ML20212C756
| ML20212C756 | |
| Person / Time | |
|---|---|
| Issue date: | 10/27/1997 |
| From: | Birmingham J NRC (Affiliation Not Assigned) |
| To: | Schomaker R FRAMATOME |
| References | |
| PROJECT-693 NUDOCS 9710300165 | |
| Download: ML20212C756 (11) | |
Text
_----_-________ _________ _ _ ___ _ _ _ - _ _ _ _ _
-October 27, 1997
.s-
.Mr. Robert Schomaker Manager Framatome togema Fuels
.-<' LP.O. Box 10935 Lynchburg,VA 24506 0935
SUBJECT:
TOPICS FOR NRC HEETING WITH FRAMATOME C0GEMA FUELS (FCF)
Dear Mr. Schomaker:
Attache'd is a set of questions and topics to be discussed during a proposed ,
meeting of the NRC with FCF personnel in late October or early November 1997.
These. questions and topics were previously provided to you and Bert Dunn in ans email on October 20, 1997. No response to these questions is requested atJ '
+ ,
'this time. . The meeting is tentatively planned for 2-3 days at the FCF site in
, Lynchburg Virginia. Please provide this information to the appropriate. FCF ' '
feg personriel to' allow them to prepare for the meeting.
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%" If you have any questions regarding the questions or the proposed meeting. +
p please contact me by telephone at 301/415 2829 or email jlb4(anrc. gov. ' ,
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l Sincerely. -
Original Signed By:
Joseph L. Birmingham, Project Manager Ceneric Issues and Environmental Projects Branch Division of Reactor. Program Management
.0ffice of Nuclear Reactor Regulation
Enclosure:
Questions and Topics on Boron .
l Precipitation / Dilution Concerns D 3 cc w/ encl: See next page DISTRIBUTl0N: See att v.h page k-:
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. WASHINGTON. D.C. SomH001
- October 27.
SUBJECT:
TOPICS FOR NRC HEETING WITH FRAMATOME C0GEMA FUELS (FCF) j
Dear Mr. Schomaker:
Attached is a set of questions and topics to be discussed during a proposed 1 meeting of the NRC with FCF personnel in late October or early November 1997. l These questions and topics were previously provided to you and Bert Dunn in an email_on October 20. 1997. No response to tl.ese questions is requested at ,
this time. The meetir,g is tentatively planned for 2-3 days at the FCF site in Lynchburg, Virginia. Please provide this information to the appropriate FCF personnel to allow them to prepare for the meeting.
If you have any questions regarding the questions or the proposed meeting, please contact me by telephone at 301/415 2829 or email jlb4@nrc. gov.
Sincerely, ll bpvr w/N -
Joseph L. Birmingham. Project Manager Generic Issues and Environmental Projects Branch Division of Reactor Program Management Office of Nuclear Reactor Regulation Project No. 693
Enclosure:
Questions and Topics on Boron Precipitation / Dilution Concerns cc w/ enc 1: See next page
. \
DISTRIBUIl0N: Ltr. to R. Schomaker Dated .0ctober 27, 1997 Project File PUBLIC PGCB r/f BSheron JBirmingham TEssig TCollins FAkstulewicz DLaBarge JRoe DMatthews TEssig OGC ACRS WLyon Y , k.
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QUESTIONS AND TOPICS FOR PROPOSED MEETING ON BORON PRECIPITATION /DIWTION CONCERNS u
This communication provides questions and topics we believe should be addressed to facilitate development of understanding, staff and industry positions, solution strategies, and closure of issues regarding boron precipitation and boron diluilon. No written response is requested at this time. We suggest a meeting at Lynchburg in late October or early
- November to discuss these topics. The first part of the meeting would address the safety significance and the second would address technical questions and observations.
Safety Significance The most significant aspect of potential boron precipitation, boron dilution and related issues is "What is the safety significance?" Since the staff must address this as part of its
_ regulatory evaluation, it requires a documented characterization of safety significance as presently understood, Broadly, the following questions apply:
- 1. . Does any of the information relative to the above issues have significance with respect to the existence of a substantial safety hazard as defined in 10 CFR 21.3(4)?
What probabilistic risk analyses have been accomplished and what were the results? ;
What other techniques are available to characterize safety and have these been applied? If so, what were the results?
3, What is the impact of addressing boron precipitation and boron dilutio'n upon response to other plant events? Do actions taken in response to boron control '
increase the risk associated with other potential accidents and, if so, by how much?
Technical Questions and Observations
' We would appreciate a briefing that provides detailed analysis ic ation, summarizes your findings, and discusses our observations.
Addressing the following would be helpful with respect to Henshaw, Michael E. , Post LOOA Boron concentration Management,' FIT Docut ant No. 51 1266113-00 (Proprietary),
March 1997,* Letter to J. L. Birmingham, NRC, frot Ohairman, B&W Owners Group .
Analysis Committee, OG-1644, March 27,19g7:
1E Further work will be necessary to establish acceptability of hot leg nozzle gaps as a means of limiting boron concentration. This includes:
Enclosure w
,- 2
- a. One must either show that water cooling of the exterio' af the reactor vessel ,
is not credible or must establish that such cooling will be acceptable, The I
_ potential influence of break flow, containment spray, sad reactor vessel cavity llooding should be addressed.
l b. Consideration of an oval reactor vessel or intomals should be addressed, including sticking of the " seal" at the hot leg noule gap during cooldown.
item a, immediately above, also applies.
- c. Further understanding of potential mechanisms for blocking the " thin" hot log L nonle gaps is needed, including elimination of mechanisms involving
. impurity deposition (including boron), corrosion, sticking, and debris,
- d. The present approach appears to be to base acceptability on analyses of gap !
behavior with little reliance on experimental or operating data other than gap j measurements taken at cold conditions. Do any other data exist? Do gap !
data exist over the life of the plants? Does any information exist from normal !
operations that provides insight into hot log nonle gap flow rates? j
- o. Can cold leg injection lead to cooling the reactor vessel shell unevenly (both axially and radially) and, if so, what is the effect upon the gap behavior?
- 2. Boron solubility:
si Boron solubility data ir, steam appears to be used to remove some of the boron from the core region. What uncertainty is associated with these data?
What substantiation exists to confirm the adequacy of the data for-determining compliance with 50.46(b)(5)?
- b. Does solubility of boron in steam lead to conditions where condensate can become saturated followed by boron precipitation due to cooling.
- c. The curvature of the boron solubility in water curve with increasing temperature means that if one mixes equal parts of saturated hot water with non-borated cold water, boron will precipitate. The situation is exacerbated if the cold water also contains boron. What are the implications for injection?
For cooldown? For mixing in such locations as the lower plenum, hot leg noule gaps, downcomer, and core - lower plenum interface and mixing region? What uncertainty is associated with these data? What substantiation exists to confirm the adequacy of the data for determining compliance with 50.46(b)(5)?
- d. What is the influence of other solutes on boron behavior? Can other solutes contribute to a precipitation problem?
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- 3. Boron related items:
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- a. Part of the boron concentration problem may be addressed if there is sufficient communication between the upper plenum and the upper downcomer annulus.- As identified, the same communication may introduce boron dilution problems. Have other potentiallinkages been identified between boron concentration and boron dilution? If so, what and how have they been addressed?
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- b. Please discuss whether boron can plate out on surfaces from water or steam that contains boron. (Potential concems are flow blockage, removal of boron from the system by unrecognized mechanisms leading to boron dilution problems, and sampling of the sump to assess boron concentration.)
- c. Please discuss the behavior of the sump boron concentration with respect to condensation of steam in the steam generators and filling of previously voided regions of the steam generator tubes, crossover pipes, and RCP bowls.
- d. If one approaches a boron-saturated condition while still hot and pressurized, we do not fully understand how one then cools down without encountering boron precipitation for some of the methods you discuss.
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- e. Can boron precipitate out in the core former region and, if so, what are the implications? 1
- f. - What is the influence of bypass flow in hot leg nozzle gaps during hot leg '
breaks?
- 4. ' Modeling items:
- a. Do the thermal-hydraulic calculaticas use pure water properties or properties of a boron solution? Do other solutes cause a change in water properties and have these changes been addressed?
- b. The analyses appear to be based upon uniform temperature / property nodes.
Occurrence of significant phenomena in the boundary areas between volume nodes'or within nodes has not been addressed. For example, what occurs between a coollower plenum node and a hot core node?
- c. What temperature variations can occur within the core volume and how does this affect your results and conclusions? In other regions of the RCS?
- . _ _ . . . -._._v.-__-_,,,-__m-
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- d. How are interactions in the downcomer and cold leg between ECCS water, steam, and upper head water accounted for in the modeling? (One of the concoms is dilution and adequate modeling of diluted water as it moves through the RCS.
- 5. Questions and observations on other topics:
! a. When crediting pressurizer spray or other methods of " hot leg injection,' what fraction of the added water becomes well mixed with core water above the core and enters into core circulation? What fraction is bypassed to the upper
)
downcomer? With respect to the latter, how much of the added water can be j carried out of the break so that it does not contribute to boron dilution in the
. core?
- b. Has consideration been given to steam generator cooldown following a la.rge break LOCA and the potential for filling the crossover pipes and lower parts of the steam generator tubes with water? If this occurs, are there any implications with respect to boron concentration?
- c. What is the meaning of 'subcooled bailing' on page 50?
- d. Page 50 references a 140 F core inlet temperature. What is the effect of a lower ECCS or core inlet temperature?
- e. Page 10 contains the statement "These results also demonstrated that there is not a significant safety concem related to post SBLOCA boron concentration control." The staff cannot agree with this statement on the basis of the material that has been provided.-
- f. Page 12 wntains the conclusion that "... larger breaks located on the bottom of the CLF0 pipe will provide the greatest potential for core boron concentration increases." Are the RVWs always predicted to open for all practical, long-term combinations of water levels in the RCS for the smaller breaks? Please discuss,
- g. Some aspects of the behavior would appear to be of more concem at lower decay heat levels, such as a lower froth level and higher density in the core for the same collapsed liquid level and the corresponding effect upon circulation, or droplet carryover. How has this been addressed and shown to be bounded by the work that has been accomplished? -
- h. The evaluation addresses operation at high power levels for an extended time prior to postulated LOCAs. You do not appear to have established that -
this bounds the behavior of potential concem.
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- 1. What is the influence of injection flow rate on the conclusions? (Can variation in flow rate cause lower temperatures so that less boron romahc in solution?)
J. In Figure 4 (page 21), what causes the increase in pressure from about 5 to 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> for the 0.01 ft' break? The increase at about 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> for the 0.05 ft'?
- k. Page 55 states "... LPl flow is doubled (i.e. 2 pumps)." is this correct?
! With respect to ' Preliminary Report to the B&W owner's Group on PSC 1 g5 Investigations,' Frematome Technologies Inc.,47-1244436-00, January 1996, we have the following questions and observations:
- 1. Why is the pump bump critical concentration based upon 486 F (page g) when page
- 18 references 300 F and one may be significantly lower than that under some circumstances?
- 2. In Table 1 (page 11), why are BWST concentrations sometimes less than refueling concentrations?
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- 3. The last paragraph on page 1g appears to attempt to justify using a homogeneous reactor model for evaluation of natural circulation conditions. We cannot accept a ,
homogeneous model unless there is in-depth substantiation.
- 4. The last paragraph on page 23 states that the potential for accumulation of low boron concentration water is nullified unless there is no circulation around the RCS.
We do not understand why this is 'somewhat obvious" for separated flow and bypass conditions. Have these been eliminated? Can one have circulation in one loop and not another? Can some tubes in a steam generator be active while otners simply accumulate cold dilute water? (What is the effect of the difference in density of boron solution vs. pure water?)
- 5. Some of the questions pertinent to boron precipitation apply to the top-of-page 25 discussion of the solubility of boron in steam. Please provide verification regarding boron carryover in steam? Include substantiation that boron cannot be removed by deposition on surfaces before reaching the break.
- 6. The bottom of page 25 states 'Because the core is likely to be highly borated, the mixing of core and downcomer fluids will improve or increase the boron concentration of the water reaching the bottom of the downcomer.* We consider steam coming off the top of the core to be a ' core fluid." Does steam not have the l potential to dilute downcomer water? How is this statement consistent with the statement on the top of page 26 that downcomer boron concentration is 1600 ppm with a BWST concentration of 2000 ppm?
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- 7. The bottom of page 28 states that the time duration for which low boration build up occurs is shown to be limited if system enntrol is restricted to above 650 pala. This
, appears to be due to decay heat being rejected by the steam generators after the ,
time duration. Is this correct? If so, how do later operator cooldown actions '
l Influence the results? What about intemal effects such as boron dilution due to !
steam condensation on incoming ECCS water?. What about later actions in which i circulation is started with dilution that has occurred prior to reaching the time .
i duration?
4 I 8. - On page 2g, reference is made to evaluation of differing types of events i sequentially, with the remainder of the work being discussed here concentrated 11 l SBLOCA conoems. What are the other events of interest and how are they being
- evaluated?
e g. . Please provide a briefing of the behavior discussed at the bottom of page 3g - top of f I page 40 on lack of bubble collapse. We do not understand part of the discussion .
- _ and the conclusions. For example, the wells of the elevated section of hot legs are
- - relatively thin when compared to the top of the reactor vessel. Why would pumo ;
j bumps that result in cooling of the top of hot legs containing voids not have the end result of expanding an upper head void to provide water to fill the hot legs? Or why j would the pressurizer not provide a filled hot leg end state if there was sufficient hot
- water in the pressurizer initially?
- 10. Page 43. What proof exists that cold water does not flow through the downcomer
- with little mixing?
- 11. Page 43. The end of the first paragraph references an assumption that the i downcomer coolant is transferred without mixing into the core and occupies the >
, entire core. Please discuss the conservatism of this with respect to the respective -- ;
J' vo!umes. '
- 12. Page 44. Did you mean to omit the effect of buoyancy of steam from the table? ;
13J Pag, '6 discusses the LOTUS model, with the flow areas of each column described by & Ning relationship, and this is stated as a preference for the flow to follow the shor, path. Why wouldn't a constant area follow the shortest path? What is the 3
4 justification of the doubling behavior?
14.- Pege 46. The end of the first paragraph states that each calculational cell is assumed to be completely mixed at each time advancement and the concentration of flow from one cell to another was based on the concentration of the supplying cell.
Pleaae discuss the validity of this modeling with respect to numerical diffusion.
R. Schomaker 7
- 15. Page 47, bottom. The rate of increase in effective reactivity at the time of criticality was considered important. How accurste is the identified 3 to 4 seconds from just critical to prompt critical in light of such modeling considerations as uniformity of boron concentration entering the core with respect to core bottom location? Nuclear modeling? Core boron distribution in the core? With respect to the page 50 conclusion regarding void generation rate fast or. ugh to meaningfully control the transient to a benign prompt critical excursion?
- 16. Page 70. It is not reasonably obvious to us that the CE calculation results are applicable to the B&W design nor can we concur with a licensing position that boron .
dilutioi should not be a licensing issue at this time. For example, the lowered loop B&W design can accumulate substantial dilute water in the t., team generator with water level at the hot and cold :eg elevation. This cannot occur in the CE design.
(We note there are numerous other differences between the CE and B&W designs, and even from one B&W designed plant to another.)
- 17. Are the flow rates on page B-2 for licensing calculation (FSAR) purposes or are these expected values?
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B&W Owners Group Project No. 693
'Mr. Robert W. Keaten,- Chairman- Mr. J. J. Kelly, Manager B&WOG-Executive Committee' B&W Owners Group Services Vice President & Director of. Framateme. Technologies. Inc.
-Technical Functions P.O.l Box 10935 GPU Nuclear. Corporation Lynchburg,'VA 24506 0935 One Upper Pond Road-Parsippany, NJ 07054.
i Mr. R. B. Borsum, Manager Rockville Licensing Operations Framatome Technologies Inc.
1700 Rockvil se Pike, Suite 525- 4
-Rockville. MD 20852 1631
-