ML19254F862

Requests Addl Info Re NEDO-24708, Addl Info Required for NRC Generic Rept on BWR Reactors

ML19254F862
Person / Time
Issue date:	11/06/1979
From:	Ross D NRC - TMI-2 BULLETINS & ORDERS TASK FORCE
To:	Keenan T GENERAL ELECTRIC OPERATING PLANT OWNERS GROUP
References
NUDOCS 7911190220
Download: ML19254F862 (9)

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Mr. Thomas D. Keenan, Chairman General Electric Operating Plant Owners' Group Vemont Yankee Nuclear Power Corporation Seventy-Seven Grove Street Rutland, Vermont 05701

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION CONCERNIt4G NED0-24708 As a result of its review of the General Electric Company Report NED0-24708,

" Additional Information Required for NRC Staff Generic Report on BWR Reactors,"

the Analysis Group of the Bulletins and Orders Task Force has determined that additional information is needed in order to complete its review.

The Analysis Group's specific requests for additional information are documented in the enclosure to this letter.

In order for us to maintain our present schedule, it is necessary that the requested information be provided to us by November 30, 1979.

If you cannot meet this date or if you desire clarification of the information requested, please contact Cecil 0. Thomas at (301) 492-7745.

Sincerely, kf' gt N D. F.

oss, Jr., Eirector Bulletins and Orders Task Force Office of Nuclear Reactor Regulation

Enclosure:

Request for Additional Information cc w/ enclosure:

See next page 1345 340 220 7911190

I ENCLOSURE REQUEST FOR ADDITIONAL INFORMATION CONCERNING NE00-24/08 ANALYSIS GROUP The following concerns were informally addressed to the Owners Group. The Owners Groep responded that the concerns will be addressed in its November, 1979 submittal, under Inadequate Core Cooling.

1.

Provide a limiting ana',ysik indicating the consequence of loss of ali ECCS except two low pressure pumps.

When would only two low pressure pumps be inadequate? For cases where two low pressure pumps are not adequate for core cooling, provide the time available to the operator #cr corrective actions (limitino case).

2.

Provide analyses where natural circulation is lost.

3.

For all analyses conducted, in NE00-24708, where operator action was required, provide the ruximum time available for the operator to perforn the required actions before exceeding the 2200*F limit f using 10 CFR 50, Appendix K assunptions).

For any breal: size, including the no break case, what is the maximum time available to the operator for actuating the ADS? Consider with and without degraded conditions, including a stuck open relief valve.

4.

For BWR/4 and 5's, having MARX 2 containment, with automatic or manual LPCI diversion, provide the following analyses:

1) Limiting small break in the recirculation suction line in combination with all high pressure systems failed, and assuming LPCI diversion at 10 minutes.

2) Same as 1), without LPCI diversion.

3) Same as 1), plus the failure of the LPCS.

4) Same as 1), with early LPCI diversion, and 1345 541

5) Same as 2}. plus the failure of the LPCS.

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_2 For these analyses, provide the following transient curves:

a) Water levels (downcomer, lower plenum, corn; and upper plenum).

b) Vessel pressure.

c) Heat transfer coefficient (core and lower plenum wall heat).

d) Peak clad temperature.

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e) ECCS, SRY, Core inlet, FW, ADS, and Stet.t li e ficw rates.

n f) lower plenum void fraction within the mixture level.

Provide a detailed description of the LPCI flow paths and discuss where the LPCI flow enters the lower plenum and at what elevation.

Describe in detail, all the variables influencing the void fraction evaluation in the lower plenum.

Also describe the models used in determining the level (i.e. Wall heat transfer models, bubble rise model, treatment of determining voids due to depressurization).

5.

Discuss all information available to the operator which will detect core uncovery.

6.

What is the system response of BWR classes, other than the SWR /4-218, to the "No Break" case? How much time is available for manual ADS?

7.

What length of time is core uncovery acce;iable before the 2200 degree limit (using 10 CFR 50, Appendix K assumptions) 1s exceeded? Provide a chart of acceptable core uncovery tima as a function of when the uncovery begins, i.e.

~

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Acceptable ~

-+4 x-seconds r+-

Core Uncovery Interval TRANSIENT TIME 8.

Conclusion 6 in section 3.1.1.1.2/2.4, states that the core level will always remain higher than the downcomer level for small break This statement appears true if CCFL is not considered.

LOCAs.

Comparisons of Figures 3.1.1.3-5 with 3.1.1.3-6 show that CCFL can With the create a higher downcomer level versus the core level.

arguments presented, the staff can not agree with the conclusion that Provide additional CCFL plays a negligible role in a small break LOCA.

justification for the neglect of CCFL and discuss the implication of hot channel behavior, where CCFL may play a crucial role.

For every analysis where the core uncovered, provide a plot of coolant velocity exiting the core as a function of time and discuss at what velocities CCFL will begin to play a role in preventing or retarding liquid penetration.

For all cases where CCFL can retard the penetration of ECC, expand your analysis by conducting a REFLOOD evaluation, which models the CCFL phenomenon.

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. The "following questions ahve been inforammly conveyed to the Owners Group without further discussion. The Owners Group is to respond to these questions.

I.

ANALYTICAL MODELING:

1.

Provide assurances that the 10 CFR 50.46 criteria (using 10 CFR.50, Appendix K assumptions) will not be exceeded for all analyses in NED0-24708, wh ch resulted in core uncovery.

2.

Describe how the SAFE computer program evaluates the internal system pressure gradients which result from liquid flashing within the core and steam condensation due to ECC injection. Are internal system flow rates affected by these pressure gradients?

If the codt.ces not model such phenomenon, povide justification for its neglect, including experimental verification.

3.

Provide assurances that the break size and the assumptions chosen in the analyses result in the most severe test for operat:r actions.

II. RECIRCULATION PUMP INFLUENCE ON SMALL BREAK LOCAs:

1.

Section 3.3.2.2 states that application of recirculation pump flow during a LOCA would require additional avcluations before a recommenda; ion can be made to restart the pumps. Verify that GE has the analytical capability to model such transients.

Provide verification to show such analyses are valid.

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For non-jet-pump plants, provide test results which verify that only one recirculation loop, provides sufficient comunication between downcomer and core to provi,de natural core circulation.

III.

NATURAL CIRCULATION IN BWRs:

1. ~ What conditions will result in negative core flow?

Ho., does this influence natural circulation?

2.

Section 3.3.1.3 addresses the need for natural circulation in a BWR.

In that section, reference was made to an experiment which showed that no dryout will occur,'~even at zero inlet flow, provided water is available i:1 the '.:ppcr plenum.

Document the experiment, provide a graphic description of the experiment, discuss what bren size will result in loss of upper plenum inventory within 10 seconds of scram, and the applicability of the ex'p'erimental geometry to all operating BWR plants.

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The staff has requested the Owners Group to infor:.1allj address the following concerns. The answers to these concerns are now requested to be formally a

documented.

1.

Analyses conducted utilizing the SAFE computer code showed numerical instabilities or non-convergence in evaluating model level and flows: i.e.

Figures 3.1.1.1.-19.2

-19.5

-20.2

-20.5

-47.5, etc.

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. Discuss, in detail, the reasons for these oscillations and verify their impact on the analytical results.

Are inertial effects accounted for in the analytical equations? If not, how does the neglect of inertia influence the system response? Verify that the code has converged to a solution for the analyses performed.

2.

Figure 3.1.1.1-19.4 and.-38.4 indicate the ADS sys tem opening and closing.

Is the on-off behavior of the ADS system an automated process? How many cycles can the ADS accomodate? Provide the settings for the on-off logic.

If the ADS valves do not cycle, describe in detail why the cycling is observed in the mentioned figures.

3.

Discuss the worst case power profile for small breaks.

What power profile was used in the analyses?

~ " 4.

Analyses indicate that part of the operator's responsibility is the requirement to throttle the ECC systems.

List all conditions for such operator action, and describe, in detail, the reasons for such actions.

What information does the operator have, which assures him of adequate NPSH for his ECC systems?

1345 346

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