UHI Upper Head Injection: Early Development Work

“Where this couldn’t be done or wasn’t enough, we proposed an upper head injection system.”
John W. Simpson, Nuclear Power from Underseas to Outer Space, ANS 1994, page 199.

Note: UHI had been removed from all of its victim nuclear plants by the time ANS published Simpson's book in 1994.

I've said a lot about UHI, Ultra High Risk, and I've said it is a very involved case. And at some point I'll put this all in some organized presentation.

The following discussion and slides relate the era during the early 1970's when UHI was in the early stages of design and development. Two systems were on the table, UHI was one, the other was In Core Spray (ICS). Each system involved the injection of emergency cooling water into the core during blowdown. (In my organized presentation all this will be clear.) The emergency cooling water was stored in a large pressure vessel and upon demand it was injected by high pressure nitrogen which was in a second large pressure vessel.

So, I bugged the project manager, Gallagher, with some questions directed to ICS, but these also applied to UHI. The problem that I identified on October 25, 1972, was the impact of dissolved nitrogen on system performance. Click on this slide to enlarge and press your return key to get back here.

Gallagher promptly responded. In the slide below, November 1, 1972, his bottom line is "In general, the effects of nitrogen saturation have not been considered."

The In-Core spray system was abandoned, and I never found out how in the world the designers expected to get by with short term pressurization of the accumulator water.

However, by January 30, 1973, the designers of the new UHI system were very well aware of the potential impact of dissolved nitrogen on UHI performance. The following two slides reveal their awareness and also the very narrowness of their awareness.

The very narrowness of the scope of their evaluation is summarized in the first sentence of the second paragraph of page 1 of their report, "The evaluation consists in determining the potential for flow choking during UHI system blowdown, the degree to which UHI system performance is affected, and the feasibility of engineering tests to confirm the calculated results." There is no recognition that the release of the large volume of nitrogen into the pressurized water reactor vessel would adversely impact the cooling of the reactor fuel elements.

As I have discussed previously, our great evaluators in our NRC also failed to recognize the hazards associated with the large nitrogen inventories. For reference, I am again attaching my appraisal of the NRC's negligent evaluation of UHI field performance. All of this will be integrated in a complete presentation sometime in the future.