ML19331E437
| ML19331E437 | |
| Person / Time | |
|---|---|
| Issue date: | 06/25/1980 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-1739, NUDOCS 8009100180 | |
| Download: ML19331E437 (10) | |
Text
DATE ISSUED: Jun 25, 19S0 e,.
o Minutes of the April 24,19F0 g
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Subcomittee Meeting on Natural Circulation Decay Heat Removal Dr. Carbon opened the meeting indicating that the Subcommittee was continuing its review o'f the information available on natural circulation decay heat removal in reactor systems under various conditions. Subcommittee consultants and members indicated that one area they were particularly interested in was conden:;ation heat removal in the steam generator under conditions when non-condensable gas was present.
Dr. McPherson, NRC Research, indicated that recent experimental data from LOFT tests has 'provided the starting point for new insights into the perform-The ance of reactors under single-phase and two-phase natural circulation.
results of these recent tests and the present understandings were presented by personnel from INEL (EG&G).
Dr. J. Linebarger indicated that the small break LOCA program had a number of objectives that included investigation of phenomena using various parametric studies, experiments in Semiscale and LOFT, code development, and code assessment 50 that similar accidents in commercial reactors could be evaluated. As a part of the overall program, a number of small break LOCAs have been conducted in LOFT wherein natural circulation has occurred under various conditions.
Tests L3-1, and L3-2 conducted in late 1979 and February 1980 both entered periods of natural circulation heat removal.
Additional small break tests are scheduled and more information is expected g(s iA h n
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di ctions fror tnese tests. The data from the tests will be compared to code pre a
The Semiscale in an attempt to accurately calculate the phenomena involved.
d facility, as well as other test facilities in the 3D program serve to exten INEL considers natural circulation to be and complement the LOFT data base.
a by density grandients in a process whereby hei.t is removed by flow caused t
core the heat transfer fluid that are induced by heat addition in the reac or This can include single phase loop flow, and removal in the steam generator.
Tests have not been done with two two-phase loop flow, and feflux boiling.
components (non-condensable gases).
At the first LOTT small break test, L 3-1, was a cold leg break of 2.5% area (4" dia equivalent) where the break flow was greater than the HPIS flow.
The primary system rapidly depressurized and at about 400 seconds into side the test the primary side pressure became lower than the secondary The reactor coolant pumps were tripped at the beginning of the pressure.
Following pump trip, a period of several (5) seconds of single phase test.
natural circulation was initiated followed rapidly by a transition to two phase natural circulation as the upper plenum and the-low plenum became At about 400 seconds ' heat removal at the steam generator saturated.
the steam sto'pped and the break became the decay heat removal path, in fact, Through generators began to add heat to the primary system at this period.
ffect out the transient the break flow itself cppeared to have a dominating e Single-phase natural upon the fluid flow and natural circulation process.
The circulation really never had a chance to fully develop in the test.
In shift to 2-phase circulation also appeared to be smooth and stable.
i this test feed and bleed on the s'econdary side, which was initiated late n Another the transient was ineffective in removing primary side heat.
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c-observation during the L3-1 test concerned the accumulator flow. Some calcu-lations have s'hown pressure oscillations as the cold fluid enters the primary system; however, in the test the accumulator emptying was smooth and gradual as the primary pres,sure decreased.
The second small breat test, L3-2, is of more interest with regard to natural ci rcul ation. This test was a small break.16% cold leg pipe area (1" dia.
squivalent) wherein the HPI flow matched the break flow.
This allowed the system pressure to stabilize at a point just above the steam generator pressure.
The break was small enough in that it could not remove the decay heat and the steam generators were required.
In this test an extended period of natural circulation was encountered.
Following pump countdown at 40 seconds single phase natural circulation was estab1'ished and extended to about 180 seconds.
At this point saturation pressures were reached and a transistion to 2-phase loop circulation began.
At about 800 seconds the system was in a fully saturated state with 2-phase loop flow. As the system continued to depressurize the fluid volumes decreased and at about 1600 seconds a second transition to reflux boiling was observed. By approximately 2300 seconds refluxing was ful?y 4
, established. At about 5500 seconds 'the primary system began to refill and the refluxing shifted back to a two phase loop flow at 6500 seconds which continued to 8,000 seconds.
Finally as the system was completely refilled, the flow shifted back to a single phase fluid at about 8750 seconds.
Each of the transitions was smooth and gradual and it appeared that there was no difficulty in remoling decay heat. Secondary side feed and bleed was used to remove decay heat and depressurize the system starting at about 4000 seconds and the test was terminated at abou't 12,000 seconds.
Some uncertainty still remains as to the fluid behavior during the refluxing and an additional test should shed new light on the phehomena. A number of difficulties were m
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encountered due to the low flow velocities and the lack of measurement Later capability under fluid stratification conditions expected in refluxing.
tests will also include a small LOCA initiated from a loss of feed water where primary side feed and bleed will be used for heat removal.
In response to questions, INEL and the, NRC staff indicated that they have no plan to introduce non-condensable gases'into LOFT at the present time.
LOFT
' does get some small quantities of non-condensables already due to dissolved gases and the nitrogen from the accumulator when it finally empties all of its water
^
The staff indicated that they have no way of tracing where at about 300 psia.
the gas goes if they should inject it.
Semiscale will be doing some tests with gas injected.
Dr. K. Condie. EG&G, reviewed the results of the calculations performed for the L3-1, and L3-2 tests. RELAP 4/ Mod 7 was used and RELAP5 is being used for tests that are upcoming. The results showed that the code was able to predict the sequence of events in tests L3-1, and L3-2 but the quantitative results of the calculations need improvement. Problems encountered included ' inadequate boundary conditions due to unidentified flow paths during In some areas the models in RELAP 4/ Mod 7 are probably inadequate as it the test.
does not simulate thermal non-equilibrium and stratified flow conditions. RELAP 5 includes improved models which take these effects into account. The pretest predictions for test L3-7 which will be run with the break closed off at a point in time indicate that an extended period of reflux boiling will be entered. This will provide additional data on the phenomena.
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' Dr. D. Hanson, EGM, reviewed the capability of the LOFT instrume'1tation to
. measure natural circulation.
Ea.ch of the modes of natural circulation require some different measurement capabilities.
Under water solid conditions low flow velocities need to be measured. Under two phase conditions void fractions at varicus locations and relative fluid (steam liquid) velocities are of interest.
Under reflux conditions measurements of. fluid under stratified flow conditions Information available at the present time is at low velocity are recessary.
based upon instrumentation developed for large break LOCAs and is not ideal for small break LOCAs where fluid velocities are much lower.
Improvements are needed on energy balances, low flow turbine meters, and shielded gamma D'evelopmt.nt is under way on low flow measurements using neutron densitometers.
activation, temperature transit time flow meters and a turbine meter rake Radioisotope (small turbine meters located at various elevations in the pipe).
tracers, Pitot tubes, drag discs, ultrasonics, and conductivity probes are all At the present under development and have been tried out on a limited bases.
tima the staff has not identified any way to measure where an injected non-condensable gas might go if they put it into LOFT.
Dr. Harvego, EG&G, reviewed the tests on natural circulation that were conducted on Semiscale as LOFT counterpart tests and the plans for future tests in Semiscale on natural circulation.
Several tests have been run to date with A number of difficulties have been encountered in the a 2.5's break area.
The pump cast down period is larger which delays natural Semiscale tests.
circulation and the system heat losses are large - equivalent to the decay heat - so core power has to be augme'nted in order to have any natural l
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Thus far Semiscale tests have not entered into n i
d irctlation at all.
Modifications to Semiscale are planned and it is bel eve
- irculation regimes.
Feed and bleed as well
- that later tests will demonstrate natural circulation.
The facility iments.
as non-condensable gases will be used in various exper I
h iping and better upgrade will provide electrical trace heating of t e pThe, insulation to eleminate heat loses.
important to natural circulation variety of parareters that have been considered and reflux boiling.
i l tests on natural Dr. L. S. Tong, f2C PES, reviewed the results of init a PKL is an electrical circulation conducted in Germany on the PKL facility.
tion steam generator.
l heated PWR model with 340 full length rods and a full e eva ll instrumented to The steam generator has 30 full size U-tubes and is very we A series of 12 single component tests have determine heat transfer conditions.
heat removal. In with subcooled, saturated, two phase, and reflux re and carried to been run each case, heat was effectively removed from the reactor co Additional tests are planned in the'near future with the steam generator.
non-condensable gas in the system.
l d and feed heat Dr. B. Sheron, NRR, presented the NRC staff position on b ee al method The staff recognizes bleed and feed as a potential heat remov A number of plants-(B&W removal.
but no regulatory requirements exist at this time.
ide sufficient makeup and some E) have high head HPI pumps which could water for feed and bleed.
in order to use feed and pumps that would require system 4epr'essurizatic' In some cases the low head pump plants may bleed as a heat removal process.
te makeup water prior d
not be able to depressurize fast enough to provide a equa i
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'Testi of the feed and bleed process will take place in the core recovery.
The staff plans additional studies future in various experimental facilities.
to review the desirability of requiring feed and bleed, or improved secondary This will be included sid2 emergency feedwater, or high pressure RHR systems.
in the NRC Action Plan.
The Subcommittee reviewed a draft of Regulatory Guide 1.139 on decay heat removal The Regulatory Guide was referred systems with the Standards Development Staff.
to the Subcom.ittee from the Regulatory Guides Subcommittee, and Mr. Etherington The NRC staff and Mr. Ebersole provided the staff with comments on the guide.
ndicated that they made a number of changes to the guide in response to the i
comm:nts and explained that the intent of the guide was to improve presently existing decay heat removal designs rather than specify any new heat removal The Subcom-systems such as hP5 pressure RHR. That may come in the future.
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mittee agreed that the guide could be issued for public comment.
i The Subcomittee members and consultants provided a number of cormients on the day's l
f Dr. Theofanous indicated presentation and recommendations for future action.
that he felt more thought and planning was needed to determine the important effects that need to be modeled in the codes and tested in the experiments.
Too much of the present program was plunging ahead without adequate attention Mr. Ebersole indicated that since to deciding before hand what is important.
the feed and bleed heat removal process can't be guaranteed, we should concentrate efforts on assuring that we have adequate secondary side heat removal.
Dr. Zudans indicated that he had' difficulties with the planned upgrading of N e
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He believes that the syster will become so complex that it will be
!Iemiscale.
' difficult to do an experiment with known boundary conditions.
The members and consultants felt that testing with non-condensable gases d natural very important to determine their effects on reflux boiling an ci rculation.
Additional detail is available Dr. Carbon adjourned the meeting at 5:00 p.m.
1717 H in the meeting transcript on file in the NRC Public Document Room at Street, N.
W., Washington, D. C. 20555.
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A complete set of slides used is on file with the second copy of the m nu e in the ACRS files.
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. E. liarley DOE-ID J. E. Solecki EG&G - ID.
- 4. A. Spencer lEG&G-ID N. C. Kaufman lEG&GIdaho,Inc.
S. A. Naff EG&G I'daho D. J. Hanson DOE - ID Willis R. Young EG&G Idaho, Inc.
Keith G. Condie EG&G Idaho, Inc.
E. A Harvego lEG&GIdaho L. P. Leach NRC/SD R. Auluck NRC/Res W. C. Lyon NRC/RES E. Odar NRC/RES L. S. Tong ACRS M. Carbon ACRS J. Ray ACRS consultant I. Catton 98 H
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