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Here is a memo (part of the public record) that some people think probably contributed to one of the worst nuclear plant accidents in history:
BABCOCK & WILCOX COMPANY
I R GENERATION GROUP
August 3, 1978
TO: Manager, Plant Integration
FROM: Manager, Plant Performance Services
SUBJECT: Operator Interruption of High Pressure Injection (HPI)
References 1 and 2 (attached) recommend a change in Babcock and Wilcox’s philosophy for HPI system use during low-pressure transients. Basically, they recommend leaving the HPI pumps on, once HPI has been indicated, until it can be determined that the hot leg temperature is more than 50o below Tsat for the RCS pressure.
Nuclear Service believes this mode can cause the RCS (including the pressurizer) to be solid. The pressurizer reliefs will lift, with a water surge through the discharge piping into the quench tank.
We believe the following incidents should be evaluated:
1. If the pressurizer goes solid with one or more HPI pumps continuing to operate, would there be a pressure spike before the reliefs open which could cause damage to the RCS?
2. What damage would the water surge through the relief valve discharge piping and quench tank cause?
To date, Nuclear Service has not notified our operating plants to change HPI policy consistent with References 1 and 2 because of our above-stated questions. Yet, the references suggest the possibility of uncovering the core if present HPI policy is continued. We request that Integration resolve the issue of how the HPI system should be used. We are available to help as needed.
(Signed) Manager, Plant Performance Services
Did you understand anything from the above letter?
About 9 months after this letter was sent, on March 29, 1979, the world woke up to the Three Mile Island near-disaster (in which the core of the Three Mile Island nuclear reactor in Pennsylvania almost melted down).
Here is my attempt to re-write some sentences of this historic memo and make it more intelligible:
ORIGINAL: SUBJECT: Operator Interruption of High Pressure Injection (HPI)
BETTER: SUBJECT: *** URGENT *** DANGER of REACTOR CORE MELTDOWN! *** URGENT ***
ORIGINAL: References 1 and 2 (attached) recommend a change in Babcock and Wilcox’s philosophy for HPI system use during low-pressure transients.
BETTER: ATTENTION — We recommend Babcock and Wilcox change its emergency procedures in case of low water pressure in the reactor (see References 1 and 2).
ORIGINAL: Basically, they recommend leaving the HPI pumps on, once HPI has been indicated, until it can be determined that the hot leg temperature is more than 50o below Tsat at that RCS pressure.
BETTER: When the High Pressure Injection (HPI) alarm goes off, turn ON the HPI pumps immediately and leave them ON until the Reactor Cooling System (RCS) temperature drops to 50o below Tsat [for the RCS pressure?].
ORIGINAL: Nuclear Service believes this mode can cause the RCS (including the pressurizer) to be solid.
BETTER: If the HPI pumps are not turned ON immediately and kept working until the temperature falls to the indicated safe level, the Reactor Cooling System (RCS) can fail and the reactor core can be exposed, with dire consequences!!!
ASSIGNMENT: Can you improve this letter? If you were the Plant Performance Services Manager,how would you write this memo so that there would be no doubts whatsoever about 1) the seriousness of the potential problem, and 2) the solution?