Pipe Rupture at a Nuclear Power Plant
A pipe rupture occurred in a steam condensing line of a residual heat removal system at the Hamaoka Nuclear Power Station Unit-1 (Hamaoka-1) during operation at rated power. The reactor was manually shut down immediately after the pipe rupture and there was no radioactive release into the environment. Although the water hammer phenomenon was identified initially as cause of the accident, on the basis of the fluid conditions presumed to exist inside the pipe, it was eventually concluded that the phenomenon did not produce an impulse sufficiently large to rupture the pipe, and the detonation of the hydrogen accumulated in the pipe was considered to be the likeliest cause of the pipe rupture. The hydrogen was considered to be generated by radiolysis of reactor water in a core.
Event Date
November 7, 2001
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
The most likely explanation is:1. Formation of hydrogen by radiolysis of reactor water in a core.2. Detonation of the hydrogen accumulated in the pipe.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
heat exchanger, steam condensing line
Storage/Process Medium
Location Type
Location description
Industrial Area
Operational Condition
Pre-event Summary
A pipe rupture occurred in a steam condensing line of a residual heat removal system at one unit of unit 1 of approx. 1000 MW of a Nuclear Power Station during operation at rated power.
Property Loss (onsite)
The actions and corrective measures taken by the bus manufacturer after the alarm are indicative of the long pathway still necessary before arriving to full deployment maturity of hydrogen-based mobility solutions. A. Collected the vehicle (VH VIN 66242) from the city Depot B. Review and analysis of the hydrogen exhaust set-up and the fuel cell cooling systemC. Re-built the bus to original set-up triggering fault/alarmD. Installed measurement equipment (8 H2 concentration sensors) to measure hydrogen concentration in exhaust and under roof panels.E. Installated 2 extra sensors to determine if the normal sensors (8) do not react to other gasses but only to hydrogenF. Installed of additional dataloggers, for extra datalogging and evaluation of principalsystem.G. Mapped the hydrogen flow via visualization of gasH. Modifiedy the vehicle to resolve issues with high hydrogen concentration if necessary.I. Brought vehicle back to the city and performed a thorough test on route to determine that sensors do not pick up any other gas concentrations that can trigger warning or alarm.K. Modified the 2nd bus accordingly
Lessons Learned
Lessons Learned
The lesson learned issued by the local or governmental authorities in relation to this specific accident are unknown. The owner of Hamaoka-1, Chubu Electric Power Company, Incorporated (the Chubu EPCO), had conducted experiments and analyses after the accident and concluded that occurrence of hydrogen detonation caused the pipe rupture and decided countermeasures to prevent similar accidents. Also the results of these investigation are unknown. The following are general recommendations to utilities, from the US NRC conclusions: (0) strongly urging all BWR licensees to perform detailed evaluations and implement mitigating actions as appropriate. (1) review piping systems to identify any potential vulnerabilities for the accumulation of radiolytic gases, (2) assess the detonation potential of vulnerable piping, (3) consider design or system operation modification(s), a (4) consider the potential for accumulation and detonation of radiolytic gases
Event Nature
Emergency Action
The reactor was manually shut down immediately after the pipe rupture and there was no radioactive release into the environment.
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
M. NAITOH et al.,
"Analysis on Pipe Rupture of Steam Condensing Line at Hamaoka-1, (I) Accumulation of Non condensable Gas in a Pipe"
Journal of Nuclear Science and Technology, 40 (December 2003) 1032-1040
Open access at https://www.tandfonline.com/doi/pdf/10.1080/18811248.2003.9715449
US NRC general conclusions from detonation-related accidents involving radiolytic hydrogen formation:
A) Hamaoka Unit 1 BWR
B) Brunsbuttel BWR
Available at (accessed 12/2019):
https://www.nrc.gov/docs/ML1606/ML16063A320.pdf