Ball 3X System

Ball 3X System which Is patterned after that now operating at the K... 

Improved detection of pump shaft breakage should he installed for safety circuit action. The Pressure Monitor does provide a degree of protection in this area, hut pressure decay time to the Pressure Monitor may he slow allowing boiling in the downcomer before initiation of a scram signal. The Ball 3X System will not protect for a single broken shaft. Pressure or differential pressure Instrumentation should he applied to... 

Changing of stack dimensions due to irradiation of the graphite presents a very s erious situation from all aspects - main--tenance, operation, safety. The continued distortion is affecting operation of the rods and in some cases, limits fuel element charging. Much of the on-reactor maintenance revolves around alleviation of problems caused by graphite distortion. Future problems with the thermal shields and Ball 3X system may result. All in all, graphite distortion is the major key to continued operation of the reactor because of its effect on all other reactor systems. Since the graphite and the shields defy replacement or major modification, their deterioration becomes a matter of serious ct ncern. 

Such coincidence circuits increase operating continuity and reliability for only a very small decrease in reactor safety. Even then, the definition of safety must be precise as this term may have different meanings as were covered by fail-safe for the VSR s and Ball 3X System. 

Graphite distortion is causing operating problems with the Ball 3X system. One problem is the loss of balls in the stack after a ball drop. The large separations that have been opened in between moderator blocks permit the balls to migrate from the VSR channels to the HCR channels. 

The Ball 3X System in conjunction with loaded supplementary control devices and inserted control and safety rods> shall be adequate for satisfying Total Control requirements. 

Such a failure would result in a rapid depressurization of the system. Any lowering of water density within the process tubes will result in a reactivity loss. Thus. the immediate effect would be a reduction in reactivity. The later addition of cold water to the lattice will result in a reactivity Increase from 3.1 to 3 6 per cent k depending on reactor conditions. In all cases I the incremental control held in safety rods and the ball 3X system are sufficient to control the excess reactivity. See Table. ... 

In both cases considered the maximum conceivable k due to the combined accident (5.0 per cent k in the reactor at equilibrium, and 3.7 per cent k in the zero power reactor) is well within the control held In either the safety rod system or the Ball 3X system alone. 

The function of the Ball 3X system is to provide backup control to the rod system in the event of an accident which would disable the rod system The design characteristics of the Ball 3X system are given in Table The control strengths are based on esq erimental... 

The shutdown margins for both the horizontal rod and Ball 3X systems for a number of reactivity slates are given in Tables 7 -l aod 7 5 2. 

It Is conceivable, but highly lisprobable, that the Primary Safety System (horizontal rods) would fall and the excursion would have to be terminated by the Ball (3X) Safety System. The Ball 3X system Is required to be able to shut down the reactor from any credible excursion before fuel melting occurs. 

Figure 7 6.2v is a plot of the characteristic scram curve of the Ball 3X system and is same as Figure A-5 of HV7-71 8 V0L2,... 

VSR - Vertical Safety Rod - Boron-containing rods suspended over open channels in the pile during operation, so arranged that when the safety circuit is tripped the rods will fall into the pile by gravity. The structure and number of rods varies considerably from pile to pile. The VSR system is the fastest reactivity control system and absorbs almost as much reactivity as the Ball 3X system. 

Certain contacts in both circuits cannot be bypassed, thus affording scram protection in the reactor in the unlikely event that it becomes supercritical during the testing period. The trips which cannot be bypassed are the intermediate range excessive flux contacts, and the excessive power rate contacts. Furthermore, the ball-3X system must be unlocked and made up, and the ball drain valves must be closed. Contacts from intermedlata range instrumentation Indicating that the reactor power is less than a value between. 001 and 4 (to be determined) must also be closed before the reset circuit can be actuated. 

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