ML19224C519
| ML19224C519 | |
| Person / Time | |
|---|---|
| Issue date: | 05/08/1979 |
| From: | Rosztoczy Z Office of Nuclear Reactor Regulation |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| FOIA-79-98 NUDOCS 7907020482 | |
| Download: ML19224C519 (7) | |
Text
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NUCLEAR REGULATORY COMMISSION Ek
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f g g g 1973 MEMORANDUM FOR:
R.W. Reid, Chief, Operating Reactors Branch No. 4, D0R FROM:
Z.R. Rosztoczy, Chief, Analysis Branch, DSS
SUBJECT:
QUESTIONS REGARDING SMALL BREAK ANALYSES FOR COMBUSTION ENGINEERING AND WESTINGHOUSE The attached questions regarding small break analyses should be transmitted to all Corbustion Engineering and Westinghouse operating reactor licensees as indicated in D. Ross' note to you. An informal copy of the questions was transmitted to Combustion Engineering and Westinghouse today.
If you have any questions, please contact Paul Norian (X27911).
z.IL~i?T2d Z.R. Rosztoczy, Chief Analysis Branch Division of Systems Safety cc:
D. Ross R. Tedesco T
]qvak A. Tha'Biant s C. Graves W. Jensen R. Audette B. She.cn F. Odar 27 2 O2 M
7907020 RolsnmA/
29-9?
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Questions Regarding Small Break Analyses The response of the primary system to a small break will differ greatly depending on the break size, its location in the system, operation of the reactor coolant pumps, number of ECCS systems functioning, and the availability of secondary side cooling. To evaluate the response of your system, the following information is needed:
1.) Provide a description of system behavior for a) a range of postulated small break LOCAs. including the zero break case, anc b) feedwater related limiting transients combined with a stuck open power operated relief valve. These cases should include situations where auxiliary feedwater is both a3'.umed available and not available. The cases considered should also discuss breaks large enough to a) depressurize the primary system, b) maintain the primary systems at some intermediate pressure, and c) repressurize the primary system to the safety valve set point pressure. The breaks should be considered at various locations in the primary system including the pressurizer.
2.) Describe the various natural circulation modes of your system following a small break LOCA. Provide justification of these modes of operation.
Discuss any ways in which natural circulation can be interruptea.
In particular, discuss the applicability of the concerns in the Michelson report to U-tube steam generators.
Assess the possible effects of non-condensible gases contained in the primary system.
3.) Provide a safety evaluation for a spectrum of small break and limiting transier.ts combined with a stuck open valve as discussed in Question No.1 (best estimate or evaluation model).
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2 a.) Show that the analysis methods can handle each of the cases discussed.
Provide appropriate verification for the methods (e.g., comparison with experiments TMI-2 evaluation).
b.) Provide a list of transients expected to lift PORVs, and justify the assumed steam and two-phase flow rates through the valves.
c.) Provide analyses for a typical plant as discussed in Question 7
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No. 1.
If the scenario is different for various classes of
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{.9f.\\ 4 plants, an example of each kind should be provided. This W peda b
o should include cases that do and do not initiate HPI.
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d.) Sensitivity studies for the above evaluations shall include consideration of a) availability of zero and one train of AFWs, b) failures in ECCS, c) operator action necessary for safe
<. 6.E shutdown, and d) factors affecting natural circulation. The analyses should also consider asymetric auxiliary feedwater to steam generators.
4.) Provide guidelines for the recovery of plants following small LOCAs.
This should include both short-term and long-term situations and follow through to a stable condition. The guidelines should include recognition of the event, precautions, actions, and prohibited ac'. ions.
If RC pump operation is assumed under two-phase conditions, a justification of pump operability should be providad. Discuss instrumentation available to the operator and any instrumentation that might not be relied upon during then events (e.g., pressurizer level). What would be the effect of this instrumentation on automatic protection actions?
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TVA (C. Michelson) Concerns 1.
Pressurizer level is an incorrect measure of primary coolant inventory.
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The isolation of small breaks (e.g., letdown line; PORV) not addressed or analyzed.
3.
Pressure boundary dama e due to loadings from a) bubble collapse in subcooled liquid and 2 injection of ECC water in steam-filleo pipes.
a.
In determining need for steam generators to remove decay heat, consider that break flow enthalpy is not core exit enthalpy.
5.
Are sources of auxiliary feedwater adequate in the event of a delay in cooldown subsequent to a small LOCA?
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6.
Is the recirculation mode of operation of the HPSI pumps an established design requirement?
7.
Are the HPSI pumps and RHR pumps run. simultaneously? Do they share comon piping?/ suction? If so, is the system properly designed to accomodate this mode of operation (i.e., are any NPSH requirements violated, etc...?)
8.
Mechanical effects of slug flow on steam generator tubes needs to be addressed.
(transitioning from solid natural circulation tt reflux boiling and back to solid natural circulation may cause slug flow in the hot leg pipes).
9.
Is there minimum flow protection for the HPSI pumps during the recirculating mode of operation?
- 10. The effect of the accumulators dumping during small break LOCAs is not taken into account.
- 11. What is the impact of continued running of the RC pumps during a small LOCA?
12.
During a small break LOCA in which offsite power is lost, the possibility and impact of pump seal damage and leakage has not been evaluated or analyzed.
13.
During transitioning from solid natural circulation to reflux boiling and back again, the vessel level will be unknown to the operators, and emergency procedures and operator training may be inadequate.
Tnis needs to be addressed and evaluated.
14.
The effect of non-condensible gas accumulation in the steam generators and its possible disruption of decay heat removal by natural circulation needs to be addressed.
15.
Delayed cooldown following a small break LOCA could raise the containment pressure and activate the containment spray system.
Impact and consequences need addressing.
Note:
Items 1 through 4 are from Michelson report cn B&W 205-FA plants; Items 5-15 are from Michelson draft report on CE system 80 plant.
All concerns considered potentially applicable to W plants.
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Small Bremy_'.0CA Analysis Method Recuirements t
(Short Term) 7...
1.1 Modify pressurizer and steam generator noding.
Justification for new noding.
2.,
Justify pressurizer surge line representation.
Does code predict flooding, should it occur?
3.) Veri fy break ficw model for each break location.
4.)
Verify natural circulation heat removal for two-phase natural circulation, including effects of non-condensables.
6.,' Justify treatment of non-condensables following safety injection discharge.
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Small Break LOCA An: lysis Requirements (Short Term) 1.) A sample analysis of each type of small break behavior (depressurization, pressure hangup at P g, repressurization, soon). - Possibly depends -on 3
ECCS design. Analyses should be carried out to a stable condition.
2.) An analysis of the worst break size and location in terms of core uncovery -
It will probably require more than one calculation to find the wc t break size. - Possibly plant type dependent - Could be a break that does not initiate HPi.
3.) A complete analysis of the pressurizer relief valve stuck open. - Depends on valve size, possibly plant type and ECCS design.
4.) An analysh assuming loss of feedwater and auxiliary feedwater. The case that provides the least time for operator action should be analyced. Single failure of ECCS should be considered. - Probably require more than one calcu-lation.
5.) An analysis assuming that one steam generator is lost either due to isolat' ion or due to loss of aux. feed.
6.) Sufficient analyses of transients to know which transient would lift relief cr safety valves.
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Plotted Output Parameters Core:
L.,
X, TCL Reactor Vessel:
Upper Head:
L, X Downcomer:
L, X Piping:
Hot Leg:
X,T,W,L (Pressurizer Leg) dt (BreakLeg)
Cold Leg:
X.,T,W L,Wgp g,, Wggg Pressurizer: Win, Xin, L, X P, T Steam Generator:
Prima ry:
X,L,T,h REL, AFW, h Secondary:
P,L,X,T,W Leak:
PORV, W, X or e
Break, W, X.,,
Wdt Pump Loop Seal:
X, L Nomenclative: P - Pressure h - film heat transfer coefficient L-Mixture Level HPI - High Pressure Injection X - Quality REL - Relief Valve T - Temperature AFW - Auxiliary Feedwater W - Mass Flow Rate 272 148