WE-NET Home Page/Summary of Annual Reports 1999

2. Task2 Study of Safety Measures

2.1 R&D Goals

The research and development of an "International Clean Energy Network Using Hydrogen Conversion," known as WE-NET (World Energy NETwork) started in fiscal 1993. PhaseITresearch and development program of WE-NET was completed in fiscal 1998 and PhaseII program has started in fiscal 1999.

We, task-2 have taken charge of safety study in WE-NET system and the objectives of this task are same as in PhaseITand are as follows.

On the total WE-NET system, we must establish a unified safety scheme. On each WE-NET system, we must specify safety features or functions to keep safety after evaluating their safety conditions using the accident analysis codes that we will study and establish.

Therefore, in the second phase, we plan to implement research regarding the following items and descriptions:

(1)Study for prescription of safety design standard for the WE-NET system.

We made the safety design guidelines for the WE-NET system in PhaseITthat shows various items that are needed to check at the construction of each WE-NET system. In PhaseII, we will further survey safety related information and will study to make the safety design standard that shows the concrete conditions needed at the construction of each WE-NET system such as required safety equipment or separation distance of and so on.

For making the safety design standard, we will study the following way.

First, we will extract phenomena that cause abnormal condition or accident at a model facility and we will make the reference scenario of an accident by estimating the event sequence. Next, we will estimate the accident frequency by using the failure rate of equipment. Then we will set the analysis condition on the representative facility, and we will evaluate the degree of safety with the method that we will study and establish. Finally, we will select the effective safety measures to mitigate the effect of an accident.

In these many studies, we will make a prescription of safety design standard for the WE-NET system.

(2)Establishment of safety evaluation method

In Phase I, we had developed the simulation models that predict the dispersion characteristics following the spillage of liquefied hydrogen and predict the effect of the explosion of the hydrogen-air mixture. In PhaseII, we will conduct experiments and will further improve the simulation models by verification using the results of the experiments. We plan to execute two types of experiments. One of them is liquid hydrogen spillage and evaporaion experiment and the other is hydrogen explosion experiment. We will also develop and improve two simulation models corresponding to these experiments. By these studies, we will establish the method to evaluate the effect of the postulated accident with high accuracy.

Considering above-mentioned goals of PhaseII and development achievements in PhaseIT, the following items were chosen for this fiscal year study. (FY1999, the first year of PhaseII)

<1>Study for prescription of safety design standard for the WE-NET system

We will present some possible accidents in the WE-NET system and extract the phenomena that are caused by each accident.

In order to estimate the frequency of each accident, we will gather various data such as failure rate of equipment.

<2>Establishment of safety evaluation method on a given condition

We will execute the experiment on liquid hydrogen spillage and evaporation in a small scale. In this experiment, we will observe the behavior of hydrogen flow and its evaporation.

And we will make a basic plan for hydrogen explosion experiment that will be conducted in next year (FY2000).

We will improve the simulation models that predict liquid hydrogen spillage and evaporation by verification using the results of the experiment mentioned above.

We will search the commercial computer program (simulation model) that predicts hydrogen deflagration and introduce one of them. We will study the application method of it and extract the problems in it.

2.2 Results in Fiscal 1999

2.2.1 Study for prescription of safety design standard for the WE-NET system

In order to analyze the cause of accident, we investigated the conceptual design of hydrogen supply station that is being studied at task 7 in WE-NET project as a model case. We sorted out the relation between the latent incidents for the accident initiation and the measures corresponding to them and studied items that are needed to consider for safety design. Then we investigated available databases that show various safety-related information in order to execute quantitative risk assessment.

2.2.2 Establishment of safety evaluation method on a given condition

2.2.2.1 Experiment

(1) Liquid hydrogen flow and evaporation

We constructed a small-scale experimental apparatus that uses for observation of liquid hydrogen flow and evaporation. With this apparatus we executed liquid hydrogen flow and evaporation experiments in various condition. We also use liquid nitrogen for comparison. We studied the results and got basic knowledge about flow and evaporation behavior of liquid hydrogen and liquid nitrogen.

(2)Hydrogen explosion

We plan to execute hydrogen explosion experiments in next year (FY2000).

This year, we studied experiment condition from various aspects and made basic plan of the experiments. The objective of the experiment is to get basic knowledge regarding hydrogen explosion and to use the results for verification of the simulation model. Accuracy improvement of simulation model can be expected by using the results of the experiments.

First, we searched the literature in this field and investigated the experiments that were done and reported in the past. We studied the results of the literature search and had various meeting to make the plan. Finally, we decided the basic plan of the experiment in the working-group meeting and the committee approved this basic plan.

2.2.2.2 Development, Improvement and Verification of the simulation models

(1)Improvement of the simulation model that predicts the behavior of liquid hydrogen spillage, evaporation

We had studied the simulation code named CHAMPAGNE that predicts the behavior of liquid hydrogen spillage and evaporation in PhaseIT. We improved the model by verification using the results of the above-mentioned experiments and extracted the remained problem.

(2) Introduction of the simulation model that predicts the hydrogen deflagration

We must estimate the effect of the case that leakage of hydrogen happen and result in ignition at a real unit with simulation model. The above-mentioned hydrogen explosion experiments have a significance to verify the simulation model.

This year we took the first step of the estimation. We studied several commercial simulation models that deal with hydrogen deflagration. We chose a simulation model named AutoReaGas and introduced it. We examined the calculation principle of this code and studied the application method of it. We will improve this code by verification using the results of hydrogen-air explosion experiments.

2.3 Future Plan