities related to severe accident sequences. Additional studies in the area of thermal fluid mixing in the presence of noncondensible gases are being planned. These studies will be coordinated with your staff. Any questions concerning the enclosed study should be directed to Jose Reyes (42-74422).

I d 91 4' Robert B. Minogue, D rector Office of Nuclear Regulatory Research

Enclosure:

"The Cooldown Aspects of the TMI-2 Accident, "dtd 08/85 l

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, Cir Branch R/F RBMinogue DFRoss QCT9 N OEBassett WMMorrison LMShotkin NZuber WDBeckner MEMORANDP4 FOR: Harold R. Denton, Director JNReyes Office of Nuclear Reactor Regulation JNReyes R/F F0dar FROM: Robert B. Minogue, Director Office of Nuclear Regulatory Research

SUBJECT:

RESEARCH INFORMATION LETTER N0.144, "THE EFFECT OF HYDR 0 GEN GAS ON 00WNCOMER FLUID TEMPERATURES DURING THE TMI ACCIDENT" This memorandum transmits research results on the effect of hydrogen gas on the downcomer fluid temperatures during the accident at Three Mile Island (TMI).

This work was performed by Professor T. G. Theofanous of Purdue University, as part of a study of fluid mixing in thermally stratified flows. Earlier models developed through this fluid mixing research program have received extensive use in NRR's pressurized thermal shock (PTS) study.

The purpose of the research described herein has been to predict the downcomer fluid temperatures for the portion of the TMI accident during which high pressure injection (HPI) flow was actuated. The Rogovin Report (Volume 2, Part 2) states that HPI actuation occurred at 200 minutes into the accident while the primary system pressure was in excess of 1000 psia. Since this was a high pressure transient with the potential for achieving low downcomer fluid temperatures, this research may interest you from a PTS standpoint.

Shortly after the TMI accident, Babcock and Wilcox (B&W) addressed this same subject. These early analyses examined HPI fluid flow into a steam filled cold leg. The presence of steam in the cold leg was attributed to vent valve fluctuations which expose the downcomer region to the steam filled upper plenum. These vent valves open when the primary system coolant approaches stagnant conditions. Such conditions are thought to have existed when HPI flow was initiated during the TMI accident. Steam condensation on the cold HPI fluid served to warm the fluid before reaching the downcomer. As a result, the B&W analyses predicted a minimum downcomer fluid temperature of approximately 280 F.

During the TMI accident, large quantities of hydrogen were produced w'1en the zircaloy cladding, which encased the fuel, reacted with the surrounding water vapor. As a result, hydrogen may have been present in the loops during the period of HPI actuation. The new analysis, presented as an enclosure to this memorandum, differs from the earlier B&W analyses in that it examines HPI fluid flow into a cold leg filled with both steam and hydrogen. It shows that the presence of hydrogen inhibits the heating of the HPI fluid prior to entering the downcomer region. As steam condenses on the cold HPI flow, a low pressure region is created in the cold leg and upper downcomer. This low pressure region induces an increased flow of steam and hydrogen through the vent valves.

As the steam condenses, it warms the HPI fluid. However, the hydrogen does not condense and its concentration increases with time. This buildup of hydrogen i

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Harold R. Denton 9 1985 in the cold leg prevents further steam condensation on the HPI fluid. As a result, this beneficial warming mechanism is shut off. Because the actual conditions (volumes present, timing of events, lower plenum obstructions) during the TMI accident have not been definitively e,stablished, Professor Theofanous has performed parametric analyses. His results indicate that the downcomer fluid temperatures may have been less than 200'F. These analyses also indicate that certain sections of the reactor vessel may have been in direct contact with HPI fluid having temperatures of less than 100 F  !

because of fluid deflection off of the thermal shield support clips. '

1 I It is recommended that the Office of Nuclear Reactor Regulation (NRR) review the effect of this new research on current activities related to severe accident sequences. Additional studies in the area of thermal fluid mixing in the presence of noncondensible gases are being planned. These studies will be coordinated with your staff. Any questions concerning the enclosed study should be directed to Jose Reyes (42-74422).

I Robert B. Minogue, Director Office of Nuclear Regulatory Research

Enclosure:

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