ML14051A066
| ML14051A066 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 02/20/2014 |
| From: | Donovan K Exelon Generation Co |
| To: | Office of Nuclear Material Safety and Safeguards |
| Garcia-Santos N | |
| References | |
| Download: ML14051A066 (9) | |
Text
Byron Loss of Annulus Cooling Event y
g Presentation for NRC Kevin Donovan Manager Dry Cask Storage Program Manager, Dry Cask Storage Program Exelon Generation Company February 6, 2014
Event Description
- In August, 2010, Byron Station was loading the first of six (6) HI-STORM 100 cask systems in their initial dry cask storage (DCS) campaign
- During the evening of August 28 or morning of August 29, a failure (chiller trip) of the annulus cooling system occurred failure (chiller trip) of the annulus cooling system occurred and went undetected until approximately 0700h on August 29, resulting in an uncontrolled temperature increase
- At the time of the chiller trip, vacuum drying was secured and HI-TRAC water jacket cooling was in service Vacuum drying system was isolated at the MPC
- Vacuum drying system was isolated at the MPC
- HI-TRAC/MPC annulus flushing was also secured at the time (inappropriate act)
(
pp p
)
Annulus flushing required by FSAR for MPC-32 Byron Loss of Annulus Cooling Event 2
Event Significance
- Event significant in that it revealed a lapse in practicing nuclear safety fundamentals, specifically maintaining nuclear fuel cooling At no time was there any risk to public health and safety Th l
f th l
li t
- The loss of the annulus cooling system was non-consequential, in that no safety limits were exceeded FSAR design operating limit for the annulus cooling FSAR design operating limit for the annulus cooling system of <125oF was assumed to have been exceeded Event did not challenge the design fuel clad temperature li it b d
th k h t l d
f 21 1 kW limit based on the cask heat load of 21.1 kW
- Campaign maximum loading was 24 kW
- It is postulated that with a heat load of 28 kW this limit
- It is postulated that with a heat load of 28 kW this limit may have been challenged Byron Loss of Annulus Cooling Event 3
Annulus Cooling System Description Annulus Circulating Pump on top of MPC Lid Annulus Water Supply to HTX (Annulus Flushing)
W t J
k t / A l
Annulus Chiller Unit (with integral Water Jacket / Annulus Cooling Heat Exchanger pump)
MPC inside of HI-TRAC Water Jacket Return Water Jacket Bypass FI Water Jacket Supply Return to Annulus AOV-AO-1 AOV-DV-1 Byron Loss of Annulus Cooling Event 4
To Floor Drain
Annulus Cooling System Description (contd)
- The annulus cooling system is made up of two major components:
Annulus chiller unit provides cool water to both the annulus and the HI-TRAC water jacket during vacuum drying activities drying activities Annulus cooling heat exchanger is used to keep annulus cooling water separated from the HI-TRAC jacket cooling water
- For purposes of clarity, there is no water exchange with the MPC provided by this system MPC provided by this system Byron Loss of Annulus Cooling Event 5
Annulus Cooling System Description (contd)
- For annulus cooling (annulus flushing), a pump takes a suction from the annulus water on top of the MPC, pumps it through the annulus cooling heat exchanger (shell side) where it is cooled, and returns it to the opposite side on the top of the MPC top of the MPC
- For HI-TRAC water jacket cooling, a separate pump on the annulus chiller skid pumps water through the HI-TRAC water jacket and through the annulus chiller heat exchanger (tube side), and returns it to the chiller skid Byron Loss of Annulus Cooling Event 6
Licensing Basis Considerations
- The procedures for establishing and maintaining annulus cooling were lacking in requirements to ensure the <125oF annulus temperature limit specified by the FSAR was not exceeded
- Further review determined that the event did not challenge
- Further review determined that the event did not challenge the design fuel clad temperature limit
- The issues surrounding this event were investigated under the Exelon Corrective Action Program (IR 1107151)
- The event and lessons learned were communicated with the industry via the INPO Operating Experience Program the industry via the INPO Operating Experience Program (OE32015/OE32411)
- NRC issued Information Notice 2011-10 to communicate the issue to the industry Byron Loss of Annulus Cooling Event 7
Conclusions A failure of the annulus cooling system went undetected, resulting in uncontrolled temperature increase in FSAR d i
ti li it f th l
l t
d t FSAR design operating limit of the annulus coolant was assumed to have been exceeded Vacuum drying was secured at the time of the chiller trip (isolation l
l d
t th MPC) valves closed at the MPC)
Event did not challenge the fuel clad temperature limit Revealed a lapse in practicing nuclear safety fundamentals, specifically maintaining nuclear fuel cooling Issues addressed within the Corrective Action Program Operating experience shared with the industry p
g p
y NRC issued Information Notice 2011-10 8
Byron Loss of Annulus Cooling Event
Questions or Comments?
9 Byron Loss of Annulus Cooling Event