ML19326A767
| ML19326A767 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 10/08/1974 |
| From: | BABCOCK & WILCOX CO. |
| To: | |
| Shared Package | |
| ML19326A755 | List: |
| References | |
| NUDOCS 8003030896 | |
| Download: ML19326A767 (4) | |
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. This report is being nade in accordance with 1v CFR 50.55 (e) on Signifi-f
~x cant Deficiencies and relates to the Gendric investigation made as a
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result of the design review of the letdown orifice in the Makeut 0-1
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Purification System.
1 IDENTIFICATION OF PROBLF.M During the generic investigation of the Makeup Pump Recirculation Orifice Erosion (previously reported), it was noted that the letdown orifice is of a similar design and may also be subject to erosion.
' design review was undertaken concurrent with the review of the " recirculation orifice design. A revision to the letdown orifice design was prepared; however, prior to its implementation the revision to the recirculation orifice design showed signs of erosion at one field installation.
Both designs were again revieked and a second revision of each orifice design was prepared. _ The second design review revealed electly that cavitation would result in the last three stages of both the Revision 1 recirculation and letdown orifices. Cavitation of the stages plates would eventually either erode the orifice shell and thus cause a leak or reduce the effectiveness of the orifice to reduce pressure.
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' SAFETY EVALUATION I,
l The' letdown orifice is located cutside of the Reactor Building in the
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Auxiliary Building as shown schematically in Figure 1.
The high pressure side of the orifice contains reactor coolant at normal RC System pressure.
If the erosion progresses in the orifice shell, there would be a release of reactor coolant outside of the Reactor Building.
If the erosion progresses in the orifice stage plates, the effective-ness of the orifice as a pressure reducer would be impaired.
The icw pressure side of the orifice is designed for 150 psig and cannot with-stand RC System pressure.
Significant erosion of the stage plates would probably result in a rupture of the downstrean piping due to overpres-surization.
This design deficiency is considered to be a Significant Deficiency as per 10 CFR 50.55 (e) in that the erosion resulting from the cavitation could cause a release of reactor coolant outside of the Reactor Building.
SAFETY ANALYSIS The following is a worst case analysis of RC System blovdown and radio-activity release by a rupture in the letdown line.
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The most severe pipe rupture i'n the't:akeup and Purification System regarding radioactivity release would be a rupture of tho letdown line' just outside the Reactor building but upstream of the letdown Tbc occurrence of a rupture at this point would control valve.
result in a loss of reactor coolant until the Reactor Coolant System k* hen this pressure is reached, the emer-pressure drops to 1600 psig.
gency injection signal initiaces 'the closure of the letdown isolation valve inside the Reactor Building.-
- This analysis assumed a complete severance of the 2-1/2 inch letdown Coolant was assumed to flow line. No operator action was assumed.
Credit was not taken for out until the isolation valve was fully closed.10 seconds shile the valve was
.the reduction in flow during the lastThe nornal makeup system was a in a slightly longer time to reach 1600 psig and a correspondingly closing.
Figure 2 hows the Reactor Coolant Systen pressure higher mass release.
As can be seen from this figure, the time to a
as a function of time.
Adding on the 10 seconds for the 1600 psig is approximately 95 seconds.
valve closure time, coolant escapes for a total period of 105 secor.ds.
The results show that the total = ass release is 7,955 pounds.
The isotopic activities released t,o the Auxiliary Building are based on a long-term reactor operation vfth.1 percent defective fuel and are
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listed in table 1.
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CORRECTIVE ACTIONS _
Both the recirculation and letdown orifices have been redesigned for Field change packages are being prepared to all affected contracts.
implement the design change.
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FIGURE 2.
i REACTOR COOLANT SYSTEM PRESSURE l
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COMPLETE SEVERANCE OF LETDOWN LINE i
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