2.2.1 Categories of Information Available for Cable Fire Tests
The PIRT panel broke down into three categories the physical configurations tested during the industry- and NRC-sponsored test programs, based on the information available from the tests: 1. Physical configurations for which the PIRT panel has significant test data. This category
has sufficient data such that the panel can predict, with high certainty, the probability and duration of spurious operations, given thermally-induced cable damage. In this category are the following physical configurations:
a. Control cables, with IEEE STD-383-qualified8 TS and non-qualified TP insulations, used
to control various power plant components via AC electric power. This category includes single conductor, multiple conductors, cables in trays, conduits and/or air drops in either grounded or ungrounded circuits.
b. Control cables, with IEEE STD-383-qualified TS and non-qualified TP insulations, used to control various power plant components using DC electric power. This includes a single conductor, multiple conductors, cables in trays, conduits, and/or air drops in ungrounded circuits.
2. Physical configurations for which the PIRT panel has sparse data, but which the electrical experts believed reasonably can be represented by the existing test data based on energy level, cable type, and circuit design. This category has sparse test data from which the PIRT panel can predict, with moderate certainty, the probability and duration of spurious operations, given thermally-induced cable damage. In this category are the following configurations:
a. Armored Control cables, with IEEE STD-383-qualified TS and non-qualified TP insulations, used to control various power-plant components using AC- or DC-electric power. This includes single conductor, multiple conductors, cables in trays, conduits and/or air drops in either grounded or ungrounded circuits.
b. Three phase AC and two phase DC power cables due to the similarity in fire-induced failure characteristics to the cables fire tested for AC and DC control circuits. The results of the control circuit testing when coupled with the expert knowledge of the PIRT panel members was considered to be an acceptable combination of knowledge for the determinations made in this report relative to AC and DC power cables.
3. Physical configurations for which the PIRT panel has little or no data, and hence the
electrical experts can offer only provisional estimates. Due to the lack of test data, the PIRT
8 Environmentally qualified per IEEE STD-383, “IEEE Standard for Type Test of Class 1E Electric Cables, Field
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES
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panel can predict only with low certainty, the probability of spurious operations, given thermally-induced cable damage. In this category are the following configurations: a. Wiring inside electrical cabinets/panels
b. Trunk cables c. Fiber optic cables
d. Electrical conductors used in digital control systems e. Instrumentation and control circuit cables
2.2.2 Cable Fire Test Data Analysis
The EPRI/NEI test data analyses were analyzed thoroughly, and results are detailed in EPRI Technical Report 1006931, dated May 2002 (Ref. 11). However, the PIRT panel initially noted that the test data obtained from both CAROLFIRE (AC tests) (Ref. 9) and DESIREE-Fire (DC tests) (Ref. 10) performed at SNL under the sponsorship of the NRC had not been analyzed for direct use in this PIRT evaluation. Based on the PIRT panel’s suggestions and oversight, all test data including both EPRI/NEI and NRC/SNL were analyzed for the following conditions: For Intra-Cable Hot short-induced Spurious Operation and Duration
• Conductor Count
• Thermal Exposure Condition • Cable Orientation
• Raceway Routing • Raceway Fill
• Insulation Type (TS or TP) • Insulation Materials
• Circuit Type (for DC tests only)
• Insulation-Jacket Material Combinations (TS-TS, TP-TP, TS-TP)9
• Control Power Transformer (CPT) Size (for AC circuits) and Fuse Size (for DC circuits) • Circuit Grounding for AC circuits only
• Wiring Configuration • Conductor Size
• Suppression Effects for AC circuits only • Cable Shielding for DC circuits only
• Circuit Concurrence of Hot Shorts for both AC and DC circuits For Inter-Cable Hot short-induced Spurious Operation and Duration • Ground Fault Equivalent Hot Shorts for DC circuits only
• Inter-cable (direct cable-to-cable) interaction for both AC and DC circuits
The panel chose several other influencing parameters for the PIRT, but did not include them in their analyses of the test data since the tests’ results would not directly exhibit their impacts on • Cable Aging
9 PIRT panel did not consider the TP-TS because the panel members did not know any US NPPs currently utilizing any such insulation-jacket material combination cables.
OVERVIEW OF ELECTRICAL EXPERT PIRT PANEL ACTIVITIES
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• Fire Suppression Effect
• Latching versus Non-Latching Device Configuration
For these four parameters, the PIRT panel used their expert knowledge, phenomenological models, and operating experience in evaluating their effects on the hot short-induced spurious operation in applicable control circuits.
The panel also discussed each of the above items thoroughly so that the outcome of the test data analyses could be used directly in the PIRT process. The NRC staff analyzed the
CAROLFIRE data on AC control circuits, including some selected EPRI/NRC data applicable to the specific analysis; the SNL staff analyzed the DESIREE-Fire data on DC control circuits. The results of both analyses then were presented to the panel members for evaluation. The NRC is in the process of publishing the final results of these evaluations in NUREG-2128 (Ref. 20).