Patent Number: 
Section: claims

1. A water-chamber working apparatus that performs a predetermined work inside a water chamber of a steam generator, the apparatus comprising:a movable body that is configured to move along a tube plate of the steam generator;an extendable member that includes a first portion and a second portion and that extends and retracts in a direction in which the first portion and the second portion approach each other and a direction in which theses portions move away from each other, where the first portion is attached to a portion of the water chamber that is away from the tube plate via a first joint including two rotation axes intersecting with each other, and the second portion is attached to the movable body via a second joint including two rotation axes intersecting with each other, which are different from the rotation axes of the first joint;a first force application unit that applies a force in a direction in which the first portion and the second portion move away from each other to the extendable member; anda second force application unit that applies a force of rotating the extendable member centering around the first joint, which is a force to cause the second portion to approach to the tube plate, to the extendable member. 2. The water-chamber working apparatus according to claim 1, whereinthe second force application unit includesan electric motor, anda counterweight mechanism including a rod-like member for weight that is extended to a direction opposite to the second portion while using the first portion as a fulcrum, and a weight provided in a portion of the rod-like member for weight that is away from the first portion. 3. The water-chamber working apparatus according to claim 2, wherein the electric motor increases the force to be applied to the extendable member as a distance between the first portion and the second portion increases, and decreases the force to be applied to the extendable member as the distance between the first portion and the second portion decreases. 4. The water-chamber working apparatus according to claim 1, whereinthe second force application unit is a counterweight mechanism includinga rod-like member for weight that is extended to a direction opposite to the second portion while using the first portion as a fulcrum, anda weight provided in a portion of the rod-like member for weight that is away from the first portion. 5. The water-chamber working apparatus according to claim 2, whereinthe rod-like member for weight extends and retracts in a direction in which the first portion and the weight approach each other and a direction in which the first portion and the weight move away from each other, andthe water-chamber working apparatus comprises an arm-length adjustment unit that adjusts a distance between the first portion and the weight so that the distance between the first portion and the weight increases as a distance between the first portion and the second portion increases, and adjusts a distance between the first portion and the weight so that the distance between the first portion and the weight decreases as the distance between the first portion and the second portion decreases. 6. The water-chamber working apparatus according to claim 2, whereinthe weight moves along the rod-like member for weight in a direction in which the weight approaches the first portion and a direction in which the weight moves away from the first portion, andthe water-chamber working apparatus comprises a weight movement unit that moves the weight in a direction in which the weight moves away from the first portion as a distance between the first portion and the second portion increases, and moves the weight in a direction in which the weight approaches the first portion as the distance between the first portion and the second portion decreases. 7. The water-chamber working apparatus according to claim 2, whereinthe weight is configured to include a container and liquid stored in the container, andthe water-chamber working apparatus comprises a liquid-amount adjustment unit that increases an amount of the liquid in the container as a distance between the first portion and the second portion increases, and decreases an amount of the liquid in the container as the distance between the first portion and the second portion decreases. 8. The water-chamber working apparatus according to claim 1, wherein the second force application unit is an electric motor. 9. The water-chamber working apparatus according to claim 8, wherein the electric motor increases the force to be applied to the extendable member as a distance between the first portion and the second portion increases, and decreases the force to be applied to the extendable member as the distance between the first portion and the second portion decreases. 10. The water-chamber working apparatus according to claim 1, wherein the first force application unit is an extension device capable of adjusting an amount of extension and retraction, and adjusts a length of the extendable member by following a movement of the movable body. 11. The water-chamber working apparatus according to claim 1, wherein the movable body performs, as a predetermined work, Eddy-current testing for probing a flaw formed in a heat transfer tube provided in the steam generator. 12. The water-chamber working apparatus according claim 11, wherein the movable body clamps the heat transfer tube.