ML19221A630
| ML19221A630 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/07/1979 |
| From: | INDUSTRY ADVISORY GROUP |
| To: | |
| References | |
| OLS-790407, NUDOCS 7905230475 | |
| Download: ML19221A630 (4) | |
Text
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NATURAL CIRCULATION
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Obiective Keep reactor. core cool by natural circulation mode.
Assymptions 1.
Heat removal on secordary side with or without power.
2.
Fump seal can be kept at temperature to avoid damage without seal flow.
. 3.
Makeup is available to compensate any leakage or loss from primary syster..
4.
Prior to natural circulation, plant is degassed encugh to avoid gas bubble formation which can block circulation at selected operating pressure.
Al terna tes A.
All licuid system 1.
Natural circulation at 1500 psig 2.
Natural circulation at current pressure 3.
Natural circulation at less than current pressure B.
Boiling System i
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Closed system 2.
Open systen (feed and bleed at reduced flow rate, being investigated by others)
Control and Instrumentation A.
Pressure maintenanct 1.
liigh pressure maintained by pressurizer heater 2.
High pressure maintained by high pressure pump 3.
Pressure below current pressure maintained by accumulation 4.
Pressure below current pressure maintained by lew pressure pump B.
Makeup and Baron Control 1.
At high pressure, high pressure pump 2.
At reduced pressure, low pressure pump C.
Degassing,
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Pressurizer vents g
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Letdown systen 3.
Add or open vent to top of steam gene.rator e
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Instrumentation
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Essential in zhdog Assurance of adequate water ruu simg in prir.ary loop.
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.s a) Solid system - need one in order of preference pressure measurement pump discharge head (charging rate useful) pressurizer level b) Boiling system ccre temperature pump flow and pressure (?)
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2.
Desira ble a) Removal of heat on secondary side core outlet tc=perature steam generator temperature b) Degree of gas in primary system
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employ present method of measurement gas balance with time Advantages Natural circulation Minimum operating equipment Operation without offsite power Minimum instru:r,entation Inherent self regulation (temperature up, more flow)
All liquid Absolute minimum instrumentation Verified in PWR operation Greater assurance of adequate inventory Better predictability No boron boiloff Less possibility of flow instability Boilings
} ()() 09i Low pressure Greater flow Reduced r.akeup J
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[ p- / gh Pressure - current and above tap to 1500 psi i
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margin above local bofling in core los Pressure - below current lower leakage easier and c: ore makeup options Disadvantages Natural Circulation
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Uncertainty of gross reactor core cooling and local core coolings Uncertainty in gas effect Greater susceptibility to loss of pressure and assurance of closing vent valves All liquid Greater susceptibility to gas
- Boiling, See advantages of all liquid High Pressure Greater makeup and control Greater impact on fuel dedding in cvent of sudden depressurization leakage to steam generator Low Pressure
%c h e gas problem Less margin to boiling Recomenda tions 1.
Natural circulation use is reconnended only when recirculation pumps not available 2.
All liquid natural cicrulation preferred over boiling and is recomended.
Boiling made should be used only as a last resort.
3.
Recomend current pressure to minimize impact on potential brittle de.dding of fuel 4.
Recomend steam generator full and as cold as possible 5.
Reccceend refill accumulator and put them on. Accumulator pressuhb b high (recognize disadvantage in event of big leak) 6.
Hold pressure with pressurizer heater, no vent in pressurizar and degas Keep all seafs run(ning as long as seal water teinperature is below col through letdown.
try to accelerate degas) 7.
leg temperature except when pumps are permanently non operable.
8.
Backup to pressurizer 13 hign pressure pumps.
9.
Reccmnend following calculations to verify feasibility (a) do calculation with B loop not avr.ilable due to potential leax
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pressures (c) study sensitivity to core pressure drop (d) evaluate sensitivity to all recirculation and injection to pump seal temperature (e) calculate toicrable gas level at various pressures to avoid gas blockage.
(f) calculate to see if this syste:n can be depressurized and cooled down over long period of time to cold shutdown code thrcugh Q) b"
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- 10. Develop contingency procedure for loss of pressure
- 11. Assure adequate maintenance of high pressure pumps and low pressure pumps.
Prerequisites
- 1. Provide secondary cobling both with and without offsite power
- 2. Continue to reduce gas level and maintain below level which will give tp digiculty at set acctc.ulater prcssure.
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