ML20137Z890

Forwards Request for Addl Info Re 850322 Submittal, Multiple Steam Generator Tube Rupture Guidelines

ML20137Z890
Person / Time
Issue date:	11/26/1985
From:	Paulson W Office of Nuclear Reactor Regulation
To:	Linn M BABCOCK & WILCOX OPERATING PLANTS OWNERS GROUP, TENNESSEE VALLEY AUTHORITY
References
NUDOCS 8512110438
Download: ML20137Z890 (13)

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i N:vember 26, 1985 Mr. _ Mark A. Linn, Chairman Operator Support Committee

Babcock & Wilcox Owners Group

' Tennessee Valley Authority 400 West Summit _ Hill Drive Knoxville, Tennessee 37902

Dear Mr.' Linn:

We have reviewed your submittal of March 22,1985, " Multiple- Steam Generator Tube Rupture Guidelines," and have compiled a partial list of questions and concerns (enclosed). The review of this submittal is continuing, and additional concerns and questions may yet be identified. However, to maintain the momentum on this issue, we request you respond to this request for additional information and provide us within 30 days from receipt of this letter your schedule for a response.

The reporting and/or recordkeeping requirements of this letter affect fewer than ten respondents; therefore, OMB clearance is not required under P.L.

511.

St!Aal st-sms hv Walt Paulson, Project Manager PWR Project Directorate #6 Division of PWR Licensing-B l

Enclosure:

As Stated cc w/ enclosure:

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Mr. Mark A. Linn, Chairman Operator Support Committee Babcock & Wilcox-Owners Group-Tennessee Valley Authority 400 West Summit Hill Drive Knoxville, Tennessee 37902

Dear Mr. Linn:

We have reviewed your submittal of March- 22,1985, " Multiple Steam Generator Tube Rupture Guidelines," and have compiled a partial list of questions and concerns. The. enclosed request for additional information (RAI) are the concerns which we have identified to date. Since the review of this effort will be within a new organization after our reorganization is implemented, our continuing review of this effort and the Technical Basis Documents may identify additional concerns and questions. However, to maintain the momentum on this issue, we request you respond to this RAI and provide us within 30 days from receipt of this letter your schedule for responding to this RAI.

The reporting and/or recordkeeping requirements of this letter affect fewer than. ten respondents; therefore, OMB clearance is not required under P.L.96-511.

Gus C. Lainas, Assistant Director for Operating Reactors Division of Licensing Office of Nuclear Reactor Regulation

Enclosure:

As Stated cc w/ enclosure:

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l Enclosure REQUEST FOR ADDITIONAL INFORMATION ON [.

TECHNICAL BASES DOCUMENT (TED) CHAPTER III-E ,

1. Appended to the TBD is a list of references; however, the text of' the TBD does not refer to any of these references. When a statement in the text is intended to be supported by one of the references, this reference should be identified in the text.

2. Sections 2.1.1 and 3.1 discuss the means for diagnosis of a SGTR and identification of the affected SGs. Since the TBD provides for subsequent recovery strategies not reviewed in the generically approved Oconee ATOG, and since selection and prioritization of the subsequent recovery strategies can rely both on the information available and the timeliness of that information, the TBD should identify timeframes that t

the alarms and indications should be available from each of the

_ monitoring methods discussed. Bases for these estimates should be identified or referenced in the text.

3. Section 2.2.4 recommends that if heat transfer doesn't exist to either SG ,

then restore heat transfer to at least one SG as soon as possible, even if it is the affected, or most affected SG. Further justification should

~ be provided for this st'rategy (e.g., are there situations where this response may not be mandated?). 7 l -

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4. (a) Section 2.3.1 and 3.3 discuss cooldown and depressurization to below the MSSV setpoint. To support this strategy, address typical effects (in terms of time to reach the MSSV setpoint, approach to Tube i

Rupture Alternate Control Criteria (TRACC) limits SG fil'1, etc) that can be expected from this maneuver in the case of a single tube rupture with loss of off-site power.

4. (b) Expand the guidance in section 2.3.1 to address the depressurization alternatives across the B&W product line. Include an evaluation of pressurizer sprays, PORVs, vents, and any other viable options, with identification of priorities. Relate the approved ATOG guidance of an additional 50 'F SCM (if PORV is used) to the absence of such guidance in the TBD.

5. Section 2.5.2 states the RCP NPSH may require a higher RC pressure than the subcooling margin. Evaluate the effect of this difference in pressure on overall tube leakage and discuss the viability of less

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conservative NPSH requirements (i.e., emergency limits for the RCP's on B&Wplants).

6. Section 2.5.10 discusses void mitigation. The Owner's Group recomends that during natural circulation, if a void develops, the operator should hold the cooldown and eliminate the void. Justification should be ,

provided for this " hold-the-cooldown" strategy considering the va'riety of situationsthatcouldexist(i.e.,whyholdupcooldowniftEevoidis notsevere?). -

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. i 7.- (a) Section 3.3.1.1 states that the cooldown rate may be increased to a maximum of 240.*F/hr (4'F/ min.) if neither of the followfng is p experienced before reaching 520*F: a) the affected SG cdbid have

-carryover or b) radiation release could exceed the TRACC limit; and that 3

"a faster r .e may increase the tube-to-shell delta T... The tube-to-shell delta T is still limited to a maximum value..." Later, this maximum value is identified as 100*F for normal cooldowns and 150'F for emergency cooldowns.

a) Provide an evaluation of the typical tube-to-shell delta T

. that could be expected for a 240*F/hr. cooldown under the l

above conditions.

b) If the resultant tube-to-shell delta T is greater than 100*F,

. justify that a suitable balance is being achieved between the radiation criterion for invoking the higher criterion and the concern that the higher cooldown rate might result in increased tube damage and subsequent greater releases (compared to a scenario in which a lower cooldown rate .

is being observed to maintain the tube-to-shell delta T at less than 100*F).

7. (b) The term " rapidly" on page 28 should be better defined to allow a clearer action level at which the operator should initiate the 240'F/hr emergency cooldown.

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'8. Section 3.3.1.4, "sumary of Limits During Cooldown," states that the fuel pin compression limit should be observed. An earlier section' implies that this limit is not a safety concern for the coolbwn in progress and identifies situations in which it recomends allowing violation of the limit. Assuming that observing the limit could slow down SGTR mitigation, and considering the previous paragraph which indicated that the limit.is not considered a safety limit, the conflicting recomendation in Section 3.3.1.4 should be deleted or modified.

9. Section 3.3.2.1 discusses the disadvantages of SG isolation. Further quantification is needed to evaluate the timing of SG isolation and for procedure writers to properly assess the relative merits of isolation versus alternative mitigation strategies. In particular; e a) The discussicn states that an isolated SG becomes a heat source, causing the cooldown to take longer. Quantitatively compare the -

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cooldown times with and without SG isolation.

b) The discussion states that the loop with an isolated SG becomes stagnant during natural circulation and the loop may void, hindering pressure control and delaying cooldown. Justify this qualitative conclusion against the consideration that since the isolated steam generator becomes a heat source, reverse flow could occur in the

, loop. Considerinthisjustificationthepotentialforheverseflow to sweep voids from the loop. If it is determined that a void would j

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develop and not be swept away, place a perspective on this consideration by identifying how much voiding would be rfquired to stop natural circulation flow and by _ quantifying how lon{~ft would take to remove the void, identifying various void removal techniques.

10. Section 3.3.2.2, " Continued Steaming-Advantages," Item I states that two loop cooldown allows the fastest possible cooldown. In order to assess the relative merits of two-loop cooldown to allow a procedure writer to select his option with a more complete understanding of the advantages .

and disadvantages, additional quantification should be provided comparing cooldowntimes(toDHRScut-inconditions)fortwo-loopcooldown, one-loop cooldown, HPI cooling, etc. (including all options permitted by theTBD). For these analyses, identify all cooldown considerations (e.g., maximum cooldown rate limitation, ADV capacity, etc.) for various

. phases of the cooldown.

11. Section 3.3.2.2, " Continued Steaming-Disadvantages," Item I states that higher integrated releases result from steaming both SGs than if the

, affected SG were isolated and allowed to fill. Quantify the --

considerations that warrant toleration of these higher releases. Compare ,

the expected typical release for a single tube rupture event with continued steaming of the ruptured SG versus the value of a comparable parameter calculated with isolation of the ruptured SG.

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12. Sections 3.4.1 and 1.3.2 state that minimizing the amount of radiation

, released to the environment is one of the objectives for the.SGTR TBD.

Sinceintentionalsteamingofanaffectedsteamgeneratorto[the environment is one of the recomended strategies (i.e. Section 3.3.2.2, Disadvantages, Item 1 states "... this method results in higher integrated releases..."), this objective is misleading'and should be reworded.

13. Section 3.4.1.1 Item a, states that " studies show that the thyroid doses, which are_due to iodine, are limiting for tube ruptures." Discuss the relevance of this statement to licensing bases of older B&W plants.

!- Some of the studies should be identified in the text. Also, the calculations mentioned in Section 3.4.1.1 should be referenced.

14. Section 3.4.1.2 cautions against overfilling steam generators into

e steamlines in condition (a), and identifies an exception in condition 1

(b). Neither item mentions other related considerations, such as

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waterhammer in steam lines and steamline qualification for water loads.

Provide a discussion of these conditions. Also the loadings should be

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j included in the SGTR TBD to provide the procedure writer,with a more complete perspective of the issues. ' '

15. Section 3.5, " Considerations For Use of SG Drains," states that for the case in which radiation release rate is the limiting TRACC, drains should

! notbeusedifthesiteboundarydoserateswouldincrease.du$tothe '

storage location of the contaminated fluid. Section3.4.4(2nd paragraph) indicates the likelihood that if one TRACC limit is reached, i

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all limits may be reached. The guidance of the above drain recommendation should be reconsidered in light of this staterpnt in Section 3.4.4, the better control of a storage location (verdhs the-uncertain alternative disposition of the dose), eid the overall philosophy in steaming recommendations.

. 16. Section 3.6.2, item 2 states that'use of feedwater spray may be beneficial in reducing steam pressure. Discuss how much this maneuver affects tube-to-shell delta T, and consider situations where this action .

might be detrimental.

17. Section 3.6.2, item 3 states that it ma'y be desirable to augment SG filling with feedwater. Evaluate whether this maneuver could lead to a) backflow into the RCS and unacceptable dilution of the RCS born concentration, orb)overpressurizationoftheSGduetomalfunctionor

inadequate pressure / inventory control.

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18. Section 3.6.2 Item 4, discusses converting the SG to a water / water heat exchanger. Insufficient guidance is provided to determine which SG is _

being discussed at any given point in this section, what the status of the other SG should be, and analyses which demonstrate the viability of this cooling mode. Also,shouldn'tlimitationa)includethepossibility that the drained water can be treated (e.g., borated, etc.)?

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19. Section 3.6.2, Item 4, cautions against backflow through the tube rupture into the RCS, Are there situations where, with supplemental',RCS boration, tube rupture backflow may be desirable? Ifso,fukther consideration of this maneuver to control the ruptured SG should be explored.

20. Section 3.7 states that the operator may attempt to limit RCS pressure increase by opening high point vents. Additional guidance should be provided by further discussing the relative effectiveness of this action -

and its prioritization versus other pressure relieving techniques.

21. Several sections (including but not necessarily limited to Section 2.2.2, Section 2.3.1, Section 3.3.2.1, Section 3.3.2.2 Section 3.3.3.1, Section 3.3.3.2, Section 3.4.4, Section 3.6. Section 3.6.1, Section 3.6.2, Section 3.6.3, Section 3.7) contain discussions related to isolation of C

affectedsteamgenerators(s). The following questions apply to this topic:

. a) Throughout the document a clear distinction between filling the -

SG, overfilling the SG, flooding or filling the steamlines, and ,

involuntary releases is not apparent. These conditions should be clearly defined, identified throughout the document, and, in each case identified, a clear discussion of the status, consequences, and influences of various operator actions should be.provided.

All discussion should be supported by analyses.

b) In any situation discussing isolation of an affected SG, the discussionshouldalsoquantifywhethertheSGisexkectedto 1

fill, overfill,etc.(ifisolated),andhowlongtheIfillor overfill would be expected to take. This supporting information is important in assessing overall dose considerations and evaluating the feasibility of operator actions, c) Qualification of steamlines should be considered for each case in which water may carryover from SG into steam lines. Though the qualification of steamlines for water loads may be plant-specific, the discussion should acconnodate this consideration, providing the flexibility of alternative actions for plants with qualified lines, and cautions and restrictions for those whose lines are not qualified.

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d) In cases of isolation of an affected SG, analyses should be provided to quantify the relative effectiveness of various relieving techniques in limiting or preventing the rise in SG

. level, the overfilling of the SG, and the rise in SG/steamline -

pressure. ,

22.InvariousSections(includingSection3.3.3.2andSection3.4.3)theTBD states that a SG, once filled, should be assumed not to be available for i

the remainder of the cooldown. This statement shed1d be clat.ified and justified. What is meant by " fill the SG7" Wh.v is the steam generator not any longer available and what phenomena would prevent or discourage j its use? Section 3.6.2. Item 4. suggests use of the SG as water / water heat exchanger. Doesn't this maneuver involve " Filling" the steam generator?

23. In discussions of subcooling margin, the SGTR TBD does not adequately identify the desirability of minimizing subcooling margin for SGTR ~

events. This should be added, or justified otherwise. -

24. Section 3.4.1.3, the second to the last paragraph describes dose limits expected by implementation cf the TBD recommended mitigation strategies.

The paragraph should be reworded to identify the scenarios for the dose limits discussed and the licensing bases for the plants which might reference the TBD. ,

25. Section 3.4.4 (" application of TRACC") recomends that if TRACC is expected to be violated due to continued steaming of the' unisolated SG, then it also should be isolated and HPI cooling initiated. The implication is that this will prevent violation of TRACC. Clarify whether isolation and HPI cooling does prevent violation of TRACC Ifmit(s).

26. There are some obvious differences in Chapter III-E compared to the approved SGTR guidelines in Reference 2, and additional clarification is .

needed. Provide a comparison summary of the significant changes in SGTR

strategiesandinclude(orreference)thebasesforthesechanges. An example is the increase in subcooling margin prior to use of the PORY (for HPI cooling) on Reference 2 compared to the absence of this guidance I in the proposed TBD Chapter III-E.

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27. Section 3.8, " Impact of Unisolable Steam Leaks," Item "b" recommends that if the steam leak is inside the RB, the SG should be steamed to the condenser, if available, only while steaming the SG is neces ary for other considerations. The discussion should be clarified to address the additional considerations that should be given if the condenser is not available. For example, conditions may dictate steaming for reasons other than TRACC limits, such as an unacceptable rise in containment pressure. Also clarify what feedwater controls are recommended.

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