Rod Control System

AMS provides state-of-the art equipment, training, and services for measurement of drop times of control and shutdown rods. Testing the timing and sequencing of control rod drive mechanisms (CRDMs) and slave cycler testing are also available. These products are useful in nuclear power plants with Pressurized Water Reactors (PWRs).

Rod Drop Time Measurements

Rod drop time testing is performed in PWRs to measure the length of time required for control and shutdown rods to travel from fully withdrawn to fully inserted position. The tests are performed at normal operating temperature, pressure, and flow conditions. The rods are fully withdrawn and then dropped by turning off the electrical power to one or more banks of rods while at the same time monitoring and recording their position indications.

Conventionally, rod drop time testing in most PWRs is performed manually on one rod or one group of rods at a time. The tests are usually performed during critical path at the end of an outage. To improve the efficiency of the test, AMS has developed computerized equipment for testing of any group of rods or all rods, at the same time. This equipment reduces the test time, provides immediate analysis, produces a test report, and provides trending and diagnostic capabilities. With this equipment, rod drop time measurements can be performed in less than one hour on all rods in a PWR plant.

Both portable and permanently installed equipment are available from AMS for rod drop time measurements. The portable equipment does not require any plant modification and is easily set up and connected to plant signals. The permanently-installed equipment requires a modification package to connect the equipment to the plant signals. This is done through isolation devices to keep the plant completely immune from any effect due to the test equipment. The advantage of the permanently installed equipment is that it automatically provides rod drop time measurements whenever the plant experiences a reactor trip.

Power-On Test

AMS has developed and patented a new technique to perform rod drop time measurements without having to turn off power to the rod position indication system. This method is referred to as "Power-On" rod drop time measurement.

CRDM tests are based on monitoring the stationary gripper coil current, movable gripper coil current, and lift coil current for a group of control and shutdown rods as they are moved in and out of the reactor.

All three coil signals are sampled for each rod and analyzed qualitatively to ensure that the CRDMs are operating properly. Furthermore, the signals are analyzed quantitatively by calculating various time differences in the data to verify that they have the expected timing characteristics.

Advantages of the AMS CRDM test method include:

• A complete bank of control and shutdown rods can be tested in a single run
  
• A complete set of withdrawal and insertion tests of all rods can be completed in 30 minutes including fitting the CRDM test traces and calculation of the timing sequences
  
• The test is performed remotely from the control room area using automated test equipment which acquires the data, calculates timing results, and produces a report

Slave cycler tests are performed by monitoring the binary counter and decoder cards located in the rod control system logic cabinets of Westinghouse PWRs. The test is performed by connecting the test equipment to the applicable test points while plant operation personnel initiate a request for rod withdrawal. A group or bank of rods can be tested, depending on the number of slave cyclers being tested concurrently. Data is sampled by a portable computer as rod withdrawal is being requested. After the withdrawal data is collected, plant operation's personnel initiate a request for rod insertion and data is collected again.