SCC coding classification advice18 September 2013
Done wrong, categorizing systems, structures and components (SSCs) can create a huge burden on nuclear component costs, conservatively quadrupling the cost of nuclear safety components in pedigrees. By James August
1. Standardize: Make a list of equipment codes avoiding multiple component subcodes for what is essentially the same equipment.
Example: 'pump' code: Pump could be abbreviated 'P', 'PMP', 'PU' or be left complete as 'PUMP', but not more than one of these methods would be used.
a) Choose one code for a given type of equipment and use it. Stick with the selected code consistently for all pumps.
b) Avoid using similar or multiple codes like 'CRP' for condensate return pump. Use of 'PMP', 'P', 'CRP' and 'PUMP' creates too many equipment type categories. Effective coding schemes address this by preventing multiple codes for use.
c) Lack of symmetry at multiple unit plants greatly increases manual effort to develop work requirements, using more time, and increasing the chance of errors. Consistent coding allows using the same work and work method patterns much more of the time. Replication of work depends on consistent coding. The potential for replication in typical nuclear plants is tremendous, because of redundant designs and repetitive use of the same components. Failure to take advantage of repetition and symmetry greatly complicates nuclear tagging programmes.
2. Be flexible and able to change. The Engineering Department must specify an equipment numbering procedure.
The large architect-engineers (Bechtel, Fluor, Burns and Roe ...) all have coding schemes that meet existing codes and work effectively. The Engineering Department should provide the equipment type codes to use, including a way to assign a code to any equipment not matching any other prescribed code. Listing equipment as code 'X' or 'to be assigned' should be minimized or avoided entirely. Listed plant equipment lacking consistent unique applicable plant codes will be of little use in automated data sorts. Construction with half of the plant equipment needing additional new codes or otherwise sharing the code 'X' will be useless later in actual operations.
3. Limit the number of new component type codes. Once a new type code is accepted, stick with it.
Example: CTG for Combustion Turbine Generator. Review all Combustion Turbine Generators at the plant to assure they are uniformly recoded, and that CTG is not used for any other equipment, once that new code has been selected.
4. Take care in deciding at what level of detail to stop coding.
Breaking down the plant, systems and equipment into its pieces -- subsystems, skids, components, and even parts -- constitutes 'partitioning'. Based on location in the plant's physical hierarchy, the partition may go as far as breaking down components into parts. Typically, in plant safety analyses, it goes only as far as the component. The last discrete component that can be installed and used 'out-of-the-box' is typically the practical limit. It is unnecessary and even pointless to go further; equipment part information is in controlled drawings. The computerized maintenance management system (CMMS) system for identifying maintenance usually stops here. However, unnecessary coding has happened in the past. Nuclear plants were notorious for overcoding in response to regulatory pressure and incomplete analysis. Following new standards should limit overcoding, holding down new nuclear facility costs.
5. Be consistent in coding equipment around system boundaries.
At the interfaces between different systems, a physical barrier usually exists. Boundaries usually provide a natural barrier for fluids, electric potential or other forms of energy. The components that form interfaces are often the most difficult to code; deciding where to put the SSC in the hierarchy requires thought. Because the physical parts are common to two or more systems, where to uniquely place them must be consistent across the entire plant, not repeated in both systems, and transparent to those using coding to classify work.
6. Be careful about modifying the coding of safety related equipment, because it could affect a plant's operating licence.
There are documented methods to fix things in nuclear plants, falling under the heading of nonconformance identification and control, or NCRs. Most utilities discourage using these methods because they must report them annually to the US nuclear regulator under operating statistics. Recoding specific items could lead to hugely expensive wholescale plant SSC recoding initiatives.
James August, professional engineer, VP operations at nuclear reliability plan developer CORE, Inc. Email: [email protected], tel: +1 (303) 425-7408.