ML21340A007
| ML21340A007 | |
| Person / Time | |
|---|---|
| Site: | National Bureau of Standards Reactor |
| Issue date: | 12/03/2021 |
| From: | US Dept of Commerce, National Institute of Standards & Technology (NIST) |
| To: | Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML21340A006 | List: |
| References | |
| Download: ML21340A007 (2) | |
Text
Analysis of cooling flow through 29 fuel elements with fuel element 1175 dislodged Normal flow through the reactor is 9000 gpm, flowing through 30 fuel elements. Per SAR 4.6.1.1, flow is divided as follows:
Inner plenum flow total 2300 gpm Number of inner plenum elements 6
Flow through each inner plenum element 383 gpm Outer plenum total flow 6400 gpm Number of outer plenum elements 24 Flow through each outer plenum element 267 gpm Approximate pressure drop through the fuel elements during normal operation is ~ 14.7 psid. Calculate the equivalent Cv for the fuel elements as per equation (1):
For a valve
= 7.9
(1)
Where Qinner = 383 gpm Qouter = 267 gpm P = ~ 14.7 psid P = ~ 14.7 psid D2O = 68.7 lb/ft3 D2O = 68.7 lb/ft3 Cv = 104.9 Cv = 73.0 With element 1175 dislodged from its spot on the lower grid plate, the open orifice diameter is 2.378 in.
Element 1175 was located on the outer plenum The flow through an orifice is calculated in equation (2).
For an orifice
= 236 0 2
(2)
Where d0 = 2.78 inch C = 0.6 With element 1175 dislodged, total flow through the reactor remains the same (9000 gpm total). Total flow is divided between the 29 fuel elements in place and the one open orifice exposed by 1175 being removed. That is:
= 23 ( ) + 6 ( ) + 1175 (3)
Plugging known Cv for the fuel elements, and using equations (1), (2) and (3), we get the following:
Qfuel element inner = 378.8 gpm Qfuel element outer = 263.5 gpm Q1175 orifice = 366.1 gpm
Note that normally Qfuel element inner = 383 gpm and Qfuel element outer = 267 gpm, so the fact that fuel element 1175 was dislodged from its socket is inconsequential. Calculated pressure drop across the grid plate and fuel elements decreases from ~ 14.7 psid to ~ 14.4 psid.
Conclusion - there is no significant risk of other fuel elements having insufficient flow to remain cooled.
John Jurns 01 December 2021