Introduction to Nuclear-Class Valve Actuators: K1/K2/K3 Classes and Five Qualification Tests

Nuclear-class valve actuators come in three classes: K1, K2 and K3. K1 is the most demanding and covers K2/K3 requirements. A K1 actuator may be installed inside the reactor containment and must perform its function under normal conditions and safe-shutdown-earthquake loads, during and after a LOCA accident.

Besides life testing, meeting the 40-year life requirement of Class 1E actuators and other safety-related demands, a K1 actuator must undergo:

• 1. Thermal ageing: accelerated method, 138℃, 300 h.
• 2. Irradiation: irradiation ageing plus accident irradiation, possibly combined: total dose 1,700 kGy (170 Mrad) at 5 kGy/h.
• 3. Mechanical wear ageing: 2,000 loaded cycles, interleaved within the thermal ageing and before/after irradiation.
• 4. Vibration and seismic tests on three orthogonal axes: a) dynamic-characteristic check (natural frequency); b) vibration at 0.75g; c) OBE at 4g; d) SSE — sine-beat at 6g, random wave at 4g. The actuator operates loaded as required throughout.
• 5. LOCA test: two rapid temperature ramps from 50℃ to 156℃ with pressure rising to 0.56 MPa(abs); during depressurisation after the second ramp, boric-acid/sodium-hydroxide solution is sprayed for 96 h; then 240 h at 100℃ and 0.2 MPa(abs). The actuator operates loaded as required.

Performance is measured before and after each test and compared to determine pass/fail. In sum, beyond meeting all 2SA3 requirements, a K1 actuator needs adequate strength, high-temperature capability and radiation resistance.

Appendix: Nuclear actuator basics

1. What does Class 1E mean?　The safety class of electrical equipment in nuclear plants, required for: reactor emergency shutdown; containment isolation; emergency core cooling; residual-heat removal; containment heat removal; prevention of significant radioactive release to the environment.

2. What do K1/K2/K3 mean?　Safety classes of nuclear plant electrical equipment. K1 — inside containment, functional under normal conditions, SL2 loads, during and after accidents; K2 — inside containment, functional under normal conditions and SL2 loads; K3 — outside containment, functional under normal conditions and SL2 loads.

Related Reading

• KZ Series Nuclear-Class Actuators: K1/K2/K3 Classes and Data
• DL/T 641-2005 Electric Valve Actuators for Power Plant — Full Text