ML20040A655
| ML20040A655 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse, Oconee, Arkansas Nuclear, Crystal River, Rancho Seco, 05000000, Crane |
| Issue date: | 12/29/1981 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20040A650 | List: |
| References | |
| RTR-NUREG-737, TASK-2.K.2.17, TASK-TM TAC-45218, NUDOCS 8201210358 | |
| Download: ML20040A655 (3) | |
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4 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION CONCERNING ITEM II.K.2.17 " VOIDING OURING PLANT TRANSIE:1TS" BABCOCK AND WILCOX REACTOR PLANTS DOCKETS NOS. 50-269, 50-270, 50-287, 50-289 50-302, 50-312, 50-313 AND 50-346 Introduction In a letter from R. Reid to all B&W operating plants dated January 9,1980, the NRC requested all B&W licensees to address the issue of primary system voiding formation during anticipated transients.
The request evolved from our concern that unanticipated primary system void formation during anticipated depressurization transients could degrade system performance by either, (1) " Holding up" the primary pressure above the HPI actuation setpoint and/or, (2) trapping steam at the top of the hot leg " candy-cane" bends, thereby impeding natural circulation.
Discussion and Evaluation 5
Drop in reactor system pressure during reactor trip events (without secondary system malfunctions) is limited by the balance of net heat 5
removal rate versus the net heat insertion rate. The energy insertion rate primarily consists of core (decay) heat, reactor coolant pump heat, and metal heat. The net energy removal rate from the primary system i
j consists of heat transfer, cor responding to turbine trip conditions in the i
l" secondary side of the steam generators and the metal heat transfer to containment. This balance of insurge and outsurge of energy limits the primary system coolant shrinkage and corresponding expansion of the pressuri:er steam volume.
For B&W plant designs, the energy balance following a reactor trip typically results in a mininum system pressure of 1750 psia.
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PDR ADOCK 05000346
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1 l B&W examined mild overcooling operational transients at Davis Besse and Oconee Units I and II. These events significantly drained, but did not empty the pressurizer. Their evaluation concluded that net steam production was highly improbable for these events.
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In previous analyses performed to show the effects of RCP trip on non-LOCA transients B&W evaluated an unmitigated, large (12.2 ft.2) steam line brea k.
For this case, which can be considered a bounding overcooling' case i
for all MW operating plants, natural circulation flow was calculated to be temporarily interrupted in the loop containing the pressurizer. The loop without the pressurizer did not have any steam formation and was predicted to continuously remove decay heat.
Based on our review of the information provided in response to Item II.K.2.17 and previous analyses of primary system void formation during limiting events, we have concluded that:
(1) Primary system void formation is not predicted to occur for operational transients as defined in the FSARs. Evaluation of operational data supports this conclusion.
(2) Limiting overcooling transients (non-LOCA) may result in temporary void formation in the primary systed. This voiding is accounted for in present analysis models and does not rt:sult in unacceptable consequences such as inadequate core cooling or uncovering the core.
We therefore conclude that the licenseas of B&W plants have demonstrated the adequacy of their plant design to accommodate anticipated operational depressurization transients, as described above. As such we consider that me
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= the licensees operating B&W plants have adequately addressed our concerns of TMI Action Plan Item II.X.2.17.
On this basis we consider this iten complete and no further action required.
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