(concurring). The record shows that the company’s unreasonable delay in completing work on masonry block walls set back the return to service of Pilgrim I by eight days unless that delay became unimportant because of the independent effect of action required by the Confirmatory Action Letter (CAL) issued by the Nuclear Regulatory Commission on February 18, 1982. The company is correct in saying that there is no substantial evidence in the record in D.P.U. 1009-F that would support a finding that the delayed work on the masonry block walls was the cause of eight days of outage of Pilgrim I. The court’s reliance on events occurring prior to the CAL ignores the basic question — the effect, if any, of the CAL on the delay.
The DPU’s position that it would not look beyond the end of February to see what caused the delay was wrong as a matter of law. The DPU should not have struck Mathis’s testimony. It related to questions of causation.
Where under G. L. c. 164, § 94G, it is shown that a company was unreasonable or imprudent in its performance and that thereby fuel costs appear to have been made higher unnecessarily, but the company claims that some supervening event “saves” it (by making the company’s mistake not a cause of any higher fuel costs), the company has the burden of coming forward with evidence that the supervening event and not its error was the cause of the delay. Here the company sought to present testimony from Mathis relating to the effect of the CAL and, as I have said, the department improperly struck it from the record. That error was not prejudicial, however, because Mathis’s proposed testimony failed in one crucial respect. We know that compliance with the CAL delayed the return of Pilgrim I to service, but there is no evidence on the record in D.P.U. 1009-F as to whether the masonry block wall delay was sequential to or subsumed within the CAL delay.
I concur in the result in D.P.U. 1009-F for the sole reason that there is no evidence in the record to show that the CAL-based work supplanted the masonry block wall work as a cause for the delay. Evidence presented in D.P.U. 1009-G on this *255point came too late, because the department was entitled (although not required) to rely on its conclusion in D.P.U. 1009-F concerning the cause of eight days’ delay. I thus join in the affirmance in D.P.U. 1009-G.