Fault Trees

The analytical method for constructions and evaluations of the fault trees is given in Appendix F. The fault trees include two or three sub-fault trees representing the instantaneous and continuous (both in liquid and vapour phases) release of hydrogen from the containment systems. The sub-fault trees are as follows:

1. Instantaneous release of hydrogen from GH2 tank in the production plant (G1. 1)

2. Continuous release of hydrogen from GH2 tank in the production plant (G1.2)

3. Instantaneous release of hydrogen from LH2 tank at depot (G2.1)

4. Continuous release of hydrogen in liquid phase from LH2 tank at depot (G2.2)

5. Continuous release of hydrogen in vapour phase from LH2 tank at depot (G2.3)

6. Instantaneous release of hydrogen from LH2 tank at filling station (G3.1)

7. Continuous release of hydrogen in liquid phase from LH2 tank at filling station (G3.2)

8. Continuous release of hydrogen in vapour phase from LH2 tank at filling station (G3.3)

9. Instantaneous release of hydrogen from LH2 tank at CHP plant (G3.1)

10. Continuous release of hydrogen in liquid phase from LH2 tank at CHP plant (G3.2)

11. Continuous release of hydrogen in vapour phase from LH2 tank at CHP plant (G3.3)

Summary of the computation results consists of the following:

(a) A list of the more significant minimal cut sets

(b) Expected frequencies of several initiating events considered in the study

(c) The top event expected frequency including with its uncertainties (i.e. median, the upper and lower 95% confidence limits, and uncertainty factor K-95).

Due to the study is focused on the societal risk, the minimal cut sets that may not result in fatality on the publics (e.g. release from relief valve, rupture disk, etc.) are not considered in the calculation of the expected frequencies, especially, in the case of continuous release of hydrogen both in liquid and gaseous phase.

Instantaneous release of GH2

Tank rupture due to external events

-Tpi

Tank rupture due to tank overpressure

External heat sources

Manual Shutoff valves fail to close

Regulator valve, PCV-19 fails stuck open

H2 supply systems fail to stop filling

External heat or fire around tank

Fire protection systems failure

Tank PIAs fail to actuate

Alarm unit (annunciator) failure

Operator fails to act

Shutoff valves fail to close

Plant valve, PCV-20 fails to stop

PSHs fail to actuate

0

0

-1 1'-

I

0

PIA-1 fails to actuate

PlA-2 fails to actuate

V-7 fails stuck open

V-10 fails stuck open

V13-1 and V13-2 fail stuck open

PSH-1 fails to actuate

PSH-2 falls to actuate

Fig. G1.1. GH2 Tank at Production Plant FAULT TREE DIAGRAM

Instantaneous Release of Hydrogen (Tank Rupture)

Tank rupture due to spontaneous events

PRDs fail blockage

PRDs of tank 1 fall blockage

PRDs of tank 2 or V13 fail blockage

Rupture disk, RD-1 does not rupture

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