ML20038B060
| ML20038B060 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 11/18/1981 |
| From: | Tauber H DETROIT EDISON CO. |
| To: | Kintner L Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.K.3.44, TASK-TM EF2-55-345, GL-81-32, NUDOCS 8111240663 | |
| Download: ML20038B060 (5) | |
Text
1 H:rry Touber N;
m C, e d x Detroit Edison m=:cac AseNer "=
2000 Se November 18, 1981 EF2 - 55,345 9;)k
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r Mr. L. L. Kintner
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Dear Mr. Kintner:
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Reference:
Enrico Fermi Atomic Power Plant, Unit 2 NRC Docket No. 50-341
Subject:
NUREG-0737, Item II.K.3 44 - Evaluation of Anticipated Transients Combined with Single Failure (Generic Letter 81-32)
This letter responds to an NRC letter from D. G.
Eisenhut to all applicants dated August 7, 1981 con-cerning a request for additional information on NUREG-0737 Item II.K.3 44 for the Enrico Fermi 2 power plant.
The letter requests a verification that the assumptions and initial conditions used in the generic analyses for Item II.K.3 44 as referenced in the BWR Owners Group report dated December 29, 1980 are representative for Fermi 2.
Detroit Edison has reviewed the analysis assumptions and initial conditions used for generic analysis and determined that they are representative for Fermi 2.
Sincerely,
/22d
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Mr. B. Little I{
8111240663 011119 PDR ADOCK 05000341
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x Enclosure to EF2-55,345 TECHNICAL JUSTIFICATION APPLICABILITY OF THE BWR OWNERS GROUP EVALUATION OF NUREG-1737 ITEM II.K.3 44 FOR FERMI 2 This report verifies the applicability of the conclusions of the BWR Owners Group evaluation of NUREG-0737 Item II.K.3 44 (Reference 1) to Fermi 2.
Also, the operator actions assumed in the study are identified for the-transients described.
I.
CONCLUSIONS OF OWNERS GROUP REPORT The worst combination of a transient and single failure for Fermi 2 as described in the Owners Group study, in the loss of feedwater (LOF) event plus a failure of HPCI.
For this event, the RCIC system will provide inventory makeup while reactor pressure remains high.
This event is the design basis for the RCIC system.
Analyses performed for reference BWRs, as referenced in the Owners Group study, show that the RCIC system will maintain the water level at least 6 feet above the top of the active fuel.
For even more degraded conditions, that is, one stuck open relief valve (SORV) in addition to the worst case transient and single failure, the reference analyses show that in some plants the RCIC system can maintain water level above the top of the active fuel.
It should be noted that these degraded conditions go beyond the current BWR design basis and the specifications of Regulatory Guide 1 70, Revision 3 The report notes that operator action to maintain adequate core cooling is straightforward in plants not equipped with RCIC or if the RCIC system cannot maintain the water level above the top of the active fuel.
II.
INITIAL CONDITIONS AND ASSUMPTIONS The analyses on which the Owners Group's conclusions were based were taken from Reference 2.
The initial conditions and assumptions of those analyses are summarized in Section 3 2.1.1.4 of Reference 2, and are reproduced below with a statement of their applicability to Fermi 2.
Assumption Rationale 1.
Reactor is initially at 105%
These are bounding steam flow and 100% core flow, conditions for Fermi 2.
Other reactor parameters are at nominal values.
. 2.
1978 ANS Standard decay heat This is the most realistic model is used.
decay heat model.
It is generically appplicable to all LWRs.
3 Nucleate boiling is assumed Recent TLTA tests have when the core is covered.
demonstrated that the core remains in nucleate boilinF as long as the core fa covered.
This assuuption is generically applicable to all GE-BWRs.
4 Simultaneous trip of all the This leads to the most feedwater pumps is assumed at rapid level reduction.
t = 0.
This assumption is conser-vative for Fermi 2.
5 Feedwater flow coastdown time This is a conservative is 5 seconds.
value for the steam-turbine-driven feed pumps installed in Fermi 2.
6.
CRD flow is neglected.
Due to the small CRD flow rate relative to feedwater flow, this assumption does not alter the conclusions of the Owners Group posi-tion, and is conservative for Fermi 2.
III.
APPLICABILITY TO FERMI 2 The major findings of the Owners Group report which apply to Fermi 2 were as follows:
1)
The worst transient and single failure is the loss of feedwater with failure of HPCI.
2)
For an isolation with loss of feedwater and failure of HPCI system, the RCIC system will prevent core uncovery.
3)
Fcr the same event compounded by an SORV, manual depressurization will maintain adequate core cooling if it canrot be provided automatically.
The following paragraphs explain why these findings are true for Fermi 2.
A.
Isolation with Lons of Feedwater.
For the II.K.3.44 analysis, the significant variable which determines the capability to adequately cool the core for this event is the RCIC system flow rate.
s c The safety design basis of the RCIC system for Fermi 2 is to provide adequate core cooling should the vessel be isolated and accompanied by loss of feedwater flow.
Consequently, the RCIC system is specifically designed to provide sufficient makeup in the event of an isola-ticn with a loss-of-feedwater and a failure of HPCI.
The adequacy of the RCIC design bases for the reference plants was confirmed by the reference plant analyses which demonstrated adequate core cooling for this event.
Since the RCIC design basis for Fermi 2 is the same as the reference plant, the conclusions drawn from the generic analysis are applicable to Fermi 2.
B.
Isolation with Loss of Feedwater and Stuck-Open Relief Valve (SORV).
/ >1 ant unique analysis for Fermi 2 has not been con-ducted to determine whether or not the RCIC system will maintain core coverage automatically for this non-design basis event, as was the case for the reference plants discussed in the Owners Group's position.
- However, straightforward operator action, as discussed in Section IV, will maintain adequate core cooling.
IV.
OPERATOR ACTIONS The following is a discussion of the operator actions necessary to place the reactor in a cold shutdown condition following a oss of feedwater plus failure of HPCI plus a stuck open relief valve.
These operator actions are spe-cified in the Emergency Procedure Guidelines (Reference 3).
As stated earlier, for some plants the RCIC system will maintain reactor water level above the top of the active fuel without any operator actions for an isolation with loss of feedwater and SORV.
Therefore, for those plants the operator can proceer through the Level Control Guideline and into the Cooldown G ideline without any specific actions to maintain core cooling other than to confirm automatic system initiations and to control injection flow to maintain water level if it exceeds the maximum level specified in the Guidelines.
For those plants for which the RCIC system can-not maintain reactor water level for this event and for plants equipped with IC but not RCIC, then manual depressurization may also be required in order to allow the low-pressure ECC systems to operate and maintain level.
The purpose of the Cooldown Guideline is to depressurize and cool down the RPV to cold shutdown conditions while main-taining RPV water level within a satisfactory range. While maintaining RPV level, the operator must confirm that an adequate supply of water exists for the RCIC pump from either the condensate storage tank or the suppression pool.
. The need to assure these conditions is provided in Caution No. 8 in the Guideline.
The SORV, if it occurs, will also continue to depressurize and cool down the reactor.
Although RCIC will act to replenish reactor inventory, the low pressure ECC systems are also available when reactor pressure falla below approximately 300 psig.
To prevent potential vessel overfill, Caution No. 11 alerts the opera-tor to the possibility of automatic low pressure ECCS injec-tion during the depressurization.
Caution No. 14 instructs the operator to have alternate injection sources available before the vessel is fully depressurized.
When the RHR shutdown cooling interlocks clear, the operator is instructed tc manually initiate the shutdown cooling mode of RHR.
Cold shitdown is then achieved by following the cooluown to cold shutdown procedures.
The operator is concurrently instructed to control suppression pool temperature.
The Containment Control Guideline, whose purpose is to control primary containment temperature, pressure, and suppression pool temperature and level, is followed for this case.
It is possible that the suppression pool temoerature may exceed 95 F due to the SORV.
If this should occur, the operator is instructed to close the SORV if possible, and to operate available suppression pool cooling.
In the event the SORV cannot be closed, the operator is instructed to maintain the suppression pool water temperature limit.
In summary, for the cooldown guideline the operator needs only to verify that the reactor water level does not become too high and to initiate RHR shutdown cooling and suppression pool cooling at the appropriate time.
V.
CONCLUSIONS This report demonstrates that the results of the BWR Owners Group etaluation of NUREG-0737 Item II.K.3.44 are applicarle to Fermi 2.
Reference plant analyses from Reference 1 adt -
quately model Fermi 2 for the transients described.
The operator actions necessary to put the plant in a cold shut-down condition are specified in the Emergency Procedure Guidelines and are applicable to Fermi 2.
VI.
REFERENCES 1)
Letter, D. B. Waters (BWROG) to D. G. Eisenhut (NRC), of Decem'aer 29, 1980, BWR Owners Group Evaluation of NUREG-0737 requirements.
2)
NEDO-24708A, " Additional Information Required for NRC Staff Generic Report on Boiling Water Reactors",
Revision 1, December 1980.
3)
NEDO-24934, " Emergency Procedure Guidelines - BWR/1/6."
Revision 1, January 1981.
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