ML19221A361
| ML19221A361 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/25/1979 |
| From: | Stroupe W INDUSTRY ADVISORY GROUP |
| To: | |
| References | |
| OSP-790425, TASK 26A, TASK-26A, NUDOCS 7905220050 | |
| Download: ML19221A361 (13) | |
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4/25/79 A-t J..HENCH D. KELLY W. STROUFE ASSIGTMENT D. TOOKER p
Review Energency Procedure EP-32, " Loss of RCP's Succcssful Natural Circulation" StMMARY The above plan was reviewed to determine if the current criteria for establish-ment natural circulation provide adequate indication of natural circulation (or lack of natural circulation) and provide sufficient protection for the primary system in the event a natural circulation attempt had to be aborted.
One measure of sufficient protection is maintaining water coverage of the pressurizer heat?rs mainta.ning pressure controllability.
This study concluded that an additional criterion should be added to those al-ready listed in EP-32.
The limits set in this criterion should not be exceeded until at least five hours af ter the reactor coolant pump trip.
Speci fic receranendations are included at the end of this report.
DISCL'5SION Calculations completed by all groups involved to date indicate that gatural circulation will be established with a very sa. ail rise less than 25 F, in 3
core outlet temperature.
Conservatively assuming a 15 F rise of the average temperature of the total primary 3 yste w ter, approximately 11,000 f t the s
volume will increase 7,q_ ft and the pressurizer level will increase
,2.2, inchas (See Attacncent I) assuming a constant nass system.
It is expected that the actual pressurizer level rise will be less than 10" for successful natural circulation However, assuming that natural circulaticq is not established, the current criteria of EP-32 would allow the water in the core to reach saturation at about 900 psig.
As shown on Attachmant II, the system expansion for the vessel water volume during this heatup is ll(D ft (1).
Clearly this volume increase is an order of that magnitude greater than that expected for successful natural circulation and would clearly indicate that the process occurring in the primary system is not understood or under control and that the natural circulation attempt should be aborted.
Thus, another criterion to confirm the achievement of natural circulation must be considered.
However, first consider the alternate means of handling this increase in the volume of the primary system if natural circulation is unsuccessful. This expansion can be handled by either allowing the water level to rise in the pressurizer or by system letdcwn.
If the expansion volume is letdown, the mass of the water in the RCS will be reduced by about 30"..
When the natural circulation attempt is aborted by the criteria currently in EP-32, a coolant ppp could be started when the entire vessel is at saturgtion temperature, 532 F.
The secondary side of the "A" OTSG would be about 230 F.
Attachment III indicates that the volume would be reduced (1) Note for these calculations:
It is assumed that the temperatures of the hot and cold leg remains unc. hanged.
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["r T-DISCUSSION (cont) 3 by 800 ft in atout five minute;.
This will definitely uncover the heaters and likely be a severe transient terminated by the operation of HPI.
This result is considered unacceptable since it effectively relinouishes pressure control.
3 The total volume of the pressurizer is approximately 1500 ft.
If the water level is at 270" and the p essurizer goes solid at 400" the expansion volume 3
is (400-270) (3 ft /inc1) 400 ft.
As an example of a case where natural circulation is not established, we choose to confine all core heat to the vessel region.
The following analysis proceeds from that assumption.
To reach saturation temperature in the entire vessel the expansion volume is about 1000 f t3 and the pressurizer will therefore go solid before saturation is reached in the vessel.
The pressurizer will go solid about 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> af ter the pump trip since the water level will rise at 40"/hr if no steam voids are accumulated in the vessel and no natural circulation occurs.
To provide more time for natural circulation to occur without coing solid the pressurizer level should be reduced to the minimum
" comfortable" (e.g.110" t 10") i. mediately af ter the event.
To provide margin to " going solid" an upper limit of 350" is proposed for the pressurizer level.
This allows a mini um of 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> -- (350-110)/40"/hr -- before the nctural circulation attempt would be aborted per this criterion.
Additional time would be provided by giving natural circulation a " nudge" by energizing a coolant pump first for 5 seconds and later for 10 seconds as pressurizer levels of 300" and 350" are reached.
If the " nudging" attempts were unsuccessful and the level reaches 350" a second time, the proposed criterion calls for an abort.* At this time the average temperature of the water in the reactor vessel would have risen from about 2300F to about 4850F (Attach.ent IV).
There are several indications that if natural circulation has not yet been achieved it is proper to abort the attempt.
These indications are:
1.
At least 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> have elapsed to establish flow and no natural circulation ficw is established.
2.
Two attempts to " nudge" the system to natural circulation flow will have been made with no success in inducing natural circulation.
3.
The vessel water average temperature has risen over 200 F -- more than sufficient heat will have been generated to cause natural circulation.
Something is definitely wrong if natural circulation does not occur.
- Footnote:
The abort criteria based on the rising water level in the pressurizer could be replaced with equivalent criteria based on levels in the makeup tank, by holding the pressurizer level constant.
This has the advantage of allowing maintenance of higher levels in the pressurizer.
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RECOMMENDATIONS (Shown schematically on Attachment VI):
It is recommended that EP-32 be amended as follows for the loss of forced circulation.
1.
Take the necessary measures to make the primary system a constant mass system.
2.
Reduce the pressurizer level to 100" +- 10.
3.
Check pzr. level every 15 minutes.
Sustained--for 5 hrs. level rise of as 10"/15 minutes expected if natural circulation not achieved.
If natural circulation is achieved, the level rise is expected to be less than 25".
4.
When (if) the pzr. level reaches 300"(*) energize pump 2k for 5 seconds (not to full pump speed).
If pump fails to start, go to pump 1A for a 5 second jog.
Expect to see:
a) Th b) pzr. level drop If neither 2A or l A jog, go to 5.2.3 of EP-32.
5.
Measure pzr. level every 15 minutes.
6.
When (if) pzr. level reaches the 350" level, energize pump 2A for 10 seconds.
If pump fails to start, go to pump 1 A for a 10 second jog.
If neither jog, go to 5.2.3.
7.
Measure level.
If the level stays at or reattains 350", abort the natural circulation criteria, i.e. go to 5.2 of EP32.
Expected to take about 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after the pump trip.
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Exercise performed to determine the volure change in going to Tsat (Reactor Vessel)
R.V. voiume T 4041 ft3,y.
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Total pzr volume 7 1500 ft Presently 9 pzr. level 267" we have substantially less than 700 f t3 before the system goes solid.
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CONSTLNT FJSS FRIMGI cob 7.0L F
This attachssnt irdicates nothods for achieving a constant primary sys tu r.as s.
The extansion of.ths p-ira y systes, consisting of 1.
the pri=a 7 system 2.
the seal flev syntes and seal raturn system 3.
the lotdoun systez 4.
the ra h up tank represents a constant nass syntas with the exception of n:r_e mil system outleakage (2 5 gal /r.In) which has been constant and fairly accurately kne-m. Erints.iM eg es level in the makeup tank at a constant value via letdown or seal ficv vi L1 assure that the prir.iry system is at a constant cass. The system can bs cads c re accurate by adding water to the nsieup tank at a rate equal to the esti=stod rate of outicatage. Moreover, the p essuri er level adjust snt desired at the begirr4 g of the transient can bs e.cconpliched on a constant nass insis by reflecting the initial differe ncs onto the initial - Voup tank level to determine a nakeup tank control level.
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