CHAPTER 8: Rules of usage

Rules of usage

'Rules of usage' should be defined for the application of SAMGs. Such rules define what needs to be done and how when guidelines are to be applied for the management of the accident.

Questions to be answered in such situation are, for example:
  - If an EOP is in execution but the point of entry to SAMG is reached, should actions in the EOP then be interrupted,
   continued if not in conflict with the applicable SAMG, or continued in any case?
  - If a SAMG is in execution, but the point of entry to another SAMG is also reached as well, should that other SAMG
    then be executed in parallel?
  - Should the consideration to initiate another SAMG be delayed while parameters that called upon the former one are
   changing value in the anticipated direction?

Therefore “rules of usage” should be developed. Examples of issues covered by rules of usage typically include:
  - Hierarchy of tools (e.g. use of the diagnostic chart, frequency of monitoring,…);
  - Correct use of tools and flowcharts (conventions, etc.);
  - Use of the tools to follow priorities;
  - Transitions to guidelines;
  - Dealing with multiple active guidelines;
  - Dealing with conflicting instrumentation.

The rules of usage form an important part of the training of SAMG users. These rules are also documented in a separate report or a dedicated chapter of the SAMG documentation (e.g. in the Executive Volume).

Further information is available in SSG-54 paragraph 3.55, and some information in paragraphs 4.1 to 4.11. Read more.

Guidelines for technical support

Many plants have a separate group of staff members to support the Control Room in case of emergencies covered by the EOPs or to support the Emergency Director in his decision-making after the transition to the SAMGs. Often, such a group has a dedicated facility to provide for this support, called the Technical Support Centre. For convenience, we describe this support group just as the TSC. Details are presented in Module 4, sec. 4.

The tasks of the TSC usually include the following:
  • Checking the measured plant parameters for their validity depending on the conditions they are exposed to and trying
   to anticipate the development of control parameters of SAMGs;
  • Checking the conditions in the various rooms/compartments where necessary instruments and mitigating equipment
   are located;
  • Using calculational aids where measured parameters are not available or to support SAM actions
   (e.g. determine how much water is needed to cool the core/core debris);
  • As a number of SAMG can have negative consequences, the TSC should estimate those and, if such conditions arise, try
    to mitigate them or decide on alternative actions;
  • Checking the status of equipment required for mitigating strategies and prioritising their repairs/restoration,
   or advising the use of portable equipment. Some plants developed and use specific tables where they
   describe the dependency of the front line systems on support systems and prioritise their restoration based on
   the degree of complexity of the interdependency of those systems;
  • Evaluating the availability of systems needed to implement EOPs and plant specific SAMGs, including portable equipment.

The TSC can also provide a guidance to the Decision Maker to facilitate his decision making responsibility in various tasks. This may include issues of occupational safety, plant damage conditions or regional impact of proposed actions. The TSC may also use specific guidance for shift turn over.

Many plants have documented the tasks of the TSC in a series of guidelines, the so-called Technical Support Guidelines (TSG).

Note: in EOP domain the TSC may help the Main Control Room with decision-making in situations where actions to be implemented may lead to equipment damage (e.g. starting an RCP at low pressure to inject a slug of water remaining at the loop seal (PWR) through the core).