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'i NUCLEAR REGULATORY COMMISSION 7,. ~ e:"Q@/ /
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JUN 1i:330
' EMORA: DUM FOR: Thomas M.
!ovak, Assistant Director for Operating Reactors Division of Licensing FROM:
L. S. Rubenstein, Assistant Cirector for Core and Containment Systems Divisicn of Systems Integration IU5 JECT-POSITIC:10:4 I:; ADEQUATE CCRE CCOLI::G (ICC) REQUIREME:JTS FOR S&W REACTORS The staff has revier ed submittals reflecting the response of scme or all B&W x
plant c.sners to the short-tem lessons learned item 2.1.2(b) of :;UREG-0578.
Their position, in summary, is that no additicnal instrumentaticn is required for detection of core cooling.
Ne find that positior unacceptable, c.nd the basis for our conclusions is detailed in tae attache 7 valuation Report.
Based on our overall review of ICC responses to date, s._.o not believe that it is possible for those plant cwners v.ho have not alrsdy initiated procure-cent action to install acceptable new instrumentation and display systems by J an ua ry, 1931.
- le w.darstand that scme of the plant c..ners have submitted ICC positions cn their individual deckets and consider their obligation ccmplete until they hear other. ise from l!RC. Therefore, we request that you forward the attached evaluation report giving the current
- 1RC position to all B&W cuners as soon as possible. Please ask them to respend with a program and schedule for installation, testing and calibration, and implementation of any proposed new instrumentation or information displays, g
.c O(.Thliht..k L. S. Rubenstein, Assistant D.irector for Core and Containment Systems Division of Systens Integration
Attachment:
As stated N w.., u u aunianit D. Ross T. Speis D. Eise' hut HFCB Chief R. Fattson A. Schwencer P. Check L. Phillips R. Tedesco M. Morris G. Lainas B. Sheron R. Reid J. Voglewede R. Satterfield G. Holahan 8008080 [ ]
Status Sur.,ary - Staff Evaluation of Subnittals Regarding Additional Instrumentation for Detection of Inadequate Core Cooling for B&W Reactors The staff has reviewed 'nfo.wation submitted by Babcock and Wilcox plant owners in response to the short-term lessons learned item 2.1.3(b) of NUREG-0578(R-1) and the subsequent clarif;:ation letter issued by the staff (R-2). The staff position and clarification as presented in the referenced docurents follows: Position Licensees shall provide a description of any additional instrumentation or controls (pricary or backup) proposed for the plant to supplement those devices cited in the preceding section giving an unambiguous, easy-to-interpret indication of inadequate core cooling. % 'iption of the functional design requirerents for the system n shall also be included. A description of the procedures to be used with the p,roposed equipment, the analysis used in developing these procedures, and a schedule fcr installing the equipment shall be provided. Clarification l. Design of new instrumentation should prcvide an unambigucus indicaticn of inadequate core ccoling. This may require new measurerents to or a synthesis of existing reasurements which meet safety-grade criteria. 2. The evaluation is to include reactor water level indication. 3. A ccrmitment to provide the necessary analysis and to study advantages of various instruments to monitor water level and core cooling is required in the resp nse to the September 13, 1979 letter. 4 The indication of inadequate core cooling rust be unambiguous, in that, it should have the follcwing properties: a) it must indicate the existence of inadequate core cooling caused by varicus phenomena (i.e., high :vid fraction pu.. red flow as well as stagnant boil off). b) it rust not errcneously indicate inadequate ccre ccaling because of the presence of an unrelated phencmenon. 5. The indication cust give advanced tearning of the approach of inadequate core cooling.
. 6. The indication must cover the full range from nornal operation to complete core uncovering. For example, if water level is chosen as the unarbiguous indication, then the range of the instrument (or instruments) must cover the full range from normal water level to the bottom of the core. The staff review to date is limited to the information provided in references R-3 and R-4, which are the B&U-developed positions based on their evaluation. Mcwever, we understand that most or all of the ESH Owner licensees have adopted the position reflected by the referenced documents. This position can be summarized as follows: 1. An advance,tarning of the approach of inademuate core cooling is provided by existing instrumentation which indicates a less of subcooling in the hot leg. ' a 2. An unambiguous indicaticn of the existence of inadequate core cooling is provided by the incore thermocouples and the hot leg RTDs. 3. Additional instrunentation concepts censidered fail to meet ;t least one of the criteria established by references R-1 and R-2. 4 Additional instrumentaticn is not needed since necessary operator act.cns for management of the accident will be taken based on existing indicators. Staff Conclusions The staff views concerning the cited positions and supporting submittals follow: 1. Advance Waining - The staff does not agree that an indicatien of loss,of hot leg subcooling provides advance warning of inadequate core cooling. While loss of subcooling is a useful early tiert, it will also occurlor severe overcooling transients which do not threaten core uncovery leading to inadecuate core cooling. The staff censiders the core to be in a state of inadequate core cooling whenever the two phase froth level falls below the tcp of the core and the core heatup is well in excess of conditiens that have been predicted fer calctlated small break scenarios for which scme core uncovery with successful reccvery from the accident have been predicted. Possible indicators of such a ccndition
. are core exit superheat temperature and/or the rate of coolant loss or level drop prior to core uncovery and the extent and duration of uncovery. ~ Instrumentation to provide advanced warning of this condition must indicate a loss of primary coolant inventory by level or other means after loss of subcooling has occurred. The time available for corrective action and/or interpretaticn of the scenario while the system is beina depleted of coolant above the top of the core wculd be significant in cc:cparison to the time frcm the start of inadequate core cooling until core damage occurs. While we recognize the difficulties inherent in the develcrment of a highly accurate level indicating system, the referenced reports do not provide evidence of any substantial effort to develop and calibrate a system which is sufficiently accurate to provide an unambiguous indication of coolant loss that would serve as a valuable advance warning to the operator. In fact, a staff review of available LOFT and Semiscale data during large and small break loss of coolant tests (L1-4, L3-1, L3-2, S-07-10, S-06-4, S-SS-PlC, S-SS-P7, S-SB-2A) and comparison to calculated values of measurable parameters (e.g., differential pressure) lead the staff to believe that correlation of measurable parar.eters to the af.ent of inadequate core ccoling is feasible. 2. ICC Indicators - The staff agrees that ccre exit thenroccupies can provide evidence that inadequate core cooling is occurring. Heuever, plans and criteria for qualification of this instrumentation for post-accident conditions need to be addressed if the core exit thermocouples are to be included in the final system. 3. The staff agrees that the individual methods ccnsidered in the referenced reports appear to be deficient in one or more of the criteria of the staff position. However, combinations of the methods do provide the information required for a system which has the potential to satisfy the staff criteria. It is probable that additional data processing and dirplay equipment uculd be needed to aid in the interpretation of the available information through appropriate correla-tions or by integration of necessary data. For exarple, an acceptable level ressurement system above the core coupled with core exit thermccouple data properly correlated in terms of level or equivalent condition of core uncovery could be displayed in a kanner to satisfy the full range indication criterion.
4 4. The staff finds the position that additional instrumentation is not needed because necessary operator actions will be taken based on existing indicators to be unacceptable. If all actions available to the operator have been taken and the system is continuing to lose coolant due to equipment malfuncticn or some unkr.cwn system condition, the operator should be clearly inforned of the situation. It is probable that additional actions such as detection and correction of the unkncwn malfunction cc initiation of system depressurization to utilize icw pressure coolant injection could be taken by the operator if circumstances warranted such action. In surrary, the staff finds the positions developed in the referenced docurents to be ur. accept abl e. 'le will require that Eabcock & 'n'ilcox c.,'ners provide an acceptable response to the Inadequate Core Cooling requirament (R-1 & R-2), including a schedules for installation, testing and calibration, and implementation of any preposed new instrumentaticn or information displays. 4
O .._.1., u - - 4 1 - 1 I l3 References R R-1
- UREG-0578, "T!!I-2 Lessons Learned Task Force Status Report and Short-Term Reco=endations," 'JSNRC, July,1979.
R-2 to letter, H. R. Derc. an to all cperating nuclear po.cer plants, " Discussion of Larscns Learned Short-Tem = Requirements," October 30, 1979. R-3 " Analysis Su=ary in Support of Inadecuate Ccre Cooling Guide-lines for a loss of RCS Inventory," B&W. ..N R-4 B S'a' Letter '.C-68, " Report cn Additional Instrumentation to Cetect Inad cuate Core Ccoling," 'oril 8,1920,.hndment No. s 18 to the TMI-1 Restart Report, t'etrc;olitan Edison. / attachment, " Status 0.eport on Additional :nstrur.sntaticn to Cetect Inadequate Core Cooling." a M s
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