The lieutenant came over and looked.  The chief engineer was pointing at an inspection valve on the heat exchanger.  Before he got an explanation, Melekhin went to the bulkhead phone.

"Comrade Captain, this is Melekhin.  I have found it.  I require the reactor to be stopped for an hour.  We can operate the caterpillar on batteries, no?"

"Of course, Comrade Chief Engineer," Ramius said, "proceed"

Melekhin turned to the assistant engineering officer.  "You will shut the reactor down and connect the batteries to the caterpillar motors."

"At once, Comrade."  The officer began to work the controls.

The time taken to find the leak had been a burden on everyone.  Once they had discovered that the Geiger counters were sabotaged and Melekhin and Borodin had repaired them, they had begun a complete check of the reactor spaces, a devilishly tricky task.  There had never been a question of a major steam leak, else Svyadov would have gone looking for it with a broomstick—even a tiny leak could easily shave off an arm.  They reasoned that it had to be a small leak in the low-pressure part of the system.  Didn't it?  It was the not knowing that had troubled everyone.

The check made by the chief engineer and executive officer had lasted no less than eight hours, during which the reactor had again been shut down.  This cut all electricity off throughout the ship except for emergency lights and the caterpillar motors.  Even the air systems had been curtailed.  That had set the crew muttering to themselves.

The problem was, Melekhin could still not find the leak, and when the badges had been developed a day earlier, there was nothing on them!  How was this possible?

"Come, Svyadov, tell me what you see."  Melekhin came back over and pointed.

"The water test valve."  Opened only in port, when the reactor was cold, it was used to flush the cooling system and to check for unusual water contamination.  The thing was grossly unremarkable, a heavy-duty valve with a large wheel.  The spout underneath it, below the pressurized part of the pipe, was threaded rather than welded.

"A large wrench, if you please, Lieutenant."  Melekhin was drawing the lesson out, Svyadov thought.  He was the slowest of teachers when he was trying to communicate something important.  Svyadov returned with a meter-long pipe wrench.  The chief engineer waited until the plant was closed down, then double-checked a gauge to make sure the pipes were depressurized.  He was a careful man.  The wrench was set on the fitting, and he turned it.  It came off easily.

"You see, Comrade Lieutenant, the threads on the pipe actually go up onto the valve casing.  Why is this permitted?"

"The threads are on the outside of the pipe, Comrade.  The valve itself bears the pressure.  The fitting which is screwed on is merely a directional spigot.  The nature of the union does not compromise the pressure loop."